BIO120 Ulife Study Guide
Bio 120: Adaptation & Biodiversity
Exam Study Notes (Lectures 12-23)
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LECTURE 12: INTRODUCTION TO EVOLUTIONARY BIOLOGY
1.
2.
3.
4.
Evolution
How it is studied
Facts supporting Evolution
Biodiversity & adaptation
Levels of biological organization:
Molecules Æ Cells Æ Organisms Æ Populations Æ Communities Æ Ecosystems
Types of questions in evolutionary biology:
- Scope: small questions can help towards solving a big question; large questions require multiple lines of evidence
- How vs. Why
How ї Wroximate ї /nvolve determining physiological or genetic mechanisms
Why ї hltimate ї etermine ecological function and significance of a trait
Approaches used in evolutionary biology:
Good studies use more than one source of evidence
- Observation – describe and quantify
- Theoretical – develop models
- Comparative – compare data across species
- Experimental – manipulate a system to address a hypothesis ї Zequires design and statistical analysis Theory of Evolution
- The central unifying concept of biology
- Affects many other areas of knowledge
- One of the most influential concepts of Western thought
Important assumptions about evolution: ї Verified by scientific study (see Coyne notes below)
Organisms on earth have changed through time
The changes are gradual not instantaneous
- Lineages split or branch by speciation resulting in the generation of biodiversity
- All species have common ancestors
- Most evolutionary change results from natural selection - the only process responsible for the evolution of biodiversity and adaptation
Biodiversity and adaptation are products of evolution:
Biodiversity
- the variety of life on earth; the number and kinds of living organisms in a given area
Adaptation
- [Noun] Any trait that contributes to fitness by making an organism better able to survive or reproduce in a given environment
- [Verb] The evolutionary process that leads to the origin and maintenance of such traits dŚĞ ďĞƐƚ ƐƚƵĚŝĞƐ ŝŶƚĞŐƌĂƚĞ ŝŶĨŽƌŵĂƚŝŽŶ ĨƌŽŵ ĞǀŽůƵƚŝŽŶĂƌLJ ŚŝƐƚŽƌLJ E ŵĞĐŚĂŶŝƐŵƐ
Evolutionary mechanisms (microevolution)
- ĞƚĞƌŵŝŶŝŶŐ ƚŚĞ ĞĐŽůŽŐŝĐĂů ĂŶĚ ŐĞŶĞƚŝĐ ŵĞĐŚĂŶŝƐŵƐ ƌĞƐƉŽŶƐŝďůĞ ĨŽƌ ĞǀŽůƵƚŝŽŶĂƌLJ ĐŚĂŶŐĞ
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/ŶǀŽůǀĞ ƉŽƉƵůĂƚŝŽŶ-level studies of natural selection, adaptation and speciation using diverse organisms - Testing of theoretical models by experiments in the laboratory and field
- Largely process orientated and experimental
Evolutionary history (macroevolution)
- ĞƚĞƌŵŝŶŝŶŐ ĞǀŽůƵƚŝŽŶĂƌLJ ƌĞůĂƚŝŽŶƐŚŝƉƐ ŽĨ ŽƌŐĂŶŝƐŵƐ ŝŶ ƚĞƌŵƐ ŽĨ ĐŽŵŵŽŶ ĂŶĐĞƐƚƌLJ phylogenetics
- Affinities of organisms provide a basis for classification – taxonomy & systematics
- Comparative data from many sources e.g. biogeography, paleontology, morphology, development and genomics
- Largely pattern-based and non-experimental
Water Hyacinth
- Novel adaptation promotes outcrossing
- Patterns of genetic diversity
- Blocks drainage canals and rivers
- Short-styled morph restricted to lowland S. America through Founder effect, by human introduction Morph: mating type
Founder effect: introduction of a small number of individuals with a small sample of genetic diversity of source population
- ŝƐƚƌŝďƵƚĞĚ ǁŽƌůĚ-wide in tropics and sub-tropics
- ZĞƉƌŽĚƵĐĞƐ ďLJ ĐůŽŶĂů ĂŶĚ ƐĞdžƵĂů ƌĞƉƌŽĚƵĐƚŝŽŶ
- Three morphs restricted to native range
Birds as pollinators
- Birds are major plant pollinators
- Hovering (NW) vs. Perching (OW) birds during nectar feeding
- ^ŽŵĞ ƉůĂŶƚƐ͕ ƐƵĐŚ ĂƐ ĂďŝĂŶĂ ƌŝŶŐĞŶƐ ;ZĂƚ͛Ɛ ƚĂŝůͿ ŚĂǀĞ ĂĚĂƉƚĞĚ ƐƉĞĐŝĂůŝnjĞĚ ƉĞƌĐŚĞƐ ĨŽƌ ďŝƌĚƐ promoting plant reproductive success
Reading Summary: Notes and quotes from Coyne - Chapter 1
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“Plants and animals seem intricately and almost perfectly designed for living their lives”
͞/ƚ ƚĞƐƚŝĨŝĞƐ ƚŽ ;ĂƌǁŝŶ͛ƐͿ ŐĞŶŝƵƐ ƚŚĂƚ ƚŚĞ ĐŽŶĐĞƉƚ ŽĨ ŶĂƚƵƌĂů ƚŚĞŽůŽŐLJ͕ ĂĐĐĞƉƚĞĚ ďLJ ŵŽƐƚ educated westerners before 1859, was vanquished within only a few years by a single fivehundred page book”
- “Life on earth evolved gradually beginning with one primitive species –perhaps a self-replicating molecule—that lived more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection”
Evolution
- A species undergoes change over time
Gradualism
- /ƚ ƚĂŬĞƐ ŵĂŶLJ ŐĞŶĞƌĂƚŝŽŶƐ ƚŽ ƉƌŽĚƵĐĞ Ă ƐƵďƐƚĂŶƚŝĂů ĞǀŽůƵƚŝŽŶĂƌLJ ĐŚĂŶŐĞ͕ ƐƵĐŚ ĂƐ ƚŚĞ evolution of birds from reptiles
Speciation
- ŝǀĞƌƐŝƚLJ ĂƌŝƐĞƐ ƚŚƌŽƵŐŚ ƐƉĞĐŝĂƚŝŽŶ
Common ancestry
- Every species goes back to a single common ancestor
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Natural selection
- Explains apparent design by nature
- ͞/Ĩ ŝŶĚŝǀŝĚƵĂůƐ ǁŝƚŚŝŶ Ă ƐƉĞĐŝĞƐ ĚŝĨĨĞƌ ŐĞŶĞƚŝĐĂůůLJ from one another, and some of those
ĚŝĨĨĞƌĞŶĐĞƐ ĂĨĨĞĐƚ ĂŶ ŝŶĚŝǀŝĚƵĂů͛Ɛ ĂďŝůŝƚLJ ƚŽ ƐƵƌǀŝǀĞ ĂŶĚ ƌĞƉƌŽĚƵĐĞ ŝŶ ŝƚƐ ĞŶǀŝƌŽŶŵĞŶƚ͕ ƚŚĞŶ ŝŶ ƚŚĞ next generation the “good” genes that lead to higher survival and reproduction will have relatively more copies than the “not so good” genes”
- Over time the population becomes more suited to its environment through helpful mutations
- Note that it is not a perfect process – See Sea turtle and human male analogy -- Natural selection merely offers improvements over what came before, therefore it produces “fitter” not the “fittest”
Processes other than natural selection can cause evolutionary change
- ZĂŶĚŽŵ ĞǀĞŶƚƐ – some families have more offspring
Scientific Theory
- A well though-out group of propositions meant to explain facts about the real world
- Explain “how” and “why” questions
- Must be testable and make verifiable predictions
͞ZĞƚƌŽĚŝĐƚŝŽŶ͟
- When facts and data only make sense in light of a particular scientific theory
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LECTURE 13: DARWIN’S BIG IDEA AND HOW IT CHANGED BIOLOGY
1. Evolution - the central unifying concept of biology
Ϯ͘ ĞǀĞůŽƉŵĞŶƚ ŽĨ ĂƌǁŝŶ͛Ɛ ŝĚĞĂ
3. Evolution facts and fiction
The theory of evolution
Living things change gradually from one form into another over time
- Challenges view of special creation (= direct creation of all things in effectively their present form) Theory of evolution involved two controversial ideas
- Concept of a changing universe ї replaced view of a static world
- A phenomenon with no purpose ї replaced view that the causes of all phenomena had to have a purpose
Jean-Baptiste de Lamarck (1744 -1829)
- First to use the term evolution
- First to provide a causal mechanism ї The inheritance of acquired characters
- Linear view of evolution (think L Z ŽĨ ůŝĨĞ͕ ƌĂƚŚĞƌ ƚŚĂŶ dZ Ϳ ї Simplest forms evolve directly to complex forms
- dŚĞ ŐŝƌĂĨĨĞ͛Ɛ ŶĞĐŬ͗ >ĂŵĂƌĐŬ͛Ɛ ĞdžĂŵƉůĞ ĨŽƌ ƚŚĞ ŝŶŚĞƌŝƚĂŶĐĞ ŽĨ ĂĐƋƵŝƌĞĚ ĐŚĂƌĂĐƚĞƌƐ
- Progressive increase in neck during the life time of an individual is passed on to offspring
- Would imply that a weightlifter would give birth to a well-defined and muscled baby, which is simply not true
August Weisman (1834-1914) Germplasm Theory
- /ŶŚĞƌŝƚĂŶĐĞ ŽŶůLJ ďLJ ŐĞƌŵ ĐĞůůƐ ;ŐĂŵĞƚĞƐͿ͖ ƐŽŵĂƚŝĐ ĐĞůůƐ ;ƐŽŵĂͿ ĚŽ ŶŽƚ ĨƵŶĐƚŝŽŶ ĂƐ ĂŐĞŶƚƐ ŽĨ heredity - Thus genetic information cannot pass from soma to gametes and onto next generation
- Modern interpretation stated in molecular terms genetic information flows in one direction
ŽŶůLJ ĨƌŽŵ E ƚŽ ƉƌŽƚĞŝŶ ďƵƚ ŶĞǀĞƌ ŝŶ ƌĞǀĞƌƐĞ
ŝƐĐŽǀĞƌLJ ŽĨ ƚŚĞ ĐŽƌƌĞĐƚ mechanism:
- ŚĂƌůĞƐ ĂƌǁŝŶ Θ ůĨƌĞĚ ZƵƐƐĞůů tĂůůĂĐĞ ĐŽ-discover the chief mechanism of evolution: Natural selection Charles Darwin (1809-1882)
- ĂƌǁŝŶ ŝŶĨůƵĞŶĐĞĚ ďLJ ƚŚĞ ďŽƚĂŶŝƐƚ :ŽŚŶ ^͘ ,ĞŶƐůŽǁ Ăƚ ĂŵďƌŝĚŐĞ
- ĂƌǁŝŶ ƌĞĂĚƐ ŚĂƌůĞƐ >LJĞůů͛Ɛ ;ϭϳϵϳ-ϭϴϳϱͿ Ŭ ͞WƌŝŶĐŝƉůĞƐ ŽĨ 'ĞŽůŽŐLJ͟ ;ϭϴϯϬͿ
- Lyell argued that present day geological processes can explain the history of the earth – gradualism - dŚĞ ŶŽƚŝŽŶ ŽĨ Ă ĚLJŶĂŵŝĐ ƌĂƚŚĞƌ ƚŚĂŶ Ă ƐƚĂƚŝĐ ǁŽƌůĚ ĞŵĞƌŐĞĚ ŝŶ ĂƌǁŝŶ͛Ɛ ƚŚŝŶŬing
- Voyage on H.M.S. Beagle around the world (1831-ϭϴϯϲͿ ĂƐ ƐŚŝƉ͛Ɛ ŶĂƚƵƌĂůŝƐƚ ї Most time spent in South America
- Made numerous observations and collections of plants, animals & fossils ї Geographical distribution of plants and animals of oceanic islands
- ZĞƚurned to England and spent the rest of his life (1842-1882) ŝŶ ƐĞĐůƵƐŝŽŶ Ăƚ ŽǁŶ ,ŽƵƐĞ developing his ideas, conducting experiments and writing books (25 in all)
- ĞǀĞůŽƉƐ ƚŚĞ ŶŽƚŝŽŶ ƚŚĂƚ species vary based on variation patterns of Galápagos mockingbirds ї ĂƌǁŝŶ ĚŽƵďƚƐ ͞ĨŝdžŝƚLJ͟ ŽĨ ƐƉĞĐŝĞƐ ;DĂƌĐŚ͕ ϭϴϯϳͿ ї There are 4 similar species endemic to the islands descended from a South American mainland ancestor
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ĂƌǁŝŶ ƌĞĂĚƐ Malthus’ ;ϭϳϵϴͿ ƐƐĂLJ ŽŶ ƚŚĞ WƌŝŶĐŝƉůĞ ŽĨ WŽƉƵůĂƚŝŽŶ ;^ĞƉƚ ϭϴϯϴͿ ǁŚŝĐŚ ŝŶĨůƵĞŶĐĞƐ his notion of selection
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1844: wrote but did not publish an essay on natural selection
1856: began work on natural selection book
:ƵŶĞ ϭϴϱϴ͗ ƌĞĐĞŝǀĞĚ ͞KŶ ƚŚĞ ƚĞŶĚĞŶĐLJ ŽĨ ǀĂƌŝĞƚŝĞƐ ƚŽ ĚĞƉĂƌƚ ŝŶĚĞĨŝŶŝƚĞůLJ ĨƌŽŵ ƚŚĞ ŽƌŝŐŝŶĂů ƚLJƉĞ͟ ďLJ ͘Z͘ tĂůůĂĐĞ
- :ƵůLJ ϭϴϱϴ͗ >ŝŶŶĞĂŶ ^ŽĐŝĞƚLJ ƉƌĞƐĞŶƚĂƚŝŽŶ ŝŶ >ŽŶĚŽŶ ŽĨ ĂƌǁŝŶ–Wallace paper
- 1859: publication of “The origin of species by means of natural selection or the preservation of favoured races in the struggle for life”
The Origin of Species
- All organisms have descended with modification from common ancestors
- The major agent of modification is natural selection operating on variation among individuals dŚĞ ĞƐƐĞŶĐĞ ŽĨ Ă ĂƌǁŝŶŝĂŶ ǁŽƌůĚ-view
- ZĞĐŽŐŶŝƚŝŽŶ ƚŚĂƚ ǀĂƌŝĂƚŝŽŶ ĂŵŽŶŐ ŝŶĚŝǀŝĚƵĂůƐ ŝƐ ŶŽƚ ŝŵƉĞƌĨĞĐƚŝŽŶ͕ ďƵƚ ƚŚĞ ŵĂƚĞƌŝĂů ĨƌŽŵ ǁŚŝĐŚ natural selection fashions better adapted forms of life
- This involves a move away from typology and the notion of an ideal species to population thinking ZĞƋƵŝƌĞŵĞŶƚƐ ĨŽƌ ĂƌǁŝŶ͛Ɛ ƚŚĞŽƌLJ ƚŽ ǁŽƌŬ – Assumptions
- Variation – variation among individuals in a population
- Heredity – progeny resemble their parents more than unrelated individuals
- Selection – some forms better at surviving and breeding than others in a given environment
ƌĞĂƚŝŽŶŝƐƚ ŽĐƚƌŝŶĞ
- Literal reading of Book Genesis
- Creation of all living organisms by divine order in 6 days
- All types of organisms individually created and designed by a purposeful creator ї /ŶĐŽŵƉĂƚŝďůĞ ǁŝƚŚ ĞǀŽůƵƚŝŽŶ
/ƚ ŝƐ ŶŽƚ ƐƵpported by any empirical observations
/ƚ ĚŽĞƐ ŶŽƚ ŝŶĨĞƌ ŝƚƐ ƉƌŝŶĐŝƉůĞƐ ĨƌŽŵ ŽďƐĞƌǀĂƚŝŽŶ͕ ĂƐ ĚŽĞƐ Ăůů ƐĐŝĞŶĐĞ
- /ƚƐ ĂƐƐƵŵƉƚŝŽŶƐ ůĞĂĚ ƚŽ ŶŽ ƚĞƐƚĂďůĞ Žƌ ĨĂůƐŝĨŝĂďůĞ ŚLJƉŽƚŚĞƐĞƐ
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LECTURE 14: WHAT DARWIN SAW: A BIOGEOGRAPHICAL PERSPECTIVE ON BIODIVERSITY AND
ADAPTATION
1. Contrasts between tropical & temperate ecosystems
2. The role of biotic and abiotic interactions in temperate and temperate ecosystems, respectively
3. Galápagos /slands as evolutionary laboratories ϰ͘ ƵƐƚƌĂůŝĂ͛Ɛ ŝƐŽůĂƚŝŽŶ ĂŶĚ ŝƚƐ ƵŶŝƋƵĞ ďŝŽƚĂ
ƵƌŝŶŐ ƚŚĞ ǀŽLJĂŐĞ ŽĨ ƚŚĞ ,͘D͘^͘ ĞĂŐůĞ ;ϭϴϯϭ-1836) Æ Spends most time in South America
- Stops in Brazil ї ĂƌǁŝŶ ŶŽƚĞƐ ŚŝŐŚ ƐƉĞĐŝĞƐ ĚŝǀĞƌƐŝƚLJ ĂŶĚ ŶŽǀĞů ĂĚĂƉƚĂƚŝŽŶƐ dƌŽƉŝĐĂů &ŽƌĞƐƚƐ ŝŶ ƌĂnjŝů
- Very high species ĚŝǀĞƌƐŝƚLJ ŽĨ ƉůĂŶƚ ĂŶĚ ĂŶŝŵĂů ŐƌŽƵƉƐ ĐŽŵƉĂƌĞĚ ǁŝƚŚ ƚĞŵƉĞƌĂƚĞ njŽŶĞ
- Many more biotic interactions, especially coevolved mutualisms between plants and animals
- Year-round warmth results in rapid growth of insect and microbial populations
- Pest and disease pressures on plants more intense
Tropical trees are largely animal-pollinated
Tropical Forests
High species diversity
/ŶĚŝǀŝĚƵĂůƐ ŽĨ ƐĂŵĞ ƐƉĞĐŝĞƐ ǁŝĚĞůLJ ƐĞƉĂƌĂƚĞĚ
Largely Evergreen
ĞŶƐĞ ĐĂŶŽƉŝĞƐ
Bee, butterfly, moth, bird and bat pollenators
Temperate Forests
Low species diversity
/ŶĚŝǀŝĚƵĂůƐ ŽĨ ƐĂŵĞ ƐƉĞĐŝĞƐ ĐůŽƐĞ ƚŽŐĞƚŚĞƌ
>ĂƌŐĞůLJ ĞĐŝĚƵŽƵƐ
Sparse canopies
Wind
ĂŶŝĞů :ĂŶnjĞŶ͗ ƵŐůŽƐƐŝŶĞ ĞĞƐ ĂƐ ůŽŶŐ-ĚŝƐƚĂŶĐĞ ƉŽůůŝŶĂƚŽƌƐ ŽĨ ƚƌŽƉŝĐĂů ƉůĂŶƚƐ ;^ĐŝĞŶĐĞ͕ ϭϵϳϭͿ
- hƐĞĚ ŵĂƌŬ-recapture techniques to demonstrate that bees travel up to 23 km during a day
- dŽĚĂLJ ǁŝĚĞůLJ ƌĞĐŽŐŶŝnjĞĚ ƚŚĂƚ ďĞĞƐ͕ ŵŽƚŚƐ ĂŶĚ ŚƵŵŵŝŶŐďŝƌĚƐ ƚƌĂǀĞů ůŽŶŐ ĚŝƐƚĂŶĐĞƐ ĚƵƌŝŶŐ
“trapline” foraging
- :ĂŶnjĞŶ͛Ɛ pest pressure hypothesis: ї Predicts that tropical tree seedlings are less likely to establish close to the maternal parent ї ZĞƐƵůƚ ĐŽŶĨŝƌŵĞĚ ƚŚƌŽƵŐŚ ĨŝĞůĚ ĞdžƉĞƌŝŵĞŶƚƐ ї Adult tree will have more pests on it, which will transfer to seedlings ї Although seedlings are most dense close to parent tree, seedling survival is highest at a greater distance
Acacia
- /ŶƚĞŶƐĞ ŚĞƌďŝǀŽƌLJ ŝŶ ƚƌŽƉŝĐĂů ĞĐŽƐLJƐƚĞŵƐ ƌĞƐƵůƚƐ ŝŶ ĐŽŶƐŝĚĞƌĂďůĞ ĚĂŵĂŐĞ ĂŶĚ ĐŽŶƐƵŵƉƚŝŽŶ ŽĨ plant biomass
- Some species of Acacia and ants have co-evolved to deal with this situation
- Symbiosis: Ant-plant mutualism in Acacia ї Pseudomyrmex Ants protect Acacia against herbivorous insects ї Manipulated with chemicals to keep ants off experimentally ї Hollow thorns provide a nesting site for ants ї Beltian bodies of Acacia provide protein and lipids while extrafloral nectarines provide sugar for the ants
- Experiment by Megan Frederickson (EEB) ;EĂƚƵƌĞ͕ ϮϬϬϱͿ
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ї emonstrated that in ͞Ğǀŝů͛Ɛ ŐĂƌĚĞŶ,” Peru -- ants defend their hosts against plant competitors using formic acid as a herbicide, thus benefitting from more nest sites
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Epiphytes:
- Epiphytes are plants that grow on other plants non-parasitically
- Common in the tropics, increasing species diversity
- Epiphytic life form has evolved independently in many unrelated families Æ Convergent evolution ї Ex: Lichens, orchids, bromeliads, mosses
- Questions: ї Are particular Trees favoured? ї How are they dispersed? ї What pollinates them? ї How and why have they evolved?
- Bright colours tend to attract pollinators
Opportunities to investigate function and adaptive significance
- Why do some flowers change colour?
- Why are some leaves red? ї DĂLJ ƉƌŽƚĞĐƚ ĂŐĂŝŶƐƚ ŚĞƌďŝǀŽƌLJ ďLJ ŝŶƐĞĐƚƐ ĂƐ ƚŚĞLJ ĚŽŶ͛ƚ ƐĞĞ ƌĞĚ ǁĞůů
- Why does mimicry occur? ї Preying mantis – mimics living leaf ї Katydid – mimics dead leaf
- Why does poinsettia have red bracts? ї May serve to attract pollinators
Finds fossils of extinct mammals – Glyptodon – giant armadillo
- Processes that occurred in the past Æ Extinction
/ƐĂďĞůĂ͗
- Prickly Pear cacti are first coůŽŶŝnjĞƌƐ ŽĨ ǀŽůĐĂŶŝĐ ůĂŶĚƐĐĂƉĞƐ
- Capable of long-distance dispersal by fleshy bird-dispersed fruits
ĂƉhne Major:
- Site of 35-year study of natural selection in Galapagos finches
- ^ƚƵĚLJ ďLJ WĞƚĞƌ Θ ZŽƐĞŵĂƌLJ 'ƌĂŶƚ ;WƌŝŶĐĞƚŽŶͿ
- 14 Galapagos finches represent an adaptive radiation
Adaptive radiation:
- The evolution of ecological and phenotypic diversity within a rapidly multiplying lineage as a result of speciation
- From a single common ancestor the process results in an array of species that differ in traits allowing exploitation of a range of habitats and resources
- Four features commonly identify an adaptive radiation ϭ͘ ZĞĐĞŶƚ ĐŽŵŵŽŶ ĂŶĐĞƐƚƌLJ ĨƌŽŵ Ă ƐŝŶŐůĞ ƐƉĞĐŝĞƐ
2. Phenotype-environment correlation
3. Trait utility ϰ͘ ZĂƉŝĚ ƐƉĞĐŝĂƚŝŽŶ
Galapagos island giant tortoise
- Largest tortoise in ƚŚĞ ǁŽƌůĚ ;ϴϴϬŬŐ͕ Ϯŵ ůŽŶŐͿ͕ ŽůĚĞƐƚ ůŝǀŝŶŐ ŝŶĚŝǀŝĚƵĂů Λ ϭϳϬLJƌƐ
- Tortoises on different islands have different shell patterns ї ϭϬ ƐƵďƐƉĞĐŝĞƐ ŽĨ Ă ƐŝŶŐůĞ ƐƉĞĐŝĞƐ ;Geochelone nigra) – endangered
/ŐƵĂŶĂƐ͗
- Marine iguanas (Amblyrhynchus cristatus) ї Feed on seaweed ї Expels salt from nasal glands ї ƐĂůƚ-encrusted foreheads
- dĞƌƌĞƐƚƌŝĂů /ŐƵĂŶĂ ;Conolophus subcristatus) ї ϴϬй ŽĨ ĚŝĞƚ ĨƌŽŵ ƉƌŝĐŬůLJ ƉĞĂƌ ĐĂĐƚƵƐ
Birds:
- Loss of flight in cormorant ї Advantages for diving? ї Lack of predation?
- Sexually dimorphic Frigate bird
ƵƌŝŶŐ ƚŚĞ ǀŽLJĂŐĞ ŽĨ ƚŚĞ ,͘D͘^͘ ĞĂŐůĞ ;ϭϴϯϭ-1836)
- Heads south to Patagonia
Patagonia
- ŝƐĐŽǀĞƌƐ ƐƚƌŝŬŝŶŐůLJ ĚŝĨĨĞƌĞnt environments
- Abiotic factors dominate Æ ŽŵƉůĞƚĞůLJ ĐŽŶƚƌĂƐƚĞĚ ďLJ ďŝŽƚŝĐ ĨĂĐƚŽƌƐ ŽĨ ƌĂnjŝů ї Wind shear and ice storm activity affect treelines
- Landscapes are geologically young
- Abiotic factors
- Finds familiar and unfamiliar animal groups, animals with relatives around the world ї Black-necked swan Æ Looks familiar, why is the neck black? ї Southern rufous bumblebee Æ >ŽŽŬƐ ĨĂŵŝůŝĂƌ͕ ǁŚLJ ŝƐ ŝƚ ƐŽ ĨƵnjnjLJ͍ dŚĞƌŵŽƌĞŐƵůĂƚŝŽŶ͍ ї ĂƌǁŝŶ͛Ɛ ƌŚĞĂ Æ Flightlessness evolved ї Guanaco Æ ZĞůĂƚĞĚ ƚŽ ĐĂŵĞů͍
ƵƌŝŶŐ the voyage of the H.M.S. Beagle (1831-1836)
- Heads west to Australia (2 months)
Australia
- ŝƐƚŝŶĐƚ ĨůŽƌĂ ĂŶĚ ĨĂƵŶĂ ǁŝƚŚ ŚŝŐŚ ůĞǀĞůƐ ŽĨ endemism and many unique adaptations
- Biological uniqueness due to long history of isolation from other land masses
- Although a continent Australia is also an island and shows many island characteristics e.g. endemism, radiations & unique adaptations
Endemism:
- Endemic species, which are restricted to a particular geographical region or habitat
Queensland
- ŝƐĐŽǀĞƌĞĚ Ɖŝphytic fern
ƵƌŝŶŐ ƚŚĞ ǀŽLJĂŐĞ ŽĨ the H.M.S. Beagle (1831-1836)
- Heads west to Galápagos Islands ї &ŝƌƐƚ ĂƌƌŝǀĞƐ ŽŶ ^ĂŶ ƌŝƐƚŽďĂů /ƐůĂŶĚ ;ŚĂƚŚĂŵͿ ŽŶ ϵͬϭϳͬϭϴϯϱ
'ĂůĄƉĂŐŽƐ /ƐůĂŶĚƐ
- 15 main islands of volcanic origin; oldest 5-ϭϬ ŵŝůůŝŽŶ LJĞĂƌƐ ŽůĚ͖ LJŽƵŶŐĞƐƚ ŵŽƌĞ ƌĞĐĞŶƚ
- &ůŽƌĂ ĂŶĚ ĨĂƵŶĂ ĐŽůŽŶŝnjĞĚ ďLJ ƐƉĞĐŝĞƐ ĐĂƉĂďůĞ ŽĨ ůŽŶŐ-distance dispersal from South American mainland - ŝƐƚŝŶĐƚ ƌĂĐĞƐ ĂŶĚ ƐƉĞĐŝĞƐ ŽŶ ĚŝĨĨĞƌĞŶƚ ŝƐůĂŶĚƐ ƉƌŽǀŝĚĞ ĞǀŝĚĞŶĐĞ ŽĨ ĞĂƌůLJ ƐƚĂŐĞƐ ŽĨ ƐƉĞĐŝĂƚŝŽŶ
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ĂƌǁŝŶ ƐƉĞŶƚ ŽŶůLJ ϱ ǁĞĞŬƐ ŽŶ ƚŚĞ ŝƐůĂŶĚƐ ďƵƚ ŚŝƐ ŽďƐĞƌǀĂƚŝons formed the foundation for his theory of evolution
EŽǁ Ă hE ^K tŽƌůĚ ,ĞƌŝƚĂŐĞ ƐŝƚĞ ĂŶĚ ĞĐŽƚŽƵƌŝƐŵ ĚĞƐƚŝŶĂƚŝŽŶ
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Page 8 of 52
New South Wales
- ƌLJ ĨŽƌĞƐƚƐ ĐŽŵƉŽƐĞĚ ŽĨ ƵĐĂůLJƉƚƵƐ ;'Ƶŵ dƌĞĞͿ ї ŽŵŝŶĂŶƚ ƚƌĞĞ ŐƌŽƵƉ ŝŶ ƵƐƚƌĂůŝĂ
Koala
- Arboreal herbivorous marsupial
- ^ƉĞĐŝĂůŝnjĞĚ ĚŝĞƚ ŽĨ ƵĐĂůLJƉƚƵƐ ůĞĂǀĞƐ
- Can detoxify phenolics and terpenes in leaves
ZŽĚĞŶƚ ƉŽůůŝŶĂƚĞĚ ĂŶŬƐŝĂ
- Plant is a shrub, but flowers are produced on the ground where rodents forage
Summary:
ƵƌŝŶŐ ƚŚĞ ǀŽLJĂŐĞ ŽĨ ƚŚĞ ,͘D͘^͘ ĞĂŐůĞ ;ϭϴϯϭ-1836)
- >ĂŶĚƐ ŝŶ ƌĂnjŝů ї Notes high species diversity and novel adaptations
- Heads south to Patagonia ї ŝƐĐŽǀĞƌƐ ƐƚƌŝŬŝŶŐůLJ ĚŝĨĨĞƌent environments where abiotic factors dominate
- ,ĞĂĚƐ ǁĞƐƚ ƚŽ 'ĂůĄƉĂŐŽƐ /ƐůĂŶĚƐ ;ϱ ǁĞĞŬƐͿ ї Evidence of early stages of speciation ї Spent only 5 weeks on the islands but his observations formed the foundation for his theory of evolution
- Heads west to Australia (2 months) ї Notes high endemism, novel adaptations and “biological uniqueness”
- ,ĞĂĚƐ ŚŽŵĞ ƚŽ h< – ŽǁŶ ŚŽƵƐĞ ї Gets married, has children, then starts work on assembling evidence for his evolutionary theory Reading Summary: Notes and quotes from Coyne - Chapter 4:
:ƵĂŶ &ĞƌŶĄŶĚĞnj ĂƌĐŚŝƉĞůĂŐŽ
- many edemic species found nowhere else in the world
- no species of amphibian, reptile or mammal
- gives evidence for evolution
/ŵƉŽƌƚĂŶƚ ƋƵĞƐƚŝŽŶƐ ƌĞŐĂƌĚŝŶŐ ŐĞŽŐƌĂƉŚŝĐ ĚŝƐƚƌŝďƵƚŝŽŶƐ͕ ŶŽǁ ĂŶƐǁĞƌĞĚ ďLJ ͞ƌĞƚƌŽĚŝĐƚŝŽŶ͟ in light of evolutionary theory:
- Why did oceanic islands have such odd and unbalanced floras and faunas compared to continental assemblages?
- Why were Australia͛s native mammals marsupials, while placental mammals dominated the rest of the world?
- Why do distant areas with similar terrains and climates have species that appear similar, but are fundamentally different?
- dŚĞƐĞ ĂƌĞ ƚŚĞ ƚLJƉĞƐ ŽĨ ƋƵĞƐƚŝŽŶƐ ƚŚĂƚ ƉůĂŐƵĞĚ ĂƌǁŝŶ ǁŚŝůĞ ŽŶ ƚŚĞ ǀŽLJĂŐĞ ŽĨ ƚŚĞ ,͘D͘^͘ ĞĂŐůĞ
Convergent evolution
- Species that live in similar habitats will experience similar selection pressures in their environment, will therefore evolve similar adaptations
Biogeographic patterns ї Continental drift
- Marsupial fossils appear in Antarctica
- Freshwater frogs appear in eastern South America and subtropical Africa
- These observations can only be answered in light of biogeography and continental drift
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- ŝŽŐĞŽŐƌĂƉŚLJ ŵĂŬĞƐ ƉƌĞĚŝĐƚŝŽŶƐ ĂŶĚ ƐŽůǀĞƐ ƉƵnjnjůĞƐ
Continental islands vs. Oceanic islands:
- Continental islands were once connected to a continent but separated by flooding or moving continental plats
- Oceanic islands were never connected to a continent
- ŝƐƉĂƌŝƚLJ ďĞƚǁĞĞŶ ƚLJƉĞƐ ŽĨ ƉůĂŶƚƐ ĂŶĚ ĂŶŝŵĂůƐ ƚŚĂƚ ĂƉƉĞĂƌ ŽŶ ĐŽŶƚŝŶĞŶƚĂů ǀƐ ŽĐĞĂŶŝĐ ŝƐůĂŶĚƐ ŝƐ hard to explain using creationist scenario
Oceanic islands:
- Mammals, amphibians, freshwater fish and reptiles often do very well when introduced to oceanic islands
- isplace and destroy native species: ї Pigs and goats on Hawaii, Cane toad in Hawaii and
Australia, ZĂďďŝƚƐ ŝŶ ƵƐƚƌĂůŝĂ, etc.
Native to oceanic island
Plants
Birds
/ŶƐĞĐƚƐ ĂŶĚ ŽƚŚĞƌ ĂƌƚŚƌŽƉŽĚƐ
Missing from oceanic island
Land Mammals
ZĞƉƚŝůĞƐ
Amphibians, Freshwater fish
-
Oceanic islands have unbalanced biotas – missing major groups of organisms, and the same ones are missing on different islands
- Types of organisms there usually comprise similar species – a radiation – most often of which are types of species that can disperse most easily over large stretches of ocean
- Species that are most similar to those inhabiting oceanic islands are usually found on the nearest mainland even though habitats may be different
- When endemic species occur on oceanic islands, it can be explained by plant seeds hitching a ride on air currents, birds and bats flying, seals swimming and other animals hitching a ride on
“rafts”
Continental Islands:
- “old” continental islands, such as New Zealand and Madagascar were isolated before many groups of species had evolved
- Had many ecological niches unfilled which opened the door for later-evolving species to
ƐƵĐĐĞƐƐĨƵůůLJ ĐŽůŽŶŝnjĞ ĂŶĚ ĞƐƚĂďůŝƐŚ ƚŚĞŵƐĞůǀĞƐ
- Have a “somewhat” unbalanced flora and fauna
- Species on the islands closely resemble those found on nearest mainland
Envoi:
- Only evolution can explain the diversity of life that appears on islands
- Time and chance determine which species will end up on an island
- Because species on islands adapt to environments isolated from the diversity of species that live elsewhere, they are not good at co-existing with others
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Page 10 of 52
LECTURE 15: NEODARWINISM AND THE EVOLUTIONARY SIGNIFICANCE OF GENETIC VARIATION
-
DƵƐƚ ŽĐĐƵƌ ŝŶ ŐĞƌŵ ĐĞůůƐ ;ƐƉĞƌŵͬĞŐŐƐͿ – somatic mutations are not inherited
Fruit fly: ї Wild type – “normal” ї ZĞĐĞƐƐŝǀĞ ŵƵƚĂŶƚ – no eye pigment ї Homeotic mutation – leg where antenna should be, severe, but not lethal
- Barbara McClintock ;ŽƌŶĞůů hŶŝǀĞƌƐŝƚLJ͕ ϭϵϬϮ-1992) ї tŽŶ ϭϵϴϯ EŽďĞů ƉƌŝnjĞ ĨŽƌ WŚLJƐŝŽůogy-Medicine ї ŽƌŶ ƉĂƚƚĞƌŶƐ ĚŝĚŶ͛ƚ Ĩŝƚ DĞŶĚĞůůŝĂŶ ƌĂƚŝŽƐ ї ŝƐĐŽǀĞƌLJ ŽĨ ͞ũƵŵƉŝŶŐ ŐĞŶĞƐ͟ Žƌ ƚƌĂŶƐƉŽƐĂďůĞ ŐĞŶĞƚŝĐ ĞůĞŵĞŶƚƐ ŝŶ ŵĂŝnjĞ ;ĐŽƌŶͿ ї Arise by mutation and can move around the genome
- Mutant Australian daisy – potential outcomes ї Pollinators will avoid it ďĞĐĂƵƐĞ ƚŚĞLJ ĚŽŶ͛ƚ ƌĞĐŽŐŶŝnjĞ ŝƚ – will disappear ї Pollinators may find it more appealing – will increase frequency in population ї May impact population via genetic drift ї May be a polymorphism Æ Both forms (White & Yellow) co-exist Æ Neutral
- Characteristics of mutation ї hnstoppable phenomenon ї ĞƐƉŝƚĞ ĐĞůůƵůĂƌ ŵĞĐŚĂŶŝƐŵƐ ƚŽ ĐŽƌƌĞĐƚ ĞƌƌŽƌƐ ĚƵƌŝŶŐ E ƌĞƉůŝĐĂƚŝŽŶ ї Not directed by the organism or the environment ї ZĂŶĚŽŵ ǁŝƚŚ ƌĞƐƉĞĐƚ ƚŽ ĞĨĨĞĐƚƐ ŽŶ ĨŝƚŶĞƐƐ ї ZĂƚĞƐ ĚĞƉĞŶĚƐ ŽŶ ƚŚĞ ƚLJƉĞ ŽĨ ŵƵƚĂƚŝŽŶ Æ Also varies among genes ї Exposure to certain environmental conditions can affect mutation rate ї Mutagens, high temperature
- DƵƚĂƚŝŽŶ ĂŶĚ ƚŚĞ ƐƚƌƵĐƚƵƌĞ ŽĨ E
1. Point mutations
ATGCAGT Æ ATCCAGT
Ϯ͘ /ŶƐĞƌƚŝŽŶƐͬĚĞůĞƚŝŽŶƐ ;ŝŶĐůƵĚŝŶŐ ͚ũƵŵƉŝŶŐ ŐĞŶĞƐ͛Ϳ ;^ĞƉĂƌĂƚĞĚ ŝŶto potential codons)
ATG|CAG|T Æ ATG|GCA|GT
ZĞƐƵůƚƐ ŝŶ frame-shift mutation – often deleterious, changing downstream codons 3. Changes in repeat number (Separated into potential codons)
ATG|ATG|ATG|ATG Æ ATG|ATG|ATG|ATG|ATG
4. Chromosomal rearrangements
ATGCAGT Æ TGACGTA
Motoo Kimura (1924-1994):
- dŚĞŽƌĞƚŝĐĂů ƉŽƉƵůĂƚŝŽŶ ŐĞŶĞƚŝĐŝƐƚ ǁĂƐ ĨŝƌƐƚ ƚŽ ƌĞĐŽŐŶŝnjĞ ƚŚĞ ŝŵƉŽƌƚĂŶĐĞ ŽĨ ŶĞƵƚƌĂů ŵƵƚĂƚŝŽŶƐ
1. Where does genetic variation come from?
2. How is it inherited?
3. How does it influence trait variation?
4. Why is genetic variation important for evolution?
ZĞƋƵŝƌĞŵĞŶƚƐ ĨŽƌ ĂƌǁŝŶ͛Ɛ ƚŚĞŽƌLJ͗
- Genetics: ї Variation – Variation among individuals in a population ї Heredity – Progeny resemble their parents more than unrelated individuals
- Selection – some forms are better at surviving and breeding in a given environment
- ĂƌǁŝŶ ŚĂĚ ŶŽ ƵŶĚĞƌƐƚĂŶĚŝŶŐ ŽĨ ŐĞŶĞƚŝĐƐ Žƌ ƚŚĞ ŵĞĐŚĂŶŝƐŵ ŽĨ ŝŶŚĞƌŝƚĂŶĐĞ
Genotype:
- Genetic constitution (makeup) of an organism
- hƐĞĚ ŝŶ ƌĞůĂƚŝŽŶ ƚŽ Ă ŐĞŶĞ͕ Žƌ ĐŽŵďŝŶĂƚŝŽŶ ŽĨ ŐĞŶĞƐ ї Ex: Aa, AaBB
Phenotype:
- The trait of an organism as observed
- hƐĞĚ ǁŚĞŶ ĚŝƐĐƵƐƐŝŶŐ Ă ƚƌĂŝƚ Žƌ ĨĞĂƚƵƌĞ ŽĨ ĂŶ ŽƌŐĂŶŝƐŵ ƚŚĂƚ ǀĂƌŝĞƐ ї Ex: The genotype AA or Aa lead to the phenotype of smooth skin while aa leads to wrinkled skin
Genome:
- dŚĞ ĞŶƚŝƌĞ ŽƌŐĂŶŝƐŵ͛Ɛ E ŝŶĐůƵĚŝŶŐ genes and non-coding regions ї Genes – lead to phenotypes ї Non-coding regions – ͞:ƵŶŬ͟ E
What is a gene? – Various definitions
- The functional unit of inheritance
- A unit of hĞƌĞĚŝƚĂƌLJ ŝŶĨŽƌŵĂƚŝŽŶ ůŽĐĂƚĞĚ ŽŶ ƚŚĞ ĐŚƌŽŵŽƐŽŵĞƐ ĐŽŶƐŝƐƚŝŶŐ ŽĨ E
E ƐĞƋƵĞŶĐĞ ĐŽŵƉŽƐĞĚ ŽĨ codons essential for a specific biological function ї Codon: Sequence of 3 nucleotides (A,T,C,G) that code for an amino acid ї A sequence of codons make up the genetic code
Evolution requires genetic variation – where does it come from?
- Mutation
- ZĞĐŽŵďŝŶĂƚŝŽŶ
- Gene flow
- ,LJďƌŝĚŝnjĂƚŝŽŶ
/ŶĚĞƉĞŶĚĞŶƚ ĂƐƐŽƌƚŵĞŶƚ Θ recombination
- /ŶĚĞƉĞŶĚĞŶƚ ĂƐƐŽƌƚŵĞŶƚ Θ ƌĞĐŽŵďŝŶĂƚŝŽŶ ĚƵƌŝŶŐ ŵĞŝŽƐŝƐ ŐĞŶĞƌĂƚĞƐ ĞŶŽƌŵŽƵƐ ĚŝǀĞƌƐŝƚLJ ї Humans with n=23 chromosomes, 223 = 8͕ϯϴϴ͕ϲϬϴ possible gamete combinations
- Most genetic variability in a population results from sexual reproduction ї in any given generation input from mutation very small
Mutations
- hůƚŝŵĂƚĞ ƐŽƵƌĐĞ ŽĨ ŐĞŶĞƚŝĐ ǀĂƌŝĂƚŝŽŶ
- StaďůĞ ĐŚĂŶŐĞ ŝŶ E ƐĞƋƵĞŶĐĞ ƌĞƐƵůƚŝŶŐ ŝŶ ĐŚĂŶŐĞ ŽĨ ŐĞŶŽƚLJƉĞ
- Occurs at low and variable rate in all organisms
- Effects vary from neutral, deleterious, lethal or beneficial ї Fitness depends on environment in many cases
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Mutation rates in eukaryotes
Number of fitness-affecting mutations per diploid genome each generation
Drosophila (fruit fly)
1.2
Caenorhabditis (worm)
Ϭ͘ϵϲ
Arabidopsis (plant)
Ϭ͘ϭ-Ϭ͘ϲ
DŽƵƐĞͬZĂƚ
Ϭ͘ϵϭ
,ƵŵĂŶͬŚŝŵƉĂŶnjĞĞ
1.6-3
Organism
Page 11 of 52
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Page 12 of 52
What about Humans?
- Each human carries 3-5 recessive lethal alleles ї ůůĞůĞƐ ĐĂƵƐŝŶŐ ĚĞĂƚŚ ǁŚĞŶ ŚŽŵŽnjLJŐŽƵƐ ї Mating among relatives causes a higher incidence of offspring mortality
/ŶŚĞƌŝƚĂŶĐĞ ĂŶĚ ƚŚĞ ƚƌĂŶƐŵŝƐƐŝŽŶ ŽĨ ŐĞŶĞƐ ĂŵŽŶŐ ŐĞŶĞƌĂƚŝŽŶƐ
- How is genetic information transmitted from parents to offspring ї Mechanism of inheritance?
- How are traits expressed in parents and offspring ї /Ɛ ƚŚŝƐ ŝŶĨůƵĞŶĐĞĚ ďLJ ŚŽǁ ŵĂŶLJ ŐĞŶĞƐ ĐŽŶƚƌŽů Ă ƚƌĂŝƚ͍
Gregor Mendel (1822-1884)
- Priest and “father of modern genetics”
- Through controlled crosses with peas established the laws of inheritance
- DĞŶĚĞů͛Ɛ >ĂǁƐ ƌĞ-ĚŝƐĐŽǀĞƌĞĚ Ăƚ ƚŚĞ ďĞŐŝŶŶŝŶŐ ŽĨ ƚŚĞ ϮϬƚŚ ĐĞŶƚƵƌLJ ďLJ ,ƵŐŽ ĚĞ sƌŝĞƐ Θ Ăƌů
Correns
ĞƐŝŐŶ ŽĨ DĞŶĚĞů͛Ɛ džƉĞƌŝŵĞŶƚ
- Cross between two pure-breeding lines of pea plants that differ in observable phenotypic trait ї (Green parent) x (Yellow parent) Æ F1 self-crossed Æ F2 ї F1 = First generation; F2 = Second generation
- Expected results: Blending inheritance ї When offspring of a cross show intermediate phenotype ї (Green parent) x (Yellow parent) Æ Lime Green F1 Offspring Æ Lime Green F2 Offspring
- Observed results: Parental phenotypes retained -- ;zͿ с zĞůůŽǁ ƉĞĂ͛ ;'Ϳ с 'ƌĞĞŶ ƉĞĂ ї (G) x (Y) Æ &ϭ͗ ϭϬϬй ;zͿ ŽĨĨƐƉƌŝŶŐ Æ F2: ¾ (Y) offspring, ¼ (G) offspring ї Therefore: Yellow (Y) is dominant, Green (G) is recessive ї 3:1 phenotypic ratio in F2 – ¾ dominant and ¼ recessive observed ї 1:2:1 genotypic ratio in F2 – ¼ YY allele = (Y), ½ Yy allele = (Y), ¼ yy allele = (G)
DĂŝŶ ĐŽŶĐůƵƐŝŽŶƐ ĨƌŽŵ DĞŶĚĞů͛Ɛ ĞdžƉĞƌŝŵĞŶƚƐ ǁŝƚŚ ƉĞĂƐ
- /ŶŚĞƌŝƚĂŶĐĞ ĚĞƚĞƌŵŝŶĞĚ ďLJ ĚŝƐĐƌĞƚĞ ƉĂƌƚŝĐůĞƐ -- genes – “particulate inheritance”
- Most organisms carry two copies of each gene – alleles -- and are diploid
- Organisms produce haploid gametes (sperm, eggs) each containing one allele
- Offspring inherit one allele from each parent at random
- ŽŵŝŶĂŶƚ ĂůůĞůĞ ŵĂƐŬƐ ŚĞƚĞƌŽnjLJŐŽƵƐ ĂůůĞůĞ ŝŶ ŚĞƚĞƌŽnjLJŐŽƵƐ genotype
ŝƐĐƌĞƚĞ ǀƐ. Continuous traits
- Discrete traits: ї Simply inherited by 1 or 2 genes (major genes) ї Mendelian genetics ї 3 potential outcomes – homozygous dominant (AA), heterozygous ; ĂͿ͕ Žƌ ŚŽŵŽnjLJŐŽƵƐ recessive (aa)
- Continuous traits: ї Complex inheritance by many genes (polygenes) of small effect ї Quantitative inheritance ї Continuum of outcomes – Ex: weight and height in humans ї ϲϱй ŽĨ ǀĂƌŝĂƚŝŽŶ ŝŶ ŚƵŵĂŶ ŚĞŝŐŚƚ ŝƐ ŚĞƌŝƚĂďůĞ
Genetic Polymorphism
- ŝĨĨĞƌĞŶƚ ƉŚĞŶŽƚLJƉĞƐ ĞdžŝƐƚ ŝŶ ƚŚĞ ƐĂŵĞ ƉŽƉƵůĂƚŝŽŶ ŽĨ Ă species
- The occurrence of two or more discrete forms of a species in the same locality in such proportions that the rarest cannot be maintained by mutation alone ї hsually means frequency of rarest mutation хϱй
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/ŶǀŽůǀĞƐ ĚŝƐĐƌĞƚĞ ƉŚĞŶŽƚLJƉĞƐ ;ĐĂůůĞĚ ĨŽƌŵ Žƌ morphs) governed by segregation of a small number of alleles at 1-2 major genes
- Ex: sexual dimorphism, blood types
Gene number & phenotypic distribution
- ZĞůĂƚŝŽŶ ďĞƚǁĞĞŶ ŶƵŵďĞƌ ŽĨ ŐĞŶĞƐ ĐŽŶƚƌŽůůŝŶŐ Ă ƚƌĂŝƚ ĂŶĚ ƉŚĞŶŽƚLJƉŝĐ ǀĂƌŝĂďŝůŝƚLJ
- Few genes – discontinuous (discrete) variation
- Many genes - continuous variation ї Gene action is co-dominant ї ,ĞƚĞƌŽnjLJŐŽƚĞ ŚĂƐ ĂŶ ŝŶƚĞƌŵĞĚŝĂƚĞ ƉŚĞŶŽƚLJƉĞ – dominance does not occur
Genetic analysis of variation
- ŝƐĐŽŶƚŝŶƵŽƵƐ ǀĂƌŝĂƚŝŽŶ - Mendelian genetics ї Major genes, dominance and recessiveness, genetic polymorphism
- Continuous variation - Quantitative genetics ї Polygenes, selection response, artificial selection experiments
&ŝƐŚĞƌ͛Ɛ &ƵŶĚĂŵĞŶƚĂů dŚĞŽƌĞŵ ŽĨ EĂƚƵƌĂů ^ĞůĞĐƚŝŽŶ
- ^ŝƌ ZŽŶĂůĚ A. Fisher ;ϭϴϵϬ-1962)
- “The rate of increase in fitness of a population at any time is equal to its genetic variance in fitness at that time”
Reading Summary: Notes and quotes from Coyne - Chapter 5:
Hornets vs. Bees
- Hornets adapt to take over bee colonies
- Bees adĂƉƚ ƵŶŝƋƵĞ ĚĞĨĞŶƐĞ ƚŽ ͚ĐŽŽŬ͛ ƐĐŽƵƚ ŚŽƌŶĞƚ ŝŶǀŽůǀŝŶŐ ĐŽŽƌĚŝŶĂƚŝŽŶ
- /ŶƚƌŽĚƵĐĞ ƵƌŽƉĞĂŶ ǀĂƌŝĞƚLJ ŽĨ ďĞĞƐ͕ ƚŚĞLJ ŐĞƚ ĚĞƐƚƌŽLJĞĚ ďLJ ŚŽƌŶĞƚƐ͕ ĂƐ ƚŚĞLJ ĂƌĞ ĚĞĨĞŶƐĞůĞƐƐ
WĂƌĂƐŝƚĞͬŚŽƐƚ ĂĚĂƉƚĂƚŝŽŶƐ Θ ŝŶƚĞƌĂĐƚŝŽŶƐ
- Plants that look like insects ї Chemicals & appearance Æ moths that want to mate end up spreading pollen
- /ŶƐĞĐƚƐ ƚŚĂƚ ůŽŽŬ ůŝŬĞ ƉůĂŶƚƐ ї Avoidance of predators
- ĂƌŬĞƌ ƐŽŝů Æ ĂƌŬĞƌ ŵŝĐĞ͖ >ŝŐŚƚĞƌ ƐŽŝů Æ lighter mice
Evolution & Selection
- “Mindless materialistic process that could achieve the same result as celestial design”
- ZĞƋƵŝƌĞƐ ŶŽ ǁŝůů Žƌ ĐŽŶƐĐŝŽƵƐ ĞĨĨŽƌƚ
- Population must be variable, variability must be heritable and any adaptations must increase potential to leave offspring
- Not all chance Æ “non-random survival of random variants”
- Selection cannot create a step that does not benefit its possessor
ZĞƉƌŽĚƵĐƚŝŽŶ͕ ŶŽƚ ƐƵƌǀŝǀĂů͕ ĚĞƚĞƌŵŝŶĞƐ ǁŚĞƚŚĞƌ ŐĞŶĞƐ ŵĂŬĞ ŝƚ ƚŽ ŶĞdžƚ ŐĞŶĞƌĂƚŝŽŶ
- Same genes that increase ability to reproduce when you are young may cause enlarged prostate when old
Acacia Æ When one species does something to help another, it always helps itself in the process
Adaptations increase the fitness of the individual, not the species
- Never see adaptations that benefit the species at the cost of the individual ї Male preying mantis & black widow spider?
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Number of offspring is finite
- Allele frequencies in offspring may not be representative of parents
- Proportion of alleles can change by chance
Genes can become fixed in the population Æ ƌŝƐĞ ƚŽ ϭϬϬй ĨƌĞƋƵĞŶĐLJ ĚƵĞ ƚŽ ŐĞŶĞƚŝĐ ĚƌŝĨƚ
ĐŽŝŶ ŚĂƐ Ă ϱϬй ĐŚĂŶĐĞ ŽĨ revealing a head or tail on a coin toss
- /Ĩ LJŽƵ ŽŶůLJ ŚĂǀĞ Ă ĨĞǁ ƚŽƐƐĞƐ͕ ƚŚĞƌĞ ŝƐ Ă ŚŝŐŚ ƉƌŽďĂďŝůŝƚLJ LJŽƵ ǁŝůů ĚĞǀŝĂƚĞ ĨƌŽŵ ƚŚĂƚ ϱϬͬϱϬ ƌĂƚŝŽ
Small populations
- Proportion of alleles can change by chance
- Change in allele frequencies over time NOT due to natural selection
- hŶƵƐƵĂů ďůŽŽĚ ƚLJƉĞ ĨƌĞƋƵĞŶĐŝĞƐ ŝŶ ŵŝƐŚ ĐŽŵŵƵŶŝƚŝĞƐ
ƌŝĨƚ с ƌĂŶĚŽŵ
- Can change allele frequencies no matter how useful they are
- Can overpower natural selection in small populations
- Sampling effect can be so large that it raises frequency of harmful genes even though selection works against them
- Even tiny advantages immeasurable by biologists can lead to important changes over time
Animal & Plant Breeding
- ŽŵĞƐƚŝĐ ĚŽŐ Æ from Eurasean grey wolf
- /Ĩ ĨŽƐƐŝůƐ ŽĨ ĚŽŐƐ ǁĞƌĞ ƚŽ ďĞ ĚŝƐĐŽǀĞƌĞĚ͕ ƚŚĞLJ ǁŽƵůĚ ďĞ ƚŚŽƵŐŚƚ of as new species
- ϭϱϬ ďƌĞĞĚƐ фϭϬ͕ϬϬϬ LJĞĂƌƐ Æ EĂƚƵƌĂů ƐĞůĞĐƚŝŽŶ ƚŽŽŬ ϭϬϬϬdž ůŽŶŐĞƌ ƚŽ ůĞĂĚ ƚŽ ƚŚĞ ĚĞǀĞůŽƉŵĞŶƚ ŽĨ the grey wolf.
- Artificial selection Æ no bearing on fitness or reproductive success Æ completely manipulated
- ĂƌǁŝŶ Æ began the origin of species with notion of artificial selection because success of artificial selection is so obvious, that the logical leap from artificial to natural selection became natural Evolution in the test tube
- Exposing captive populations to new environmental challenges
- hƐing microbes you can observe thousands of generations in real-time ї Genuine evolution Æ although challenge may be man-made ї More “natural” than artificial selection
- Lenski (See lecture 19) ї depleted then renewed glucose substrate of E. coli ї ĐƌĞĂƚĞĚ Ă ĨĞĂƐƚͬĨĂmine environment ї ŶŽǁ ŐƌŽǁ ϳϬй ĨĂƐƚĞƌ ƚŚĂŶ ƵŶƐĞůĞĐƚĞĚ ƐƚƌĂŝŶ
- /Ĩ LJŽƵ ƌĞŵŽǀĞ Ă ŐĞŶĞ Ă ŵŝĐƌŽďĞ ŶĞĞĚƐ ƚŽ ƐƵƌǀŝĐĞ͕ ǁŝůů ƚŚĞ ŵŝĐƌŽďĞ ĞǀŽůǀĞ Ă ǁĂLJ ĂƌŽƵŶĚ ƚŚĞ
ƉƌŽďůĞŵ͍ hƐƵĂůůLJ LJĞƐ
- Barry Hall ї ĞůĞƚĞĚ ŐĞŶĞ ƚŚĂƚ ĐƌĞĂƚĞƐ ůĂĐƚĂƐĞ ĞŶnjLJŵĞ ї Grew bacteria on lactose substrate ї ǀĞŶƚƵĂůůLJ ďĂĐƚĞƌŝĂ ĞǀŽůǀĞĚ ǁŽƌŬĂƌŽƵŶĚƐ ƚŽ ƵƚŝůŝnjĞ ůĂĐƚŽƐĞ
- Natural selection can promote the evolution of complex, interconnected biochemical systems in which all parts are codependent
- Selection does not create new traits out of thin air – produces “new” adaptations by modifying preexisting features
- WĂƵů ZĂŝŶĞLJ ї Yielded a small-scale “adaptive radiation” of Pseudomonas under laboratory conditions
ZĞƐŝƐƚĂŶĐĞ ƚŽ ƌƵŐƐ ĂŶĚ WŽŝƐŽŶƐ
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'ŝǀĞŶ ŚƵŐĞ ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞƐ ĂŶĚ ƐŚŽƌƚ ŐĞŶĞƌĂƚŝŽŶ ƚŝŵĞƐ͕ ƚŚĞ ĐŚĂŶĐĞ ŽĨ Ă mutation producing antibiotic resistance is high
- Best example we have of selection in action
- Creates an arms race between humans and microorganisms
- However, polio and measles have not evolved resistance to vaccines yet ї dŚĞŽƌLJ ŽĨ ĞǀŽůƵƚŝŽŶ ĚŽĞƐŶ͛ƚ ƉƌĞĚŝĐƚ ƚhat everything will evolve
- tŚĞŶ Ă ƉŽƉƵůĂƚŝŽŶ ĞŶĐŽƵŶƚĞƌƐ Ă ƐƚƌĞƐƐ ƚŚĂƚ ĚŽĞƐŶ͛ƚ ĐŽŵĞ ĨƌŽŵ ŚƵŵĂŶƐ͕ ƐƵĐŚ ĂƐ Ă ĐŚĂŶŐĞ ŝŶ salinity, temperature, or rainfall, natural selection will often produce an adaptive response
Selection in the Wild
- Natural selection in the wild is incredibly slow
- Given the gradual pace of evolution it would be unreasonable to expect to see selection transforming one “type” of plant or animal into another – macroevolution, within a human lifetime ї We know that macroevolution happens, we just ĐĂŶ͛ƚ see it happening
- Medium ground finch of Galapagos ї ^ĞǀĞƌĞ ĚƌŽƵŐŚƚ ƌĞĚƵĐĞĚ ƐƵƉƉůLJ ŽĨ ƐĞĞĚƐ ŽŶ ŝƐůĂŶĚ ŽĨ ĂƉŚŶĞ DĂũŽƌ ї Finch was forced to turn to larger and harder seeds when small soft seeds ran out of supply ї Big-beaked individuals got food, survived, left more offspring ї ǀĞƌĂŐĞ ďĞĂŬ ƐŝnjĞ ŝŶĐƌĞĂƐĞĚ ďLJ ϭϬй ŽǀĞƌ ƚŚĞ ŶĞdžƚ ŐĞŶĞƌĂƚŝŽŶ
- hŶĚĞƌ ƉƌŽůŽŶŐĞĚ ĚƌŽƵŐŚƚ͕ ƐŽŝůƐ ĚƌLJ ŽƵƚ ƋƵŝĐŬĞƌ ĂĨƚĞƌ ƚŚĞ ƌĂŝŶƐ Æ Should produce seeds quicker
- hŶĚĞƌ ŶŽƌŵĂů ĐŽŶĚŝƚŝŽŶƐ͕ ŝƚ ƉĂLJƐ ƚŽ ĚĞůĂLJ ƐĞĞĚ ƉƌŽĚƵĐƚŝŽŶ ƚŽ ŐƌŽǁ ůĂƌŐĞƌ ĂŶĚ ƉŽƚĞŶtially grow more seeds ї Tested experimentally with wild mustard by Arthur Weis
Can selection build complexity?
- Complex features take a long time to develop
- /ƚ ŝƐ ƌĞĂƐŽŶĂďůĞ ƚŽ ƚŚŝŶŬ ƚŚĂƚ ƚŚĞƌĞ ĂƌĞ ĂĚĂƉƚĂƚŝŽŶƐ ƚŚĂƚ ĐŽƵůĚ ŶŽƚ ŚĂǀĞ ďĞĞŶ ďƵŝůƚ ďLJ ƐĞůĞĐƚŝŽŶ͕ which would require thinking of another mechanism
- Advocates for intelligent design ;/Ϳ argue that complex mechanisms such as bacterial flagellum, blood clotting and the human brain must be due to / ĂƐ ƚŚĞLJ ĚĞĨLJ ĂƌǁŝŶŝĂŶ explanation Æ
“god of the gaps” ї / itself makes no testable scientific claims, but only offers half-baked criticisms of
ĂƌǁŝŶŝƐŵ
ї tĞ͛ůů ŶĞǀĞƌ ďĞ ĂďůĞ ƚŽ ŬŶŽǁ ŚŽǁ ĞǀŽůƵƚŝŽŶ ĐƌĞĂƚĞĚ ĞǀĞƌLJƚŚŝŶŐ ї Science, like everything, has mysteries
- Clotting could have been built up in an adaptive way from simpler precursors ї Must have been an ancestral protein from which fibrinogen evolved ї Found likely precursor in sea cucumber
- ͞/ŐŶŽƌĂŶĐĞ ŵŽƌĞ ĨƌĞƋƵĞŶƚůLJ ďĞŐĞƚƐ ĐŽŶĨŝĚĞŶĐĞ ƚŚĂŶ ĚŽĞƐ ŬŶŽǁůĞĚŐĞ͟ – ŚĂƌůĞƐ ĂƌǁŝŶ
- Selection is perfectly adequate to explain changes that we see in the fossil record
- A span of ten million years is beyond our intuitive grasp
- /Ɛ ŶĂƚƵƌĂů ƐĞůĞĐƚŝŽŶ ƐƵĨĨŝĐŝĞŶƚ ƚŽ ĞdžƉůĂŝŶ Ă ƌĞĂůůLJ ĐŽŵƉůĞdž ŽƌŐĂŶ͕ ƐƵĐŚ ĂƐ ƚŚĞ ĞLJĞ͍ ї Complex arrangement of the iris, lens, cornea; all of which must work together to create an image ї / ĂƌŐƵŵĞŶƚ͗ ŽƵůĚ ŶŽƚ ŚĂǀĞ ďĞĞŶ ĨŽƌŵĞĚ ŝŶ ŐƌĂĚƵĂů ƐƚĞƉƐ Æ how could “half an eye” be of any use? ї A possible sequence of events: ї Eyespots made of light-sensitive pigment, as seen in flatworms
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ї Skin eventually folds in, which forms a cup that protects the eyespot and allows ŝƚ ƚŽ ďĞƚƚĞƌ ůŽĐĂůŝnjĞ ƚŚĞ ůŝŐŚƚ ƐŽƵƌĐĞ͕ ĂƐ ƐĞĞŶ ŝŶ ůŝŵƉĞƚƐ ї /Ŷ ĂďĂůŽŶĞƐ͕ ƉĂƌƚ ŽĨ ƚŚĞ ĨůƵŝĚ ŝŶ ƚŚĞ ĞLJĞ ŚĂƐ ĐŽĂŐƵůĂƚĞĚ ƚŽ ĨŽƌŵ Ă ůĞŶƐ ї Nearby muscles have been co-opted to move the lens and vary its focus ї ĂŶ-Eric Nilsson and ^ƵƐĂŶŶĞ WĞůŐĞƌ ŽĨ >ƵŶĚ hŶŝǀĞƌƐŝƚLJ ŝŶ ^ǁĞĚĞŶ ї Created a mathematical model starting with light-sensitive pigment ї Accepted “mutations” that improved visual acuity, rejected those that degraded it ї Through a series of 1,829 adaptive steps, their model yielded an eye,
ĂƉƉƌŽdžŝŵĂƚĞůLJ ϰϬϬ͕ϬϬϬ LJĞĂƌƐ ƵƐŝŶŐ ŵŽƐƚ ĐŽŶƐĞƌǀĂƚŝǀĞ ŵĞƚŚŽĚƐ ї ͞/ƚ͛Ɛ ŽďǀŝŽƵƐ ƚŚĂƚ ƚŚĞ ĞLJĞ ǁĂƐ ŶĞǀĞƌ Ă ƌĞĂů ƚŚƌĞĂƚ ƚŽ ĂƌǁŝŶ͛Ɛ ƚŚĞŽƌLJ ŽĨ evolution” Weak forces operating over long periods of time create large and dramatic change
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LECTURE 16: MAINTENANCE AND MEASUREMENT OF GENETIC VARIATION
1. What processes influence the maintenance of genetic variation in populations?
2. How do we measure genetic variation and how much exists in populations?
Foundations of population genetics
- ϭϵϯϬ-ϱϬ ƚŚĞŽƌĞƚŝĐĂů ƉŽƉƵůĂƚŝŽŶ ŐĞŶĞƚŝĐƐ ǁĂƐ ŝŶŝƚŝĂƚĞĚ ďLJ ^ŝƌ ZŽŶĂůĚ ͘ &ŝƐŚĞƌ ;ϭϴϵϬ-ϭϵϲϮͿ͕ :͘͘^͘
Haldane (1882-1964) & S. Wright (1889-1998) and provided the foundations for “NeoĂƌǁŝŶŝƐŵ͟ ĂŶĚ ƚŚĞ ͞EĞǁ ^LJŶƚŚĞƐŝƐ͟
- They showed that conƚŝŶƵŽƵƐ ǀĂƌŝĂƚŝŽŶ ĂŶĚ ĂƌǁŝŶŝĂŶ ŶĂƚƵƌĂů ƐĞůĞĐƚŝŽŶ ǁĞƌĞ ĞŶƚŝƌĞůLJ ĐŽŶƐŝƐƚĞŶƚ
ǁŝƚŚ DĞŶĚĞů͛Ɛ >ĂǁƐ
- They also demonstrated the evolutionary significance of genetic variation leading to several key questions and development of the field of ecological & evolutionary genetics
Key questions in ecological & evolutionary genetics
- What processes influence patterns of genetic diversity in natural populations?
- How much and what types of genetic variation occur in populations?
- How can we obtain empirical estimates of the amounts of variation in populations?
/mportant parameters used to measure patterns of genetic variation
- Polymorphism (P) ї Proportion of gene loci that are polymorphic
- ,ĞƚĞƌŽnjLJŐŽƐŝƚLJ ;,Ϳ ї ǀĞƌĂŐĞ ĨƌĞƋƵĞŶĐLJ ŽĨ ŚĞƚĞƌŽnjLJŐŽƵƐ ŝŶĚŝǀŝĚƵĂůƐ ƉĞƌ ŐĞŶĞ locus ї Locus: location on a chromosome that is usually a gene
Processes that influence patterns of genetic diversity
- Mutation ;/ŶĐƌĞĂƐĞƐ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJͿ ї hůƚŝŵĂƚĞ ƐŽƵƌĐĞ ŽĨ ŐĞŶĞƚŝĐ ǀĂƌŝĂƚŝŽŶ ї Caused by random errors during replication ї Can be any of the four types discussed in lecture 15
- ZĞĐŽŵďŝŶĂƚŝŽŶ ;/ŶĐƌĞĂƐĞƐ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJͿ ї /ŶƚƌŽĚƵĐĞƐ ŶĞǁ ĐŽŵďŝŶĂƚŝŽŶƐ ŽĨ ŵƵƚĂƚŝŽŶƐ ŝŶƚŽ Ă ƉŽƉƵůĂƚŝŽŶ ї No new mutations, just shuffling existing mutations ї Ex: mutations from one allele can recombine with another allele to create new combinations - ZĂŶĚŽŵ ŐĞŶĞƚŝĐ ĚƌŝĨƚ ;ZĞĚƵĐĞƐ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJͿ ї Change in the frequency of a gene due to random sampling ї Variability gets lost ї ƌŝĨƚ ŝŵƉŽƌƚĂŶƚ ǁŚĞŶ ƉŽƉƵůĂƚŝŽŶƐ ďĞĐŽŵĞ ƐŵĂůů
- Natural selection (Can reduce or increase genetic diversity) ї Purifying (negative) selection Æ mutations that reduce fitness removed from population by selection ї Positive selection (adaptation) Æ mutations that increase fitness become fixed in the population ї Balancing selection Æ natural selection maintains diversity (heƚĞƌŽnjLJŐŽƚĞ ĂĚǀĂŶƚĂŐĞͿ ї Polymorphism͕ ĐĂŶ͛ƚ Ĩŝdž Ă ŚĞƚĞƌŽnjLJŐŽƚĞ
- Many controversies in evolutionary biology concern the relative importance of these forces in evolution ŝǀĞƌƐĞ ŵĞĐŚĂŶŝƐŵƐ ŵĂŝŶƚĂŝŶ ŐĞŶĞƚŝĐ ǀĂƌŝĂƚŝŽŶ ǁŝƚŚŝŶ ƉŽƉƵůĂƚŝŽŶƐ Æ Classes of explanations
- Mutation-selection balance
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ї Less fit genotypes maintained by repeated mutation
ŝĨĨĞƌĞŶƚ ƐĞůĞĐƚŝǀĞ ĨŽƌĐĞƐ ї ,ĞƚĞƌŽnjLJŐŽƚĞ ĂĚǀĂŶƚĂŐĞ͕ ĨƌĞƋƵĞŶĐLJ-dependent selection, fitness varies in space and time - Variation selectively neutral ї Alleles at polymorphic loci (plural form of locus) do not differ in fitness, hence none eliminated by selection
Artificial Selection
- Early evidence for the existence of genetic variation ї Selection experiments on quantitative traits in different groups of organisms ї /ŶǀŽůǀĞƐ ĐŽŶƚƌŽůůĞĚ ďƌĞĞĚŝŶŐ ĂŶĚ ƐĞůĞĐƚŝŽŶ ŽĨ ŝŶĚŝǀŝĚƵĂůƐ ĨŽƌ ŵĂŶLJ ŐĞŶĞƌĂƚŝŽŶƐ ї Ex: creation of dog breeds from wolf ancestor Æ goal ŽĨ ĐƌĞĂƚŝŶŐ ƉĞƚͬǁŽƌŬŝŶŐ ĂŶŝŵĂů
- Selection response for bristle number in fruit flies - Drosophila melanogaster ї Selection for high bristle number increases bristle number through generations ї /ŵƉůŝĞƐ ǀĂƌŝĂďŝůŝƚLJ ǁŝƚŚŝŶ ƐƚĂƌƚŝŶŐ ƉŽƉƵůĂƚŝŽŶ ї dŽƉ ϱй ŽĨ ĚŝƐƚƌŝďƵƚŝŽŶ ї ZĞůĂdž ĂĨƚĞƌ ϮϬth generation Æ Starts to level off ї Control involves random mating Æ bristle number remains constant
- SelecƚŝŽŶ ƌĞƐƉŽŶƐĞ ŝŶ ŵĂŝnjĞ ї Shows that when you relax selection (high or low), levels return to normal over time ї This type of artificial selection is the basis of plant breeding and is used to improve crop varieties - Selection response in monkey flowers (:ŽŚŶ Kelly, h͘ ŽĨ Žǁ ŚŽŵŽnjLJŐŽƐŝƚLJ
Low polymorphism
High polymorphism
Wild type is best genotype
No best or ideal genotype
Purifying selection reduces diversity
Balancing selection favours diversity
+ + + + + + + + + + 2 + + + + +
3 1 2 2 2 5 4 1 1 1 ϳ 5 3 2 1 3
AABBCCMMNNOOPP
AABBCCMMNNOOPP
Note: + = wild type, # = polymorphic allele
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Classical
- Wild type allele Æ Occasional new allele that become new wild-type ї Wild Type: Fittest genotype
- Purifying selection removes “bad” alleles
Balance
- No fittest type – some organisms found all over the world
- Variability is important
Electrophoresis revolution (ZŝĐŚĂƌĚ ͘ >ĞǁŽŶƚŝŶ, ,ĂƌǀĂƌĚ hŶŝǀĞƌƐŝƚLJͿ
- Allozyme gel electrophoresis ї ůůŽnjLJŵĞ – different forms of the same protein
- Provided a way to ask - “what proportion of genes are variable (polymorphic)?” ї Fundamental dispute between the classical and balance schools
- /ŶŝƚŝĂƚĞĚ ůĂƌŐĞ ƐĐĂůĞ ƐƵƌǀĞLJƐ ŽĨ ĞůĞĐƚƌŽƉŚŽƌĞƚŝĐ ǀĂƌŝĂƚŝŽŶ ŝŶ ĞŶnjLJŵĞƐ Θ ƉƌŽƚĞŝŶƐ ŝŶ ĚŝǀĞƌƐĞ organisms and provided the first empirical evidence supporting the balance school
- hŶŝǀersal for any organism Æ ůů ŽƌŐĂŶŝƐŵƐ ŚĂǀĞ ŐĞŶĞƐ ǁŚŝĐŚ ŵĂŬĞ ƉƌŽƚĞŝŶƐ ĂŶĚ ĞŶnjLJŵĞƐ
- sŝƐƵĂůŝnjĞ ŐĞŶĞƚŝĐ ǀĂƌŝĂďŝůŝƚLJ ї ,ŽŵŽnjLJŐŽƚĞƐ ŚĂǀĞ ƐƚƌŽŶŐĞƌ ďĂŶĚƐ (F = Fast migrating, S = Slow migrating) ї ,ĞƚĞƌŽnjLJŐŽƚĞƐ – no dominance͕ ĐĂŶ ǀŝƐƵĂůŝnjĞ ďŽƚŚ ĂůůĞůĞƐ
- Measuring diveƌƐŝƚLJ Ăƚ ŐĞŶĞƐ ĐŽŶƚƌŽůůŝŶŐ ĞŶnjLJŵĞƐ Θ ƉƌŽƚĞŝŶƐ
- Monomorphic gene: ї FF FF FF FF FF FF FF FF
- Polymorphic gene: ї FF FS SS MM FM MS FF FS
^ƚƵĚŝĞƐ ŽĨ ĞŶnjLJŵĞ ƉŽůLJŵŽƌƉŚŝƐŵ͗
- Advantages ї Many loci can be examined ї Can be used in nearly any organism ї Loci co-dominant, ŚĞƚĞƌŽnjLJŐŽƚĞƐ ĐĂŶ ďĞ ŝĚĞŶƚŝĨŝĞĚ ї sĂƌŝĂƚŝŽŶ ĞdžĂŵŝŶĞĚ ĐůŽƐĞ ƚŽ E ůĞǀĞů ї Provides genetic marker loci for other studies
- ŝƐĂĚǀĂŶƚĂŐĞƐ ї Variation is largely neutral or nearly neutral ї Not under selection ї Studies of quantitative inheritance are necessary to find out how much variation occurs for ecologically-relevant traits ї ŽĚLJ ƐŝnjĞ͕ ĨĞĐƵŶĚŝƚLJ ĂŶĚ ŽƚŚĞƌ ůŝĨĞ-history traits
Contrasting patterns of genetic diversity in generalist vs. specialist barnyard grasses
- Generalist – High diversity
- Specialist – Low diversity
Contrasting levels of polymorphism in plant species
- Polymorphisms compared in rare vs. widespread species ї Higher polymorphisms in widespread species ї ZĂƌĞ ƐƉĞĐŝĞƐ ŚĂǀĞ ůŽǁ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJ
- Extinction ї Low genetic variability ї No habitat
E ƐĞƋƵĞŶĐŝŶŐ Ăůlows differences between individuals in single nucleotides to be identified
- SNP – single nucleotide polymorphism
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Can be measured for thousands of genes
Can get measure of SNP frequencies Æ DĞĂƐƵƌĞŵĞŶƚƐ ŽĨ ƉŽůLJŵŽƌƉŚŝƐŵ ŝŶ E
LECTURE 17: ORGANISMAL REPRODUCTIVE DIVERSITY
1. Why did sex evolve?
2. How do we explain the diversity of reproductive systems?
3. What are the costs and benefits of inbreeding & outbreeding?
DNA sequence variation among different organisms
Organism
DNA polymorphism
Human
ϭͬϭϬϬϬ ďƉ
ZŝĐĞ
ϭͬϭϬϬϬ ďƉ
Mosquito
ϭͬϮϬϬ ďƉ
Fruit fly ϭͬϱϬ ďƉ
E. coli ϭͬϮϬ ďƉ
Bp = Base pair
Steven Wright (EEB)
- &ŽƵŶĚ ƚŚĂƚ ĚŽŵĞƐƚŝĐĂƚŝŽŶ ŽĨ ŵĂŝnjĞ ĨƌŽŵ ŝƚƐ ƉƌŽŐĞŶŝƚŽƌ ƚĞŽƐŝŶƚĞ ĐĂƵƐĞĚ ϱϳй ƌĞĚƵĐƚŝŽŶ ŝŶ variation at SNPs
- ƐƚŝŵĂƚĞ ƚŚĂƚ ϭϮϬϬ ŐĞŶĞƐ ŚĂǀĞ ďĞĞŶ ĂĨĨĞĐƚĞĚ ďLJ ĂƌƚŝĨŝĐŝĂů ƐĞůĞĐƚŝŽŶ
- ŽŵĞƐƚŝĐĂƚŝŽŶ ŽĨ ĐƌŽƉ ƌĞĚƵĐĞĚ ǀĂƌŝĂďŝůŝƚLJ
Human genome project
- dŚĞƌĞ ŝƐ ŶŽ ƐŝŶŐůĞ ͚ŚƵŵĂŶ ŐĞŶŽŵĞ͛
- /ŶĚŝǀŝĚƵĂůƐ ĚŝĨĨĞƌ ďLJ ƚŚŽƵƐĂŶĚƐ ŽĨ ^EWƐ ŝŶ ƚŚĞir genome sequence
- dŽĚĂLJ ƚŚĞ ŐĞŶŽŵĞƐ ŽĨ хϭϬϬϬ ƉƌŽŬĂƌLJŽƚĞƐ ĂŶĚ хϭϬϬ ĞƵŬĂƌLJŽƚĞ ƐƉĞĐŝĞƐ ŚĂǀĞ ďĞĞŶ ƐĞƋƵĞŶĐĞĚ
See Lecture 15 for Reading Summary: Notes and quotes from Coyne - Chapter 5:
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ZĞƉƌŽĚƵĐƚŝǀĞ DŽĚĞƐ
- Asexual
- Sexual
Sexual System Æ ŝŽĞĐŝŽƵƐ
Æ Hermaphrodite
Mating System Æ Cross-ĨĞƌƚŝůŝnjĂƚŝŽŶ
Æ Self-ĨĞƌƚŝůŝnjĂƚŝŽŶ
ĂƌǁŝŶ ŽŶ ƐĞdž
- “We do not even in the least know the final cause of sexuality ... why new beings should be produced by the union of the two sexual elements, instead of by a process of parthenogenesis…
The whole sƵďũĞĐƚ ŝƐ ĂƐ LJĞƚ ŚŝĚĚĞŶ ŝŶ ĚĂƌŬŶĞƐƐ͟ ;ĂƌǁŝŶ͕ ϭϴϲϮͿ
Water fleas (Daphnia)
- ŝĨĨĞƌĞŶƚ ƌĞƉƌŽĚƵĐƚŝǀĞ ƐLJƐƚĞŵƐ ŽĐĐƵƌ ŝŶ ĚŝĨĨĞƌĞŶƚ ĞŶǀŝƌŽŶŵĞŶƚƐ
- Cooler, calm water – Asexual
- Warmer, turbulent water – Sexual
Many perennial plants reproduce through sexual and clonal reproduction – Water Hyacinth
- ZĞƉƌŽĚƵĐĞƐ ƐĞdžƵĂůůLJ ŽǀĞƌ ƐŽŝů
- Clonally over water
Sex
- Costs ї Time and energy to find and attract mates ї /ŶĐƌĞĂƐĞĚ ĞŶĞƌŐĞƚŝĐ ĐŽƐƚƐ ї ZŝƐŬ ŽĨ ƉƌĞĚĂƚŝŽŶ Θ ŝŶĨĞĐƚŝŽŶ ї Cost of producing males ї ϱϬй ůĞƐƐ ŐĞŶĞƚŝĐ ƚƌĂŶƐŵŝƐƐŝŽŶ ї Break up of adaptive genes combinations
- Benefits ї This is the big question – ŬŶŽǁŶ ĂƐ ͚ƚŚĞ ƉĂƌĂĚŽdž ŽĨ ƐĞdž͛
Canadian researchers studying evolution of sex
- ^ĂƌĂŚ KƚƚŽ ;hͿ͕ ŶĞŝů ŐƌĂǁĂů ; ͕ dŽƌŽŶƚŽͿ͕ 'ƌĂŚĂŵ ďĞůů ;DĐ'ŝůůͿ
The two-fold cost of meiosis
- A ƐĞdžƵĂů ĨĞŵĂůĞ ĐŽŶƚƌŝďƵƚĞƐ ŽŶůLJ ϱϬй ŽĨ ŚĞƌ ŐĞŶĞƐ ƚŽ ƚŚĞ ŶĞdžƚ ŐĞŶĞƌĂƚŝŽŶ ĐŽŵƉĂƌĞĚ ǁŝƚŚ ĂŶ asexual female
- This is known as a transmission bias favouring asexual
Hypothesis for the advantages of sex
- Bringing together favourable mutations – long term benefit
- Benefits of genetic variation in variable environments – short term benefit – “lottery model” ї Environment is a lottery Æ Better to buy more tickets, or photocopy a ticket multiple times? ї Variable offspring – some may be adapted to variable conditions
- SpatiaůůLJ ŚĞƚĞƌŽŐĞŶĞŽƵƐ ĞŶǀŝƌŽŶŵĞŶƚƐ ͚dĂŶŐůĞĚ ĂŶŬ ŚLJƉŽƚŚĞƐŝƐ͛ ї Environments themselves vary
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dĞŵƉŽƌĂůůLJ ŚĞƚĞƌŽŐĞŶĞŽƵƐ ĞŶǀŝƌŽŶŵĞŶƚƐ ͚ZĞĚ YƵĞĞŶ ŚLJƉŽƚŚĞƐŝƐ͛ ї Environments vary over time Æ Some organisms evolve faster than others ї Pests vs. Hosts
- Numerous theoretical models but a paucity of experimental evidence
Favourable combinations of mutations brought together more rapidly by sex
- Over time, large populations will more rapidly reach the “fittest” genotype
- ĞůĞƚĞƌŝŽƵƐ ŵƵƚĂƚŝŽŶƐ ĂƌĞ ĞůŝŵŝŶĂƚĞĚ ĨĂƐƚĞƌ
Theory predicts spatial heterogeneity in selection can facilitate the evolution of sex
- No data to prove this until recently
Brachionus calyciflorus, a planktonic freshwater rotifer
- Facultatively sexual ї Can reproduce sexually or asexually ї Benefit to being able to do both
- džƉĞƌŝŵĞŶƚ ďLJ >Ƶƚnj ĞĐŬƐ ĂŶĚ ŶĞŝů ŐƌĂǁĂů ;EĂƚƵƌĞ͕ ϮϬϭϬͿ ї Placed in B. calyciflorus in 3 types of environments ї Homogeneous A, Homogeneous B, Heterogeneous AB ї Higher rates of sex maintained in populations evolving in heterogeneous habitats ї KǀĞƌ ϭϮ ǁĞĞŬƐ ;ΕϳϬ generations) Æ Experimental evolution ї Sex declined rapidly in homogenous environments ї Persisted at a much higher level with spatial heterogeneity ї ŝƐĂĚǀĂŶƚĂŐĞ ƚŽ ĂƐĞdžƵĂůŝƚLJ ŝŶ ǀĂƌŝĂďůĞ ĞŶǀŝƌŽŶŵĞŶƚƐ
Evolutionary history of asexuality
- Asexuality (parthenogenesis) is sporadically distributed across the animal kingdom; more common in invertebrates but rare in vertebrates
- Asexuality (clonal propagation) is much more common in plants although few species (if any) are exclusively asexual
- Asexual species are usually at the tips of phylogenies; their long term evolutionary potential is probably low due to lack of genetic variation
Mystery of the Bdelloid rotifers - no sex for millions of years!
- A rare case of ancient asexuality in which mĂůĞƐ ĂƌĞ ƵŶŬŶŽǁŶ ďƵƚ ĚŝǀĞƌƐŝĨŝĐĂƚŝŽŶ ŚĂƐ ůĞĚ ƚŽ х ϯϬϬ spp. Mating patterns – who mates with who and how often?
- Mates less closely related than random = Outbreeding
- DĂƚĞƐ ŵŽƌĞ ĐůŽƐĞůLJ ƌĞůĂƚĞĚ ƚŚĂŶ ƌĂŶĚŽŵ с /ŶďƌĞĞĚŝŶŐ
- /Ŷ ƉƌĂĐƚŝĐĞ ƚŚĞƌĞ ŝƐ Ă ĐŽŶƚŝŶƵƵŵ ďĞƚǁeen outbreeding & inbreeding
The genetic consequences of inbreeding
- Genotypic frequencies changed
- Allele frequencies unchanged
- ,ĞƚĞƌŽnjLJŐŽƐŝƚLJ ƌĞĚƵĐĞĚ ďLJ ϱϬй ƉĞƌ ŐĞŶĞƌĂƚŝŽŶ ǁŝƚŚ ƐĞůĨ-ĨĞƌƚŝůŝnjĂƚŝŽŶ
- ,ŽŵŽnjLJŐŽƐŝƚLJ ĨŽƌ ĚĞůĞƚĞƌŝŽƵƐ ƌĞĐĞƐƐŝǀĞ ĂůůĞůĞƐ ƌĞƐƵůƚƐ in inbreeding depression
- Frequency of alleles are unchanged Æ Combined in different genotypes
How do these two populations reproduce?
- Population 1 Æ FS FS FS FS FS FS FS FS ї ,ĞƚĞƌŽnjLJŐŽƵƐ Æ Fixed Æ ďƐĞŶƐĞ ŽĨ ŚŽŵŽnjLJŐŽƚĞƐ ї Asexual cloning population with ŚĞƚĞƌŽnjLJŐŽƵƐ ŐĞŶĞ
- Population 2 Æ FF SS SS FF FF SS FF SS ї EŽ ŚĞƚĞƌŽnjLJŐŽƚĞƐ ї High level of self-ĨĞƌƚŝůŝnjĂƚŝŽŶ
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- hƐŝŶŐ ĂůůŽnjLJŵĞƐ ĂƐ ŐĞnetic markers to study how populations reproduce
,ĞƚĞƌŽnjLJŐŽƐŝƚLJ ŝŶ ƉŽƉƵůĂƚŝŽŶƐ
- ,ĞƚĞƌŽnjLJŐŽƐŝƚLJ decreases at different rates depending on mating patterns ї More related to self Æ >ĂƌŐĞƌ ĚĞĐƌĞĂƐĞ ŝŶ ŚĞƚĞƌŽnjLJŐŽƐŝƚLJ
- ,ĞƚĞƌŽnjLJŐŽƐŝƚLJ ĚĞĐƌĞĂƐĞƐ Ăƚ ĚŝĨĨĞƌĞŶƚ ƌĂƚĞƐ ĚĞƉĞŶĚŝŶŐ ŽŶ ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞ ї Smaller population Æ >ĂƌŐĞƌ ĚĞĐƌĞĂƐĞ ŝŶ ŚĞƚĞƌŽnjLJŐŽƐŝƚLJ
/ŶďƌĞĞĚŝŶŐ Ěepression
- The reduction in fitness of inbred offspring in comparison with outcrossed offspring
- Manifested by reductions in viability (survival) and fertility (reproductive output)
- Strong inbreeding depression favours survival of outbred offspring thus favouring outcrossed mating systems
Plants
- ĂƌǁŝŶ ŚĂĚ Ă ĨĂƐĐŝŶĂƚŝŽŶ ǁŝƚŚ ŝŶďƌĞĞĚŝŶŐ Θ ŽƵƚďƌĞĞĚŝŶŐ ƉůĂŶƚƐ ї A pioneer in inbreeding depression studies
- Most plants are hermaphroditic, containing both male & female parts
- ŝŽĞĐLJ ŽŶůLJ ŽĐĐƵƌƐ ŝŶ ϳй ŽĨ ĨůŽǁĞƌŝŶŐ Ɖůants ї Sexual selection results in gender dimorphism ї Male Æ dispersing pollen Æ big flowers ї Female Æ making fruit
Evolution of selfing from outcrossing in annual Water Hyacinth
- WŽƉƵůĂƚŝŽŶƐ ŝŶ ƌĂnjŝů ĂƌĞ ŵŽƐƚůLJ ŽƵƚĐƌŽƐƐŝŶŐ ĂŶĚ ǀŝƐŝƚĞĚ ďLJ ůŽŶŐ-tongued bees ї (although selfing forms do occur) ї Larger flowers to attract bees
- Long-distance dispersal favours selfing forms ї A single individual can start a colony without mates or pollinators ї Ăǁ͛ ї :ĂŵĂŝĐĂŶ ĂŶĚ ƵďĂŶ ƉŽƉƵůĂƚŝŽŶƐ ĂƌĞ ůĂƌŐĞůLJ ƐĞůĨŝŶŐ ї No pollinators on Caribbean islands
ƵƚŽŵĂƚŝĐ ƐĞůĞĐƚŝŽŶ ŽĨ Ă ƐĞůĨŝŶŐ ŐĞŶĞ ;Z͘ ͘ &ŝƐŚĞƌ͕ ϭϵϰϭͿ
Outcrosser
Selfer
Seed
1
2
Pollen
1
1
Total Gene Copies
2
3
Selfing form has a transmission advantage – Mother and Father to its own seed
Quantitative argument – Quality of offspring…?
Reading Summary: Notes and quotes from Coyne - Chapter 6:
How sex drives evolution
- dŚĞ ƉĞĂĐŽĐŬ ĂƉƉĞĂƌƐ ƚŽ ǀŝŽůĂƚĞ ĞǀĞƌLJ ĂƐƉĞĐƚ ŽĨ ĂƌǁŝŶŝƐŵ ї Long tail produces aerodynamic problems in flight ї The sparkling colours attract predators ї A lot of metabolic energy is diverted to the tail which has to be regrown each year ї dŚĞ ƋƵĞƐƚŝŽŶ ŽĨ ŚŽǁ ŝƚ ĐĂŵĞ ƚŽ ďĞ ǁŽƵůĚ ƉůĂŐƵĞ ĂƌǁŝŶ
- Sexual dimorphisms ї Appear to violate evolutionary theory
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ї Waste time, energy, and may actually reduce survival
The solutions
- /Ĩ ƚƌĂŝƚƐ ĚŝĨĨĞƌ ďĞƚǁĞĞŶ ŵĂůĞƐ ĂŶĚ ĨĞŵĂůĞƐ ŽĨ Ă ƐƉĞĐŝĞƐ͕ ƚŚĞ ĞůĂďŽƌĂƚĞ ďĞŚĂǀŝŽƵƌƐ͕ ƐƚƌƵĐƚƵƌĞƐ ĂŶĚ ornaments are nearly always restricted to males
- The currency of selection is not really survival ї Successful reproduction
- Sexual selection comes in two forms ї ŝƌĞĐƚ ĐŽŵƉĞƚŝƚŝŽŶ ďĞƚǁĞĞŶ ŵĂůĞƐ ї Males battle each other ї Males battle to control territory ї Female choosiness ї /ŶĚŝƌĞĐƚ ĐŽŵƉĞƚŝƚŝŽŶ ďĞƚǁĞĞŶ ŵĂůĞƐ ї Ex: African long-tailed widowbird ї Experiments conducted where males with clipped tails, normal tails and elongated tails were allowed to mate ї Males with artificially long tails gained an increase in matings ї /Ĩ ŵĂůĞƐ ǁŝƚŚ ƵŶŶĂƚƵƌĂůůLJ ůŽŶŐ ƚĂŝůƐ ǁŽŶ ŵŽƌĞ ĨĞŵĂůĞƐ͕ ǁŚLJ
ŚĂǀĞŶ͛ƚ ůŽŶŐĞƌ ƚĂŝůƐ ĞǀŽůǀĞĚ͍ ї Likely because having tails that long would reduce longevity more than they would increase ability to get mates ї Malte Andersson describes 232 experiments in 186 species showing that a huge variety of male traits are correlated with mating success involving female choice
Why sex?
- Why sex evolved is one ŽĨ ĞǀŽůƵƚŝŽŶ͛Ɛ ŐƌĞĂƚĞƐƚ ŵLJƐƚĞƌŝĞƐ
ŶLJ ŝŶĚŝǀŝĚƵĂů ŝŶǀŽůǀĞĚ ŝŶ ƚŚĞ ĂĐƚ ŝƐ ƐĂĐƌŝĨŝĐŝŶŐ ϱϬй ŽĨ ƚŚĞŝƌ ŐĞŶĞƚŝĐ ĐŽŶƚƌŝďƵƚŝŽŶ ƚŽ ƚŚĞ ŶĞdžƚ generation - tŚLJ ŚĂƐŶ͛ƚ ƚŚĞ ĐŽƐƚ ŽĨ ƐĞdž ůĞĚ ƚŽ ŝƚƐ ƌĞƉůĂĐĞŵĞŶƚ ďLJ WĂƌƚĞŶŽŐĞŶĞƐŝƐ – development of eggs
ǁŝƚŚŽƵƚ ĨĞƌƚŝůŝnjĂƚŝŽŶ͍ ї Sex must have some sort of evolutionary advantage that outweighs the cost ї Several theories exist that offer explanations
- Why are there only two sexes that mate and combine gametes? ї Two is the most robust and stable
- Why do two sexes have different numbers aŶĚ ƐŝnjĞƐ ŽĨ ŐĂŵĞƚĞƐ͍ ї WƌĞƐƵŵĂďůLJ ĞǀŽůǀĞĚ ĨƌŽŵ Ă ĐŽŶĚŝƚŝŽŶ ǁŚĞƌĞ ŐĂŵĞƚĞƐ ǁĞƌĞ ŽĨ ĞƋƵĂů ƐŝnjĞ ї ZĞĐŽƌĚ ŶƵŵďĞƌ ŽĨ ĐŚŝůĚƌĞŶ ƉƌŽĚƵĐĞĚ ďLJ Ă ǁŽŵĂŶ͗ ϲϵ ї ZĞĐŽƌĚ ŶƵŵďĞƌ ŽĨ ĐŚŝůĚƌĞŶ ƉƌŽĚƵĐĞĚ ďLJ Ă ŵĂŶ͗ ΕϭϬϬϬ
- ŝĨĨĞƌĞŶƚŝĂů ŝŶǀĞƐƚŵĞŶƚ ї /ŶǀĞƐƚŵĞŶƚ ŝŶ ĞdžƉĞŶƐŝǀĞ ĞŐŐƐ ǁŚŝĐŚ ĂƌĞ limited in number ї /ŶǀĞƐƚŵĞŶƚ ŝŶ ƉƌĞŐŶĂŶĐLJ ї Because of their investment, it is in their best interest to be picky rather than promiscuous ї KŶůLJ Ϯй ŽĨ ĂŶŝŵĂů ƐƉĞĐŝĞƐ ĂƌĞ ŵŽŶŽŐĂŵŽƵƐ ї Male sticks around to take care of offspring
- Explanations for sexual dimorphism ƚŚĂƚ ĚŽŶ͛ƚ ŝŶǀŽůǀĞ ƐĞdžƵĂů ƐĞůĞĐƚŝŽŶ ї Some females are larger because they produce larger gametes ї Copyright © 2008-2012 ULife Academics Ltd.
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ƌĞĂŬŝŶŐ ƚŚĞ ZƵůĞƐ
- Sexual dimorphisms occur in “socially monogamous” species
- DĂůĞƐ ĂƌĞŶ͛ƚ ĐŽŵƉĞƚŝŶŐ ĨŽƌ ĨĞŵĂůĞƐ͕ ǁŚLJ ĞǀŽůǀĞ ďƌŝŐŚƚ ĐŽůŽƵƌƐ ĂŶĚ ŽƌŶĂŵĞŶƚƐ͍ ї Appearances are deceiving ї Appear monogamous, not actually monogamous
- Species showing little dimorphism in behavior and appearance tend to be truly monogamous ї Geese, penguins, pigeons, parrots
- /Ŷ ƐŽŵĞ ƐƉĞĐŝĞƐ ǁŚĞƌĞ ŵĂůĞƐ ĐĂƌƌLJ ďƌŽŽĚ ƉŽƵĐŚĞƐ͕ ŵĂůĞƐ ƚĞŶĚ ƚŽ ŝŶǀĞst more in offspring than females ї ZĞƉƌŽĚƵĐƚŝǀĞ ƐƚƌĂƚĞŐLJ ƌĞǀĞƌƐĞĚ ї Females compete for non-pregnant males, colourful and showy ї Seahorses, pipefish and phalaropes are the exceptions that prove the rule ї Their “reverse” decoration is what one would expect if the evolutionary explanation of sexual dimorphism is true ї tŽƵůĚŶ͛ƚ ŵĂŬĞ ƐĞŶƐĞ ŝĨ ƚŚĞƐĞ ƐƉĞĐŝĞƐ ǁĞƌĞ ͞ĐƌĞĂƚĞĚ͟
Why Choose?
- What benefit does a female have by choosing a particular mate? ї ŝƌĞĐƚůLJ – by picking a mate that will help her produce more, or healthier young during the act of child care ї Choosing males with better territories ї /ŶĚŝƌĞĐƚůLJ – by choosing a mate with better genes than those of other males ї ZĞĚ ĐŽůŽƵƌ ŝŶ ĨŝŶĐŚĞƐ ĐŽŵĞ ĨƌŽŵ ĐĂƌŽƚĞŶŽŝĚ ƉŝŐŵĞŶƚƐ ŝŶ ƐĞĞĚƐ ƚŚĞLJ ĞĂƚ ї Colour preference may be linked to diet and health ї Male gray tree frogs with longer calls produce tadpoles that grew faster and survived better
- Evolutionary theory shows that three types of genes will increase in frequency together ї Genes for a male “indicator” trait reflecting good genes ї Genes that make a female prefer that indicator trait ї The “good” genes reflected by the indicator
- Sensory-bias model ї ǀŽůƵƚŝŽŶ ŽĨ ƐĞdžƵĂů ĚŝŵŽƌƉŚŝƐŵ ĚƌŝǀĞŶ ďLJ ƉƌĞĞdžŝƐƚŝŶŐ ďŝĂƐ ŝŶ ĨĞŵĂůĞ͛Ɛ ŶĞƌǀŽƵƐ ƐLJƐƚĞŵ ї Bias can be by-product of natural selection from function other than mate selection, such as finding food ї /Ĩ ƚŚĞƌĞ ǁĂƐ Ă ƉƌĞĨĞƌĞŶĐĞ ĨŽƌ ƚŚĞ ĐŽůŽƵƌ ƌĞĚ ďĞĐĂƵƐĞ ŝƚ ŚĞůƉĞĚ ƚŚĞŵ ůŽĐĂƚĞ ƌŝƉĞ ĨƌƵŝƚƐ and a mutant male appeared with red patch, he might be preferred due to the favourable colour ї Females may simply like novel features ї Females derive neither direct nor indirect benefits from choosing a particular mate ї Experiments with several species show that females have preference for traits for which they have never been exposed
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LECTURE 18: POPULATION STRUCTURE, GENE FLOW AND GENETIC DRIFT
1. Geographical variation and the genetic differentiation of populations
2. Gene flow – the movement of genes across the landscape
3. Genetic drift and other stochastic forces
Stochastic – random forces
The Fisher-Wright debate
- Wright saw an important role for population structure and genetic drift in evolution
- Fisher disagreed and argued that most evolution occurred in large populations by natural selection - Continues to be a debate
North- versus south-facing slopes have different microclimates
- Habitats very close together
- South facing slope heats up faster in spring Æ Genetic differentiation
Population
- A group of individuals of a single species occupying a given area at the same time
- Mark-recapture studies ƚŽ ĞƐƚŝŵĂƚĞ ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞƐ of mobile organisms
- WŽƉƵůĂƚŝŽŶ ƐŝnjĞ ŝƐ ĚŝĨĨŝĐƵůƚ ƚŽ ĞƐƚŝŵĂƚĞ
Migration
- The movement of individuals from one population to another
- Ecological phenomenon
Gene flow
- The movement of genes from one population to another
- Genetic phenomenon
Variation within populations
- How much of the observed variation among individuals is genetic in origin? ї Heritable variation
- ŽĞƐ ƚŚĞ ǀĂƌŝĂƚŝŽŶ ĐŽŶƚƌŝďƵƚĞ ƚŽ ĨŝƚŶĞƐƐ ĚŝĨĨĞƌĞŶĐĞƐ ĂŵŽŶŐ ŝŶĚŝǀŝĚƵĂůƐ͍
- What about variation among populations? ї Analysis of variance Æ How much variation is within group vs. between groups? ї Ex: Humans – More variation within racial groups than between racial groups (Ex: Skin colour has small numbers of loci)
Geographic differentiation
- What proportion of all genetic variation in a species is due to differences between populations? ї How is diversity distributed within vs. between populations?
- Are some loci or traits more differentiated than the genome-wide average? ї Population differentiation due to local adaptation?
Effects of selection, gene flow & genetic drift on population divergence
- Two populations from same origin
- Natural selection drives them apart due to differing geographical environments
- Genetic drift ї ZĂŶĚŽŵ ƉƌŽĐĞƐƐ ďLJ ǁŚŝĐŚ ŐĞŶĞƐ ďĞĐŽŵĞ ĚŝĨĨĞƌĞŶƚ ŝŶ small population, irrespective of fitness ї Loss in rare alleles
- Gene flow ї Acts as cohesive force to keep populations from pulling apart
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Gene flow
- ŝĨĨŝĐƵůƚ ƚŽ ŽďƐĞƌǀĞ ĂŶĚ ŵĞĂƐƵƌĞ
- ŝƐƚŝŶŐƵŝƐŚ ƉŽƚĞŶƚŝĂů (migration) vs. actual
- ŝƐƚŝŶŐƵŝƐŚ ŐĂŵĞƚĞ ǀƐ͘ ŝŶĚŝǀŝĚƵĂů ї ŝĨĨĞƌĞŶƚ ŐĞŶĞƚŝĐ ŝŵƉĂĐƚƐ
- hƐĞ ĞdžƉĞƌŝŵĞŶƚĂů ĂƉƉƌŽĂĐŚĞƐ
- hƐĞ ŶĞƵƚƌĂů ŐĞŶĞƚŝĐ ŵĂƌŬĞƌƐ ї Polymorphic neutral genetic variation used to study population processes affecting genetic diversity ї Can count genotypes on a gel
Two populations fixed for alternative alleles
- dǁŽ ƉŽƉƵůĂƚŝŽŶƐ ŚŽŵŽnjLJŐŽƵƐ ďƵƚ ĨŽƌ ĂůƚĞƌŶĂƚŝǀĞ ĂůůĞůĞƐ
- How much gene flow occurs between them?
- (FF FF FF FF) ' (SS SS SS SS) ї Collect offspring over time ї ^ĐŽƌĞ ŚĞƚĞƌŽnjLJŐŽƚĞƐ &^ ŝŶ ŽĨĨƐƉƌŝŶŐ ї &ƌĞƋƵĞŶĐLJ ŽĨ ŚĞƚĞƌŽnjLJŐŽƚĞƐ с estimate of gene flow ї May be asymmetric Æ gametes moving downstream of a river
Genetically-modified organism (GMO)
- Concern ї Anti-multinational corporation ї Health concerns -- frankenfoods ї Scientists plating god -- Naturalist fallacy – ,ŽƌŝnjŽŶƚĂů ŐĞŶĞ ƚƌĂŶƐĨĞƌ ї Biodiversity issues
- Canola ї Measuring gene flow – an example from modern agriculture ї Escape of transgenes into wild relatives by gene flow ї dƌĂŶƐŐĞŶĞ с ŐĞŶĞ ƚƌĂŶƐĨĞƌ ƵƐŝŶŐ ƌĞĐŽŵďŝŶĂŶƚ E ƚĞĐŚŶŽůŽŐLJ ї Many crops have close relatives with which they are inter-fertile ї ZŝĐĞ͕ ŽĂƚƐ͕ Đanola, carrots ї ,LJďƌŝĚŝnjĂƚŝŽŶ ďĞƚǁĞĞŶ ĐƌŽƉƐ ĂŶĚ ƌĞůĂƚĞĚ ǁĞĞĚƐ ŝƐ ǁĞůů ĚŽĐƵŵĞŶƚĞĚ ї Gene flow between crop and weed sunflowers ї Most gene flow occurs over a short distance, but a small amount occurs as far as
1km
ї Escape of crop transgenes into wild relatives by gene flow ї ZŝƐŬ ĂƐƐĞƐƐŵĞŶƚ - /ƐŽůĂƚŝŽŶ ĚŝƐƚĂŶĐĞ ї Proximity of wild (weed) relatives ї Pollination system – wind vs. animal ї Mating system – selfer vs. outcrosser ї High risk: Wind pollinated outcrosser with relatives nearby ї Low risk: Selfer with no relatives nearby ї Corn: in Mexico, wild teosinte populations are contaminated with GMO alleles
ZĂŶĚŽŵ
- Stochastic (unpredictable or random) evolutionary forces: ї Mutation ї ZĞĐŽŵďŝŶĂƚŝŽŶ ї Gene flow ї Genetic drift
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-
ĞƚĞƌŵŝŶŝƐƚŝĐ ;ƉƌĞĚŝĐƚĂďůĞ Žƌ ŶŽŶ-random) evolutionary force: ї Natural selection
- Stochastic processes resulting in a loss of diversity ї Genetic drift: stochastic changes in allele frequency due to random variation in fecundity & mortality; most important when populations are small ї Population bottlenecks: a single sharp reduction in numbers causing a loss of diversity ї &ŽƵŶĚĞƌ ĞǀĞŶƚƐ͗ ĐŽůŽŶŝnjĂƚŝŽŶ ďLJ Ă ĨĞǁ ŝŶĚŝǀŝĚƵĂůƐ ƚŚĂƚ ƐƚĂƌƚ Ă ŶĞǁ ƉŽƉƵůĂƚŝŽŶ ǁŝƚŚ ŽŶůLJ limited diversity compared with the source population
- ZĂŶĚŽŵ ĨůƵĐƚƵĂƚŝŽŶƐ ŝŶ ĂůůĞůĞ ĨƌĞƋƵĞŶĐŝĞƐ ŝŶ ƉŽƉƵůĂƚŝŽŶƐ ŽĨ ĚŝĨĨĞƌĞŶƚ ƐŝnjĞ ї Genetic drift is more evident in small populations ї Movement of alleles overall ї ZĂƌĞ ĂůůĞůĞƐ ůŽƐƚ ŝŶ ƐŵĂůů ƉŽƉƵůĂƚŝŽŶƐ
- Founder events and population bottlenecks can reduce population to a single allele
Can genetic drift be important for adaptation?
- Controversial issue
- ƌŝĨƚ ŽĨƚĞŶ ƌĞƋƵŝƌĞƐ ĐĞƌƚĂŝŶ ĐŽŶĚŝƚŝŽŶƐ ƚŽ ŽĐĐƵƌ
- The role of genetic drift in the evolution of selfing in annual water hyacinth ї dŚĞŽƌĞƚŝĐĂů ŵŽĚĞůƐ ĂŶĚ ĨŝĞůĚ ƐƚƵĚŝĞƐ ŝŶ ƌĂnjŝů͕ :ĂŵĂŝĐĂ Θ ƵďĂ ƚŽ ƚĞƐƚ ƚŚĞ ŵŽĚĞůƐ
Tristyly – a plant sexual polymorphism
- Genetic polymorphism with phenotypic expression ї Symmetrical mating system ї ŝƐĂƐƐŽƌƚĂƚŝǀĞ ŵĂƚŝŶŐ͕ ďĞƚǁĞĞŶ ƵŶůŝŬĞ ƉŚĞŶŽƚLJƉĞƐ ї No selfing ї Governed by two diallelic loci (S,M) with epistasis between S and M ї Epistasis: ї interaction between alleles at different loci affecting phenotype ї One allele affects and overrides other allele
- Three morphs ї ZĂƌĞ ŵŽƌƉŚ ĞŶũŽLJƐ ĨŝƚŶĞƐƐ ĂĚǀĂŶƚĂŐĞ ї 1:1:1 morph frequencies at equilibrium ї Genetic drift will affect morph ї Ž LJŽƵ ůŽƐĞ ŵŽƌƉŚƐ ĞƋƵĂůůLJ͍ ї S-allele is at lowest frequency Æ Lost first Æ Becomes dimorphic ї /ŶďƌĞĞĚŝŶŐ ďĞŐŝŶƐ ƚŽ ŽĐĐƵƌ – ,ŽŵŽnjLJŐŽƐŝƚLJ Æ M-allele is next to disappear ї Genetic polymorphism Æ genetic monomorphism ї Natural selection begins selecting those that self
- Polymorphism maintained by frequency-dependent selection
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LECTURE 19: NATURAL SELECTION AND ADAPTATION
1. Types of selection
Ϯ͘ ĞƚĞƌŵŝŶŝŶŐ ƚŚĞ ŵĞĐŚĂŶŝƐŵƐ ŽĨ ƐĞůĞĐƚŝŽŶ
3. Evolution by pollution
4. Experimental evolution
Orchid from Madagascar with long floral tube pollinated by night-flying moth with exceptionally long proboscis - ĂƌǁŝŶ ƉƌĞĚŝĐƚĞĚ ƚŚĞ ĞdžŝƐƚĞŶĐĞ ŽĨ ƚŚĞ ŵŽƚŚ
- A century later it was discovered
- Example of co-adaptation
Fitness:
- ZĞůĂƚŝǀĞ ŐĞŶĞƚŝĐ ĐŽŶƚƌŝďƵƚŝŽŶ ŽĨ ŝŶĚŝǀŝĚƵĂůƐ ƚŽ ŶĞdžƚ ŐĞŶĞƌĂƚŝŽŶ ĂƐ Ă ƌĞƐƵůƚ ŽĨ ĚŝĨĨĞƌĞŶĐĞƐ ŝŶ
ǀŝĂďŝůŝƚLJ ĂŶĚ ĨĞƌƚŝůŝƚLJ ;с ĂƌǁŝŶŝĂŶ ĨŝƚŶĞƐƐͿ
Selective advantage:
- Some individuals better adapted to the environment and thus have higher fitness
Adaptation:
- Noun -- Any trait that contributes to fitness by making an organism better able to survive or reproduce in a given environment
- Verb -- The evolutionary process that leads to the origin and maintenance of such traits
Artificial selection
- ŽŵĞƐƚŝĐĂƚĞĚ ƉůĂŶƚ ĂŶĚ ĂŶŝŵĂůƐ ї Selection experiments in genetics
- Selection by humans
- Has a purpose or goal
Natural selection
- All organisms
- Selection by abiotic & biotic environment
- No purpose or goal ї Simply a blind mechanistic process with no foresight ї EŽƚĞ͗ ZĂŶĚŽŵ ї ŽŵƉĂƌĞ ƚŽ >ĂŵĂƌŬ͛Ɛ ;ŝŶĐŽƌƌĞĐƚͿ ǀŝĞǁ Æ 'ŝƌĂĨĨĞ͛Ɛ ŐŽĂů ǁĂƐ ƚŽ ƌĞĂĐŚ ŚŝŐŚĞƌ ůĞĂǀĞƐ
Phenotypic traits and distributions
Continuous distributions
- Normal distribution with mean & standard deviations
- dLJƉŝĐĂů ǁŝƚŚ ƐŝnjĞ Žƌ ŶƵŵďĞƌ ƚƌĂŝƚƐ
- Example of quantitative inheritance
Stabilizing selection
- Favoured traits are close to the population mean (average)
- Leads to a narrower peak distribution
- Ex: Human birth weight ї Very small and very large babies have higher mortality rates
Directional selection
- Favoured traits favour one extreme, either right or left of the mean
- Leads to a skew, either right or left of the mean
- dž͗ ĞĂŬ ƐŝnjĞ ŝŶ 'ĂůĂƉĂŐŽƐ ĨŝŶĐŚĞƐ ї As seed abundance decreased, the population fell
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ї As ƐĞĞĚƐ ďĞĐĂŵĞ ŚĂƌĚĞƌ͕ ĂǀĞƌĂŐĞ ďĞĂŬ ƐŝnjĞ ŝŶĐƌĞĂƐĞĚ
Disruptive selection
- Favours both extremes
- Leads to a shallower, or twin-peak distribution
- Leads to character divergence and sometimes speciation
- ZĞƋƵŝƌĞƐ ƐƉĂƚŝĂů ŚĞƚĞƌŽŐĞŶĞŝƚLJ Žƌ ĚŝƐĐƌĞƚĞ ƌĞƐŽƵƌĐĞƐ
- Ex: Beak ƐŝnjĞ ŝŶ ĨƌŝĐĂŶ ĨŝŶĐŚĞƐ ї Beaks of one group became smaller, adapting for soft seeds ї Beaks of another group became larger, adapting for hard seeds
The struggle to determine the mechanisms of selection
- Today hundreds of measurements of selection demonstrating fitness differences & evolutionary change in traits
- Fewer convincing cases that demonstrate the mechanisms (agents) of selection in natural populations – ecology is difficult!
Evolution of cyanide resistance - scale insects
- Alleles conferring cyanide resistance are originally found at low frequency in populations
- ZĞƐŝƐƚĂŶĐĞ ƐƉƌĞĂĚƐ ƚŚƌŽƵŐŚ ƚŚĞ ƉŽƉƵůĂƚŝŽŶ ǁŚĞŶ ƐĞůĞĐƚŝŽŶ ŝƐ ŝŵƉŽƐĞĚ ďLJ ĐLJĂŶŝĚĞ ĨƵŵŝŐĂƚŝŽŶ ї ZĞƐŝƐƚĂŶƚ ŝŶĚŝǀŝĚƵĂůƐ ŚĂǀĞ ŚŝŐŚĞƌ ƌĞƉƌŽĚƵĐƚŝǀĞ ƐƵĐĐĞƐƐ
- This process serves as model for the evolution of many forms of resistance e.g. antibiotics, insecticides, herbicides
Evolution by pollution
- Evolution of heavy-metal tolerance in grass species
- Evolution of industrial melanism in the peppered moth
- The peppered moth (Biston betularia) and industrial melanism ї Light and dark forms of species that rest on trees ї /Ŷ hĂŬĞƐ
EĞŐĂƚŝǀĞ ĞŶǀŝƌŽŶŵĞŶƚĂů ĐŽŶƐĞƋƵĞŶĐĞƐ ŽĨ ďŝŽůŽŐŝĐĂů /ŶǀĂƐŝŽŶƐ
- ŝƐƌƵƉƚ ĞĐŽůŽŐŝĐĂů ƉƌŽĐĞƐƐĞƐ ŝŶ ŶĂƚƵƌĂů ƉůĂŶƚ Θ ĂŶŝŵĂů Đommunities
- ŝƐƉůĂĐĞ ŶĂƚŝǀĞ ƐƉĞĐŝĞƐ ůĞĂĚŝŶŐ ƚŽ ƚŚĞŝƌ ĞdžƚŝŶĐƚŝŽŶ
- Adverse effects on human health
- Serious economic & social impacts through reduction of yields in agriculture & fisheries
/ŶǀĂƐŝǀĞ ƐƉĞĐŝĞƐ ŝŶ ƚŚĞ h^
- ĐŽŶŽŵŝĐ ĐŽƐƚ с ΨϭϮϬ ďŝůůŝŽŶ ƉĞƌ LJĞĂƌ
- ϱϬ͕ϬϬϬ ŝŶƚƌŽĚƵĐĞĚ ƐƉĞĐŝĞƐ͕ ŶƵŵďĞƌ ƌŝƐŝŶŐ
- Ε ϰϮй ŽĨ ƚŚƌĞĂƚĞŶĞĚ Θ ĞŶĚĂŶŐĞƌĞĚ ƐƉĞĐŝĞƐ Ăƚ ƌŝƐŬ ƉƌŝŵĂƌŝůLJ ĚƵĞ ƚŽ ĂůŝĞŶ ŝŶǀĂƐŝǀĞƐ
Questions on invading species
- Why are invading species usually only aggressive in their introduced not their native ranges?
- Are certain ecosystems more susceptible to invasions than others?
- What are the ecological & genetic characteristics of successful invaders?
- /Ɛ ƚŚĞŝƌ ĞǀŝĚĞŶĐĞ ĨŽƌ ƚŚĞ ĐŽŶƚĞŵƉŽƌĂƌLJ ĞǀŽůƵƚŝŽŶ ŽĨ ůŽĐĂů ĂĚĂƉƚĂƚŝŽŶ ŝŶ ŝŶǀĂĚĞƌs?
- How can invaders be controlled?
ŶĞŵLJ ZĞůĞĂƐĞ ,LJƉŽƚŚĞƐŝƐ͗
- Plant species on introduction to an exotic region experiences a decrease in regulation by herbivores and other natural enemies ї rapid increase in distribution and abundance
- Ex: ŝĨĨĞƌĞŶĐĞƐ ŝŶ enemy attack in populations of white campion (Silene latifolia) from Europe and North America (Lorne Wolfe, -- ŵĞƌŝĐĂŶ EĂƚƵƌĂůŝƐƚ͕ ϮϬϬϮͿ ї Native to Europe, Western Asia, Northern Africa ї Alien to North America – Now Naturalised
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ї Specialist and generalist pĞƐƚ ĂŶĚ ĚŝƐĞĂƐĞ ƉƌĞƐƐƵƌĞ ǁĂƐ ϭϳ x higher in the native range compared to the alien range
/ŶǀĂƐŝǀĞ ƐƉĞĐŝĞƐ ƚŚƌŝǀĞ ŝŶ ĚŝƐƚƵƌďĞĚ ƐŝƚĞƐ͗ ƚŚĞ ŵŽƌĞ ĚŝƐƚƵƌďĂŶĐĞ͕ ƚŚĞ ŵŽƌĞ ǀƵůŶĞƌĂďůĞ ƚŽ ŝŶǀĂƐŝŽŶ
- ŝƐƚƵƌďĂŶĐĞ ĐĂŶ ďĞ ĐĂƵƐĞĚ ďLJ ŚƵŵĂŶƐ – ŵĂnjŽŶ ĨŽƌĞƐƚ͖ Žƌ EĂƚƵƌĂů – Volcanic eruption, forest fire Common attributes of successful invasive species
- ZĂƉŝĚ ĚĞǀĞůŽƉŵĞŶƚ ƚŽ ƌĞƉƌŽĚƵĐƚŝŽŶ
- High reproductive output
- Well-developed dispersal mechanisms
- Broad ecological tolerance
- High phenotypic plasticity ї Plasticity: The ability of a genotype to alter its phenotype in response to environmental change – important trait in unpredictable environments
Evolution in invasive species of agriculture
- Selection of barnyard grass plants that mimic cultivated rice (SE Asia, Latin America, Africa) ї Weed removal involves ability to distinguish visually between crop and weed ї Weeds that look more like the crop escape detection Æ inadvertently selecting for mimicry - Selection of herbicide resistant weed species (worldwide) ї Widespread adoption of herbicide spraying in mid-to late- ƐĞǀĞŶƚŝĞƐ͛ Æ inadvertently selecting for weed strains resistant to herbicides
/ŶǀĂƐŝǀĞ ƐƉĞĐŝĞƐ ŝŶ KŶƚĂƌŝŽ
- Zebra mussels (Dreissena polymorpha) ї Freshwater mollusk native to Eurasia arrived in ballast water of ocean-going freighters in ůĂƚĞ ϴϬ͛Ɛ ї First reported in 1988, now abundant throughout Great Lakes ї ^ŝŶŐůĞ ĨĞŵĂůĞ ĐĂŶ ƉƌŽĚƵĐĞ ϯϬ͕ϬϬϬ – 1 million eggs per season, free swimming larvae easily dispersed in water ї Extensive damage to water intake pipes and commercial & sport fisheries ї Filter feeders Æ have increased water quality ї Source of avian botulism leading to death of many birds
- Purple loosestrife (Lythrum salicaria) ї Aquatic perennial with showy purple flowers native to Europe; used as an ornamental. ї Multiple introductions to eastern North America during past century followed by invasion of wetlands ї Plants competitive with high phenotypic plasticity, produce millions of small, easily dispersed seeds with high viability ї Populations genetically diverse due to multiple introductions, outbreeding and polyploidy; provides opportunities for evolution of local adaptation ї /Ɛ ƚŚĞƌĞ ĞǀŝĚĞŶĐĞ ĨŽƌ ƌĂƉŝĚ ĂĚĂƉƚŝǀĞ ĞǀŽůƵƚŝŽŶ ŝŶ ŝŶǀĂƐŝǀĞ ƉŽƉƵůĂƚŝŽŶƐ ŽĨ WƵƌƉůĞ
>ŽŽƐĞƐƚƌŝĨĞ͍ ;ZŽď ŽůĂƵƚƚŝ͕ ϮϬϬϵ – WƌŽĐ ZŽLJ ^ŽĐ ͕ ϮϬϭϬͿ ї Flowering time correlated with latitudinal gradient of seasonality ї Common garden studies indicate significant genetic differentiation among populations ї Variation forms a cline in time to flowering with northern populations flowering faster than southern populations ї Cline: A gradual change in trait means over a geographical transect ї Populations farther north have adapted to shorter growing season
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Aquatic plant invasion in the tropics -- dŚĞ ǁŽƌůĚ͛Ɛ ǁŽƌƐƚ ĂƋƵĂƚŝĐ ŝŶǀĂĚĞƌƐ͗
- Water hyacinth (Eichhornia crassipes) ї Native to lowland South America, now worldwide in tropical & warm temperate regions
- Kariba weed (Salvinia molesta) ї Genetically sterile floating fern
- Both native to South America, introduced by humans to Old World tropics,
- Free-floating with prolific clonal propagation
- Populations genetically uniform
- Tnvasiveness due to high phenotypic plasticity NOT genetic diversity
- Herbicide control causes pollution of aquatic habitats so biological control methods used
Management of invasives – methods of control
- Mechanical Ex: hand weeding, machines
- Chemical Ex: herbicides, pesticides
- Ecological Ex: burning, flooding
- Biological control ї The planned introduction of natural enemies (e.g. predators, parasites, pathogens) to control unwanted populations of invaders in alien range ї Mode of reproduction of plant invaders & likelihood of success from biological control
(Burdon & Marshall, 1981 – :͘ ƉƉů͘ ĐŽůŽŐLJͿ ї Asexual species easier to control than sexual species ї /ŶĨůƵĞŶĐĞ ŽĨ ƌĞƉƌŽĚƵĐƚŝǀĞ ƐLJƐƚĞŵƐ ŽŶ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJ ї Genetic diversity will determine whether resistance evolves ї Advantages ї Non-toxic to humans; if conducted carefully no serious environmental impacts ї /Ĩ ƐƵĐĐĞƐƐĨƵů ƚŚĞ ĞĨĨĞĐƚƐ ĂƌĞ ƉĞƌŵĂŶĞŶƚ ї Economically cheap ($1 for biological control vs. $5 for chemical control) ї ĂŶŐĞƌƐ ї Sloppy science creates new invasion
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LECTURE 23: BIODIVERSITY, EXTINCTION AND EVOLUTIONARY BIOLOGY
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1. Ecological & evolutionary consequences of global environmental change
2. What is biodiversity and why does it matter?
3. The causes of extinction today
4. Conservation biology – ecological & genetic perspectives on a crisis-driven science
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ŵĂnjŽŶ – logging of tropical forest for cattle farms
dŽĚĂLJ͛Ɛ ŐůŽďĂů ĞŶǀŝƌŽŶŵĞŶƚĂů ƉƌŽďůĞŵƐ
- Global warming & climate change
- Loss of biodiversity
- Environmental pollution
- Human famine
- Spread of infectious diseases
- Human population growth
Greenhouse gas emissions
- Longest direct measurements of CO2 in the atmosphere
- Atmospheric CO2 ŚĂƐ ŝŶĐƌĞĂƐĞĚ ƐƚĞĂĚŝůLJ ƐŝŶĐĞ ϭϵϲϬ
- /ŶĐƌĞĂƐĞ ŝŶ K2 a result of the burning of fossil fuels – Human impact
How will organisms respond to climate change?
- Migrate to more favourable environmental conditions (=ecology)
- Adapt to changing environmental conditions (=evolution)
- Go locally (or globally) extinct (=evolution)
Climate change alters phenology, but how much of this response is evolution?
- Phenology – study of periodic plant and animal life cycle events and how they are influenced by seasonal climate variations and habitat factors
Can drought cause rapid contemporary evolution by natural selection? (Art Weis, EEB)
- ŝƌĞĐƚŝŽŶĂů ƐĞůĞĐƚŝŽŶ ŽŶ ĨůŽǁĞƌŝŶŐ ƚŝŵĞ ŝŶ ĨŝĞůĚ mustard
- Evidence for directional selection for early flowering as an evolutionary response to drought ї Set more seed than later flowering plants
Biodiversity
- “the variety of life on earth”
- The number and kinds of living organisms in a given area
- Two elements: ї /ŶƚĞƌƐƉĞĐŝĨŝĐ ǀĂƌŝĂƚŝŽŶ Žƌ ƐƉĞĐŝĞƐ ĚŝǀĞƌƐŝƚLJ ;ƐƚƵĚŝĞĚ ďLJ ĞĐŽůŽŐŝƐƚͿ ї /ŶƚƌĂƐƉĞĐŝĨŝĐ ǀĂƌŝĂƚŝŽŶ Žƌ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJ ;ƐƚƵĚŝĞĚ ďLJ ŐĞŶĞƚŝĐŝƐƚƐͿ
- Four components ї Species diversity ї Ecological (functional) diversity ї Genetic diversity ї Phylogenetic diversity
- Loss of biodiversity is irreversible and consequences are least predictable – E.O. Wilson (1989)
- Twenty-five biodiversity hotspots identified around the globe, receiving special conservation efforts Extinction is natural but its current rate is not!
- Extinction is the permanent elimination of a species – extinction is forever!
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džƚŝŶĐƚŝŽŶ ŝƐ Ă ŶŽƌŵĂů ĞǀŽůƵƚŝŽŶĂƌLJ ƉƌŽĐĞƐƐ͖ ϵϵй of all species that have ever lived are now extinct - ƵƌŝŶŐ ƚŚĞ ƉĂƐƚ ĐĞŶƚƵƌLJ ŵĂƐƐŝǀĞ ŚĂďŝƚĂƚ ĚĞƐƚƌƵĐƚŝŽŶ͕ ƉĂƌƚŝĐƵůĂƌůLJ ŝŶ ƚƌŽƉŝĐĂů ƌĞŐions, has increased rates of extinction
- Studies of the causes of extinction require demographic and genetic investigations on the causes of rarity
- Three types of extinction ї Background extinction ї Turnover of species at a low rate, a natural feature of ecosystems ї Estimated at ~1 species per year ї Mass extinction ї Very large numbers of extinctions due to natural catastrophes ї Anthropogenic extinction ї Caused by humans now estimated at 4-ϲϬϬϬ ƐƉĞĐŝĞƐ ƉĞƌ LJĞĂƌ
- Major causes of species extinction today ї Habitat destruction ї Overexploitation of species ї /ŶƚƌŽĚƵĐƚŝŽŶ ŽĨ ƉĞƐƚƐ͕ ƉƌĞĚĂƚŽƌƐ Θ ĐŽŵƉĞƚŝƚŽƌƐ
Conservation Biology
- The study of those species, ecological communities & ecosystems being negatively affected by human activities
- Provides the biological concepts & tools for preserving biodiversity & ecosystem function
- Multidisciplinary but with a core ecological and genetic framework
- Ecological issues in conservation biology ї Community-level studies ї Habitat preservation & the maintenance of species diversity ї Application of island biogeographic theory to design of nature reserves ї SLOSS: Single large vs. several small ї ĞďĂƚĞ ŝŶ ĞĐŽůŽŐLJ ĂŶĚ ĐŽŶƐĞƌǀĂƚŝŽŶ ďŝŽůŽŐLJ ї What is more effective? ї Single large community of organisms? ї Several small? ї Studies of individual species ї Effects of habitat fragmentation on population ecology & demography ї ,ĂďŝƚĂƚ ĨƌĂŐŵĞŶƚĂƚŝŽŶ ŽĨ ƚŚĞ ƚůĂŶƚŝĐ ĐŽĂƐƚĂů ĨŽƌĞƐƚ ŽĨ ƌĂnjŝů ĚƵƌŝŶŐ ƚŚĞ
ƉĂƐƚ ϲϬLJƌƐ ƚŚƌĞĂƚĞŶƐ ƚŚĞ ĞŶĚĞŵŝĐ ŐŽůĚĞŶ ůŝŽŶ ƚĂŵĂƌŝŶ ї Keystone species ї Beaver – Has ability to create dams and manipulate waterways ї DŝŶŝŵƵŵ ǀŝĂďůĞ ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞƐ ї The number of individuals necessary for a species to maintain or increase its numbers in a region ї The smallest population of a species that can sustain itself in the face of environmental variation ї No single number for all species; will vary ї Ex: cats higher than orchids
- Genetic issues in conservation biology ї The maintenance of genetic diversity in rare & endangered species ї ZĞůĂƚŝŽŶ ďĞƚǁĞĞŶ ŚĞƚĞƌŽnjLJŐŽƐŝƚLJ Θ ĨŝƚŶĞƐƐ
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ї Preventing inbreeding & inbreeding depression ї ZĞĚƵĐŝŶŐ ƚŚĞ ƐƚŽĐŚĂƐƚŝĐ ůŽƐƐ ŽĨ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJ ĨƌŽŵ ƐŵĂůů ƉŽƉƵůĂƚŝŽŶƐ ї 'ĞŶĞƚŝĐ ĐŽŶƐĞƋƵĞŶĐĞƐ ŽĨ ƐŵĂůů ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞ Æ Mating among relatives ї >ŽƐƐ ŽĨ ŚĞƚĞƌŽnjLJŐŽƐŝƚƐ ї /ŶďƌĞĞĚŝŶŐ ĚĞƉƌĞƐƐŝŽŶ ї Strategies for reducing inbreeding depression in small populations of captive animal species ї &ŽƵŶĚŝŶŐ /ŶĚŝǀŝĚƵĂůƐ͗ ї ^ƉĞŬĞ͛Ɛ 'ĂnjĞůůĞ͗ ϰ ї /ŶĚŝĂŶ ZŚŝŶŽ͗ ϭϳ ї European Bison: 13 ї Siberian Tiger: 25 ї Fixation of deleterious genes ї Ex: Cheetah (Acinonyx jubatus) ї ZĞƐƚƌŝĐƚĞĚ ƚŽ ƚǁŽ ǁŝůĚ ƉŽƉƵůĂƚŝŽŶƐ ŝŶ ƐŽƵƚŚĞƌŶ Θ ĞĂƐƚĞƌŶ ĨƌŝĐĂ ї ƐƵƌǀĞLJ ŽĨ ϱϮ ĞŶnjLJŵĞ ůŽĐŝ ŝŶĚŝĐĂƚĞĚ ĐŽŵƉůĞƚĞ ŵŽŶŽŵŽƌƉŝƐŵ͘ ї Other cats have 8-Ϯϭй ŽĨ ůŽĐŝ ƉŽůLJŵŽƌƉŚŝĐ ї ,ŝŐŚ ũƵǀĞŶŝůĞ ŵŽƌƚĂůŝƚLJ Θ ůŽǁ ƐƉĞƌŵĂƚŽnjŽĂů ĐŽƵŶƚƐ ї Suggesting inbreeding depression in the species as a whole ї /ƚ ŚĂƐ ďĞĞŶ ƉƌŽƉŽƐĞĚ ƚŚĂƚ ůŽǁ ŐĞŶĞƚŝĐ ǀĂƌŝĂƚŝŽŶ ƌĞƐƵůƚƐ ĨƌŽŵ ĂŶ
ŚŝƐƚŽƌŝĐĂů ďŽƚƚůĞŶĞĐŬ ŝŶ ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞ
EŝŬŽůĂŝ sĂǀŝůŽǀ ;ϭϴϴϳ-1943)
- ZƵƐƐŝĂŶ ĐƌŽƉ ŐĞŶĞƚŝĐŝƐƚ ĂŶĚ ĨŽƵŶĚĞƌ ŽĨ ĐƌŽƉ ŐĞŶĞƚŝĐ ƌĞƐŽƵƌĐĞ ĐŽŶƐĞƌǀĂƚŝŽŶ
Hunt for wild cotton
- Gene poŽů ĐŽůůĞĐƚŝŶŐ ĞdžƉĞĚŝƚŝŽŶ ƚŽ E ƌĂnjŝů͕ :ĂŶ-DĂLJ͕ ϭϵϳϭ
- ŝƐĐŽǀĞƌĞĚ Gossypium mustelinum – wild cotton
Last thoughts
- Future requires fresh ideas and changing paradigms
Reading Summary: Notes and quotes from Coyne - Chapter 7:
ϮϱͿ 'ĞƌďĞƌ >͘ ϮϬϭϬ͘ Conservation biology. Nature Education Knowledge 1(11):14 htƚƉ͗ͬͬǁǁǁ͘ŶĂƚƵƌĞ͘ĐŽŵͬƐĐŝƚĂďůĞͬŬŶŽǁůĞĚŐĞͬůŝďƌĂƌLJͬĐŽŶƐĞƌǀĂƚŝŽŶ-biology-ϭϲϬϴϵϮϱϲ Conservation Biology: A multidisciplinary science developed to address the loss of biological diversity
- Evaluates human impacts on biological diversity
- ĞǀĞůŽƉƐ ƉƌĂĐƚŝĐĂů approaches to prevent extinction of species
Evil Quartet
- Habitat loss and fragmentation
- Overharvesting
- /ŶƚƌŽĚƵĐĞĚ ƉƌĞĚĂƚŽƌƐ ĂŶĚ ĐŽŵƉĞƚŝƚŽƌƐ
- /ŶĚŝƌĞĐƚ ĞĨĨĞĐƚƐ ŽĨ ƚŚĞƐĞ ƚŚƌĞĂƚƐ ŽŶ ĞĐŽůŽŐŝĐĂů ŝŶƚĞƌĂĐƚŝŽŶƐ
Conservation Biology aims to provide answers to specific questions
- Point of view of resource managers
- Best strategies for protecting threatened species ї Nature reserves ї Breeding programs ї ZĞĐŽŶĐŝůŝŶŐ ĐŽŶƐĞƌǀĂƚŝŽŶ ĐŽŶĐĞƌŶƐ ǁŝƚŚ ŶĞĞĚƐ ŽĨ ůŽĐĂů ƉĞŽƉůĞ
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/ŶƚĞƌĨĂĐĞ ďĞƚǁĞĞŶ ƚŚĞŽƌLJ ĂŶĚ ƉƌĂĐƚŝĐĞ ї Statistical and computational tools integral in development of analytical methods to address issue of uncertainty
Statistical and computational tools
- Population Viability Analysis ї Evaluates full range of forces impinging on populations ї Makes determinations about viability ї Not viable for predicting when species will go extinct ї hƐĞĨƵů ĨŽƌ ĐŽŵƉĂƌŝŶŐ ƌĞůĂƚŝǀĞ ĞdžƚŝŶĐƚŝŽŶ ƌŝƐŬƐ ĂŵŽŶŐ ƐƉĞĐŝĞƐ ĂŶĚ ƉŽƉƵůĂƚŝŽŶƐ ĂŶĚ ĨŽƌ
ƉƌŝŽƌŝƚŝnjŝŶŐ ƌĞƐĞĂƌĐŚ ĂŶĚ ŵĂŶĂŐĞŵĞŶƚ ĂĐƚŝŽŶƐ
- Minimum Viable Population ї Threshold below which populations can no longer sustain themselves ї Allows a quantitative “rule of thumb” estimate of minimum population ƐŝnjĞ ї hƐĞĨƵů ĨŽƌ ĞƐƚŝŵĂƚŝŶŐ ĞĨĨĞĐƚŝǀĞ ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞ ĂŶĚ ƚŝŵĞĨƌĂŵĞ ŽĨ ĐŽŶĐĞƌŶ
- ĞĐŝƐŝŽŶ ŶĂůLJƐŝƐ ĂŶĚ DƵůƚŝƉůĞ-Criteria Approaches ї Tool for guiding business decisions under uncertainty ї hƐĞƐ ƐƚĂƚŝƐƚŝĐĂů ĂƉƉƌŽĂĐŚĞƐ ї Additional analysis are necessary to develop and refine analytical tools
Broad Speculation on the Future of Conservation Biology
- A burgeoning discipline since its inception
- Lack of adequate funding remains a critical problem
- Current models have drawbacks
- Precise role of conservation biologists as advocates between conservation priorities and human
ŶĞĞĚƐ ŚĂƐ LJĞƚ ƚŽ ďĞ ĨŽƌŵĂůŝnjĞĚ ї Most scientists are not trained to be advocates
- Many of the theoretical underpinnings of conservation biology are misguided in that they treat
ĂŶ ĞĨĨĞĐƚ͕ ƐƵĐŚ ĂƐ ƐŵĂůů ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞ͕ ĂƐ ŝĨ ŝƚ ǁĞƌĞ Ă ĐĂƵƐĞ͘
- Conservation efforts should instead be focused on determining causes of population declines and the means by which agents of a decline can be identified
- This idea has reoriented many theoreticians to consider the broader scope of their work and has encouraged field biologists to more closely align their research to conservation-related questions ;ϮϲͿ Ăǁ KůŵƐƚĞĂĚ͕ ǁŚŽ ŝŶ ƚŚĞ ϭϴϬϬƐ ĚĞƐŝŐŶĞĚ ĂŶĚ ŵĂŶĂŐĞĚ ƉĂƌŬ ƐLJƐƚĞŵƐ ĂŶĚ ƵƌďĂŶ ƉĂƌŬƐ such as Central Park in New York City, believed in the rejuvenating powers of nature
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ї ,Ğ ĨĞůƚ ƚŚĂƚ ĐŽŶƚĞŵƉůĂƚŝŶŐ ŶĂƚƵƌĞ͛s grandeur allowed man to put his life into perspective /Ŷ ŵŽĚĞƌŶ ƚŝŵĞƐ͕ ǁŝƚŚ ŝŶĐƌĞĂƐŝŶŐ ƵƌďĂŶŝnjĂƚŝŽŶ͕ ƉĞŽƉůĞ ƐĞĞŬ ŽƵƚ ůŽĐĂů ƉĂƌŬƐ͕ ŽƉĞŶ ƐƉĂĐĞ ĂŶĚ trails, and travel to national parks and wild places where they can enjoy nature ї Birding, hiking, fishing, hunting, gardening, and other forms of recreation in nature are popular activities, and are economically important
Glossary: Topics & Concepts
Adaptive radiation: The evolution of ecological and phenotypic diversity within a rapidly multiplying lineage as a result of speciation from a single common ancestor
Allopatric: Speciation that occurs due to geographical separation
Bateman’s principle: Females almost always invest more energy into producing offspring than males invest Clade: Monophylum containing a species and all its descendants
Cladistics: Classifying species based on phylogenetic relationships and shared characteristics
Cline: A gradual change in trait means over a geographical transect
Continuous traits: Complex inheritance by polygenes of small effect with quantitative inheritance and a continuum of outcomes
Convergence: When structures that evolve separately perform similar roles due to similar ecologies
Discrete traits͗ /ŶŚĞƌŝƚĞĚ ďLJ ϭ Žƌ Ϯ ŵĂũŽƌ ŐĞŶĞƐ ǁŝƚŚ ŚŽŵŽnjLJŐŽƵƐ Žƌ ŚĞƚĞƌŽnjLJŐŽƵƐ ŽƵƚĐŽŵĞƐ
Homology: Similarity of traits due to shared ancestry
Homoplasy: Similarity of traits as a result of convergent evolution
Key innovation: Origin in a novel trait resulting in an adaptive radiation which can exploit new resources or habitats previously unavailable prior to trait acquisition
Monophyletic: Arise from a single ancestor single ancestor
Naturalisation: A process by which an alien species spreads into the wild and reproduces sufficiently to maintain its population
Non-monophyletic: Arise from two or more ancestors
Phenetics: Classifying species based on overall resemblance
Phylogentics: Study of evolutionary relationships among species
Plasticity: The ability of a genotype to alter its phenotype in response to environmental change – important trait in unpredictable environments
Polyploidy: Having more than two complete sets of homologous chromosomes
Sympatric: Speciation occurring where a subset of the population becomes genetically different, Ex: through polyploidy
Taxonomy: The theory and practice of classification geographic variation, population differentiation, gene flow, models of population structure, stochastic processes, genetic drift, genetic markers, measuring gene flow, transgenic escape, tristyly and its inheritance, frequency-dependent mating, equilibrium morph frequencies, evolution of selfing from outcrossing adaptation, types of selection on quantitative traits, measurement and response to selection, evolution of cyanide resistance, mechanisms of selection, industrial melanism, heavy-metal tolerance, costs to resistance, experimental evolution in E. coli. native, alien, biological invasion, invasive species, attributes of successful invasives, disturbance, crop ŵŝŵŝĐƌLJ͕ ŚĞƌďŝĐŝĚĞ ƌĞƐŝƐƚĂŶĐĞ͕ njĞďƌĂ ŵƵƐƐĞůƐ͕ ƉƵƌƉůĞ ůŽŽƐĞƐƚƌŝĨĞ͕ ĐŽŵŵŽŶ ŐĂƌĚĞŶ ƐƚƵĚŝĞƐ͕ local adaptation, crop mimicry, water hyacinth, Kariba weed, biological control
– global climate change, rapid evolution, resurrection paradigm, components of biodiversity, biodiversity hotspots, types and causes of extinction, habitat fragmentation, SLOSS, keystone species,
DsW͕ ŝŶďƌĞĞĚŝŶŐ ŝŶ njŽŽ ĂŶŝŵĂůƐ͕ ĐŽŶƐĞƌǀĂƚŝŽŶ ŽĨ ĐƌŽƉ ŐĞŶĞƚŝĐ resources
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Exam Study Notes (Lectures 12-23)
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LECTURE 12: INTRODUCTION TO EVOLUTIONARY BIOLOGY
1.
2.
3.
4.
Evolution
How it is studied
Facts supporting Evolution
Biodiversity & adaptation
Levels of biological organization:
Molecules Æ Cells Æ Organisms Æ Populations Æ Communities Æ Ecosystems
Types of questions in evolutionary biology:
- Scope: small questions can help towards solving a big question; large questions require multiple lines of evidence
- How vs. Why
How ї Wroximate ї /nvolve determining physiological or genetic mechanisms
Why ї hltimate ї etermine ecological function and significance of a trait
Approaches used in evolutionary biology:
Good studies use more than one source of evidence
- Observation – describe and quantify
- Theoretical – develop models
- Comparative – compare data across species
- Experimental – manipulate a system to address a hypothesis ї Zequires design and statistical analysis Theory of Evolution
- The central unifying concept of biology
- Affects many other areas of knowledge
- One of the most influential concepts of Western thought
Important assumptions about evolution: ї Verified by scientific study (see Coyne notes below)
Organisms on earth have changed through time
The changes are gradual not instantaneous
- Lineages split or branch by speciation resulting in the generation of biodiversity
- All species have common ancestors
- Most evolutionary change results from natural selection - the only process responsible for the evolution of biodiversity and adaptation
Biodiversity and adaptation are products of evolution:
Biodiversity
- the variety of life on earth; the number and kinds of living organisms in a given area
Adaptation
- [Noun] Any trait that contributes to fitness by making an organism better able to survive or reproduce in a given environment
- [Verb] The evolutionary process that leads to the origin and maintenance of such traits dŚĞ ďĞƐƚ ƐƚƵĚŝĞƐ ŝŶƚĞŐƌĂƚĞ ŝŶĨŽƌŵĂƚŝŽŶ ĨƌŽŵ ĞǀŽůƵƚŝŽŶĂƌLJ ŚŝƐƚŽƌLJ E ŵĞĐŚĂŶŝƐŵƐ
Evolutionary mechanisms (microevolution)
- ĞƚĞƌŵŝŶŝŶŐ ƚŚĞ ĞĐŽůŽŐŝĐĂů ĂŶĚ ŐĞŶĞƚŝĐ ŵĞĐŚĂŶŝƐŵƐ ƌĞƐƉŽŶƐŝďůĞ ĨŽƌ ĞǀŽůƵƚŝŽŶĂƌLJ ĐŚĂŶŐĞ
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/ŶǀŽůǀĞ ƉŽƉƵůĂƚŝŽŶ-level studies of natural selection, adaptation and speciation using diverse organisms - Testing of theoretical models by experiments in the laboratory and field
- Largely process orientated and experimental
Evolutionary history (macroevolution)
- ĞƚĞƌŵŝŶŝŶŐ ĞǀŽůƵƚŝŽŶĂƌLJ ƌĞůĂƚŝŽŶƐŚŝƉƐ ŽĨ ŽƌŐĂŶŝƐŵƐ ŝŶ ƚĞƌŵƐ ŽĨ ĐŽŵŵŽŶ ĂŶĐĞƐƚƌLJ phylogenetics
- Affinities of organisms provide a basis for classification – taxonomy & systematics
- Comparative data from many sources e.g. biogeography, paleontology, morphology, development and genomics
- Largely pattern-based and non-experimental
Water Hyacinth
- Novel adaptation promotes outcrossing
- Patterns of genetic diversity
- Blocks drainage canals and rivers
- Short-styled morph restricted to lowland S. America through Founder effect, by human introduction Morph: mating type
Founder effect: introduction of a small number of individuals with a small sample of genetic diversity of source population
- ŝƐƚƌŝďƵƚĞĚ ǁŽƌůĚ-wide in tropics and sub-tropics
- ZĞƉƌŽĚƵĐĞƐ ďLJ ĐůŽŶĂů ĂŶĚ ƐĞdžƵĂů ƌĞƉƌŽĚƵĐƚŝŽŶ
- Three morphs restricted to native range
Birds as pollinators
- Birds are major plant pollinators
- Hovering (NW) vs. Perching (OW) birds during nectar feeding
- ^ŽŵĞ ƉůĂŶƚƐ͕ ƐƵĐŚ ĂƐ ĂďŝĂŶĂ ƌŝŶŐĞŶƐ ;ZĂƚ͛Ɛ ƚĂŝůͿ ŚĂǀĞ ĂĚĂƉƚĞĚ ƐƉĞĐŝĂůŝnjĞĚ ƉĞƌĐŚĞƐ ĨŽƌ ďŝƌĚƐ promoting plant reproductive success
Reading Summary: Notes and quotes from Coyne - Chapter 1
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“Plants and animals seem intricately and almost perfectly designed for living their lives”
͞/ƚ ƚĞƐƚŝĨŝĞƐ ƚŽ ;ĂƌǁŝŶ͛ƐͿ ŐĞŶŝƵƐ ƚŚĂƚ ƚŚĞ ĐŽŶĐĞƉƚ ŽĨ ŶĂƚƵƌĂů ƚŚĞŽůŽŐLJ͕ ĂĐĐĞƉƚĞĚ ďLJ ŵŽƐƚ educated westerners before 1859, was vanquished within only a few years by a single fivehundred page book”
- “Life on earth evolved gradually beginning with one primitive species –perhaps a self-replicating molecule—that lived more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection”
Evolution
- A species undergoes change over time
Gradualism
- /ƚ ƚĂŬĞƐ ŵĂŶLJ ŐĞŶĞƌĂƚŝŽŶƐ ƚŽ ƉƌŽĚƵĐĞ Ă ƐƵďƐƚĂŶƚŝĂů ĞǀŽůƵƚŝŽŶĂƌLJ ĐŚĂŶŐĞ͕ ƐƵĐŚ ĂƐ ƚŚĞ evolution of birds from reptiles
Speciation
- ŝǀĞƌƐŝƚLJ ĂƌŝƐĞƐ ƚŚƌŽƵŐŚ ƐƉĞĐŝĂƚŝŽŶ
Common ancestry
- Every species goes back to a single common ancestor
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Natural selection
- Explains apparent design by nature
- ͞/Ĩ ŝŶĚŝǀŝĚƵĂůƐ ǁŝƚŚŝŶ Ă ƐƉĞĐŝĞƐ ĚŝĨĨĞƌ ŐĞŶĞƚŝĐĂůůLJ from one another, and some of those
ĚŝĨĨĞƌĞŶĐĞƐ ĂĨĨĞĐƚ ĂŶ ŝŶĚŝǀŝĚƵĂů͛Ɛ ĂďŝůŝƚLJ ƚŽ ƐƵƌǀŝǀĞ ĂŶĚ ƌĞƉƌŽĚƵĐĞ ŝŶ ŝƚƐ ĞŶǀŝƌŽŶŵĞŶƚ͕ ƚŚĞŶ ŝŶ ƚŚĞ next generation the “good” genes that lead to higher survival and reproduction will have relatively more copies than the “not so good” genes”
- Over time the population becomes more suited to its environment through helpful mutations
- Note that it is not a perfect process – See Sea turtle and human male analogy -- Natural selection merely offers improvements over what came before, therefore it produces “fitter” not the “fittest”
Processes other than natural selection can cause evolutionary change
- ZĂŶĚŽŵ ĞǀĞŶƚƐ – some families have more offspring
Scientific Theory
- A well though-out group of propositions meant to explain facts about the real world
- Explain “how” and “why” questions
- Must be testable and make verifiable predictions
͞ZĞƚƌŽĚŝĐƚŝŽŶ͟
- When facts and data only make sense in light of a particular scientific theory
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LECTURE 13: DARWIN’S BIG IDEA AND HOW IT CHANGED BIOLOGY
1. Evolution - the central unifying concept of biology
Ϯ͘ ĞǀĞůŽƉŵĞŶƚ ŽĨ ĂƌǁŝŶ͛Ɛ ŝĚĞĂ
3. Evolution facts and fiction
The theory of evolution
Living things change gradually from one form into another over time
- Challenges view of special creation (= direct creation of all things in effectively their present form) Theory of evolution involved two controversial ideas
- Concept of a changing universe ї replaced view of a static world
- A phenomenon with no purpose ї replaced view that the causes of all phenomena had to have a purpose
Jean-Baptiste de Lamarck (1744 -1829)
- First to use the term evolution
- First to provide a causal mechanism ї The inheritance of acquired characters
- Linear view of evolution (think L Z ŽĨ ůŝĨĞ͕ ƌĂƚŚĞƌ ƚŚĂŶ dZ Ϳ ї Simplest forms evolve directly to complex forms
- dŚĞ ŐŝƌĂĨĨĞ͛Ɛ ŶĞĐŬ͗ >ĂŵĂƌĐŬ͛Ɛ ĞdžĂŵƉůĞ ĨŽƌ ƚŚĞ ŝŶŚĞƌŝƚĂŶĐĞ ŽĨ ĂĐƋƵŝƌĞĚ ĐŚĂƌĂĐƚĞƌƐ
- Progressive increase in neck during the life time of an individual is passed on to offspring
- Would imply that a weightlifter would give birth to a well-defined and muscled baby, which is simply not true
August Weisman (1834-1914) Germplasm Theory
- /ŶŚĞƌŝƚĂŶĐĞ ŽŶůLJ ďLJ ŐĞƌŵ ĐĞůůƐ ;ŐĂŵĞƚĞƐͿ͖ ƐŽŵĂƚŝĐ ĐĞůůƐ ;ƐŽŵĂͿ ĚŽ ŶŽƚ ĨƵŶĐƚŝŽŶ ĂƐ ĂŐĞŶƚƐ ŽĨ heredity - Thus genetic information cannot pass from soma to gametes and onto next generation
- Modern interpretation stated in molecular terms genetic information flows in one direction
ŽŶůLJ ĨƌŽŵ E ƚŽ ƉƌŽƚĞŝŶ ďƵƚ ŶĞǀĞƌ ŝŶ ƌĞǀĞƌƐĞ
ŝƐĐŽǀĞƌLJ ŽĨ ƚŚĞ ĐŽƌƌĞĐƚ mechanism:
- ŚĂƌůĞƐ ĂƌǁŝŶ Θ ůĨƌĞĚ ZƵƐƐĞůů tĂůůĂĐĞ ĐŽ-discover the chief mechanism of evolution: Natural selection Charles Darwin (1809-1882)
- ĂƌǁŝŶ ŝŶĨůƵĞŶĐĞĚ ďLJ ƚŚĞ ďŽƚĂŶŝƐƚ :ŽŚŶ ^͘ ,ĞŶƐůŽǁ Ăƚ ĂŵďƌŝĚŐĞ
- ĂƌǁŝŶ ƌĞĂĚƐ ŚĂƌůĞƐ >LJĞůů͛Ɛ ;ϭϳϵϳ-ϭϴϳϱͿ Ŭ ͞WƌŝŶĐŝƉůĞƐ ŽĨ 'ĞŽůŽŐLJ͟ ;ϭϴϯϬͿ
- Lyell argued that present day geological processes can explain the history of the earth – gradualism - dŚĞ ŶŽƚŝŽŶ ŽĨ Ă ĚLJŶĂŵŝĐ ƌĂƚŚĞƌ ƚŚĂŶ Ă ƐƚĂƚŝĐ ǁŽƌůĚ ĞŵĞƌŐĞĚ ŝŶ ĂƌǁŝŶ͛Ɛ ƚŚŝŶŬing
- Voyage on H.M.S. Beagle around the world (1831-ϭϴϯϲͿ ĂƐ ƐŚŝƉ͛Ɛ ŶĂƚƵƌĂůŝƐƚ ї Most time spent in South America
- Made numerous observations and collections of plants, animals & fossils ї Geographical distribution of plants and animals of oceanic islands
- ZĞƚurned to England and spent the rest of his life (1842-1882) ŝŶ ƐĞĐůƵƐŝŽŶ Ăƚ ŽǁŶ ,ŽƵƐĞ developing his ideas, conducting experiments and writing books (25 in all)
- ĞǀĞůŽƉƐ ƚŚĞ ŶŽƚŝŽŶ ƚŚĂƚ species vary based on variation patterns of Galápagos mockingbirds ї ĂƌǁŝŶ ĚŽƵďƚƐ ͞ĨŝdžŝƚLJ͟ ŽĨ ƐƉĞĐŝĞƐ ;DĂƌĐŚ͕ ϭϴϯϳͿ ї There are 4 similar species endemic to the islands descended from a South American mainland ancestor
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ĂƌǁŝŶ ƌĞĂĚƐ Malthus’ ;ϭϳϵϴͿ ƐƐĂLJ ŽŶ ƚŚĞ WƌŝŶĐŝƉůĞ ŽĨ WŽƉƵůĂƚŝŽŶ ;^ĞƉƚ ϭϴϯϴͿ ǁŚŝĐŚ ŝŶĨůƵĞŶĐĞƐ his notion of selection
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1844: wrote but did not publish an essay on natural selection
1856: began work on natural selection book
:ƵŶĞ ϭϴϱϴ͗ ƌĞĐĞŝǀĞĚ ͞KŶ ƚŚĞ ƚĞŶĚĞŶĐLJ ŽĨ ǀĂƌŝĞƚŝĞƐ ƚŽ ĚĞƉĂƌƚ ŝŶĚĞĨŝŶŝƚĞůLJ ĨƌŽŵ ƚŚĞ ŽƌŝŐŝŶĂů ƚLJƉĞ͟ ďLJ ͘Z͘ tĂůůĂĐĞ
- :ƵůLJ ϭϴϱϴ͗ >ŝŶŶĞĂŶ ^ŽĐŝĞƚLJ ƉƌĞƐĞŶƚĂƚŝŽŶ ŝŶ >ŽŶĚŽŶ ŽĨ ĂƌǁŝŶ–Wallace paper
- 1859: publication of “The origin of species by means of natural selection or the preservation of favoured races in the struggle for life”
The Origin of Species
- All organisms have descended with modification from common ancestors
- The major agent of modification is natural selection operating on variation among individuals dŚĞ ĞƐƐĞŶĐĞ ŽĨ Ă ĂƌǁŝŶŝĂŶ ǁŽƌůĚ-view
- ZĞĐŽŐŶŝƚŝŽŶ ƚŚĂƚ ǀĂƌŝĂƚŝŽŶ ĂŵŽŶŐ ŝŶĚŝǀŝĚƵĂůƐ ŝƐ ŶŽƚ ŝŵƉĞƌĨĞĐƚŝŽŶ͕ ďƵƚ ƚŚĞ ŵĂƚĞƌŝĂů ĨƌŽŵ ǁŚŝĐŚ natural selection fashions better adapted forms of life
- This involves a move away from typology and the notion of an ideal species to population thinking ZĞƋƵŝƌĞŵĞŶƚƐ ĨŽƌ ĂƌǁŝŶ͛Ɛ ƚŚĞŽƌLJ ƚŽ ǁŽƌŬ – Assumptions
- Variation – variation among individuals in a population
- Heredity – progeny resemble their parents more than unrelated individuals
- Selection – some forms better at surviving and breeding than others in a given environment
ƌĞĂƚŝŽŶŝƐƚ ŽĐƚƌŝŶĞ
- Literal reading of Book Genesis
- Creation of all living organisms by divine order in 6 days
- All types of organisms individually created and designed by a purposeful creator ї /ŶĐŽŵƉĂƚŝďůĞ ǁŝƚŚ ĞǀŽůƵƚŝŽŶ
/ƚ ŝƐ ŶŽƚ ƐƵpported by any empirical observations
/ƚ ĚŽĞƐ ŶŽƚ ŝŶĨĞƌ ŝƚƐ ƉƌŝŶĐŝƉůĞƐ ĨƌŽŵ ŽďƐĞƌǀĂƚŝŽŶ͕ ĂƐ ĚŽĞƐ Ăůů ƐĐŝĞŶĐĞ
- /ƚƐ ĂƐƐƵŵƉƚŝŽŶƐ ůĞĂĚ ƚŽ ŶŽ ƚĞƐƚĂďůĞ Žƌ ĨĂůƐŝĨŝĂďůĞ ŚLJƉŽƚŚĞƐĞƐ
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LECTURE 14: WHAT DARWIN SAW: A BIOGEOGRAPHICAL PERSPECTIVE ON BIODIVERSITY AND
ADAPTATION
1. Contrasts between tropical & temperate ecosystems
2. The role of biotic and abiotic interactions in temperate and temperate ecosystems, respectively
3. Galápagos /slands as evolutionary laboratories ϰ͘ ƵƐƚƌĂůŝĂ͛Ɛ ŝƐŽůĂƚŝŽŶ ĂŶĚ ŝƚƐ ƵŶŝƋƵĞ ďŝŽƚĂ
ƵƌŝŶŐ ƚŚĞ ǀŽLJĂŐĞ ŽĨ ƚŚĞ ,͘D͘^͘ ĞĂŐůĞ ;ϭϴϯϭ-1836) Æ Spends most time in South America
- Stops in Brazil ї ĂƌǁŝŶ ŶŽƚĞƐ ŚŝŐŚ ƐƉĞĐŝĞƐ ĚŝǀĞƌƐŝƚLJ ĂŶĚ ŶŽǀĞů ĂĚĂƉƚĂƚŝŽŶƐ dƌŽƉŝĐĂů &ŽƌĞƐƚƐ ŝŶ ƌĂnjŝů
- Very high species ĚŝǀĞƌƐŝƚLJ ŽĨ ƉůĂŶƚ ĂŶĚ ĂŶŝŵĂů ŐƌŽƵƉƐ ĐŽŵƉĂƌĞĚ ǁŝƚŚ ƚĞŵƉĞƌĂƚĞ njŽŶĞ
- Many more biotic interactions, especially coevolved mutualisms between plants and animals
- Year-round warmth results in rapid growth of insect and microbial populations
- Pest and disease pressures on plants more intense
Tropical trees are largely animal-pollinated
Tropical Forests
High species diversity
/ŶĚŝǀŝĚƵĂůƐ ŽĨ ƐĂŵĞ ƐƉĞĐŝĞƐ ǁŝĚĞůLJ ƐĞƉĂƌĂƚĞĚ
Largely Evergreen
ĞŶƐĞ ĐĂŶŽƉŝĞƐ
Bee, butterfly, moth, bird and bat pollenators
Temperate Forests
Low species diversity
/ŶĚŝǀŝĚƵĂůƐ ŽĨ ƐĂŵĞ ƐƉĞĐŝĞƐ ĐůŽƐĞ ƚŽŐĞƚŚĞƌ
>ĂƌŐĞůLJ ĞĐŝĚƵŽƵƐ
Sparse canopies
Wind
ĂŶŝĞů :ĂŶnjĞŶ͗ ƵŐůŽƐƐŝŶĞ ĞĞƐ ĂƐ ůŽŶŐ-ĚŝƐƚĂŶĐĞ ƉŽůůŝŶĂƚŽƌƐ ŽĨ ƚƌŽƉŝĐĂů ƉůĂŶƚƐ ;^ĐŝĞŶĐĞ͕ ϭϵϳϭͿ
- hƐĞĚ ŵĂƌŬ-recapture techniques to demonstrate that bees travel up to 23 km during a day
- dŽĚĂLJ ǁŝĚĞůLJ ƌĞĐŽŐŶŝnjĞĚ ƚŚĂƚ ďĞĞƐ͕ ŵŽƚŚƐ ĂŶĚ ŚƵŵŵŝŶŐďŝƌĚƐ ƚƌĂǀĞů ůŽŶŐ ĚŝƐƚĂŶĐĞƐ ĚƵƌŝŶŐ
“trapline” foraging
- :ĂŶnjĞŶ͛Ɛ pest pressure hypothesis: ї Predicts that tropical tree seedlings are less likely to establish close to the maternal parent ї ZĞƐƵůƚ ĐŽŶĨŝƌŵĞĚ ƚŚƌŽƵŐŚ ĨŝĞůĚ ĞdžƉĞƌŝŵĞŶƚƐ ї Adult tree will have more pests on it, which will transfer to seedlings ї Although seedlings are most dense close to parent tree, seedling survival is highest at a greater distance
Acacia
- /ŶƚĞŶƐĞ ŚĞƌďŝǀŽƌLJ ŝŶ ƚƌŽƉŝĐĂů ĞĐŽƐLJƐƚĞŵƐ ƌĞƐƵůƚƐ ŝŶ ĐŽŶƐŝĚĞƌĂďůĞ ĚĂŵĂŐĞ ĂŶĚ ĐŽŶƐƵŵƉƚŝŽŶ ŽĨ plant biomass
- Some species of Acacia and ants have co-evolved to deal with this situation
- Symbiosis: Ant-plant mutualism in Acacia ї Pseudomyrmex Ants protect Acacia against herbivorous insects ї Manipulated with chemicals to keep ants off experimentally ї Hollow thorns provide a nesting site for ants ї Beltian bodies of Acacia provide protein and lipids while extrafloral nectarines provide sugar for the ants
- Experiment by Megan Frederickson (EEB) ;EĂƚƵƌĞ͕ ϮϬϬϱͿ
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ї emonstrated that in ͞Ğǀŝů͛Ɛ ŐĂƌĚĞŶ,” Peru -- ants defend their hosts against plant competitors using formic acid as a herbicide, thus benefitting from more nest sites
-
Epiphytes:
- Epiphytes are plants that grow on other plants non-parasitically
- Common in the tropics, increasing species diversity
- Epiphytic life form has evolved independently in many unrelated families Æ Convergent evolution ї Ex: Lichens, orchids, bromeliads, mosses
- Questions: ї Are particular Trees favoured? ї How are they dispersed? ї What pollinates them? ї How and why have they evolved?
- Bright colours tend to attract pollinators
Opportunities to investigate function and adaptive significance
- Why do some flowers change colour?
- Why are some leaves red? ї DĂLJ ƉƌŽƚĞĐƚ ĂŐĂŝŶƐƚ ŚĞƌďŝǀŽƌLJ ďLJ ŝŶƐĞĐƚƐ ĂƐ ƚŚĞLJ ĚŽŶ͛ƚ ƐĞĞ ƌĞĚ ǁĞůů
- Why does mimicry occur? ї Preying mantis – mimics living leaf ї Katydid – mimics dead leaf
- Why does poinsettia have red bracts? ї May serve to attract pollinators
Finds fossils of extinct mammals – Glyptodon – giant armadillo
- Processes that occurred in the past Æ Extinction
/ƐĂďĞůĂ͗
- Prickly Pear cacti are first coůŽŶŝnjĞƌƐ ŽĨ ǀŽůĐĂŶŝĐ ůĂŶĚƐĐĂƉĞƐ
- Capable of long-distance dispersal by fleshy bird-dispersed fruits
ĂƉhne Major:
- Site of 35-year study of natural selection in Galapagos finches
- ^ƚƵĚLJ ďLJ WĞƚĞƌ Θ ZŽƐĞŵĂƌLJ 'ƌĂŶƚ ;WƌŝŶĐĞƚŽŶͿ
- 14 Galapagos finches represent an adaptive radiation
Adaptive radiation:
- The evolution of ecological and phenotypic diversity within a rapidly multiplying lineage as a result of speciation
- From a single common ancestor the process results in an array of species that differ in traits allowing exploitation of a range of habitats and resources
- Four features commonly identify an adaptive radiation ϭ͘ ZĞĐĞŶƚ ĐŽŵŵŽŶ ĂŶĐĞƐƚƌLJ ĨƌŽŵ Ă ƐŝŶŐůĞ ƐƉĞĐŝĞƐ
2. Phenotype-environment correlation
3. Trait utility ϰ͘ ZĂƉŝĚ ƐƉĞĐŝĂƚŝŽŶ
Galapagos island giant tortoise
- Largest tortoise in ƚŚĞ ǁŽƌůĚ ;ϴϴϬŬŐ͕ Ϯŵ ůŽŶŐͿ͕ ŽůĚĞƐƚ ůŝǀŝŶŐ ŝŶĚŝǀŝĚƵĂů Λ ϭϳϬLJƌƐ
- Tortoises on different islands have different shell patterns ї ϭϬ ƐƵďƐƉĞĐŝĞƐ ŽĨ Ă ƐŝŶŐůĞ ƐƉĞĐŝĞƐ ;Geochelone nigra) – endangered
/ŐƵĂŶĂƐ͗
- Marine iguanas (Amblyrhynchus cristatus) ї Feed on seaweed ї Expels salt from nasal glands ї ƐĂůƚ-encrusted foreheads
- dĞƌƌĞƐƚƌŝĂů /ŐƵĂŶĂ ;Conolophus subcristatus) ї ϴϬй ŽĨ ĚŝĞƚ ĨƌŽŵ ƉƌŝĐŬůLJ ƉĞĂƌ ĐĂĐƚƵƐ
Birds:
- Loss of flight in cormorant ї Advantages for diving? ї Lack of predation?
- Sexually dimorphic Frigate bird
ƵƌŝŶŐ ƚŚĞ ǀŽLJĂŐĞ ŽĨ ƚŚĞ ,͘D͘^͘ ĞĂŐůĞ ;ϭϴϯϭ-1836)
- Heads south to Patagonia
Patagonia
- ŝƐĐŽǀĞƌƐ ƐƚƌŝŬŝŶŐůLJ ĚŝĨĨĞƌĞnt environments
- Abiotic factors dominate Æ ŽŵƉůĞƚĞůLJ ĐŽŶƚƌĂƐƚĞĚ ďLJ ďŝŽƚŝĐ ĨĂĐƚŽƌƐ ŽĨ ƌĂnjŝů ї Wind shear and ice storm activity affect treelines
- Landscapes are geologically young
- Abiotic factors
- Finds familiar and unfamiliar animal groups, animals with relatives around the world ї Black-necked swan Æ Looks familiar, why is the neck black? ї Southern rufous bumblebee Æ >ŽŽŬƐ ĨĂŵŝůŝĂƌ͕ ǁŚLJ ŝƐ ŝƚ ƐŽ ĨƵnjnjLJ͍ dŚĞƌŵŽƌĞŐƵůĂƚŝŽŶ͍ ї ĂƌǁŝŶ͛Ɛ ƌŚĞĂ Æ Flightlessness evolved ї Guanaco Æ ZĞůĂƚĞĚ ƚŽ ĐĂŵĞů͍
ƵƌŝŶŐ the voyage of the H.M.S. Beagle (1831-1836)
- Heads west to Australia (2 months)
Australia
- ŝƐƚŝŶĐƚ ĨůŽƌĂ ĂŶĚ ĨĂƵŶĂ ǁŝƚŚ ŚŝŐŚ ůĞǀĞůƐ ŽĨ endemism and many unique adaptations
- Biological uniqueness due to long history of isolation from other land masses
- Although a continent Australia is also an island and shows many island characteristics e.g. endemism, radiations & unique adaptations
Endemism:
- Endemic species, which are restricted to a particular geographical region or habitat
Queensland
- ŝƐĐŽǀĞƌĞĚ Ɖŝphytic fern
ƵƌŝŶŐ ƚŚĞ ǀŽLJĂŐĞ ŽĨ the H.M.S. Beagle (1831-1836)
- Heads west to Galápagos Islands ї &ŝƌƐƚ ĂƌƌŝǀĞƐ ŽŶ ^ĂŶ ƌŝƐƚŽďĂů /ƐůĂŶĚ ;ŚĂƚŚĂŵͿ ŽŶ ϵͬϭϳͬϭϴϯϱ
'ĂůĄƉĂŐŽƐ /ƐůĂŶĚƐ
- 15 main islands of volcanic origin; oldest 5-ϭϬ ŵŝůůŝŽŶ LJĞĂƌƐ ŽůĚ͖ LJŽƵŶŐĞƐƚ ŵŽƌĞ ƌĞĐĞŶƚ
- &ůŽƌĂ ĂŶĚ ĨĂƵŶĂ ĐŽůŽŶŝnjĞĚ ďLJ ƐƉĞĐŝĞƐ ĐĂƉĂďůĞ ŽĨ ůŽŶŐ-distance dispersal from South American mainland - ŝƐƚŝŶĐƚ ƌĂĐĞƐ ĂŶĚ ƐƉĞĐŝĞƐ ŽŶ ĚŝĨĨĞƌĞŶƚ ŝƐůĂŶĚƐ ƉƌŽǀŝĚĞ ĞǀŝĚĞŶĐĞ ŽĨ ĞĂƌůLJ ƐƚĂŐĞƐ ŽĨ ƐƉĞĐŝĂƚŝŽŶ
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ĂƌǁŝŶ ƐƉĞŶƚ ŽŶůLJ ϱ ǁĞĞŬƐ ŽŶ ƚŚĞ ŝƐůĂŶĚƐ ďƵƚ ŚŝƐ ŽďƐĞƌǀĂƚŝons formed the foundation for his theory of evolution
EŽǁ Ă hE ^K tŽƌůĚ ,ĞƌŝƚĂŐĞ ƐŝƚĞ ĂŶĚ ĞĐŽƚŽƵƌŝƐŵ ĚĞƐƚŝŶĂƚŝŽŶ
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Page 8 of 52
New South Wales
- ƌLJ ĨŽƌĞƐƚƐ ĐŽŵƉŽƐĞĚ ŽĨ ƵĐĂůLJƉƚƵƐ ;'Ƶŵ dƌĞĞͿ ї ŽŵŝŶĂŶƚ ƚƌĞĞ ŐƌŽƵƉ ŝŶ ƵƐƚƌĂůŝĂ
Koala
- Arboreal herbivorous marsupial
- ^ƉĞĐŝĂůŝnjĞĚ ĚŝĞƚ ŽĨ ƵĐĂůLJƉƚƵƐ ůĞĂǀĞƐ
- Can detoxify phenolics and terpenes in leaves
ZŽĚĞŶƚ ƉŽůůŝŶĂƚĞĚ ĂŶŬƐŝĂ
- Plant is a shrub, but flowers are produced on the ground where rodents forage
Summary:
ƵƌŝŶŐ ƚŚĞ ǀŽLJĂŐĞ ŽĨ ƚŚĞ ,͘D͘^͘ ĞĂŐůĞ ;ϭϴϯϭ-1836)
- >ĂŶĚƐ ŝŶ ƌĂnjŝů ї Notes high species diversity and novel adaptations
- Heads south to Patagonia ї ŝƐĐŽǀĞƌƐ ƐƚƌŝŬŝŶŐůLJ ĚŝĨĨĞƌent environments where abiotic factors dominate
- ,ĞĂĚƐ ǁĞƐƚ ƚŽ 'ĂůĄƉĂŐŽƐ /ƐůĂŶĚƐ ;ϱ ǁĞĞŬƐͿ ї Evidence of early stages of speciation ї Spent only 5 weeks on the islands but his observations formed the foundation for his theory of evolution
- Heads west to Australia (2 months) ї Notes high endemism, novel adaptations and “biological uniqueness”
- ,ĞĂĚƐ ŚŽŵĞ ƚŽ h< – ŽǁŶ ŚŽƵƐĞ ї Gets married, has children, then starts work on assembling evidence for his evolutionary theory Reading Summary: Notes and quotes from Coyne - Chapter 4:
:ƵĂŶ &ĞƌŶĄŶĚĞnj ĂƌĐŚŝƉĞůĂŐŽ
- many edemic species found nowhere else in the world
- no species of amphibian, reptile or mammal
- gives evidence for evolution
/ŵƉŽƌƚĂŶƚ ƋƵĞƐƚŝŽŶƐ ƌĞŐĂƌĚŝŶŐ ŐĞŽŐƌĂƉŚŝĐ ĚŝƐƚƌŝďƵƚŝŽŶƐ͕ ŶŽǁ ĂŶƐǁĞƌĞĚ ďLJ ͞ƌĞƚƌŽĚŝĐƚŝŽŶ͟ in light of evolutionary theory:
- Why did oceanic islands have such odd and unbalanced floras and faunas compared to continental assemblages?
- Why were Australia͛s native mammals marsupials, while placental mammals dominated the rest of the world?
- Why do distant areas with similar terrains and climates have species that appear similar, but are fundamentally different?
- dŚĞƐĞ ĂƌĞ ƚŚĞ ƚLJƉĞƐ ŽĨ ƋƵĞƐƚŝŽŶƐ ƚŚĂƚ ƉůĂŐƵĞĚ ĂƌǁŝŶ ǁŚŝůĞ ŽŶ ƚŚĞ ǀŽLJĂŐĞ ŽĨ ƚŚĞ ,͘D͘^͘ ĞĂŐůĞ
Convergent evolution
- Species that live in similar habitats will experience similar selection pressures in their environment, will therefore evolve similar adaptations
Biogeographic patterns ї Continental drift
- Marsupial fossils appear in Antarctica
- Freshwater frogs appear in eastern South America and subtropical Africa
- These observations can only be answered in light of biogeography and continental drift
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- ŝŽŐĞŽŐƌĂƉŚLJ ŵĂŬĞƐ ƉƌĞĚŝĐƚŝŽŶƐ ĂŶĚ ƐŽůǀĞƐ ƉƵnjnjůĞƐ
Continental islands vs. Oceanic islands:
- Continental islands were once connected to a continent but separated by flooding or moving continental plats
- Oceanic islands were never connected to a continent
- ŝƐƉĂƌŝƚLJ ďĞƚǁĞĞŶ ƚLJƉĞƐ ŽĨ ƉůĂŶƚƐ ĂŶĚ ĂŶŝŵĂůƐ ƚŚĂƚ ĂƉƉĞĂƌ ŽŶ ĐŽŶƚŝŶĞŶƚĂů ǀƐ ŽĐĞĂŶŝĐ ŝƐůĂŶĚƐ ŝƐ hard to explain using creationist scenario
Oceanic islands:
- Mammals, amphibians, freshwater fish and reptiles often do very well when introduced to oceanic islands
- isplace and destroy native species: ї Pigs and goats on Hawaii, Cane toad in Hawaii and
Australia, ZĂďďŝƚƐ ŝŶ ƵƐƚƌĂůŝĂ, etc.
Native to oceanic island
Plants
Birds
/ŶƐĞĐƚƐ ĂŶĚ ŽƚŚĞƌ ĂƌƚŚƌŽƉŽĚƐ
Missing from oceanic island
Land Mammals
ZĞƉƚŝůĞƐ
Amphibians, Freshwater fish
-
Oceanic islands have unbalanced biotas – missing major groups of organisms, and the same ones are missing on different islands
- Types of organisms there usually comprise similar species – a radiation – most often of which are types of species that can disperse most easily over large stretches of ocean
- Species that are most similar to those inhabiting oceanic islands are usually found on the nearest mainland even though habitats may be different
- When endemic species occur on oceanic islands, it can be explained by plant seeds hitching a ride on air currents, birds and bats flying, seals swimming and other animals hitching a ride on
“rafts”
Continental Islands:
- “old” continental islands, such as New Zealand and Madagascar were isolated before many groups of species had evolved
- Had many ecological niches unfilled which opened the door for later-evolving species to
ƐƵĐĐĞƐƐĨƵůůLJ ĐŽůŽŶŝnjĞ ĂŶĚ ĞƐƚĂďůŝƐŚ ƚŚĞŵƐĞůǀĞƐ
- Have a “somewhat” unbalanced flora and fauna
- Species on the islands closely resemble those found on nearest mainland
Envoi:
- Only evolution can explain the diversity of life that appears on islands
- Time and chance determine which species will end up on an island
- Because species on islands adapt to environments isolated from the diversity of species that live elsewhere, they are not good at co-existing with others
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Page 10 of 52
LECTURE 15: NEODARWINISM AND THE EVOLUTIONARY SIGNIFICANCE OF GENETIC VARIATION
-
DƵƐƚ ŽĐĐƵƌ ŝŶ ŐĞƌŵ ĐĞůůƐ ;ƐƉĞƌŵͬĞŐŐƐͿ – somatic mutations are not inherited
Fruit fly: ї Wild type – “normal” ї ZĞĐĞƐƐŝǀĞ ŵƵƚĂŶƚ – no eye pigment ї Homeotic mutation – leg where antenna should be, severe, but not lethal
- Barbara McClintock ;ŽƌŶĞůů hŶŝǀĞƌƐŝƚLJ͕ ϭϵϬϮ-1992) ї tŽŶ ϭϵϴϯ EŽďĞů ƉƌŝnjĞ ĨŽƌ WŚLJƐŝŽůogy-Medicine ї ŽƌŶ ƉĂƚƚĞƌŶƐ ĚŝĚŶ͛ƚ Ĩŝƚ DĞŶĚĞůůŝĂŶ ƌĂƚŝŽƐ ї ŝƐĐŽǀĞƌLJ ŽĨ ͞ũƵŵƉŝŶŐ ŐĞŶĞƐ͟ Žƌ ƚƌĂŶƐƉŽƐĂďůĞ ŐĞŶĞƚŝĐ ĞůĞŵĞŶƚƐ ŝŶ ŵĂŝnjĞ ;ĐŽƌŶͿ ї Arise by mutation and can move around the genome
- Mutant Australian daisy – potential outcomes ї Pollinators will avoid it ďĞĐĂƵƐĞ ƚŚĞLJ ĚŽŶ͛ƚ ƌĞĐŽŐŶŝnjĞ ŝƚ – will disappear ї Pollinators may find it more appealing – will increase frequency in population ї May impact population via genetic drift ї May be a polymorphism Æ Both forms (White & Yellow) co-exist Æ Neutral
- Characteristics of mutation ї hnstoppable phenomenon ї ĞƐƉŝƚĞ ĐĞůůƵůĂƌ ŵĞĐŚĂŶŝƐŵƐ ƚŽ ĐŽƌƌĞĐƚ ĞƌƌŽƌƐ ĚƵƌŝŶŐ E ƌĞƉůŝĐĂƚŝŽŶ ї Not directed by the organism or the environment ї ZĂŶĚŽŵ ǁŝƚŚ ƌĞƐƉĞĐƚ ƚŽ ĞĨĨĞĐƚƐ ŽŶ ĨŝƚŶĞƐƐ ї ZĂƚĞƐ ĚĞƉĞŶĚƐ ŽŶ ƚŚĞ ƚLJƉĞ ŽĨ ŵƵƚĂƚŝŽŶ Æ Also varies among genes ї Exposure to certain environmental conditions can affect mutation rate ї Mutagens, high temperature
- DƵƚĂƚŝŽŶ ĂŶĚ ƚŚĞ ƐƚƌƵĐƚƵƌĞ ŽĨ E
1. Point mutations
ATGCAGT Æ ATCCAGT
Ϯ͘ /ŶƐĞƌƚŝŽŶƐͬĚĞůĞƚŝŽŶƐ ;ŝŶĐůƵĚŝŶŐ ͚ũƵŵƉŝŶŐ ŐĞŶĞƐ͛Ϳ ;^ĞƉĂƌĂƚĞĚ ŝŶto potential codons)
ATG|CAG|T Æ ATG|GCA|GT
ZĞƐƵůƚƐ ŝŶ frame-shift mutation – often deleterious, changing downstream codons 3. Changes in repeat number (Separated into potential codons)
ATG|ATG|ATG|ATG Æ ATG|ATG|ATG|ATG|ATG
4. Chromosomal rearrangements
ATGCAGT Æ TGACGTA
Motoo Kimura (1924-1994):
- dŚĞŽƌĞƚŝĐĂů ƉŽƉƵůĂƚŝŽŶ ŐĞŶĞƚŝĐŝƐƚ ǁĂƐ ĨŝƌƐƚ ƚŽ ƌĞĐŽŐŶŝnjĞ ƚŚĞ ŝŵƉŽƌƚĂŶĐĞ ŽĨ ŶĞƵƚƌĂů ŵƵƚĂƚŝŽŶƐ
1. Where does genetic variation come from?
2. How is it inherited?
3. How does it influence trait variation?
4. Why is genetic variation important for evolution?
ZĞƋƵŝƌĞŵĞŶƚƐ ĨŽƌ ĂƌǁŝŶ͛Ɛ ƚŚĞŽƌLJ͗
- Genetics: ї Variation – Variation among individuals in a population ї Heredity – Progeny resemble their parents more than unrelated individuals
- Selection – some forms are better at surviving and breeding in a given environment
- ĂƌǁŝŶ ŚĂĚ ŶŽ ƵŶĚĞƌƐƚĂŶĚŝŶŐ ŽĨ ŐĞŶĞƚŝĐƐ Žƌ ƚŚĞ ŵĞĐŚĂŶŝƐŵ ŽĨ ŝŶŚĞƌŝƚĂŶĐĞ
Genotype:
- Genetic constitution (makeup) of an organism
- hƐĞĚ ŝŶ ƌĞůĂƚŝŽŶ ƚŽ Ă ŐĞŶĞ͕ Žƌ ĐŽŵďŝŶĂƚŝŽŶ ŽĨ ŐĞŶĞƐ ї Ex: Aa, AaBB
Phenotype:
- The trait of an organism as observed
- hƐĞĚ ǁŚĞŶ ĚŝƐĐƵƐƐŝŶŐ Ă ƚƌĂŝƚ Žƌ ĨĞĂƚƵƌĞ ŽĨ ĂŶ ŽƌŐĂŶŝƐŵ ƚŚĂƚ ǀĂƌŝĞƐ ї Ex: The genotype AA or Aa lead to the phenotype of smooth skin while aa leads to wrinkled skin
Genome:
- dŚĞ ĞŶƚŝƌĞ ŽƌŐĂŶŝƐŵ͛Ɛ E ŝŶĐůƵĚŝŶŐ genes and non-coding regions ї Genes – lead to phenotypes ї Non-coding regions – ͞:ƵŶŬ͟ E
What is a gene? – Various definitions
- The functional unit of inheritance
- A unit of hĞƌĞĚŝƚĂƌLJ ŝŶĨŽƌŵĂƚŝŽŶ ůŽĐĂƚĞĚ ŽŶ ƚŚĞ ĐŚƌŽŵŽƐŽŵĞƐ ĐŽŶƐŝƐƚŝŶŐ ŽĨ E
E ƐĞƋƵĞŶĐĞ ĐŽŵƉŽƐĞĚ ŽĨ codons essential for a specific biological function ї Codon: Sequence of 3 nucleotides (A,T,C,G) that code for an amino acid ї A sequence of codons make up the genetic code
Evolution requires genetic variation – where does it come from?
- Mutation
- ZĞĐŽŵďŝŶĂƚŝŽŶ
- Gene flow
- ,LJďƌŝĚŝnjĂƚŝŽŶ
/ŶĚĞƉĞŶĚĞŶƚ ĂƐƐŽƌƚŵĞŶƚ Θ recombination
- /ŶĚĞƉĞŶĚĞŶƚ ĂƐƐŽƌƚŵĞŶƚ Θ ƌĞĐŽŵďŝŶĂƚŝŽŶ ĚƵƌŝŶŐ ŵĞŝŽƐŝƐ ŐĞŶĞƌĂƚĞƐ ĞŶŽƌŵŽƵƐ ĚŝǀĞƌƐŝƚLJ ї Humans with n=23 chromosomes, 223 = 8͕ϯϴϴ͕ϲϬϴ possible gamete combinations
- Most genetic variability in a population results from sexual reproduction ї in any given generation input from mutation very small
Mutations
- hůƚŝŵĂƚĞ ƐŽƵƌĐĞ ŽĨ ŐĞŶĞƚŝĐ ǀĂƌŝĂƚŝŽŶ
- StaďůĞ ĐŚĂŶŐĞ ŝŶ E ƐĞƋƵĞŶĐĞ ƌĞƐƵůƚŝŶŐ ŝŶ ĐŚĂŶŐĞ ŽĨ ŐĞŶŽƚLJƉĞ
- Occurs at low and variable rate in all organisms
- Effects vary from neutral, deleterious, lethal or beneficial ї Fitness depends on environment in many cases
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Mutation rates in eukaryotes
Number of fitness-affecting mutations per diploid genome each generation
Drosophila (fruit fly)
1.2
Caenorhabditis (worm)
Ϭ͘ϵϲ
Arabidopsis (plant)
Ϭ͘ϭ-Ϭ͘ϲ
DŽƵƐĞͬZĂƚ
Ϭ͘ϵϭ
,ƵŵĂŶͬŚŝŵƉĂŶnjĞĞ
1.6-3
Organism
Page 11 of 52
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Page 12 of 52
What about Humans?
- Each human carries 3-5 recessive lethal alleles ї ůůĞůĞƐ ĐĂƵƐŝŶŐ ĚĞĂƚŚ ǁŚĞŶ ŚŽŵŽnjLJŐŽƵƐ ї Mating among relatives causes a higher incidence of offspring mortality
/ŶŚĞƌŝƚĂŶĐĞ ĂŶĚ ƚŚĞ ƚƌĂŶƐŵŝƐƐŝŽŶ ŽĨ ŐĞŶĞƐ ĂŵŽŶŐ ŐĞŶĞƌĂƚŝŽŶƐ
- How is genetic information transmitted from parents to offspring ї Mechanism of inheritance?
- How are traits expressed in parents and offspring ї /Ɛ ƚŚŝƐ ŝŶĨůƵĞŶĐĞĚ ďLJ ŚŽǁ ŵĂŶLJ ŐĞŶĞƐ ĐŽŶƚƌŽů Ă ƚƌĂŝƚ͍
Gregor Mendel (1822-1884)
- Priest and “father of modern genetics”
- Through controlled crosses with peas established the laws of inheritance
- DĞŶĚĞů͛Ɛ >ĂǁƐ ƌĞ-ĚŝƐĐŽǀĞƌĞĚ Ăƚ ƚŚĞ ďĞŐŝŶŶŝŶŐ ŽĨ ƚŚĞ ϮϬƚŚ ĐĞŶƚƵƌLJ ďLJ ,ƵŐŽ ĚĞ sƌŝĞƐ Θ Ăƌů
Correns
ĞƐŝŐŶ ŽĨ DĞŶĚĞů͛Ɛ džƉĞƌŝŵĞŶƚ
- Cross between two pure-breeding lines of pea plants that differ in observable phenotypic trait ї (Green parent) x (Yellow parent) Æ F1 self-crossed Æ F2 ї F1 = First generation; F2 = Second generation
- Expected results: Blending inheritance ї When offspring of a cross show intermediate phenotype ї (Green parent) x (Yellow parent) Æ Lime Green F1 Offspring Æ Lime Green F2 Offspring
- Observed results: Parental phenotypes retained -- ;zͿ с zĞůůŽǁ ƉĞĂ͛ ;'Ϳ с 'ƌĞĞŶ ƉĞĂ ї (G) x (Y) Æ &ϭ͗ ϭϬϬй ;zͿ ŽĨĨƐƉƌŝŶŐ Æ F2: ¾ (Y) offspring, ¼ (G) offspring ї Therefore: Yellow (Y) is dominant, Green (G) is recessive ї 3:1 phenotypic ratio in F2 – ¾ dominant and ¼ recessive observed ї 1:2:1 genotypic ratio in F2 – ¼ YY allele = (Y), ½ Yy allele = (Y), ¼ yy allele = (G)
DĂŝŶ ĐŽŶĐůƵƐŝŽŶƐ ĨƌŽŵ DĞŶĚĞů͛Ɛ ĞdžƉĞƌŝŵĞŶƚƐ ǁŝƚŚ ƉĞĂƐ
- /ŶŚĞƌŝƚĂŶĐĞ ĚĞƚĞƌŵŝŶĞĚ ďLJ ĚŝƐĐƌĞƚĞ ƉĂƌƚŝĐůĞƐ -- genes – “particulate inheritance”
- Most organisms carry two copies of each gene – alleles -- and are diploid
- Organisms produce haploid gametes (sperm, eggs) each containing one allele
- Offspring inherit one allele from each parent at random
- ŽŵŝŶĂŶƚ ĂůůĞůĞ ŵĂƐŬƐ ŚĞƚĞƌŽnjLJŐŽƵƐ ĂůůĞůĞ ŝŶ ŚĞƚĞƌŽnjLJŐŽƵƐ genotype
ŝƐĐƌĞƚĞ ǀƐ. Continuous traits
- Discrete traits: ї Simply inherited by 1 or 2 genes (major genes) ї Mendelian genetics ї 3 potential outcomes – homozygous dominant (AA), heterozygous ; ĂͿ͕ Žƌ ŚŽŵŽnjLJŐŽƵƐ recessive (aa)
- Continuous traits: ї Complex inheritance by many genes (polygenes) of small effect ї Quantitative inheritance ї Continuum of outcomes – Ex: weight and height in humans ї ϲϱй ŽĨ ǀĂƌŝĂƚŝŽŶ ŝŶ ŚƵŵĂŶ ŚĞŝŐŚƚ ŝƐ ŚĞƌŝƚĂďůĞ
Genetic Polymorphism
- ŝĨĨĞƌĞŶƚ ƉŚĞŶŽƚLJƉĞƐ ĞdžŝƐƚ ŝŶ ƚŚĞ ƐĂŵĞ ƉŽƉƵůĂƚŝŽŶ ŽĨ Ă species
- The occurrence of two or more discrete forms of a species in the same locality in such proportions that the rarest cannot be maintained by mutation alone ї hsually means frequency of rarest mutation хϱй
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/ŶǀŽůǀĞƐ ĚŝƐĐƌĞƚĞ ƉŚĞŶŽƚLJƉĞƐ ;ĐĂůůĞĚ ĨŽƌŵ Žƌ morphs) governed by segregation of a small number of alleles at 1-2 major genes
- Ex: sexual dimorphism, blood types
Gene number & phenotypic distribution
- ZĞůĂƚŝŽŶ ďĞƚǁĞĞŶ ŶƵŵďĞƌ ŽĨ ŐĞŶĞƐ ĐŽŶƚƌŽůůŝŶŐ Ă ƚƌĂŝƚ ĂŶĚ ƉŚĞŶŽƚLJƉŝĐ ǀĂƌŝĂďŝůŝƚLJ
- Few genes – discontinuous (discrete) variation
- Many genes - continuous variation ї Gene action is co-dominant ї ,ĞƚĞƌŽnjLJŐŽƚĞ ŚĂƐ ĂŶ ŝŶƚĞƌŵĞĚŝĂƚĞ ƉŚĞŶŽƚLJƉĞ – dominance does not occur
Genetic analysis of variation
- ŝƐĐŽŶƚŝŶƵŽƵƐ ǀĂƌŝĂƚŝŽŶ - Mendelian genetics ї Major genes, dominance and recessiveness, genetic polymorphism
- Continuous variation - Quantitative genetics ї Polygenes, selection response, artificial selection experiments
&ŝƐŚĞƌ͛Ɛ &ƵŶĚĂŵĞŶƚĂů dŚĞŽƌĞŵ ŽĨ EĂƚƵƌĂů ^ĞůĞĐƚŝŽŶ
- ^ŝƌ ZŽŶĂůĚ A. Fisher ;ϭϴϵϬ-1962)
- “The rate of increase in fitness of a population at any time is equal to its genetic variance in fitness at that time”
Reading Summary: Notes and quotes from Coyne - Chapter 5:
Hornets vs. Bees
- Hornets adapt to take over bee colonies
- Bees adĂƉƚ ƵŶŝƋƵĞ ĚĞĨĞŶƐĞ ƚŽ ͚ĐŽŽŬ͛ ƐĐŽƵƚ ŚŽƌŶĞƚ ŝŶǀŽůǀŝŶŐ ĐŽŽƌĚŝŶĂƚŝŽŶ
- /ŶƚƌŽĚƵĐĞ ƵƌŽƉĞĂŶ ǀĂƌŝĞƚLJ ŽĨ ďĞĞƐ͕ ƚŚĞLJ ŐĞƚ ĚĞƐƚƌŽLJĞĚ ďLJ ŚŽƌŶĞƚƐ͕ ĂƐ ƚŚĞLJ ĂƌĞ ĚĞĨĞŶƐĞůĞƐƐ
WĂƌĂƐŝƚĞͬŚŽƐƚ ĂĚĂƉƚĂƚŝŽŶƐ Θ ŝŶƚĞƌĂĐƚŝŽŶƐ
- Plants that look like insects ї Chemicals & appearance Æ moths that want to mate end up spreading pollen
- /ŶƐĞĐƚƐ ƚŚĂƚ ůŽŽŬ ůŝŬĞ ƉůĂŶƚƐ ї Avoidance of predators
- ĂƌŬĞƌ ƐŽŝů Æ ĂƌŬĞƌ ŵŝĐĞ͖ >ŝŐŚƚĞƌ ƐŽŝů Æ lighter mice
Evolution & Selection
- “Mindless materialistic process that could achieve the same result as celestial design”
- ZĞƋƵŝƌĞƐ ŶŽ ǁŝůů Žƌ ĐŽŶƐĐŝŽƵƐ ĞĨĨŽƌƚ
- Population must be variable, variability must be heritable and any adaptations must increase potential to leave offspring
- Not all chance Æ “non-random survival of random variants”
- Selection cannot create a step that does not benefit its possessor
ZĞƉƌŽĚƵĐƚŝŽŶ͕ ŶŽƚ ƐƵƌǀŝǀĂů͕ ĚĞƚĞƌŵŝŶĞƐ ǁŚĞƚŚĞƌ ŐĞŶĞƐ ŵĂŬĞ ŝƚ ƚŽ ŶĞdžƚ ŐĞŶĞƌĂƚŝŽŶ
- Same genes that increase ability to reproduce when you are young may cause enlarged prostate when old
Acacia Æ When one species does something to help another, it always helps itself in the process
Adaptations increase the fitness of the individual, not the species
- Never see adaptations that benefit the species at the cost of the individual ї Male preying mantis & black widow spider?
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Number of offspring is finite
- Allele frequencies in offspring may not be representative of parents
- Proportion of alleles can change by chance
Genes can become fixed in the population Æ ƌŝƐĞ ƚŽ ϭϬϬй ĨƌĞƋƵĞŶĐLJ ĚƵĞ ƚŽ ŐĞŶĞƚŝĐ ĚƌŝĨƚ
ĐŽŝŶ ŚĂƐ Ă ϱϬй ĐŚĂŶĐĞ ŽĨ revealing a head or tail on a coin toss
- /Ĩ LJŽƵ ŽŶůLJ ŚĂǀĞ Ă ĨĞǁ ƚŽƐƐĞƐ͕ ƚŚĞƌĞ ŝƐ Ă ŚŝŐŚ ƉƌŽďĂďŝůŝƚLJ LJŽƵ ǁŝůů ĚĞǀŝĂƚĞ ĨƌŽŵ ƚŚĂƚ ϱϬͬϱϬ ƌĂƚŝŽ
Small populations
- Proportion of alleles can change by chance
- Change in allele frequencies over time NOT due to natural selection
- hŶƵƐƵĂů ďůŽŽĚ ƚLJƉĞ ĨƌĞƋƵĞŶĐŝĞƐ ŝŶ ŵŝƐŚ ĐŽŵŵƵŶŝƚŝĞƐ
ƌŝĨƚ с ƌĂŶĚŽŵ
- Can change allele frequencies no matter how useful they are
- Can overpower natural selection in small populations
- Sampling effect can be so large that it raises frequency of harmful genes even though selection works against them
- Even tiny advantages immeasurable by biologists can lead to important changes over time
Animal & Plant Breeding
- ŽŵĞƐƚŝĐ ĚŽŐ Æ from Eurasean grey wolf
- /Ĩ ĨŽƐƐŝůƐ ŽĨ ĚŽŐƐ ǁĞƌĞ ƚŽ ďĞ ĚŝƐĐŽǀĞƌĞĚ͕ ƚŚĞLJ ǁŽƵůĚ ďĞ ƚŚŽƵŐŚƚ of as new species
- ϭϱϬ ďƌĞĞĚƐ фϭϬ͕ϬϬϬ LJĞĂƌƐ Æ EĂƚƵƌĂů ƐĞůĞĐƚŝŽŶ ƚŽŽŬ ϭϬϬϬdž ůŽŶŐĞƌ ƚŽ ůĞĂĚ ƚŽ ƚŚĞ ĚĞǀĞůŽƉŵĞŶƚ ŽĨ the grey wolf.
- Artificial selection Æ no bearing on fitness or reproductive success Æ completely manipulated
- ĂƌǁŝŶ Æ began the origin of species with notion of artificial selection because success of artificial selection is so obvious, that the logical leap from artificial to natural selection became natural Evolution in the test tube
- Exposing captive populations to new environmental challenges
- hƐing microbes you can observe thousands of generations in real-time ї Genuine evolution Æ although challenge may be man-made ї More “natural” than artificial selection
- Lenski (See lecture 19) ї depleted then renewed glucose substrate of E. coli ї ĐƌĞĂƚĞĚ Ă ĨĞĂƐƚͬĨĂmine environment ї ŶŽǁ ŐƌŽǁ ϳϬй ĨĂƐƚĞƌ ƚŚĂŶ ƵŶƐĞůĞĐƚĞĚ ƐƚƌĂŝŶ
- /Ĩ LJŽƵ ƌĞŵŽǀĞ Ă ŐĞŶĞ Ă ŵŝĐƌŽďĞ ŶĞĞĚƐ ƚŽ ƐƵƌǀŝĐĞ͕ ǁŝůů ƚŚĞ ŵŝĐƌŽďĞ ĞǀŽůǀĞ Ă ǁĂLJ ĂƌŽƵŶĚ ƚŚĞ
ƉƌŽďůĞŵ͍ hƐƵĂůůLJ LJĞƐ
- Barry Hall ї ĞůĞƚĞĚ ŐĞŶĞ ƚŚĂƚ ĐƌĞĂƚĞƐ ůĂĐƚĂƐĞ ĞŶnjLJŵĞ ї Grew bacteria on lactose substrate ї ǀĞŶƚƵĂůůLJ ďĂĐƚĞƌŝĂ ĞǀŽůǀĞĚ ǁŽƌŬĂƌŽƵŶĚƐ ƚŽ ƵƚŝůŝnjĞ ůĂĐƚŽƐĞ
- Natural selection can promote the evolution of complex, interconnected biochemical systems in which all parts are codependent
- Selection does not create new traits out of thin air – produces “new” adaptations by modifying preexisting features
- WĂƵů ZĂŝŶĞLJ ї Yielded a small-scale “adaptive radiation” of Pseudomonas under laboratory conditions
ZĞƐŝƐƚĂŶĐĞ ƚŽ ƌƵŐƐ ĂŶĚ WŽŝƐŽŶƐ
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'ŝǀĞŶ ŚƵŐĞ ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞƐ ĂŶĚ ƐŚŽƌƚ ŐĞŶĞƌĂƚŝŽŶ ƚŝŵĞƐ͕ ƚŚĞ ĐŚĂŶĐĞ ŽĨ Ă mutation producing antibiotic resistance is high
- Best example we have of selection in action
- Creates an arms race between humans and microorganisms
- However, polio and measles have not evolved resistance to vaccines yet ї dŚĞŽƌLJ ŽĨ ĞǀŽůƵƚŝŽŶ ĚŽĞƐŶ͛ƚ ƉƌĞĚŝĐƚ ƚhat everything will evolve
- tŚĞŶ Ă ƉŽƉƵůĂƚŝŽŶ ĞŶĐŽƵŶƚĞƌƐ Ă ƐƚƌĞƐƐ ƚŚĂƚ ĚŽĞƐŶ͛ƚ ĐŽŵĞ ĨƌŽŵ ŚƵŵĂŶƐ͕ ƐƵĐŚ ĂƐ Ă ĐŚĂŶŐĞ ŝŶ salinity, temperature, or rainfall, natural selection will often produce an adaptive response
Selection in the Wild
- Natural selection in the wild is incredibly slow
- Given the gradual pace of evolution it would be unreasonable to expect to see selection transforming one “type” of plant or animal into another – macroevolution, within a human lifetime ї We know that macroevolution happens, we just ĐĂŶ͛ƚ see it happening
- Medium ground finch of Galapagos ї ^ĞǀĞƌĞ ĚƌŽƵŐŚƚ ƌĞĚƵĐĞĚ ƐƵƉƉůLJ ŽĨ ƐĞĞĚƐ ŽŶ ŝƐůĂŶĚ ŽĨ ĂƉŚŶĞ DĂũŽƌ ї Finch was forced to turn to larger and harder seeds when small soft seeds ran out of supply ї Big-beaked individuals got food, survived, left more offspring ї ǀĞƌĂŐĞ ďĞĂŬ ƐŝnjĞ ŝŶĐƌĞĂƐĞĚ ďLJ ϭϬй ŽǀĞƌ ƚŚĞ ŶĞdžƚ ŐĞŶĞƌĂƚŝŽŶ
- hŶĚĞƌ ƉƌŽůŽŶŐĞĚ ĚƌŽƵŐŚƚ͕ ƐŽŝůƐ ĚƌLJ ŽƵƚ ƋƵŝĐŬĞƌ ĂĨƚĞƌ ƚŚĞ ƌĂŝŶƐ Æ Should produce seeds quicker
- hŶĚĞƌ ŶŽƌŵĂů ĐŽŶĚŝƚŝŽŶƐ͕ ŝƚ ƉĂLJƐ ƚŽ ĚĞůĂLJ ƐĞĞĚ ƉƌŽĚƵĐƚŝŽŶ ƚŽ ŐƌŽǁ ůĂƌŐĞƌ ĂŶĚ ƉŽƚĞŶtially grow more seeds ї Tested experimentally with wild mustard by Arthur Weis
Can selection build complexity?
- Complex features take a long time to develop
- /ƚ ŝƐ ƌĞĂƐŽŶĂďůĞ ƚŽ ƚŚŝŶŬ ƚŚĂƚ ƚŚĞƌĞ ĂƌĞ ĂĚĂƉƚĂƚŝŽŶƐ ƚŚĂƚ ĐŽƵůĚ ŶŽƚ ŚĂǀĞ ďĞĞŶ ďƵŝůƚ ďLJ ƐĞůĞĐƚŝŽŶ͕ which would require thinking of another mechanism
- Advocates for intelligent design ;/Ϳ argue that complex mechanisms such as bacterial flagellum, blood clotting and the human brain must be due to / ĂƐ ƚŚĞLJ ĚĞĨLJ ĂƌǁŝŶŝĂŶ explanation Æ
“god of the gaps” ї / itself makes no testable scientific claims, but only offers half-baked criticisms of
ĂƌǁŝŶŝƐŵ
ї tĞ͛ůů ŶĞǀĞƌ ďĞ ĂďůĞ ƚŽ ŬŶŽǁ ŚŽǁ ĞǀŽůƵƚŝŽŶ ĐƌĞĂƚĞĚ ĞǀĞƌLJƚŚŝŶŐ ї Science, like everything, has mysteries
- Clotting could have been built up in an adaptive way from simpler precursors ї Must have been an ancestral protein from which fibrinogen evolved ї Found likely precursor in sea cucumber
- ͞/ŐŶŽƌĂŶĐĞ ŵŽƌĞ ĨƌĞƋƵĞŶƚůLJ ďĞŐĞƚƐ ĐŽŶĨŝĚĞŶĐĞ ƚŚĂŶ ĚŽĞƐ ŬŶŽǁůĞĚŐĞ͟ – ŚĂƌůĞƐ ĂƌǁŝŶ
- Selection is perfectly adequate to explain changes that we see in the fossil record
- A span of ten million years is beyond our intuitive grasp
- /Ɛ ŶĂƚƵƌĂů ƐĞůĞĐƚŝŽŶ ƐƵĨĨŝĐŝĞŶƚ ƚŽ ĞdžƉůĂŝŶ Ă ƌĞĂůůLJ ĐŽŵƉůĞdž ŽƌŐĂŶ͕ ƐƵĐŚ ĂƐ ƚŚĞ ĞLJĞ͍ ї Complex arrangement of the iris, lens, cornea; all of which must work together to create an image ї / ĂƌŐƵŵĞŶƚ͗ ŽƵůĚ ŶŽƚ ŚĂǀĞ ďĞĞŶ ĨŽƌŵĞĚ ŝŶ ŐƌĂĚƵĂů ƐƚĞƉƐ Æ how could “half an eye” be of any use? ї A possible sequence of events: ї Eyespots made of light-sensitive pigment, as seen in flatworms
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ї Skin eventually folds in, which forms a cup that protects the eyespot and allows ŝƚ ƚŽ ďĞƚƚĞƌ ůŽĐĂůŝnjĞ ƚŚĞ ůŝŐŚƚ ƐŽƵƌĐĞ͕ ĂƐ ƐĞĞŶ ŝŶ ůŝŵƉĞƚƐ ї /Ŷ ĂďĂůŽŶĞƐ͕ ƉĂƌƚ ŽĨ ƚŚĞ ĨůƵŝĚ ŝŶ ƚŚĞ ĞLJĞ ŚĂƐ ĐŽĂŐƵůĂƚĞĚ ƚŽ ĨŽƌŵ Ă ůĞŶƐ ї Nearby muscles have been co-opted to move the lens and vary its focus ї ĂŶ-Eric Nilsson and ^ƵƐĂŶŶĞ WĞůŐĞƌ ŽĨ >ƵŶĚ hŶŝǀĞƌƐŝƚLJ ŝŶ ^ǁĞĚĞŶ ї Created a mathematical model starting with light-sensitive pigment ї Accepted “mutations” that improved visual acuity, rejected those that degraded it ї Through a series of 1,829 adaptive steps, their model yielded an eye,
ĂƉƉƌŽdžŝŵĂƚĞůLJ ϰϬϬ͕ϬϬϬ LJĞĂƌƐ ƵƐŝŶŐ ŵŽƐƚ ĐŽŶƐĞƌǀĂƚŝǀĞ ŵĞƚŚŽĚƐ ї ͞/ƚ͛Ɛ ŽďǀŝŽƵƐ ƚŚĂƚ ƚŚĞ ĞLJĞ ǁĂƐ ŶĞǀĞƌ Ă ƌĞĂů ƚŚƌĞĂƚ ƚŽ ĂƌǁŝŶ͛Ɛ ƚŚĞŽƌLJ ŽĨ evolution” Weak forces operating over long periods of time create large and dramatic change
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LECTURE 16: MAINTENANCE AND MEASUREMENT OF GENETIC VARIATION
1. What processes influence the maintenance of genetic variation in populations?
2. How do we measure genetic variation and how much exists in populations?
Foundations of population genetics
- ϭϵϯϬ-ϱϬ ƚŚĞŽƌĞƚŝĐĂů ƉŽƉƵůĂƚŝŽŶ ŐĞŶĞƚŝĐƐ ǁĂƐ ŝŶŝƚŝĂƚĞĚ ďLJ ^ŝƌ ZŽŶĂůĚ ͘ &ŝƐŚĞƌ ;ϭϴϵϬ-ϭϵϲϮͿ͕ :͘͘^͘
Haldane (1882-1964) & S. Wright (1889-1998) and provided the foundations for “NeoĂƌǁŝŶŝƐŵ͟ ĂŶĚ ƚŚĞ ͞EĞǁ ^LJŶƚŚĞƐŝƐ͟
- They showed that conƚŝŶƵŽƵƐ ǀĂƌŝĂƚŝŽŶ ĂŶĚ ĂƌǁŝŶŝĂŶ ŶĂƚƵƌĂů ƐĞůĞĐƚŝŽŶ ǁĞƌĞ ĞŶƚŝƌĞůLJ ĐŽŶƐŝƐƚĞŶƚ
ǁŝƚŚ DĞŶĚĞů͛Ɛ >ĂǁƐ
- They also demonstrated the evolutionary significance of genetic variation leading to several key questions and development of the field of ecological & evolutionary genetics
Key questions in ecological & evolutionary genetics
- What processes influence patterns of genetic diversity in natural populations?
- How much and what types of genetic variation occur in populations?
- How can we obtain empirical estimates of the amounts of variation in populations?
/mportant parameters used to measure patterns of genetic variation
- Polymorphism (P) ї Proportion of gene loci that are polymorphic
- ,ĞƚĞƌŽnjLJŐŽƐŝƚLJ ;,Ϳ ї ǀĞƌĂŐĞ ĨƌĞƋƵĞŶĐLJ ŽĨ ŚĞƚĞƌŽnjLJŐŽƵƐ ŝŶĚŝǀŝĚƵĂůƐ ƉĞƌ ŐĞŶĞ locus ї Locus: location on a chromosome that is usually a gene
Processes that influence patterns of genetic diversity
- Mutation ;/ŶĐƌĞĂƐĞƐ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJͿ ї hůƚŝŵĂƚĞ ƐŽƵƌĐĞ ŽĨ ŐĞŶĞƚŝĐ ǀĂƌŝĂƚŝŽŶ ї Caused by random errors during replication ї Can be any of the four types discussed in lecture 15
- ZĞĐŽŵďŝŶĂƚŝŽŶ ;/ŶĐƌĞĂƐĞƐ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJͿ ї /ŶƚƌŽĚƵĐĞƐ ŶĞǁ ĐŽŵďŝŶĂƚŝŽŶƐ ŽĨ ŵƵƚĂƚŝŽŶƐ ŝŶƚŽ Ă ƉŽƉƵůĂƚŝŽŶ ї No new mutations, just shuffling existing mutations ї Ex: mutations from one allele can recombine with another allele to create new combinations - ZĂŶĚŽŵ ŐĞŶĞƚŝĐ ĚƌŝĨƚ ;ZĞĚƵĐĞƐ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJͿ ї Change in the frequency of a gene due to random sampling ї Variability gets lost ї ƌŝĨƚ ŝŵƉŽƌƚĂŶƚ ǁŚĞŶ ƉŽƉƵůĂƚŝŽŶƐ ďĞĐŽŵĞ ƐŵĂůů
- Natural selection (Can reduce or increase genetic diversity) ї Purifying (negative) selection Æ mutations that reduce fitness removed from population by selection ї Positive selection (adaptation) Æ mutations that increase fitness become fixed in the population ї Balancing selection Æ natural selection maintains diversity (heƚĞƌŽnjLJŐŽƚĞ ĂĚǀĂŶƚĂŐĞͿ ї Polymorphism͕ ĐĂŶ͛ƚ Ĩŝdž Ă ŚĞƚĞƌŽnjLJŐŽƚĞ
- Many controversies in evolutionary biology concern the relative importance of these forces in evolution ŝǀĞƌƐĞ ŵĞĐŚĂŶŝƐŵƐ ŵĂŝŶƚĂŝŶ ŐĞŶĞƚŝĐ ǀĂƌŝĂƚŝŽŶ ǁŝƚŚŝŶ ƉŽƉƵůĂƚŝŽŶƐ Æ Classes of explanations
- Mutation-selection balance
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ї Less fit genotypes maintained by repeated mutation
ŝĨĨĞƌĞŶƚ ƐĞůĞĐƚŝǀĞ ĨŽƌĐĞƐ ї ,ĞƚĞƌŽnjLJŐŽƚĞ ĂĚǀĂŶƚĂŐĞ͕ ĨƌĞƋƵĞŶĐLJ-dependent selection, fitness varies in space and time - Variation selectively neutral ї Alleles at polymorphic loci (plural form of locus) do not differ in fitness, hence none eliminated by selection
Artificial Selection
- Early evidence for the existence of genetic variation ї Selection experiments on quantitative traits in different groups of organisms ї /ŶǀŽůǀĞƐ ĐŽŶƚƌŽůůĞĚ ďƌĞĞĚŝŶŐ ĂŶĚ ƐĞůĞĐƚŝŽŶ ŽĨ ŝŶĚŝǀŝĚƵĂůƐ ĨŽƌ ŵĂŶLJ ŐĞŶĞƌĂƚŝŽŶƐ ї Ex: creation of dog breeds from wolf ancestor Æ goal ŽĨ ĐƌĞĂƚŝŶŐ ƉĞƚͬǁŽƌŬŝŶŐ ĂŶŝŵĂů
- Selection response for bristle number in fruit flies - Drosophila melanogaster ї Selection for high bristle number increases bristle number through generations ї /ŵƉůŝĞƐ ǀĂƌŝĂďŝůŝƚLJ ǁŝƚŚŝŶ ƐƚĂƌƚŝŶŐ ƉŽƉƵůĂƚŝŽŶ ї dŽƉ ϱй ŽĨ ĚŝƐƚƌŝďƵƚŝŽŶ ї ZĞůĂdž ĂĨƚĞƌ ϮϬth generation Æ Starts to level off ї Control involves random mating Æ bristle number remains constant
- SelecƚŝŽŶ ƌĞƐƉŽŶƐĞ ŝŶ ŵĂŝnjĞ ї Shows that when you relax selection (high or low), levels return to normal over time ї This type of artificial selection is the basis of plant breeding and is used to improve crop varieties - Selection response in monkey flowers (:ŽŚŶ Kelly, h͘ ŽĨ Žǁ ŚŽŵŽnjLJŐŽƐŝƚLJ
Low polymorphism
High polymorphism
Wild type is best genotype
No best or ideal genotype
Purifying selection reduces diversity
Balancing selection favours diversity
+ + + + + + + + + + 2 + + + + +
3 1 2 2 2 5 4 1 1 1 ϳ 5 3 2 1 3
AABBCCMMNNOOPP
AABBCCMMNNOOPP
Note: + = wild type, # = polymorphic allele
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Classical
- Wild type allele Æ Occasional new allele that become new wild-type ї Wild Type: Fittest genotype
- Purifying selection removes “bad” alleles
Balance
- No fittest type – some organisms found all over the world
- Variability is important
Electrophoresis revolution (ZŝĐŚĂƌĚ ͘ >ĞǁŽŶƚŝŶ, ,ĂƌǀĂƌĚ hŶŝǀĞƌƐŝƚLJͿ
- Allozyme gel electrophoresis ї ůůŽnjLJŵĞ – different forms of the same protein
- Provided a way to ask - “what proportion of genes are variable (polymorphic)?” ї Fundamental dispute between the classical and balance schools
- /ŶŝƚŝĂƚĞĚ ůĂƌŐĞ ƐĐĂůĞ ƐƵƌǀĞLJƐ ŽĨ ĞůĞĐƚƌŽƉŚŽƌĞƚŝĐ ǀĂƌŝĂƚŝŽŶ ŝŶ ĞŶnjLJŵĞƐ Θ ƉƌŽƚĞŝŶƐ ŝŶ ĚŝǀĞƌƐĞ organisms and provided the first empirical evidence supporting the balance school
- hŶŝǀersal for any organism Æ ůů ŽƌŐĂŶŝƐŵƐ ŚĂǀĞ ŐĞŶĞƐ ǁŚŝĐŚ ŵĂŬĞ ƉƌŽƚĞŝŶƐ ĂŶĚ ĞŶnjLJŵĞƐ
- sŝƐƵĂůŝnjĞ ŐĞŶĞƚŝĐ ǀĂƌŝĂďŝůŝƚLJ ї ,ŽŵŽnjLJŐŽƚĞƐ ŚĂǀĞ ƐƚƌŽŶŐĞƌ ďĂŶĚƐ (F = Fast migrating, S = Slow migrating) ї ,ĞƚĞƌŽnjLJŐŽƚĞƐ – no dominance͕ ĐĂŶ ǀŝƐƵĂůŝnjĞ ďŽƚŚ ĂůůĞůĞƐ
- Measuring diveƌƐŝƚLJ Ăƚ ŐĞŶĞƐ ĐŽŶƚƌŽůůŝŶŐ ĞŶnjLJŵĞƐ Θ ƉƌŽƚĞŝŶƐ
- Monomorphic gene: ї FF FF FF FF FF FF FF FF
- Polymorphic gene: ї FF FS SS MM FM MS FF FS
^ƚƵĚŝĞƐ ŽĨ ĞŶnjLJŵĞ ƉŽůLJŵŽƌƉŚŝƐŵ͗
- Advantages ї Many loci can be examined ї Can be used in nearly any organism ї Loci co-dominant, ŚĞƚĞƌŽnjLJŐŽƚĞƐ ĐĂŶ ďĞ ŝĚĞŶƚŝĨŝĞĚ ї sĂƌŝĂƚŝŽŶ ĞdžĂŵŝŶĞĚ ĐůŽƐĞ ƚŽ E ůĞǀĞů ї Provides genetic marker loci for other studies
- ŝƐĂĚǀĂŶƚĂŐĞƐ ї Variation is largely neutral or nearly neutral ї Not under selection ї Studies of quantitative inheritance are necessary to find out how much variation occurs for ecologically-relevant traits ї ŽĚLJ ƐŝnjĞ͕ ĨĞĐƵŶĚŝƚLJ ĂŶĚ ŽƚŚĞƌ ůŝĨĞ-history traits
Contrasting patterns of genetic diversity in generalist vs. specialist barnyard grasses
- Generalist – High diversity
- Specialist – Low diversity
Contrasting levels of polymorphism in plant species
- Polymorphisms compared in rare vs. widespread species ї Higher polymorphisms in widespread species ї ZĂƌĞ ƐƉĞĐŝĞƐ ŚĂǀĞ ůŽǁ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJ
- Extinction ї Low genetic variability ї No habitat
E ƐĞƋƵĞŶĐŝŶŐ Ăůlows differences between individuals in single nucleotides to be identified
- SNP – single nucleotide polymorphism
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Can be measured for thousands of genes
Can get measure of SNP frequencies Æ DĞĂƐƵƌĞŵĞŶƚƐ ŽĨ ƉŽůLJŵŽƌƉŚŝƐŵ ŝŶ E
LECTURE 17: ORGANISMAL REPRODUCTIVE DIVERSITY
1. Why did sex evolve?
2. How do we explain the diversity of reproductive systems?
3. What are the costs and benefits of inbreeding & outbreeding?
DNA sequence variation among different organisms
Organism
DNA polymorphism
Human
ϭͬϭϬϬϬ ďƉ
ZŝĐĞ
ϭͬϭϬϬϬ ďƉ
Mosquito
ϭͬϮϬϬ ďƉ
Fruit fly ϭͬϱϬ ďƉ
E. coli ϭͬϮϬ ďƉ
Bp = Base pair
Steven Wright (EEB)
- &ŽƵŶĚ ƚŚĂƚ ĚŽŵĞƐƚŝĐĂƚŝŽŶ ŽĨ ŵĂŝnjĞ ĨƌŽŵ ŝƚƐ ƉƌŽŐĞŶŝƚŽƌ ƚĞŽƐŝŶƚĞ ĐĂƵƐĞĚ ϱϳй ƌĞĚƵĐƚŝŽŶ ŝŶ variation at SNPs
- ƐƚŝŵĂƚĞ ƚŚĂƚ ϭϮϬϬ ŐĞŶĞƐ ŚĂǀĞ ďĞĞŶ ĂĨĨĞĐƚĞĚ ďLJ ĂƌƚŝĨŝĐŝĂů ƐĞůĞĐƚŝŽŶ
- ŽŵĞƐƚŝĐĂƚŝŽŶ ŽĨ ĐƌŽƉ ƌĞĚƵĐĞĚ ǀĂƌŝĂďŝůŝƚLJ
Human genome project
- dŚĞƌĞ ŝƐ ŶŽ ƐŝŶŐůĞ ͚ŚƵŵĂŶ ŐĞŶŽŵĞ͛
- /ŶĚŝǀŝĚƵĂůƐ ĚŝĨĨĞƌ ďLJ ƚŚŽƵƐĂŶĚƐ ŽĨ ^EWƐ ŝŶ ƚŚĞir genome sequence
- dŽĚĂLJ ƚŚĞ ŐĞŶŽŵĞƐ ŽĨ хϭϬϬϬ ƉƌŽŬĂƌLJŽƚĞƐ ĂŶĚ хϭϬϬ ĞƵŬĂƌLJŽƚĞ ƐƉĞĐŝĞƐ ŚĂǀĞ ďĞĞŶ ƐĞƋƵĞŶĐĞĚ
See Lecture 15 for Reading Summary: Notes and quotes from Coyne - Chapter 5:
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ZĞƉƌŽĚƵĐƚŝǀĞ DŽĚĞƐ
- Asexual
- Sexual
Sexual System Æ ŝŽĞĐŝŽƵƐ
Æ Hermaphrodite
Mating System Æ Cross-ĨĞƌƚŝůŝnjĂƚŝŽŶ
Æ Self-ĨĞƌƚŝůŝnjĂƚŝŽŶ
ĂƌǁŝŶ ŽŶ ƐĞdž
- “We do not even in the least know the final cause of sexuality ... why new beings should be produced by the union of the two sexual elements, instead of by a process of parthenogenesis…
The whole sƵďũĞĐƚ ŝƐ ĂƐ LJĞƚ ŚŝĚĚĞŶ ŝŶ ĚĂƌŬŶĞƐƐ͟ ;ĂƌǁŝŶ͕ ϭϴϲϮͿ
Water fleas (Daphnia)
- ŝĨĨĞƌĞŶƚ ƌĞƉƌŽĚƵĐƚŝǀĞ ƐLJƐƚĞŵƐ ŽĐĐƵƌ ŝŶ ĚŝĨĨĞƌĞŶƚ ĞŶǀŝƌŽŶŵĞŶƚƐ
- Cooler, calm water – Asexual
- Warmer, turbulent water – Sexual
Many perennial plants reproduce through sexual and clonal reproduction – Water Hyacinth
- ZĞƉƌŽĚƵĐĞƐ ƐĞdžƵĂůůLJ ŽǀĞƌ ƐŽŝů
- Clonally over water
Sex
- Costs ї Time and energy to find and attract mates ї /ŶĐƌĞĂƐĞĚ ĞŶĞƌŐĞƚŝĐ ĐŽƐƚƐ ї ZŝƐŬ ŽĨ ƉƌĞĚĂƚŝŽŶ Θ ŝŶĨĞĐƚŝŽŶ ї Cost of producing males ї ϱϬй ůĞƐƐ ŐĞŶĞƚŝĐ ƚƌĂŶƐŵŝƐƐŝŽŶ ї Break up of adaptive genes combinations
- Benefits ї This is the big question – ŬŶŽǁŶ ĂƐ ͚ƚŚĞ ƉĂƌĂĚŽdž ŽĨ ƐĞdž͛
Canadian researchers studying evolution of sex
- ^ĂƌĂŚ KƚƚŽ ;hͿ͕ ŶĞŝů ŐƌĂǁĂů ; ͕ dŽƌŽŶƚŽͿ͕ 'ƌĂŚĂŵ ďĞůů ;DĐ'ŝůůͿ
The two-fold cost of meiosis
- A ƐĞdžƵĂů ĨĞŵĂůĞ ĐŽŶƚƌŝďƵƚĞƐ ŽŶůLJ ϱϬй ŽĨ ŚĞƌ ŐĞŶĞƐ ƚŽ ƚŚĞ ŶĞdžƚ ŐĞŶĞƌĂƚŝŽŶ ĐŽŵƉĂƌĞĚ ǁŝƚŚ ĂŶ asexual female
- This is known as a transmission bias favouring asexual
Hypothesis for the advantages of sex
- Bringing together favourable mutations – long term benefit
- Benefits of genetic variation in variable environments – short term benefit – “lottery model” ї Environment is a lottery Æ Better to buy more tickets, or photocopy a ticket multiple times? ї Variable offspring – some may be adapted to variable conditions
- SpatiaůůLJ ŚĞƚĞƌŽŐĞŶĞŽƵƐ ĞŶǀŝƌŽŶŵĞŶƚƐ ͚dĂŶŐůĞĚ ĂŶŬ ŚLJƉŽƚŚĞƐŝƐ͛ ї Environments themselves vary
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dĞŵƉŽƌĂůůLJ ŚĞƚĞƌŽŐĞŶĞŽƵƐ ĞŶǀŝƌŽŶŵĞŶƚƐ ͚ZĞĚ YƵĞĞŶ ŚLJƉŽƚŚĞƐŝƐ͛ ї Environments vary over time Æ Some organisms evolve faster than others ї Pests vs. Hosts
- Numerous theoretical models but a paucity of experimental evidence
Favourable combinations of mutations brought together more rapidly by sex
- Over time, large populations will more rapidly reach the “fittest” genotype
- ĞůĞƚĞƌŝŽƵƐ ŵƵƚĂƚŝŽŶƐ ĂƌĞ ĞůŝŵŝŶĂƚĞĚ ĨĂƐƚĞƌ
Theory predicts spatial heterogeneity in selection can facilitate the evolution of sex
- No data to prove this until recently
Brachionus calyciflorus, a planktonic freshwater rotifer
- Facultatively sexual ї Can reproduce sexually or asexually ї Benefit to being able to do both
- džƉĞƌŝŵĞŶƚ ďLJ >Ƶƚnj ĞĐŬƐ ĂŶĚ ŶĞŝů ŐƌĂǁĂů ;EĂƚƵƌĞ͕ ϮϬϭϬͿ ї Placed in B. calyciflorus in 3 types of environments ї Homogeneous A, Homogeneous B, Heterogeneous AB ї Higher rates of sex maintained in populations evolving in heterogeneous habitats ї KǀĞƌ ϭϮ ǁĞĞŬƐ ;ΕϳϬ generations) Æ Experimental evolution ї Sex declined rapidly in homogenous environments ї Persisted at a much higher level with spatial heterogeneity ї ŝƐĂĚǀĂŶƚĂŐĞ ƚŽ ĂƐĞdžƵĂůŝƚLJ ŝŶ ǀĂƌŝĂďůĞ ĞŶǀŝƌŽŶŵĞŶƚƐ
Evolutionary history of asexuality
- Asexuality (parthenogenesis) is sporadically distributed across the animal kingdom; more common in invertebrates but rare in vertebrates
- Asexuality (clonal propagation) is much more common in plants although few species (if any) are exclusively asexual
- Asexual species are usually at the tips of phylogenies; their long term evolutionary potential is probably low due to lack of genetic variation
Mystery of the Bdelloid rotifers - no sex for millions of years!
- A rare case of ancient asexuality in which mĂůĞƐ ĂƌĞ ƵŶŬŶŽǁŶ ďƵƚ ĚŝǀĞƌƐŝĨŝĐĂƚŝŽŶ ŚĂƐ ůĞĚ ƚŽ х ϯϬϬ spp. Mating patterns – who mates with who and how often?
- Mates less closely related than random = Outbreeding
- DĂƚĞƐ ŵŽƌĞ ĐůŽƐĞůLJ ƌĞůĂƚĞĚ ƚŚĂŶ ƌĂŶĚŽŵ с /ŶďƌĞĞĚŝŶŐ
- /Ŷ ƉƌĂĐƚŝĐĞ ƚŚĞƌĞ ŝƐ Ă ĐŽŶƚŝŶƵƵŵ ďĞƚǁeen outbreeding & inbreeding
The genetic consequences of inbreeding
- Genotypic frequencies changed
- Allele frequencies unchanged
- ,ĞƚĞƌŽnjLJŐŽƐŝƚLJ ƌĞĚƵĐĞĚ ďLJ ϱϬй ƉĞƌ ŐĞŶĞƌĂƚŝŽŶ ǁŝƚŚ ƐĞůĨ-ĨĞƌƚŝůŝnjĂƚŝŽŶ
- ,ŽŵŽnjLJŐŽƐŝƚLJ ĨŽƌ ĚĞůĞƚĞƌŝŽƵƐ ƌĞĐĞƐƐŝǀĞ ĂůůĞůĞƐ ƌĞƐƵůƚƐ in inbreeding depression
- Frequency of alleles are unchanged Æ Combined in different genotypes
How do these two populations reproduce?
- Population 1 Æ FS FS FS FS FS FS FS FS ї ,ĞƚĞƌŽnjLJŐŽƵƐ Æ Fixed Æ ďƐĞŶƐĞ ŽĨ ŚŽŵŽnjLJŐŽƚĞƐ ї Asexual cloning population with ŚĞƚĞƌŽnjLJŐŽƵƐ ŐĞŶĞ
- Population 2 Æ FF SS SS FF FF SS FF SS ї EŽ ŚĞƚĞƌŽnjLJŐŽƚĞƐ ї High level of self-ĨĞƌƚŝůŝnjĂƚŝŽŶ
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- hƐŝŶŐ ĂůůŽnjLJŵĞƐ ĂƐ ŐĞnetic markers to study how populations reproduce
,ĞƚĞƌŽnjLJŐŽƐŝƚLJ ŝŶ ƉŽƉƵůĂƚŝŽŶƐ
- ,ĞƚĞƌŽnjLJŐŽƐŝƚLJ decreases at different rates depending on mating patterns ї More related to self Æ >ĂƌŐĞƌ ĚĞĐƌĞĂƐĞ ŝŶ ŚĞƚĞƌŽnjLJŐŽƐŝƚLJ
- ,ĞƚĞƌŽnjLJŐŽƐŝƚLJ ĚĞĐƌĞĂƐĞƐ Ăƚ ĚŝĨĨĞƌĞŶƚ ƌĂƚĞƐ ĚĞƉĞŶĚŝŶŐ ŽŶ ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞ ї Smaller population Æ >ĂƌŐĞƌ ĚĞĐƌĞĂƐĞ ŝŶ ŚĞƚĞƌŽnjLJŐŽƐŝƚLJ
/ŶďƌĞĞĚŝŶŐ Ěepression
- The reduction in fitness of inbred offspring in comparison with outcrossed offspring
- Manifested by reductions in viability (survival) and fertility (reproductive output)
- Strong inbreeding depression favours survival of outbred offspring thus favouring outcrossed mating systems
Plants
- ĂƌǁŝŶ ŚĂĚ Ă ĨĂƐĐŝŶĂƚŝŽŶ ǁŝƚŚ ŝŶďƌĞĞĚŝŶŐ Θ ŽƵƚďƌĞĞĚŝŶŐ ƉůĂŶƚƐ ї A pioneer in inbreeding depression studies
- Most plants are hermaphroditic, containing both male & female parts
- ŝŽĞĐLJ ŽŶůLJ ŽĐĐƵƌƐ ŝŶ ϳй ŽĨ ĨůŽǁĞƌŝŶŐ Ɖůants ї Sexual selection results in gender dimorphism ї Male Æ dispersing pollen Æ big flowers ї Female Æ making fruit
Evolution of selfing from outcrossing in annual Water Hyacinth
- WŽƉƵůĂƚŝŽŶƐ ŝŶ ƌĂnjŝů ĂƌĞ ŵŽƐƚůLJ ŽƵƚĐƌŽƐƐŝŶŐ ĂŶĚ ǀŝƐŝƚĞĚ ďLJ ůŽŶŐ-tongued bees ї (although selfing forms do occur) ї Larger flowers to attract bees
- Long-distance dispersal favours selfing forms ї A single individual can start a colony without mates or pollinators ї Ăǁ͛ ї :ĂŵĂŝĐĂŶ ĂŶĚ ƵďĂŶ ƉŽƉƵůĂƚŝŽŶƐ ĂƌĞ ůĂƌŐĞůLJ ƐĞůĨŝŶŐ ї No pollinators on Caribbean islands
ƵƚŽŵĂƚŝĐ ƐĞůĞĐƚŝŽŶ ŽĨ Ă ƐĞůĨŝŶŐ ŐĞŶĞ ;Z͘ ͘ &ŝƐŚĞƌ͕ ϭϵϰϭͿ
Outcrosser
Selfer
Seed
1
2
Pollen
1
1
Total Gene Copies
2
3
Selfing form has a transmission advantage – Mother and Father to its own seed
Quantitative argument – Quality of offspring…?
Reading Summary: Notes and quotes from Coyne - Chapter 6:
How sex drives evolution
- dŚĞ ƉĞĂĐŽĐŬ ĂƉƉĞĂƌƐ ƚŽ ǀŝŽůĂƚĞ ĞǀĞƌLJ ĂƐƉĞĐƚ ŽĨ ĂƌǁŝŶŝƐŵ ї Long tail produces aerodynamic problems in flight ї The sparkling colours attract predators ї A lot of metabolic energy is diverted to the tail which has to be regrown each year ї dŚĞ ƋƵĞƐƚŝŽŶ ŽĨ ŚŽǁ ŝƚ ĐĂŵĞ ƚŽ ďĞ ǁŽƵůĚ ƉůĂŐƵĞ ĂƌǁŝŶ
- Sexual dimorphisms ї Appear to violate evolutionary theory
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ї Waste time, energy, and may actually reduce survival
The solutions
- /Ĩ ƚƌĂŝƚƐ ĚŝĨĨĞƌ ďĞƚǁĞĞŶ ŵĂůĞƐ ĂŶĚ ĨĞŵĂůĞƐ ŽĨ Ă ƐƉĞĐŝĞƐ͕ ƚŚĞ ĞůĂďŽƌĂƚĞ ďĞŚĂǀŝŽƵƌƐ͕ ƐƚƌƵĐƚƵƌĞƐ ĂŶĚ ornaments are nearly always restricted to males
- The currency of selection is not really survival ї Successful reproduction
- Sexual selection comes in two forms ї ŝƌĞĐƚ ĐŽŵƉĞƚŝƚŝŽŶ ďĞƚǁĞĞŶ ŵĂůĞƐ ї Males battle each other ї Males battle to control territory ї Female choosiness ї /ŶĚŝƌĞĐƚ ĐŽŵƉĞƚŝƚŝŽŶ ďĞƚǁĞĞŶ ŵĂůĞƐ ї Ex: African long-tailed widowbird ї Experiments conducted where males with clipped tails, normal tails and elongated tails were allowed to mate ї Males with artificially long tails gained an increase in matings ї /Ĩ ŵĂůĞƐ ǁŝƚŚ ƵŶŶĂƚƵƌĂůůLJ ůŽŶŐ ƚĂŝůƐ ǁŽŶ ŵŽƌĞ ĨĞŵĂůĞƐ͕ ǁŚLJ
ŚĂǀĞŶ͛ƚ ůŽŶŐĞƌ ƚĂŝůƐ ĞǀŽůǀĞĚ͍ ї Likely because having tails that long would reduce longevity more than they would increase ability to get mates ї Malte Andersson describes 232 experiments in 186 species showing that a huge variety of male traits are correlated with mating success involving female choice
Why sex?
- Why sex evolved is one ŽĨ ĞǀŽůƵƚŝŽŶ͛Ɛ ŐƌĞĂƚĞƐƚ ŵLJƐƚĞƌŝĞƐ
ŶLJ ŝŶĚŝǀŝĚƵĂů ŝŶǀŽůǀĞĚ ŝŶ ƚŚĞ ĂĐƚ ŝƐ ƐĂĐƌŝĨŝĐŝŶŐ ϱϬй ŽĨ ƚŚĞŝƌ ŐĞŶĞƚŝĐ ĐŽŶƚƌŝďƵƚŝŽŶ ƚŽ ƚŚĞ ŶĞdžƚ generation - tŚLJ ŚĂƐŶ͛ƚ ƚŚĞ ĐŽƐƚ ŽĨ ƐĞdž ůĞĚ ƚŽ ŝƚƐ ƌĞƉůĂĐĞŵĞŶƚ ďLJ WĂƌƚĞŶŽŐĞŶĞƐŝƐ – development of eggs
ǁŝƚŚŽƵƚ ĨĞƌƚŝůŝnjĂƚŝŽŶ͍ ї Sex must have some sort of evolutionary advantage that outweighs the cost ї Several theories exist that offer explanations
- Why are there only two sexes that mate and combine gametes? ї Two is the most robust and stable
- Why do two sexes have different numbers aŶĚ ƐŝnjĞƐ ŽĨ ŐĂŵĞƚĞƐ͍ ї WƌĞƐƵŵĂďůLJ ĞǀŽůǀĞĚ ĨƌŽŵ Ă ĐŽŶĚŝƚŝŽŶ ǁŚĞƌĞ ŐĂŵĞƚĞƐ ǁĞƌĞ ŽĨ ĞƋƵĂů ƐŝnjĞ ї ZĞĐŽƌĚ ŶƵŵďĞƌ ŽĨ ĐŚŝůĚƌĞŶ ƉƌŽĚƵĐĞĚ ďLJ Ă ǁŽŵĂŶ͗ ϲϵ ї ZĞĐŽƌĚ ŶƵŵďĞƌ ŽĨ ĐŚŝůĚƌĞŶ ƉƌŽĚƵĐĞĚ ďLJ Ă ŵĂŶ͗ ΕϭϬϬϬ
- ŝĨĨĞƌĞŶƚŝĂů ŝŶǀĞƐƚŵĞŶƚ ї /ŶǀĞƐƚŵĞŶƚ ŝŶ ĞdžƉĞŶƐŝǀĞ ĞŐŐƐ ǁŚŝĐŚ ĂƌĞ limited in number ї /ŶǀĞƐƚŵĞŶƚ ŝŶ ƉƌĞŐŶĂŶĐLJ ї Because of their investment, it is in their best interest to be picky rather than promiscuous ї KŶůLJ Ϯй ŽĨ ĂŶŝŵĂů ƐƉĞĐŝĞƐ ĂƌĞ ŵŽŶŽŐĂŵŽƵƐ ї Male sticks around to take care of offspring
- Explanations for sexual dimorphism ƚŚĂƚ ĚŽŶ͛ƚ ŝŶǀŽůǀĞ ƐĞdžƵĂů ƐĞůĞĐƚŝŽŶ ї Some females are larger because they produce larger gametes ї Copyright © 2008-2012 ULife Academics Ltd.
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ƌĞĂŬŝŶŐ ƚŚĞ ZƵůĞƐ
- Sexual dimorphisms occur in “socially monogamous” species
- DĂůĞƐ ĂƌĞŶ͛ƚ ĐŽŵƉĞƚŝŶŐ ĨŽƌ ĨĞŵĂůĞƐ͕ ǁŚLJ ĞǀŽůǀĞ ďƌŝŐŚƚ ĐŽůŽƵƌƐ ĂŶĚ ŽƌŶĂŵĞŶƚƐ͍ ї Appearances are deceiving ї Appear monogamous, not actually monogamous
- Species showing little dimorphism in behavior and appearance tend to be truly monogamous ї Geese, penguins, pigeons, parrots
- /Ŷ ƐŽŵĞ ƐƉĞĐŝĞƐ ǁŚĞƌĞ ŵĂůĞƐ ĐĂƌƌLJ ďƌŽŽĚ ƉŽƵĐŚĞƐ͕ ŵĂůĞƐ ƚĞŶĚ ƚŽ ŝŶǀĞst more in offspring than females ї ZĞƉƌŽĚƵĐƚŝǀĞ ƐƚƌĂƚĞŐLJ ƌĞǀĞƌƐĞĚ ї Females compete for non-pregnant males, colourful and showy ї Seahorses, pipefish and phalaropes are the exceptions that prove the rule ї Their “reverse” decoration is what one would expect if the evolutionary explanation of sexual dimorphism is true ї tŽƵůĚŶ͛ƚ ŵĂŬĞ ƐĞŶƐĞ ŝĨ ƚŚĞƐĞ ƐƉĞĐŝĞƐ ǁĞƌĞ ͞ĐƌĞĂƚĞĚ͟
Why Choose?
- What benefit does a female have by choosing a particular mate? ї ŝƌĞĐƚůLJ – by picking a mate that will help her produce more, or healthier young during the act of child care ї Choosing males with better territories ї /ŶĚŝƌĞĐƚůLJ – by choosing a mate with better genes than those of other males ї ZĞĚ ĐŽůŽƵƌ ŝŶ ĨŝŶĐŚĞƐ ĐŽŵĞ ĨƌŽŵ ĐĂƌŽƚĞŶŽŝĚ ƉŝŐŵĞŶƚƐ ŝŶ ƐĞĞĚƐ ƚŚĞLJ ĞĂƚ ї Colour preference may be linked to diet and health ї Male gray tree frogs with longer calls produce tadpoles that grew faster and survived better
- Evolutionary theory shows that three types of genes will increase in frequency together ї Genes for a male “indicator” trait reflecting good genes ї Genes that make a female prefer that indicator trait ї The “good” genes reflected by the indicator
- Sensory-bias model ї ǀŽůƵƚŝŽŶ ŽĨ ƐĞdžƵĂů ĚŝŵŽƌƉŚŝƐŵ ĚƌŝǀĞŶ ďLJ ƉƌĞĞdžŝƐƚŝŶŐ ďŝĂƐ ŝŶ ĨĞŵĂůĞ͛Ɛ ŶĞƌǀŽƵƐ ƐLJƐƚĞŵ ї Bias can be by-product of natural selection from function other than mate selection, such as finding food ї /Ĩ ƚŚĞƌĞ ǁĂƐ Ă ƉƌĞĨĞƌĞŶĐĞ ĨŽƌ ƚŚĞ ĐŽůŽƵƌ ƌĞĚ ďĞĐĂƵƐĞ ŝƚ ŚĞůƉĞĚ ƚŚĞŵ ůŽĐĂƚĞ ƌŝƉĞ ĨƌƵŝƚƐ and a mutant male appeared with red patch, he might be preferred due to the favourable colour ї Females may simply like novel features ї Females derive neither direct nor indirect benefits from choosing a particular mate ї Experiments with several species show that females have preference for traits for which they have never been exposed
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LECTURE 18: POPULATION STRUCTURE, GENE FLOW AND GENETIC DRIFT
1. Geographical variation and the genetic differentiation of populations
2. Gene flow – the movement of genes across the landscape
3. Genetic drift and other stochastic forces
Stochastic – random forces
The Fisher-Wright debate
- Wright saw an important role for population structure and genetic drift in evolution
- Fisher disagreed and argued that most evolution occurred in large populations by natural selection - Continues to be a debate
North- versus south-facing slopes have different microclimates
- Habitats very close together
- South facing slope heats up faster in spring Æ Genetic differentiation
Population
- A group of individuals of a single species occupying a given area at the same time
- Mark-recapture studies ƚŽ ĞƐƚŝŵĂƚĞ ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞƐ of mobile organisms
- WŽƉƵůĂƚŝŽŶ ƐŝnjĞ ŝƐ ĚŝĨĨŝĐƵůƚ ƚŽ ĞƐƚŝŵĂƚĞ
Migration
- The movement of individuals from one population to another
- Ecological phenomenon
Gene flow
- The movement of genes from one population to another
- Genetic phenomenon
Variation within populations
- How much of the observed variation among individuals is genetic in origin? ї Heritable variation
- ŽĞƐ ƚŚĞ ǀĂƌŝĂƚŝŽŶ ĐŽŶƚƌŝďƵƚĞ ƚŽ ĨŝƚŶĞƐƐ ĚŝĨĨĞƌĞŶĐĞƐ ĂŵŽŶŐ ŝŶĚŝǀŝĚƵĂůƐ͍
- What about variation among populations? ї Analysis of variance Æ How much variation is within group vs. between groups? ї Ex: Humans – More variation within racial groups than between racial groups (Ex: Skin colour has small numbers of loci)
Geographic differentiation
- What proportion of all genetic variation in a species is due to differences between populations? ї How is diversity distributed within vs. between populations?
- Are some loci or traits more differentiated than the genome-wide average? ї Population differentiation due to local adaptation?
Effects of selection, gene flow & genetic drift on population divergence
- Two populations from same origin
- Natural selection drives them apart due to differing geographical environments
- Genetic drift ї ZĂŶĚŽŵ ƉƌŽĐĞƐƐ ďLJ ǁŚŝĐŚ ŐĞŶĞƐ ďĞĐŽŵĞ ĚŝĨĨĞƌĞŶƚ ŝŶ small population, irrespective of fitness ї Loss in rare alleles
- Gene flow ї Acts as cohesive force to keep populations from pulling apart
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Gene flow
- ŝĨĨŝĐƵůƚ ƚŽ ŽďƐĞƌǀĞ ĂŶĚ ŵĞĂƐƵƌĞ
- ŝƐƚŝŶŐƵŝƐŚ ƉŽƚĞŶƚŝĂů (migration) vs. actual
- ŝƐƚŝŶŐƵŝƐŚ ŐĂŵĞƚĞ ǀƐ͘ ŝŶĚŝǀŝĚƵĂů ї ŝĨĨĞƌĞŶƚ ŐĞŶĞƚŝĐ ŝŵƉĂĐƚƐ
- hƐĞ ĞdžƉĞƌŝŵĞŶƚĂů ĂƉƉƌŽĂĐŚĞƐ
- hƐĞ ŶĞƵƚƌĂů ŐĞŶĞƚŝĐ ŵĂƌŬĞƌƐ ї Polymorphic neutral genetic variation used to study population processes affecting genetic diversity ї Can count genotypes on a gel
Two populations fixed for alternative alleles
- dǁŽ ƉŽƉƵůĂƚŝŽŶƐ ŚŽŵŽnjLJŐŽƵƐ ďƵƚ ĨŽƌ ĂůƚĞƌŶĂƚŝǀĞ ĂůůĞůĞƐ
- How much gene flow occurs between them?
- (FF FF FF FF) ' (SS SS SS SS) ї Collect offspring over time ї ^ĐŽƌĞ ŚĞƚĞƌŽnjLJŐŽƚĞƐ &^ ŝŶ ŽĨĨƐƉƌŝŶŐ ї &ƌĞƋƵĞŶĐLJ ŽĨ ŚĞƚĞƌŽnjLJŐŽƚĞƐ с estimate of gene flow ї May be asymmetric Æ gametes moving downstream of a river
Genetically-modified organism (GMO)
- Concern ї Anti-multinational corporation ї Health concerns -- frankenfoods ї Scientists plating god -- Naturalist fallacy – ,ŽƌŝnjŽŶƚĂů ŐĞŶĞ ƚƌĂŶƐĨĞƌ ї Biodiversity issues
- Canola ї Measuring gene flow – an example from modern agriculture ї Escape of transgenes into wild relatives by gene flow ї dƌĂŶƐŐĞŶĞ с ŐĞŶĞ ƚƌĂŶƐĨĞƌ ƵƐŝŶŐ ƌĞĐŽŵďŝŶĂŶƚ E ƚĞĐŚŶŽůŽŐLJ ї Many crops have close relatives with which they are inter-fertile ї ZŝĐĞ͕ ŽĂƚƐ͕ Đanola, carrots ї ,LJďƌŝĚŝnjĂƚŝŽŶ ďĞƚǁĞĞŶ ĐƌŽƉƐ ĂŶĚ ƌĞůĂƚĞĚ ǁĞĞĚƐ ŝƐ ǁĞůů ĚŽĐƵŵĞŶƚĞĚ ї Gene flow between crop and weed sunflowers ї Most gene flow occurs over a short distance, but a small amount occurs as far as
1km
ї Escape of crop transgenes into wild relatives by gene flow ї ZŝƐŬ ĂƐƐĞƐƐŵĞŶƚ - /ƐŽůĂƚŝŽŶ ĚŝƐƚĂŶĐĞ ї Proximity of wild (weed) relatives ї Pollination system – wind vs. animal ї Mating system – selfer vs. outcrosser ї High risk: Wind pollinated outcrosser with relatives nearby ї Low risk: Selfer with no relatives nearby ї Corn: in Mexico, wild teosinte populations are contaminated with GMO alleles
ZĂŶĚŽŵ
- Stochastic (unpredictable or random) evolutionary forces: ї Mutation ї ZĞĐŽŵďŝŶĂƚŝŽŶ ї Gene flow ї Genetic drift
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ĞƚĞƌŵŝŶŝƐƚŝĐ ;ƉƌĞĚŝĐƚĂďůĞ Žƌ ŶŽŶ-random) evolutionary force: ї Natural selection
- Stochastic processes resulting in a loss of diversity ї Genetic drift: stochastic changes in allele frequency due to random variation in fecundity & mortality; most important when populations are small ї Population bottlenecks: a single sharp reduction in numbers causing a loss of diversity ї &ŽƵŶĚĞƌ ĞǀĞŶƚƐ͗ ĐŽůŽŶŝnjĂƚŝŽŶ ďLJ Ă ĨĞǁ ŝŶĚŝǀŝĚƵĂůƐ ƚŚĂƚ ƐƚĂƌƚ Ă ŶĞǁ ƉŽƉƵůĂƚŝŽŶ ǁŝƚŚ ŽŶůLJ limited diversity compared with the source population
- ZĂŶĚŽŵ ĨůƵĐƚƵĂƚŝŽŶƐ ŝŶ ĂůůĞůĞ ĨƌĞƋƵĞŶĐŝĞƐ ŝŶ ƉŽƉƵůĂƚŝŽŶƐ ŽĨ ĚŝĨĨĞƌĞŶƚ ƐŝnjĞ ї Genetic drift is more evident in small populations ї Movement of alleles overall ї ZĂƌĞ ĂůůĞůĞƐ ůŽƐƚ ŝŶ ƐŵĂůů ƉŽƉƵůĂƚŝŽŶƐ
- Founder events and population bottlenecks can reduce population to a single allele
Can genetic drift be important for adaptation?
- Controversial issue
- ƌŝĨƚ ŽĨƚĞŶ ƌĞƋƵŝƌĞƐ ĐĞƌƚĂŝŶ ĐŽŶĚŝƚŝŽŶƐ ƚŽ ŽĐĐƵƌ
- The role of genetic drift in the evolution of selfing in annual water hyacinth ї dŚĞŽƌĞƚŝĐĂů ŵŽĚĞůƐ ĂŶĚ ĨŝĞůĚ ƐƚƵĚŝĞƐ ŝŶ ƌĂnjŝů͕ :ĂŵĂŝĐĂ Θ ƵďĂ ƚŽ ƚĞƐƚ ƚŚĞ ŵŽĚĞůƐ
Tristyly – a plant sexual polymorphism
- Genetic polymorphism with phenotypic expression ї Symmetrical mating system ї ŝƐĂƐƐŽƌƚĂƚŝǀĞ ŵĂƚŝŶŐ͕ ďĞƚǁĞĞŶ ƵŶůŝŬĞ ƉŚĞŶŽƚLJƉĞƐ ї No selfing ї Governed by two diallelic loci (S,M) with epistasis between S and M ї Epistasis: ї interaction between alleles at different loci affecting phenotype ї One allele affects and overrides other allele
- Three morphs ї ZĂƌĞ ŵŽƌƉŚ ĞŶũŽLJƐ ĨŝƚŶĞƐƐ ĂĚǀĂŶƚĂŐĞ ї 1:1:1 morph frequencies at equilibrium ї Genetic drift will affect morph ї Ž LJŽƵ ůŽƐĞ ŵŽƌƉŚƐ ĞƋƵĂůůLJ͍ ї S-allele is at lowest frequency Æ Lost first Æ Becomes dimorphic ї /ŶďƌĞĞĚŝŶŐ ďĞŐŝŶƐ ƚŽ ŽĐĐƵƌ – ,ŽŵŽnjLJŐŽƐŝƚLJ Æ M-allele is next to disappear ї Genetic polymorphism Æ genetic monomorphism ї Natural selection begins selecting those that self
- Polymorphism maintained by frequency-dependent selection
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LECTURE 19: NATURAL SELECTION AND ADAPTATION
1. Types of selection
Ϯ͘ ĞƚĞƌŵŝŶŝŶŐ ƚŚĞ ŵĞĐŚĂŶŝƐŵƐ ŽĨ ƐĞůĞĐƚŝŽŶ
3. Evolution by pollution
4. Experimental evolution
Orchid from Madagascar with long floral tube pollinated by night-flying moth with exceptionally long proboscis - ĂƌǁŝŶ ƉƌĞĚŝĐƚĞĚ ƚŚĞ ĞdžŝƐƚĞŶĐĞ ŽĨ ƚŚĞ ŵŽƚŚ
- A century later it was discovered
- Example of co-adaptation
Fitness:
- ZĞůĂƚŝǀĞ ŐĞŶĞƚŝĐ ĐŽŶƚƌŝďƵƚŝŽŶ ŽĨ ŝŶĚŝǀŝĚƵĂůƐ ƚŽ ŶĞdžƚ ŐĞŶĞƌĂƚŝŽŶ ĂƐ Ă ƌĞƐƵůƚ ŽĨ ĚŝĨĨĞƌĞŶĐĞƐ ŝŶ
ǀŝĂďŝůŝƚLJ ĂŶĚ ĨĞƌƚŝůŝƚLJ ;с ĂƌǁŝŶŝĂŶ ĨŝƚŶĞƐƐͿ
Selective advantage:
- Some individuals better adapted to the environment and thus have higher fitness
Adaptation:
- Noun -- Any trait that contributes to fitness by making an organism better able to survive or reproduce in a given environment
- Verb -- The evolutionary process that leads to the origin and maintenance of such traits
Artificial selection
- ŽŵĞƐƚŝĐĂƚĞĚ ƉůĂŶƚ ĂŶĚ ĂŶŝŵĂůƐ ї Selection experiments in genetics
- Selection by humans
- Has a purpose or goal
Natural selection
- All organisms
- Selection by abiotic & biotic environment
- No purpose or goal ї Simply a blind mechanistic process with no foresight ї EŽƚĞ͗ ZĂŶĚŽŵ ї ŽŵƉĂƌĞ ƚŽ >ĂŵĂƌŬ͛Ɛ ;ŝŶĐŽƌƌĞĐƚͿ ǀŝĞǁ Æ 'ŝƌĂĨĨĞ͛Ɛ ŐŽĂů ǁĂƐ ƚŽ ƌĞĂĐŚ ŚŝŐŚĞƌ ůĞĂǀĞƐ
Phenotypic traits and distributions
Continuous distributions
- Normal distribution with mean & standard deviations
- dLJƉŝĐĂů ǁŝƚŚ ƐŝnjĞ Žƌ ŶƵŵďĞƌ ƚƌĂŝƚƐ
- Example of quantitative inheritance
Stabilizing selection
- Favoured traits are close to the population mean (average)
- Leads to a narrower peak distribution
- Ex: Human birth weight ї Very small and very large babies have higher mortality rates
Directional selection
- Favoured traits favour one extreme, either right or left of the mean
- Leads to a skew, either right or left of the mean
- dž͗ ĞĂŬ ƐŝnjĞ ŝŶ 'ĂůĂƉĂŐŽƐ ĨŝŶĐŚĞƐ ї As seed abundance decreased, the population fell
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ї As ƐĞĞĚƐ ďĞĐĂŵĞ ŚĂƌĚĞƌ͕ ĂǀĞƌĂŐĞ ďĞĂŬ ƐŝnjĞ ŝŶĐƌĞĂƐĞĚ
Disruptive selection
- Favours both extremes
- Leads to a shallower, or twin-peak distribution
- Leads to character divergence and sometimes speciation
- ZĞƋƵŝƌĞƐ ƐƉĂƚŝĂů ŚĞƚĞƌŽŐĞŶĞŝƚLJ Žƌ ĚŝƐĐƌĞƚĞ ƌĞƐŽƵƌĐĞƐ
- Ex: Beak ƐŝnjĞ ŝŶ ĨƌŝĐĂŶ ĨŝŶĐŚĞƐ ї Beaks of one group became smaller, adapting for soft seeds ї Beaks of another group became larger, adapting for hard seeds
The struggle to determine the mechanisms of selection
- Today hundreds of measurements of selection demonstrating fitness differences & evolutionary change in traits
- Fewer convincing cases that demonstrate the mechanisms (agents) of selection in natural populations – ecology is difficult!
Evolution of cyanide resistance - scale insects
- Alleles conferring cyanide resistance are originally found at low frequency in populations
- ZĞƐŝƐƚĂŶĐĞ ƐƉƌĞĂĚƐ ƚŚƌŽƵŐŚ ƚŚĞ ƉŽƉƵůĂƚŝŽŶ ǁŚĞŶ ƐĞůĞĐƚŝŽŶ ŝƐ ŝŵƉŽƐĞĚ ďLJ ĐLJĂŶŝĚĞ ĨƵŵŝŐĂƚŝŽŶ ї ZĞƐŝƐƚĂŶƚ ŝŶĚŝǀŝĚƵĂůƐ ŚĂǀĞ ŚŝŐŚĞƌ ƌĞƉƌŽĚƵĐƚŝǀĞ ƐƵĐĐĞƐƐ
- This process serves as model for the evolution of many forms of resistance e.g. antibiotics, insecticides, herbicides
Evolution by pollution
- Evolution of heavy-metal tolerance in grass species
- Evolution of industrial melanism in the peppered moth
- The peppered moth (Biston betularia) and industrial melanism ї Light and dark forms of species that rest on trees ї /Ŷ hĂŬĞƐ
EĞŐĂƚŝǀĞ ĞŶǀŝƌŽŶŵĞŶƚĂů ĐŽŶƐĞƋƵĞŶĐĞƐ ŽĨ ďŝŽůŽŐŝĐĂů /ŶǀĂƐŝŽŶƐ
- ŝƐƌƵƉƚ ĞĐŽůŽŐŝĐĂů ƉƌŽĐĞƐƐĞƐ ŝŶ ŶĂƚƵƌĂů ƉůĂŶƚ Θ ĂŶŝŵĂů Đommunities
- ŝƐƉůĂĐĞ ŶĂƚŝǀĞ ƐƉĞĐŝĞƐ ůĞĂĚŝŶŐ ƚŽ ƚŚĞŝƌ ĞdžƚŝŶĐƚŝŽŶ
- Adverse effects on human health
- Serious economic & social impacts through reduction of yields in agriculture & fisheries
/ŶǀĂƐŝǀĞ ƐƉĞĐŝĞƐ ŝŶ ƚŚĞ h^
- ĐŽŶŽŵŝĐ ĐŽƐƚ с ΨϭϮϬ ďŝůůŝŽŶ ƉĞƌ LJĞĂƌ
- ϱϬ͕ϬϬϬ ŝŶƚƌŽĚƵĐĞĚ ƐƉĞĐŝĞƐ͕ ŶƵŵďĞƌ ƌŝƐŝŶŐ
- Ε ϰϮй ŽĨ ƚŚƌĞĂƚĞŶĞĚ Θ ĞŶĚĂŶŐĞƌĞĚ ƐƉĞĐŝĞƐ Ăƚ ƌŝƐŬ ƉƌŝŵĂƌŝůLJ ĚƵĞ ƚŽ ĂůŝĞŶ ŝŶǀĂƐŝǀĞƐ
Questions on invading species
- Why are invading species usually only aggressive in their introduced not their native ranges?
- Are certain ecosystems more susceptible to invasions than others?
- What are the ecological & genetic characteristics of successful invaders?
- /Ɛ ƚŚĞŝƌ ĞǀŝĚĞŶĐĞ ĨŽƌ ƚŚĞ ĐŽŶƚĞŵƉŽƌĂƌLJ ĞǀŽůƵƚŝŽŶ ŽĨ ůŽĐĂů ĂĚĂƉƚĂƚŝŽŶ ŝŶ ŝŶǀĂĚĞƌs?
- How can invaders be controlled?
ŶĞŵLJ ZĞůĞĂƐĞ ,LJƉŽƚŚĞƐŝƐ͗
- Plant species on introduction to an exotic region experiences a decrease in regulation by herbivores and other natural enemies ї rapid increase in distribution and abundance
- Ex: ŝĨĨĞƌĞŶĐĞƐ ŝŶ enemy attack in populations of white campion (Silene latifolia) from Europe and North America (Lorne Wolfe, -- ŵĞƌŝĐĂŶ EĂƚƵƌĂůŝƐƚ͕ ϮϬϬϮͿ ї Native to Europe, Western Asia, Northern Africa ї Alien to North America – Now Naturalised
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ї Specialist and generalist pĞƐƚ ĂŶĚ ĚŝƐĞĂƐĞ ƉƌĞƐƐƵƌĞ ǁĂƐ ϭϳ x higher in the native range compared to the alien range
/ŶǀĂƐŝǀĞ ƐƉĞĐŝĞƐ ƚŚƌŝǀĞ ŝŶ ĚŝƐƚƵƌďĞĚ ƐŝƚĞƐ͗ ƚŚĞ ŵŽƌĞ ĚŝƐƚƵƌďĂŶĐĞ͕ ƚŚĞ ŵŽƌĞ ǀƵůŶĞƌĂďůĞ ƚŽ ŝŶǀĂƐŝŽŶ
- ŝƐƚƵƌďĂŶĐĞ ĐĂŶ ďĞ ĐĂƵƐĞĚ ďLJ ŚƵŵĂŶƐ – ŵĂnjŽŶ ĨŽƌĞƐƚ͖ Žƌ EĂƚƵƌĂů – Volcanic eruption, forest fire Common attributes of successful invasive species
- ZĂƉŝĚ ĚĞǀĞůŽƉŵĞŶƚ ƚŽ ƌĞƉƌŽĚƵĐƚŝŽŶ
- High reproductive output
- Well-developed dispersal mechanisms
- Broad ecological tolerance
- High phenotypic plasticity ї Plasticity: The ability of a genotype to alter its phenotype in response to environmental change – important trait in unpredictable environments
Evolution in invasive species of agriculture
- Selection of barnyard grass plants that mimic cultivated rice (SE Asia, Latin America, Africa) ї Weed removal involves ability to distinguish visually between crop and weed ї Weeds that look more like the crop escape detection Æ inadvertently selecting for mimicry - Selection of herbicide resistant weed species (worldwide) ї Widespread adoption of herbicide spraying in mid-to late- ƐĞǀĞŶƚŝĞƐ͛ Æ inadvertently selecting for weed strains resistant to herbicides
/ŶǀĂƐŝǀĞ ƐƉĞĐŝĞƐ ŝŶ KŶƚĂƌŝŽ
- Zebra mussels (Dreissena polymorpha) ї Freshwater mollusk native to Eurasia arrived in ballast water of ocean-going freighters in ůĂƚĞ ϴϬ͛Ɛ ї First reported in 1988, now abundant throughout Great Lakes ї ^ŝŶŐůĞ ĨĞŵĂůĞ ĐĂŶ ƉƌŽĚƵĐĞ ϯϬ͕ϬϬϬ – 1 million eggs per season, free swimming larvae easily dispersed in water ї Extensive damage to water intake pipes and commercial & sport fisheries ї Filter feeders Æ have increased water quality ї Source of avian botulism leading to death of many birds
- Purple loosestrife (Lythrum salicaria) ї Aquatic perennial with showy purple flowers native to Europe; used as an ornamental. ї Multiple introductions to eastern North America during past century followed by invasion of wetlands ї Plants competitive with high phenotypic plasticity, produce millions of small, easily dispersed seeds with high viability ї Populations genetically diverse due to multiple introductions, outbreeding and polyploidy; provides opportunities for evolution of local adaptation ї /Ɛ ƚŚĞƌĞ ĞǀŝĚĞŶĐĞ ĨŽƌ ƌĂƉŝĚ ĂĚĂƉƚŝǀĞ ĞǀŽůƵƚŝŽŶ ŝŶ ŝŶǀĂƐŝǀĞ ƉŽƉƵůĂƚŝŽŶƐ ŽĨ WƵƌƉůĞ
>ŽŽƐĞƐƚƌŝĨĞ͍ ;ZŽď ŽůĂƵƚƚŝ͕ ϮϬϬϵ – WƌŽĐ ZŽLJ ^ŽĐ ͕ ϮϬϭϬͿ ї Flowering time correlated with latitudinal gradient of seasonality ї Common garden studies indicate significant genetic differentiation among populations ї Variation forms a cline in time to flowering with northern populations flowering faster than southern populations ї Cline: A gradual change in trait means over a geographical transect ї Populations farther north have adapted to shorter growing season
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Aquatic plant invasion in the tropics -- dŚĞ ǁŽƌůĚ͛Ɛ ǁŽƌƐƚ ĂƋƵĂƚŝĐ ŝŶǀĂĚĞƌƐ͗
- Water hyacinth (Eichhornia crassipes) ї Native to lowland South America, now worldwide in tropical & warm temperate regions
- Kariba weed (Salvinia molesta) ї Genetically sterile floating fern
- Both native to South America, introduced by humans to Old World tropics,
- Free-floating with prolific clonal propagation
- Populations genetically uniform
- Tnvasiveness due to high phenotypic plasticity NOT genetic diversity
- Herbicide control causes pollution of aquatic habitats so biological control methods used
Management of invasives – methods of control
- Mechanical Ex: hand weeding, machines
- Chemical Ex: herbicides, pesticides
- Ecological Ex: burning, flooding
- Biological control ї The planned introduction of natural enemies (e.g. predators, parasites, pathogens) to control unwanted populations of invaders in alien range ї Mode of reproduction of plant invaders & likelihood of success from biological control
(Burdon & Marshall, 1981 – :͘ ƉƉů͘ ĐŽůŽŐLJͿ ї Asexual species easier to control than sexual species ї /ŶĨůƵĞŶĐĞ ŽĨ ƌĞƉƌŽĚƵĐƚŝǀĞ ƐLJƐƚĞŵƐ ŽŶ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJ ї Genetic diversity will determine whether resistance evolves ї Advantages ї Non-toxic to humans; if conducted carefully no serious environmental impacts ї /Ĩ ƐƵĐĐĞƐƐĨƵů ƚŚĞ ĞĨĨĞĐƚƐ ĂƌĞ ƉĞƌŵĂŶĞŶƚ ї Economically cheap ($1 for biological control vs. $5 for chemical control) ї ĂŶŐĞƌƐ ї Sloppy science creates new invasion
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LECTURE 23: BIODIVERSITY, EXTINCTION AND EVOLUTIONARY BIOLOGY
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1. Ecological & evolutionary consequences of global environmental change
2. What is biodiversity and why does it matter?
3. The causes of extinction today
4. Conservation biology – ecological & genetic perspectives on a crisis-driven science
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ŵĂnjŽŶ – logging of tropical forest for cattle farms
dŽĚĂLJ͛Ɛ ŐůŽďĂů ĞŶǀŝƌŽŶŵĞŶƚĂů ƉƌŽďůĞŵƐ
- Global warming & climate change
- Loss of biodiversity
- Environmental pollution
- Human famine
- Spread of infectious diseases
- Human population growth
Greenhouse gas emissions
- Longest direct measurements of CO2 in the atmosphere
- Atmospheric CO2 ŚĂƐ ŝŶĐƌĞĂƐĞĚ ƐƚĞĂĚŝůLJ ƐŝŶĐĞ ϭϵϲϬ
- /ŶĐƌĞĂƐĞ ŝŶ K2 a result of the burning of fossil fuels – Human impact
How will organisms respond to climate change?
- Migrate to more favourable environmental conditions (=ecology)
- Adapt to changing environmental conditions (=evolution)
- Go locally (or globally) extinct (=evolution)
Climate change alters phenology, but how much of this response is evolution?
- Phenology – study of periodic plant and animal life cycle events and how they are influenced by seasonal climate variations and habitat factors
Can drought cause rapid contemporary evolution by natural selection? (Art Weis, EEB)
- ŝƌĞĐƚŝŽŶĂů ƐĞůĞĐƚŝŽŶ ŽŶ ĨůŽǁĞƌŝŶŐ ƚŝŵĞ ŝŶ ĨŝĞůĚ mustard
- Evidence for directional selection for early flowering as an evolutionary response to drought ї Set more seed than later flowering plants
Biodiversity
- “the variety of life on earth”
- The number and kinds of living organisms in a given area
- Two elements: ї /ŶƚĞƌƐƉĞĐŝĨŝĐ ǀĂƌŝĂƚŝŽŶ Žƌ ƐƉĞĐŝĞƐ ĚŝǀĞƌƐŝƚLJ ;ƐƚƵĚŝĞĚ ďLJ ĞĐŽůŽŐŝƐƚͿ ї /ŶƚƌĂƐƉĞĐŝĨŝĐ ǀĂƌŝĂƚŝŽŶ Žƌ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJ ;ƐƚƵĚŝĞĚ ďLJ ŐĞŶĞƚŝĐŝƐƚƐͿ
- Four components ї Species diversity ї Ecological (functional) diversity ї Genetic diversity ї Phylogenetic diversity
- Loss of biodiversity is irreversible and consequences are least predictable – E.O. Wilson (1989)
- Twenty-five biodiversity hotspots identified around the globe, receiving special conservation efforts Extinction is natural but its current rate is not!
- Extinction is the permanent elimination of a species – extinction is forever!
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džƚŝŶĐƚŝŽŶ ŝƐ Ă ŶŽƌŵĂů ĞǀŽůƵƚŝŽŶĂƌLJ ƉƌŽĐĞƐƐ͖ ϵϵй of all species that have ever lived are now extinct - ƵƌŝŶŐ ƚŚĞ ƉĂƐƚ ĐĞŶƚƵƌLJ ŵĂƐƐŝǀĞ ŚĂďŝƚĂƚ ĚĞƐƚƌƵĐƚŝŽŶ͕ ƉĂƌƚŝĐƵůĂƌůLJ ŝŶ ƚƌŽƉŝĐĂů ƌĞŐions, has increased rates of extinction
- Studies of the causes of extinction require demographic and genetic investigations on the causes of rarity
- Three types of extinction ї Background extinction ї Turnover of species at a low rate, a natural feature of ecosystems ї Estimated at ~1 species per year ї Mass extinction ї Very large numbers of extinctions due to natural catastrophes ї Anthropogenic extinction ї Caused by humans now estimated at 4-ϲϬϬϬ ƐƉĞĐŝĞƐ ƉĞƌ LJĞĂƌ
- Major causes of species extinction today ї Habitat destruction ї Overexploitation of species ї /ŶƚƌŽĚƵĐƚŝŽŶ ŽĨ ƉĞƐƚƐ͕ ƉƌĞĚĂƚŽƌƐ Θ ĐŽŵƉĞƚŝƚŽƌƐ
Conservation Biology
- The study of those species, ecological communities & ecosystems being negatively affected by human activities
- Provides the biological concepts & tools for preserving biodiversity & ecosystem function
- Multidisciplinary but with a core ecological and genetic framework
- Ecological issues in conservation biology ї Community-level studies ї Habitat preservation & the maintenance of species diversity ї Application of island biogeographic theory to design of nature reserves ї SLOSS: Single large vs. several small ї ĞďĂƚĞ ŝŶ ĞĐŽůŽŐLJ ĂŶĚ ĐŽŶƐĞƌǀĂƚŝŽŶ ďŝŽůŽŐLJ ї What is more effective? ї Single large community of organisms? ї Several small? ї Studies of individual species ї Effects of habitat fragmentation on population ecology & demography ї ,ĂďŝƚĂƚ ĨƌĂŐŵĞŶƚĂƚŝŽŶ ŽĨ ƚŚĞ ƚůĂŶƚŝĐ ĐŽĂƐƚĂů ĨŽƌĞƐƚ ŽĨ ƌĂnjŝů ĚƵƌŝŶŐ ƚŚĞ
ƉĂƐƚ ϲϬLJƌƐ ƚŚƌĞĂƚĞŶƐ ƚŚĞ ĞŶĚĞŵŝĐ ŐŽůĚĞŶ ůŝŽŶ ƚĂŵĂƌŝŶ ї Keystone species ї Beaver – Has ability to create dams and manipulate waterways ї DŝŶŝŵƵŵ ǀŝĂďůĞ ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞƐ ї The number of individuals necessary for a species to maintain or increase its numbers in a region ї The smallest population of a species that can sustain itself in the face of environmental variation ї No single number for all species; will vary ї Ex: cats higher than orchids
- Genetic issues in conservation biology ї The maintenance of genetic diversity in rare & endangered species ї ZĞůĂƚŝŽŶ ďĞƚǁĞĞŶ ŚĞƚĞƌŽnjLJŐŽƐŝƚLJ Θ ĨŝƚŶĞƐƐ
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ї Preventing inbreeding & inbreeding depression ї ZĞĚƵĐŝŶŐ ƚŚĞ ƐƚŽĐŚĂƐƚŝĐ ůŽƐƐ ŽĨ ŐĞŶĞƚŝĐ ĚŝǀĞƌƐŝƚLJ ĨƌŽŵ ƐŵĂůů ƉŽƉƵůĂƚŝŽŶƐ ї 'ĞŶĞƚŝĐ ĐŽŶƐĞƋƵĞŶĐĞƐ ŽĨ ƐŵĂůů ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞ Æ Mating among relatives ї >ŽƐƐ ŽĨ ŚĞƚĞƌŽnjLJŐŽƐŝƚƐ ї /ŶďƌĞĞĚŝŶŐ ĚĞƉƌĞƐƐŝŽŶ ї Strategies for reducing inbreeding depression in small populations of captive animal species ї &ŽƵŶĚŝŶŐ /ŶĚŝǀŝĚƵĂůƐ͗ ї ^ƉĞŬĞ͛Ɛ 'ĂnjĞůůĞ͗ ϰ ї /ŶĚŝĂŶ ZŚŝŶŽ͗ ϭϳ ї European Bison: 13 ї Siberian Tiger: 25 ї Fixation of deleterious genes ї Ex: Cheetah (Acinonyx jubatus) ї ZĞƐƚƌŝĐƚĞĚ ƚŽ ƚǁŽ ǁŝůĚ ƉŽƉƵůĂƚŝŽŶƐ ŝŶ ƐŽƵƚŚĞƌŶ Θ ĞĂƐƚĞƌŶ ĨƌŝĐĂ ї ƐƵƌǀĞLJ ŽĨ ϱϮ ĞŶnjLJŵĞ ůŽĐŝ ŝŶĚŝĐĂƚĞĚ ĐŽŵƉůĞƚĞ ŵŽŶŽŵŽƌƉŝƐŵ͘ ї Other cats have 8-Ϯϭй ŽĨ ůŽĐŝ ƉŽůLJŵŽƌƉŚŝĐ ї ,ŝŐŚ ũƵǀĞŶŝůĞ ŵŽƌƚĂůŝƚLJ Θ ůŽǁ ƐƉĞƌŵĂƚŽnjŽĂů ĐŽƵŶƚƐ ї Suggesting inbreeding depression in the species as a whole ї /ƚ ŚĂƐ ďĞĞŶ ƉƌŽƉŽƐĞĚ ƚŚĂƚ ůŽǁ ŐĞŶĞƚŝĐ ǀĂƌŝĂƚŝŽŶ ƌĞƐƵůƚƐ ĨƌŽŵ ĂŶ
ŚŝƐƚŽƌŝĐĂů ďŽƚƚůĞŶĞĐŬ ŝŶ ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞ
EŝŬŽůĂŝ sĂǀŝůŽǀ ;ϭϴϴϳ-1943)
- ZƵƐƐŝĂŶ ĐƌŽƉ ŐĞŶĞƚŝĐŝƐƚ ĂŶĚ ĨŽƵŶĚĞƌ ŽĨ ĐƌŽƉ ŐĞŶĞƚŝĐ ƌĞƐŽƵƌĐĞ ĐŽŶƐĞƌǀĂƚŝŽŶ
Hunt for wild cotton
- Gene poŽů ĐŽůůĞĐƚŝŶŐ ĞdžƉĞĚŝƚŝŽŶ ƚŽ E ƌĂnjŝů͕ :ĂŶ-DĂLJ͕ ϭϵϳϭ
- ŝƐĐŽǀĞƌĞĚ Gossypium mustelinum – wild cotton
Last thoughts
- Future requires fresh ideas and changing paradigms
Reading Summary: Notes and quotes from Coyne - Chapter 7:
ϮϱͿ 'ĞƌďĞƌ >͘ ϮϬϭϬ͘ Conservation biology. Nature Education Knowledge 1(11):14 htƚƉ͗ͬͬǁǁǁ͘ŶĂƚƵƌĞ͘ĐŽŵͬƐĐŝƚĂďůĞͬŬŶŽǁůĞĚŐĞͬůŝďƌĂƌLJͬĐŽŶƐĞƌǀĂƚŝŽŶ-biology-ϭϲϬϴϵϮϱϲ Conservation Biology: A multidisciplinary science developed to address the loss of biological diversity
- Evaluates human impacts on biological diversity
- ĞǀĞůŽƉƐ ƉƌĂĐƚŝĐĂů approaches to prevent extinction of species
Evil Quartet
- Habitat loss and fragmentation
- Overharvesting
- /ŶƚƌŽĚƵĐĞĚ ƉƌĞĚĂƚŽƌƐ ĂŶĚ ĐŽŵƉĞƚŝƚŽƌƐ
- /ŶĚŝƌĞĐƚ ĞĨĨĞĐƚƐ ŽĨ ƚŚĞƐĞ ƚŚƌĞĂƚƐ ŽŶ ĞĐŽůŽŐŝĐĂů ŝŶƚĞƌĂĐƚŝŽŶƐ
Conservation Biology aims to provide answers to specific questions
- Point of view of resource managers
- Best strategies for protecting threatened species ї Nature reserves ї Breeding programs ї ZĞĐŽŶĐŝůŝŶŐ ĐŽŶƐĞƌǀĂƚŝŽŶ ĐŽŶĐĞƌŶƐ ǁŝƚŚ ŶĞĞĚƐ ŽĨ ůŽĐĂů ƉĞŽƉůĞ
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/ŶƚĞƌĨĂĐĞ ďĞƚǁĞĞŶ ƚŚĞŽƌLJ ĂŶĚ ƉƌĂĐƚŝĐĞ ї Statistical and computational tools integral in development of analytical methods to address issue of uncertainty
Statistical and computational tools
- Population Viability Analysis ї Evaluates full range of forces impinging on populations ї Makes determinations about viability ї Not viable for predicting when species will go extinct ї hƐĞĨƵů ĨŽƌ ĐŽŵƉĂƌŝŶŐ ƌĞůĂƚŝǀĞ ĞdžƚŝŶĐƚŝŽŶ ƌŝƐŬƐ ĂŵŽŶŐ ƐƉĞĐŝĞƐ ĂŶĚ ƉŽƉƵůĂƚŝŽŶƐ ĂŶĚ ĨŽƌ
ƉƌŝŽƌŝƚŝnjŝŶŐ ƌĞƐĞĂƌĐŚ ĂŶĚ ŵĂŶĂŐĞŵĞŶƚ ĂĐƚŝŽŶƐ
- Minimum Viable Population ї Threshold below which populations can no longer sustain themselves ї Allows a quantitative “rule of thumb” estimate of minimum population ƐŝnjĞ ї hƐĞĨƵů ĨŽƌ ĞƐƚŝŵĂƚŝŶŐ ĞĨĨĞĐƚŝǀĞ ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞ ĂŶĚ ƚŝŵĞĨƌĂŵĞ ŽĨ ĐŽŶĐĞƌŶ
- ĞĐŝƐŝŽŶ ŶĂůLJƐŝƐ ĂŶĚ DƵůƚŝƉůĞ-Criteria Approaches ї Tool for guiding business decisions under uncertainty ї hƐĞƐ ƐƚĂƚŝƐƚŝĐĂů ĂƉƉƌŽĂĐŚĞƐ ї Additional analysis are necessary to develop and refine analytical tools
Broad Speculation on the Future of Conservation Biology
- A burgeoning discipline since its inception
- Lack of adequate funding remains a critical problem
- Current models have drawbacks
- Precise role of conservation biologists as advocates between conservation priorities and human
ŶĞĞĚƐ ŚĂƐ LJĞƚ ƚŽ ďĞ ĨŽƌŵĂůŝnjĞĚ ї Most scientists are not trained to be advocates
- Many of the theoretical underpinnings of conservation biology are misguided in that they treat
ĂŶ ĞĨĨĞĐƚ͕ ƐƵĐŚ ĂƐ ƐŵĂůů ƉŽƉƵůĂƚŝŽŶ ƐŝnjĞ͕ ĂƐ ŝĨ ŝƚ ǁĞƌĞ Ă ĐĂƵƐĞ͘
- Conservation efforts should instead be focused on determining causes of population declines and the means by which agents of a decline can be identified
- This idea has reoriented many theoreticians to consider the broader scope of their work and has encouraged field biologists to more closely align their research to conservation-related questions ;ϮϲͿ Ăǁ KůŵƐƚĞĂĚ͕ ǁŚŽ ŝŶ ƚŚĞ ϭϴϬϬƐ ĚĞƐŝŐŶĞĚ ĂŶĚ ŵĂŶĂŐĞĚ ƉĂƌŬ ƐLJƐƚĞŵƐ ĂŶĚ ƵƌďĂŶ ƉĂƌŬƐ such as Central Park in New York City, believed in the rejuvenating powers of nature
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ї ,Ğ ĨĞůƚ ƚŚĂƚ ĐŽŶƚĞŵƉůĂƚŝŶŐ ŶĂƚƵƌĞ͛s grandeur allowed man to put his life into perspective /Ŷ ŵŽĚĞƌŶ ƚŝŵĞƐ͕ ǁŝƚŚ ŝŶĐƌĞĂƐŝŶŐ ƵƌďĂŶŝnjĂƚŝŽŶ͕ ƉĞŽƉůĞ ƐĞĞŬ ŽƵƚ ůŽĐĂů ƉĂƌŬƐ͕ ŽƉĞŶ ƐƉĂĐĞ ĂŶĚ trails, and travel to national parks and wild places where they can enjoy nature ї Birding, hiking, fishing, hunting, gardening, and other forms of recreation in nature are popular activities, and are economically important
Glossary: Topics & Concepts
Adaptive radiation: The evolution of ecological and phenotypic diversity within a rapidly multiplying lineage as a result of speciation from a single common ancestor
Allopatric: Speciation that occurs due to geographical separation
Bateman’s principle: Females almost always invest more energy into producing offspring than males invest Clade: Monophylum containing a species and all its descendants
Cladistics: Classifying species based on phylogenetic relationships and shared characteristics
Cline: A gradual change in trait means over a geographical transect
Continuous traits: Complex inheritance by polygenes of small effect with quantitative inheritance and a continuum of outcomes
Convergence: When structures that evolve separately perform similar roles due to similar ecologies
Discrete traits͗ /ŶŚĞƌŝƚĞĚ ďLJ ϭ Žƌ Ϯ ŵĂũŽƌ ŐĞŶĞƐ ǁŝƚŚ ŚŽŵŽnjLJŐŽƵƐ Žƌ ŚĞƚĞƌŽnjLJŐŽƵƐ ŽƵƚĐŽŵĞƐ
Homology: Similarity of traits due to shared ancestry
Homoplasy: Similarity of traits as a result of convergent evolution
Key innovation: Origin in a novel trait resulting in an adaptive radiation which can exploit new resources or habitats previously unavailable prior to trait acquisition
Monophyletic: Arise from a single ancestor single ancestor
Naturalisation: A process by which an alien species spreads into the wild and reproduces sufficiently to maintain its population
Non-monophyletic: Arise from two or more ancestors
Phenetics: Classifying species based on overall resemblance
Phylogentics: Study of evolutionary relationships among species
Plasticity: The ability of a genotype to alter its phenotype in response to environmental change – important trait in unpredictable environments
Polyploidy: Having more than two complete sets of homologous chromosomes
Sympatric: Speciation occurring where a subset of the population becomes genetically different, Ex: through polyploidy
Taxonomy: The theory and practice of classification geographic variation, population differentiation, gene flow, models of population structure, stochastic processes, genetic drift, genetic markers, measuring gene flow, transgenic escape, tristyly and its inheritance, frequency-dependent mating, equilibrium morph frequencies, evolution of selfing from outcrossing adaptation, types of selection on quantitative traits, measurement and response to selection, evolution of cyanide resistance, mechanisms of selection, industrial melanism, heavy-metal tolerance, costs to resistance, experimental evolution in E. coli. native, alien, biological invasion, invasive species, attributes of successful invasives, disturbance, crop ŵŝŵŝĐƌLJ͕ ŚĞƌďŝĐŝĚĞ ƌĞƐŝƐƚĂŶĐĞ͕ njĞďƌĂ ŵƵƐƐĞůƐ͕ ƉƵƌƉůĞ ůŽŽƐĞƐƚƌŝĨĞ͕ ĐŽŵŵŽŶ ŐĂƌĚĞŶ ƐƚƵĚŝĞƐ͕ local adaptation, crop mimicry, water hyacinth, Kariba weed, biological control
– global climate change, rapid evolution, resurrection paradigm, components of biodiversity, biodiversity hotspots, types and causes of extinction, habitat fragmentation, SLOSS, keystone species,
DsW͕ ŝŶďƌĞĞĚŝŶŐ ŝŶ njŽŽ ĂŶŝŵĂůƐ͕ ĐŽŶƐĞƌǀĂƚŝŽŶ ŽĨ ĐƌŽƉ ŐĞŶĞƚŝĐ resources
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