Animal Behavior

Outline of Lecture Notes for Sept. 9

What is Animal Behaviour?
Scientific study of how and why animals behave the way they do
Uses both evolutionary theory and behavioural physiology

Why study animal behaviour?
Establish general rules regulating behaviour
Determine how best to preserve endangered animals
Control economically important pests
Develop better conditions for domestic animals and animals in zoos

Cane Toads in Australia
Ecological disaster due to lack of understanding of toad behaviour
Video: Cane Toads – An unnatural history (available at Video Difference and YouTube) (Mark Lewis)

1.Why was the cane toad introduced into Queensland, Australia? The cane toad was introduced into Queensland, Australia in 1935 to control the sugar cane beetle (sugar cane beetles eat the leaves and produce larvae who feed on the roots of sugar cane crops)

2. Why was the toad unsuccessful as a biological control agent? Different behaviours than the cane beetle - active at different times of the day and preferred different areas of activity.
The toad was unsuccessful in catching the beetles because they couldn’t jump high enough. 102 cane toads were released into Australia, and have since multiplied to over two million. The toad’s main defense mechanism is their toxin, therefore they don’t tend to hide from predators. Cane toads eat anything, and outcompete native species for food. They prey on native animals, and are also eaten by native animals and in turn they are poisoned.

3. What makes the cane toad an excellent invader? Toads are extremely adaptable, and can live in virtually any habitat with breeding sites (still water) and food (any insect). They have a high reproduction rate, develop quickly and rapidly, and are poisonous to all predators. Breed quickly with little water requirement.

4. What did the agricultural scientists fail to do that led to the ecological disaster? They did not perform any preliminary studies to see if the toads would actually be successful. Didn't investigate the specific species that they were introducing and just assumed that because it worked in other areas that it would work in Australia

5.What is the effect of the cane toad on Australian ecology? Depletion of native predator and prey species, poisoning of pets and humans, reduction of food for native species.

Questions in Animal Behaviour

Types of questions and Levels of Analysis

Niko Tinbergen’s 4 questions:
1. Mechanism – What stimuli elicit behavior? What sort of neurobiological and hormonal changes occur in response to or in anticipation of, such stimuli? (PROXIMATE)
2. Development – How does behavior change as an animal matures? (PROXIMATE)
3. Survival Value – How does behavior affect survival and reproduction? (ULTIMATE)
4. Evolutionary History – How does behavior vary as a function of the evolutionary history, or phylogeny, of the animal. When did a behavior first appear? (ULTIMATE)

1. Why do male caribou grow antlers?
-Testosterone secreted by testes in spring (PROXIMATE)
-To win fights during fall rut (ULTIMATE)
- Winning fights increases number of offspring
Proximate (how – mechanisms)
Focuses on - immediate causes
Ultimate (why – evolutionary purpose)
Focuses on – evolutionary forces that have shaped a trait over time.
Both answers correct

Example. Monarch Butterfly (Danaus plexippus) – Found in Nova Scotia
-insect (adult has 6 legs)
-poikliotherm (ectotherm – cold blooded)
-exoskeleton
-holometabolous (undergoes complete metamorphosis)
-eggs laid by female butterfly on milkweed plant
-larvae (caterpillars) eat milkweed which makes them poisonous to birds (by chewing holes in the base of the main veins of leaves before they eat them, thus preventing excess "milk" from pouring into the leaf)
-caterpillars grow, molt, pupate, emerge as adults
-fall generation migrates to warmer areas in winter
-poisonous to most vertebrates

Monarch butterflies have 2 unusual traits
1.Eat milkweed (poisonous – few other animals can eat it)
2. Migratory insect (Only butterflies that migrate. Migrate south 3000km away to central Mexico)

-Important for ecosystem, pollinators (Food for adult monarch butterflies consists mainly of flower nectar. They fuel their great travels and reproductive efforts by sipping this sugary solution from obliging plants. The plants are, of course, taking advantage of the monarchs and other insects to do the job of pollination)

Monarch Butterfly in Nova Scotia
Abundant milkweed
But
Cold winters (e.g. no food)
Winter a problem for insects
Most insects enter winter diapause (hibernate)
Insect reduces or ceases metabolic activity
Anti-freeze proteins
Monarchs migrate, cannot make anti-freeze proteins (tropical ancestors)

Proximate (how) and Ultimate (Why) Questions
1. Why do birds avoid eating Monarchs (i.e. what is it about Monarchs that discourages birds?)? (proximate question) Milkweed tissues contain compounds, called cardenolides, that are quite toxic. Intended by the plant as a chemical deterrent to being eaten, monarch caterpillars are immune to these and actually accumulate the toxins in their own tissues, rendering them toxic, too. The bold patterning of monarch caterpillars advertises this fact. Should a bird attempt to eat a monarch caterpillar, it will become ill, usually vomiting out the caterpillar, and will refrain from eating any more. Bold warning coloration, reinforced by the occasional bad meal, leaves monarch caterpillars safe from most avian predators.
2. Monarchs sequester cardioglycosides from milkweed in their bodies. Why did this evolve? (ultimate question) - Access to abundant food source; obtain poisons to reduce predation
3. Why do monarchs migrate? (proximate and ultimate answers) Proximate - Sensory cues, possibly magnetic cues and angle of polarization of light
Ultimate - flight north gives access to milkweed; flight south to avoid lethal cold temps; unable to overwinter 4. How does the life cycle of a monarch relate to their migration? Overwinter in California or Mexico, mate in the spring. Fly north to lay eggs on milkweed. Larva eat milkweed and develop up north, then fly south to overwinter

Costs vs. benefits
Benefits ultimately in terms of increased number of offspring
Costs usually energetic, other physiological constraints

Costs vs. Benefits of Eating Milkweed (ultimate question)
Benefits
Access to abundant food resource
Greater growth, more offspring
Obtain poisonous substances, reducing predation
Greater survival, more offspring

Costs
Physiological cost of enzymes needed to detoxify, sequester cardioglycosides
Less energy for reproduction

Proximate (how) and Ultimate (Why) Questions
1. For what reasons do Monarchs migrate to Mexico? (i.e. how does this benefit the Monarch). In their Mexican retreat, the monarchs have fairly stable weather conditions, with cool, but not freezing temperatures (monarchs are not freeze-tolerant), high humidity and protection from damaging winds. They converge on very small patches of forest and cluster together, often covering the individual trees. They rest and conserve their energy, drawing slowly on their stores of body fat, produced from the nectar of flowers they visited on their journey south. And there they remain, rousing occasionally to flutter about and perhaps sip some water from local ponds, then return to their hibernation, until about mid-March. With the return of spring, they rouse and begin their journey northward.
2. What are the sensory cues that lead to the development of the migratory generation? It's thought that monarchs use the position of the sun, combined with an innate circadian rhythm, and the earth's magnetic field to determine north and south while on their journey
3. Why do Monarchs migrate instead of overwintering? (i.e. how did migration evolve)? In spring and summer their northward journey gives them access to more and more emerging milkweed plants for their caterpillars and gets the adults into areas where there is less competition for flower nectar.

Proximate (how) and Ultimate (Why) Questions
Both perspectives needed to understand Animal Behaviour
Proximate questions – mechanisms. How behaviour accomplished (e.g. sensory systems, hormones, physical cues)
Ultimate questions – evolutionary significance. How behaviour benefits individuals ability to survive and produce. Evolution of behaviour (e.g. does behaviour exist in relatives)

Darwin’s theory of Evolution – Natural Selection
Any trait that provided an animal with reproductive advantage over others in its population would be favored by natural selection.
Occurs when variants of a trait that best suit an organism to its environment, and that are inheritable, increase in frequency over time.
Requires: Variation, fitness differences, heritability, behavioral traits as well as morphological, anatomical and developmental traits.

- Reproduction leads to an increase in the number of individuals in a species
- But resources are limited. Number of individuals in a species tends to remain constant (e.g. Monarchs)

- Individuals vary from one another due to heritable differences (e.g. different genes)
- There is DIFFERENTIAL REPRODUCTION in the population, with animals with certain traits having more surviving offspring than others

Evolution occurs because of differential reproduction (i.e. some individuals have more surviving offspring)

-Gradually individuals that produce more surviving offspring will increase in proportion in the population (gene will increase over time)
Modern definition of evolution - Changes in gene frequencies with time
-Animals with traits that increase reproductive success will be ‘selected for’ by natural selection and will increase in the population

Ex. Raven (pg. 39) – Ravens that approach novel objects quickly may add new food items to their diet and hence have relatively high reproductive success. More eggs hence more offspring.

Natural Selection
Selection for reproduction, not necessarily lifespan
e.g. mutation increases female egg output, decreases lifespan.
If increased egg output larger than # eggs lost due to decreased lifespan, will be selected for
Genetic variation – variations caused by genetic differences
Ex. Mutation –Any change in genetic structure creates new variation in population.

Evolution
No goal
Local adaptation. Not necessarily smarter, faster, increased complexity
Local adaption – A trait that results in the highest fitness among a specified set of behaviors in a particular environment (result of natural selection). To match organism to an environment so exquisitely.

Additional Evolution Videos http://www.cbc.ca/documentaries/natureofthings/2009/darwin/timeline.html

Natural Selection
Animals can produce more offspring than environment can support
Competition among individuals of the same species for resources
Only best adapted to environment (e.g. strongest, fastest, best able to withstand cold) survive to reproduce
Genes that give animals an edge in their environment will increase in the population

Animals with traits that increase reproductive success will be ‘selected for’ by natural selection and will increase in the population

Example of Natural Selection
Crickets vs parasitic fly (Ormia ochracea)
Adult male crickets attract females by rubbing wings together (singing)
Females phonotactic - Female crickets are attracted to the sound of males chirping, and chirping sounds are meaningful. More attracted to louder (songs) chirps with a longer duration.

Singing cricket T. oceanicus attracts females and parasites. Flatwinged crickets stay near singing males to attract the females (no parasites) therefore flatwings are favored by natural selection.

Crickets vs. Parasitic Fly
Male song also attract predators

Parasitoid – Larval stage of insect develops inside a single insect host.

How do parasitoid flies affect crickets? Lay eggs of cricket; larva bury inside cricket where they develop/feed. Fitness of the cricket is decreased during larval development, and the cricket is eventually killed when the pupae emerge.