Study on Wild Guppies: Online Simulation of Endler's Work

Abstract
In the 1970s, an investigator named John Endler traveled to Trinidad in the 1970s to study wild guppies. The guppies live in small streams that flow down the mountains from pool to pool. The experiment will take part on an online simulation of Endler's work. The group of members is responsible for collecting data, formulating a hypothesis, and running a series of experiments. They will find out about the interplay between natural selection and sexual selection in this wild population of guppies. They will ultimately find out the effects on the guppy population and their color distribution depending on the predator that lives in their environment. Endler wondered how the trade-off between attracting mates and affecting predators affects the coloration in male guppies. In pools that had few predator species, male guppies tended to be brightly colored, whereas predators are causing guppy populations to become drabber. This occurs because the predators are preying on the most brightly colored individuals and eliminating them from the gene pool. Therefore, guppy populations are evolving to more closely match, or stand out from their environment. Endler hypothesized that intense predation caused natural selection in male guppies, favoring the trait of drab coloration. He further tested his hypothesis by transferring brightly colors guppies to a pool with many predators. As he predicted, over time the transplanted guppy population became less brightly colored. Females tend to look for the bright colored male guppies in the pool and mate with them. This enables those males to have a higher probability of passing their genes on to their next generation. In the simulation, predators can dramatically influence the evolution of a population of guppies, but change does not occur quickly during the testing of one generation for each trial. (Before columns on graphs in the Data section of the simulation report) Scientists believe that they see changes in just a few generations, but more often there are significant trends when the simulation is ran after 7 generations or more. So, the ten generations for each different trial was calculated under the after columns of the graphs also in the Data section of the simulation. There were three predators involved in the experiment. There were Rivulus, Acara, and Cichlid predators. Also, there were different types of colored guppies in the gene pool. They are the brightest, bright, drab, and the drabbest colored guppies. There were certain trials that were tested to reveal the certain descriptions about the predators affecting the guppy population. Since the average male guppy in pool 1 is brightly colored and 30 Rivulus are living there, Rivulus do not prefer to eat brightly-colored guppies. Also, since pool 2 and pool 3 show differences in guppy appearances, Blue acara eat bright and drab colored guppies. Then, since pool 3 has few Rivulus and many Blue acara and Cichlids, and the average male guppy is like drab with drabbed spots, Blue acara and cichlids do not prefer drab colored guppies.
Problem/Objectives
The purpose of this activity is to analyze how guppy populations change over time. The simulation activity allows individuals to start with a pool of guppies and a choice of predators, in this case there are three. Certain predator or predators may be in the guppy population at the same time. Individuals will be able to watch what happens to the guppy population and how the introduction of predators can affect the guppy's appearance. The simulation will help a person understand what pressures drive guppy evolution. The field of population genetics examines the amount of genetic variation within populations and the processes that influence this variation. A population is defined as a group of interbreeding individuals that exist together at the same time. The guppy simulation represents this definition of a population because there are male guppies that mate with the females depending on which male guppies would still be alive from the different predators affecting them. There is also genetic variation, which refers to the degree of difference found among individuals, for instance in height, coat color, or other less observable traits. As I mentioned earlier, the brightest colored guppies have the best chance to mate, but also shrink in their population because predators feast on easy-to-see prey. The particular set of genes carried by an individual is known as their genotype, while all the genes in a population together comprise the "gene pool." The guppy simulation will be testing the coat color and the appearance of the guppies along with certain predators involved.
Introduction
Imagine being in a population where organisms are battling against one another and it is difficult to survive. Well, an English naturalist named, Charles Darwin, got credited with the idea of this description known as Natural Selection. Natural Selection is a major part of the main theory of evolution. Also, there is two major parts that go along with the theory of evolution. There is a pattern and a process of evolution. In the simulation to test the guppy population and its color distribution from a pond with predators, shows a process of Natural Selection. For guppies that were exposed to different predators, they needed to be tested to see which predator wants to eat what kind of guppy. The same predators were used for this simulation. The pattern of evolution is revealed by data and observations of environments to test a wide variety of scientific disciplines. There were different results for the different types of guppies in the population that were affected by the predators. The process of evolution deals with the observed pattern of change. The Rivulus predator likes to enjoy the drab colored guppies, the Acara likes to enjoy the bright and drab colored guppies and the Cichlid likes to enjoy the bright and drabbed colored guppies as well, for their food source. The power of evolution as a unifying theory is its ability to explain and connect a variety array of observations about the living world. An individual is able to explain the changes that occurred when the different predators were added to the guppy population. He can tell which predator preferred a certain guppy and what happened when two or all three predators were added at a time. This all ties into the main discussion of evolution, which is the change in the genetic composition of a population from generation to generation. It only affects a change of a population because organisms cannot evolve. It can also be said in broad terms as “change over time,” but that is referred to as Descent of Modification. Whether it is Lamarck's theory that evolution is driven by an innate tendency towards greater complexity, Darwin's theory of natural selection, or the belief that the evolution of plant and animal life is controlled by a higher being, the process of evolution cannot be denied. Archaeological investigations have proven that species evolve over time, but the unanswered questions are "How?" and "Why?" The answer lies in Charles Darwin's theory of evolution. Darwin’s theory of evolution entails the following fundamental ideas. The first three ideas were already under discussion among earlier naturalists working on what they called the species problem, as Darwin began his research. Darwin’s original contributions were the mechanism of natural selection and bountiful amounts of evidence for evolutionary change from many sources. He also provided thoughtful explanations of the consequences of evolution for our true understanding of the history of life and modern biological diversity. First, species (populations of interbreeding organisms) change over time and space, as I mentioned earlier. The representatives of species living today differ from those that lived in the recent past, and populations in different geographic regions today differ slightly in form or behavior, not just the guppy population. These differences extend into the fossil record, which provides full support for this claim. Secondly, all organisms share common ancestors with other organisms. Over time, populations may divide into different species, which share a common ancestral population. Far enough back in time, any pair of organisms shares a common ancestor. For example, humans shared a common ancestor with chimpanzees about eight million years ago, with whales about 60 million years ago, and with kangaroos over 100 million years ago. The shared ancestry explains the similarities of organisms that are classified together. Their similarities reflect the inheritance of traits from a common ancestor. Lastly, evolutionary change is gradual and slow in Darwin’s view. This claim was supported by the long episodes of gradual change in organisms in the fossil record and the fact that no naturalist had observed the sudden appearance of a new species in Darwin’s time. Since then, biologists and paleontologists have documented a broad spectrum of slow to rapid rates of evolutionary change within lineages. This links to Darwin’s theory. Darwin’s process of natural selection has seven components. They include overproduction, variation, change in environment, struggle for existence, survival of the fittest, inheritance of “selected” features, and new species that are better adapted to the new environment. In variation, organisms, within populations, exhibit individual variation in appearance and behavior. These variations may involve body size, hair color, facial markings, voice properties, or number of offspring. (Variation) The bright colored male guppies reproduce more because the females are attracted to them and they can also be hunted by predators, since they stick out like a sore thumb to them. So, variation is involved. On the other hand, some traits show little to no variation among individuals—for example, number of eyes in vertebrates. In inheritance, some traits are consistently passed on from parent to offspring. Such traits are heritable, whereas other traits are strongly influenced by environmental conditions and show weak heritability. (Inheritance of “selected” features) The bright guppies can pass their bright colored coat trait to their offspring. In the high rate of population growth (Overproduction), most populations have more offspring each year than local resources can support, which leads to a struggle for resources. Each generation experiences substantial mortality. Also involved in populations are differential survival and reproduction, what Darwin called the (Struggle for existence). These compose of individuals that are possessing traits well suited for the struggle for local resources and that will contribute more offspring to the next generation. From one generation to the next, the struggle for resources will favor individuals with some variations over others and thereby change the frequency of traits within the population. This process as mentioned before is natural selection. The traits that render an advantage to those individuals who leave more offspring are called adaptations. (Survival of the Fittest) In order for natural selection to operate on a trait, the trait must possess heritable variation and must confer an advantage in the competition for resources. If any of these requirements does not occur, then the trait does not experience natural selection. We now know that such traits may change by other evolutionary mechanisms that have been discovered since Darwin’s time. Natural selection operates by a qualified advantage, not an absolute standard of design. In Charles Darwin’s book, On the Origin of Species, 1859, it says “…as natural selection acts by competition for resources, it adapts the inhabitants of each country only in relation to the degree of perfection of their associates.” (Changes in environment) The bright guppies that have the strong heritable trait can use the females to a certain degree until a predator comes out and takes the population of them out.
Around the twentieth century, genetics was integrated with Darwin’s mechanism, allowing us to evaluate natural selection as the differential survival and reproduction of genotypes, corresponding to particular phenotypes. Natural selection can only work on existing variation within a population. Such variations arise by mutation, which is known as a change in some part of the genetic code for a specific trait. Mutations arise by chance and without foresight for the potential advantage or disadvantage of the mutation. In other words, variations do not arise because they are needed. So, when traits of a population differ significantly from the earlier population and can no longer reproduce with the earlier population, then it is known as a new species. (New Species) There is also a theory that ties into natural selection and it is called sexual selection. Many may ponder the question, “Why are the sexes different in some species?” Darwin suggested that many reproductive characteristics of males and females arise by means of sexual selection. He recognized two different but complementary aspects of sexual selection. First of all, selection may be the result of competition among individuals of one sex for access to the other. The brightest male guppies can pass their trait from generation to generation if they can mate with the female guppies in time before the predators come back for them. Alternatively, selection could take the form of choices made by one sex among individuals of the opposite sex. However, if the brightest colored male guppies diminish, the females will try to go to the other bright or other guppies that have some color on them. Next, if the colored males are eliminated then there is no choice but to mate with the drab guppies. After all, the females choose the brighter guppies to mate with because they may have better genes than the other guppies. They do not do it consciously, but if they choose the flashier male, then that male’s group of traits will be found in the female’s sons. Females put more energy into reproduction and reproduce less frequently than males. So, it is more likely for males to engage in competition with other males and for females to be the more selective sex. However, there are instances where males are the fastidious sex. We expect males to become deliberate if females differ in their quality, and males are confronted either with limited resources for reproduction or with the opportunity to choose among several females at any one time. Among the species, where egg number is a function of body size, there may commonly be opportunities for males to choose among females, since a male mating with a large female will father more young than one who spends the same time and energy mating with a smaller female. In many other fish, productiveness is a function of size and growth that is inexact, suggesting that these opportunities occur frequently.