Monday, April 6, 2009
Coloring of Organisms
Throughout the novel there have been many examples of species that differ in terms of coloring. Give an example of a species where the colorings of the organisms differ. How did the differences evolve and what is the selective advantage to the organism of having that specific coloring?
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Coloring is especially significant in snow geese, because the young snow geese are susceptible to sexual imprinting. These young geese see the coloring of their parents, and later on in life prefer to mate with geese that are colored similarly. The selective advantage of this is that this drastically increases the chance that a goose will mate with a member of the same species, so that procreation can occur. Another example of this is shown by blue tits, birds that see ultraviolet colors in members of the same species, allowing for proper mate selection. Also, coloring can be seen as an evolutionary "currency" whereby the most brilliantly colored organisms only reproduce, the prime example of this is the peacock.
ReplyDeleteIn many instances, the color(s) of individuals of a species aids largely in the mating of the individuals. I agree with Sam in that the color can enhance the individual’s own chance of reproduction, as shown by the blue tits. In addition to the color differences of male individuals (e.g. the blue tit), there are significant color differences between the males and the females of certain species.
ReplyDeleteThe male three-spined stickleback fish have a red underbelly while the females do not have a gray underbelly. Because of the color difference, the male sticklebacks can act aggressively toward the other males if the other males invade his territory. In further experiments conducted by Niko Tinbergen, the male stickleback would attack any shape that had a red underside even if the shape did not resemble a fish. This behavior is an example of a fixed action pattern, as the behavior to attack shapes with red underbellies was an automatic response. The fixed action pattern of the stickleback would not require the stickleback to expend energy or time to process information about a situation.
The attack against other male sticklebacks with red underbellies would allow the stickleback to maintain its territory. The attack against other potential competitors would relate to the theme of interaction with the environment, which deals with the interactions between individuals (2 male stickleback fish) as well as the exchange of materials and energy in one’s surroundings. Automatically attacking other males to defend one’s territory would be a selective advantage because the territory can provide the stickleback with the area to reproduce as well as provide exclusive access to the resources like food. The stickleback would also attack other males to prevent them from mating with the stickleback’s possible mates. The selective advantage of attacking potential competitors of mates would be to increase one’s chances of reproduction because the competitors would not be able to mate with the females in the stickleback’s territory. The male stickleback can differentiate females from males by the absence or presence of the red underbelly. Because the females do not have the red underbelly, the male stickleback fish would not attack them. The selective advantage for the female sticklebacks would be that they do not get attacked by the males, and that the females could engage in courtship behavior with the male sticklebacks in their territory, which would lead to reproduction. Since the pigmentation of the stickleback fish seems to depend on the gene Kitlg (italicized), changes in the gene would alter the skin color of the fish. Some fish have mutations that only reduce the gene expression in some areas of the body, so the body would be different colors in different areas. The changes in the gene expression in the different areas of the body can be exhibited by the male stickleback fish having a gray body and a red underbelly. The different coloring could have evolved in the two sexes due to mutations in the Kitlg (italicized) gene, and natural selection would have acted on the stickleback to maintain the color differentiation.
Sources: http://www.news-medical.net/?id=33559 (stickleback fish gene)
According to the 8th theme of biology, evolution, natural selection screens for genetic variations in a population so allows only the fittest organisms to occupy a given niche. An organism’s coloring is just one of the many advantages that an organism could have over other members of the population. The variation in color is the result of mutations that have occurred on the MCIR gene; the gene responsible for coloration in animals. Usually, one or two point mutations on the MCIR gene is enough to change an organism from being light colored to being dark colored. The classical example of the selective advantage of coloring is the story of pepper moth during the 19th century England. The pollutants that were given off by factories “altered the coloration and lichen growth on trees where the pepped moth rests” (Carroll 52). The change in the environment condition has shifted natural selection in favor of dark, melanic forms of the moth. The selective agents in this case are the birds who eat the moths. A bird would more likely notice a white moth on black bark than a black moth camouflaged on the black bark. As a result, predators would target and kill mostly the white moth, causing the white moth population to decline. The decrease in white moth population also benefits the black moths. Black and white moths compete for the same resources in the environment. So when white moth dies off, the black moth game more access to the food and shelter. Thus the black moth population would experience rapid growth until they depleted their resources and reach the environment’s carrying capacity. It was estimated that from 1848 to 1896, “the dark from arose and evolved to as high as a 98 percent frequency in some areas” (Carroll 52). However, as clean air laws were enacted by the government and the amount of pollutants decreased and the tree became cleaner, the selection pressure on the moth was reversed. Now, natural selection agents, the birds, would notice the black moths more easily on the light colored trees. As a result, the black moth declined from 90% to 10 % in some areas. The pepper moth story reinforces Jen and Sam’s assertion that coloration aide an organism’s reproduction. Since coloration directly helps the organism’s survival, it also enhances the organism’s chance of reproduction.
ReplyDeleteAnother example of a species that has different colorings is that of the notorious Homo sapiens (I can't italicize it, but note that it should be). The myriad shades of skin in humans has caused some of the worst social problems in history and has brought out the worst in humanity, but its biological basis is quite simple.
ReplyDeleteFirst off, here is an explanation of the selective pressure: UV rays. UV rays are harmful to humans in many ways; they can be carcinogens that cause melanoma, or they can cause sever burns. Therefore, humans, like many other organisms, need melanin in their skin to absorb this harmful form of radiation. Melanin is coded for by the gene MC1R and melanin production is controlled by the hormone MSH (melanocyte stimulating hormone). High levels of melanin cause a darker skin color in humans.
Humans found near the equator are usually characterized as having darker skin. This means that they have high levels of melanin in their skin. At the equator, radiation from the sun is at its highest level because of the direct nature of the light wave that are "hitting" the earth. Therefore, in regions such as Africa, Oceania, and Southern Asia, there is also a high amount of UV radiation. This means that the selective pressure of UV radiation is higher in this area, so it would be a selective advantage for humans in this area to have high amounts of melanin to absorb the UV radiation. Therefore, this accounts for why humans in these areas have less known mutations in the MC1R gene (5) than humans in regions of the earth closer to the poles (13). This shows that natural selection has favored the maintenance of the MC1R gene in the equatorial regions, which accounts for the darker coloring of the skin of these peoples.
In my opinion, it is better to have darker skin because you become less susceptible to UV radiation damaging your body. It is a selective disadvantage to have low amounts of melanin in your skin and live in a place with high levels of direct sunlight. For example, many people from the North Shore go on vacation to Mexican resorts or Florida to lay on the beaches. A lot of these people are "white" and have little melanin in their skin. As a result, many of them get sunburned by the UV rays in these equatorial places because their melanin levels in their skin were not suitably equipped to deal with the radiation levels in these areas.
An example of a species where the coloring of the organisms differ is lizards, which come in almost every color possible. The various colors serve many purposes. For example, bright colored lizards may serve as a warning for predators. Other lizards may mimic the colors or patterns to hide from predators as well. Different color patterns also serve as warning or ways to communicate and find a mate. Color allows lizards to camouflage into their environments also protecting them against predators.
ReplyDeleteThis color difference is a result or learning and natural selection. The lizards learned how a certain color could help them communicate and hide from predators and these lizards were able to survive and reproduce successfully. The other lizards, whose colors were not able to help them, are not able to survive and reproduce as well as the successful lizards.