In his chapter “The Engine of Evolution”, Mr. Coyne defines the requirements of an adaptive trait that underwent natural selection. He goes into detail of the bone structure in whales and humans and how their development clearly contains all of these requirements, therefore underwent natural selection, and therefore prove evolution. Since we know that evolution is in fact true, we also know that all adaptive traits evolved via natural selection.
That being said, name me a trait (not in the book) that demonstrates all of the requirements of being an adaptation that underwent natural selection. Describe in detail how the trait follows all of the guidelines of natural selection. Finally, relate this concept to one of our first units previously studied in class. How does your trait help an organism fill in its niche in the environment and help it to survive and reproduce?
Venus Fly Traps have evolved well enough to be able to live in areas that don’t have a lot of nitrogen in their soil (Newton BBS). Although other plant species are not able to live in these nitrogen-poor soil areas, the venus fly trap’s adaptation of being able to take nitrogen from the insects it consumes has allowed the venus fly trap to survive.
ReplyDeleteOne may seem surprised that venus fly traps have evolved this adaptation of being able to digest insects and take an insect’s nitrogen. However, we have studied in class how plants colonized land. Though it was not a short process, and even though plants had to start off as very minute life forms in the sea, plants were able to slowly come onto land and colonizing (Campbell 601-604). This is analogous to venus fly traps that have colonized nitrogen-poor soil. Plants slowly evolved to mutate and pass on genes that slowly transformed a normal plant into one that was able to digest insects for nitrogen. Eventually, this plant would colonize bogs, and further generations of plants that stopped expressing genes for insect digestion died while those that passed the gene survived.
Coyne would agree that the venus fly trap’s ability to digest insects proves to be a good adaptation because it is “beautifully designed to fit [its] environment… that [this] species must deal with” (115). The venus fly trap’s interactions with its environment expresses the theme interdependence in nature. If there were no insects in bogs where this plant lives in, then the venus fly trap would die. Likewise, a possible ordeal that might happen if there were no venus fly traps in bogs would be the proliferation of insects, disrupting the whole entire rest of a bog’s ecosystem as well as the bog’s primary productivity.
In addition to Henry Lin’s example of the venus fly trap, another classic example of natural selection would be the change in color of peppered moths during the Industrial Era in England. Prior to the Industrial Revolution, the majority of peppered moths had the typica phenotype, which was white with darker speckles (http://www.millerandlevine.com/km/evol/Moths/moths.html). This coloration provided camouflage for the moths against the lighter-colored lichens on the tree trunks where they rested.
ReplyDeleteHowever, during the Industrial Revolution, the burning of coal created pollution, which covered the trees with soot, or killed the lichens and exposed the darker tree trunks. Consequently, the carbonaria phenotype, which was darker than the typica moths, provided a selective advantage; since the darker moths blended in better with the darker surroundings, they were less likely to be seen and eaten by birds, their predators.
The adaptation of moth colors demonstrates all of the requirements of being an adaptation that underwent natural selection. The first requirement, according to Coyne, is that “the starting population has to be variable” (117). Peppered moths have three different colors: typica, white morph; carbonaria, black morph; and insularia, which is actually a gradient of intermediate forms (http://jhered.oxfordjournals.org/cgi/content/full/95/2/97).
The experiment from the above source also fulfills the second requirement, by proving that the variations have a genetic basis. The alleles for color in peppered moths display polygenic inheritance, since several genes affect the phenotype, resulting in the intermediate phenotypes (Campbell 274).
The third requirement, that the adaptation increases the organisms’ reproductive chances, is also fulfilled. In the polluted, darker habitats, the carbonaria moths had the advantage of cryptic coloration which, as we learned in the ecology unit, “makes prey difficult to spot” (Campbell 1201). As a result, more carbonaria moths could survive and reproduce, while the typica moths that did not have the advantage of camouflage were more likely to be eaten.
The adaptation of peppered moth phenotypes demonstrates the theme of continuity and change, or the similarities and differences in genetic code that can result in the development of different traits (Campbell 8). During the Industrial Era, the commonness of darker moths increased, because the darker color provided a selective advantage. However, in recent years, the amount of smoke pollution has declined. As a result, the abundance of lighter moths is now increasing, since the lighter color provides more camouflage nowadays (http://www.truthinscience.org.uk/site/content/view/127/65/).
To add on to the Venus Fly Trap and Peppered Moth examples from Henry and Jamie, polar bear feet demonstrate an adaptive trait. According to one source, polar bears have "large thickly furred, webbed feet with rough foot pads, and short claws that are immune to frostbite" (http://scienceray.com/biology/zoology/adaptive-traits-of-the-polar-bear-ursus-maritimus/). The first of Coyne's three guidelines for a naturally selected trait is that "the starting population has to be variable" (Coyne 117). There was certainly a variety in preceeding feet of the polar bear's ancestors, which come from brown bears and do not possess the same immunity to frostbite and extra cause of friction (since there was no need for these qualities on dry land). The second requirement for the trait is heritability. We know that the polar bear foot's adaptation is genetic since we see it being passed on through all generations (http://www.seaworld.org/infobooks/PolarBears/pbphysical.html). Lastly, possession of such a foot meets the third necessity of affecting an individual's probability of leaving offspring. The friction caused by the rough pad and the claws' immunity to frostbite led to the bears' ability to colonize icy lands and to survive in such locations by having easier mobility in order to catch prey and avoid predation. Once the bears were able to survive in the new location, the number of offspring left there increased rapidly. The polar bear's foot appeals to all aspects of its role in the environment: the thick fur and short claws allow the organism to survive the cold, the rough padding reduces slips on icy land, and the webbed feet facilitate swimming. Thus, the relationship between structure and function is very clear after witnessing the new abilities in polar bear movement due to the structural differences that evolved from brown bear feet.
ReplyDeletehttp://scienceray.com/biology/zoology/adaptive-traits-of-the-polar-bear-ursus-maritimus/
In addition to the previous examples of venus fly traps, peppered moths, and polar bears, I would like to present the example of the drug-resistance that is developing in certain strains of staphylococcus aureus.
ReplyDeleteCoyne mentions the issue briefly on page 131. However, this issue definitely deserves some more discussion. MRSA is the official acronym, which is short for Methicillin-resistant Staphylococcus aureus (staph). Over time, natural selection has driven the evolution of Staph bacteria. MRSA is the most modern strain, and the bacteria is resistant to basically all antibiotics available today, including vancomycin, widely considered the "last line of antibacterial defense" (http://evolution.berkeley.edu/evolibrary/news/080401_mrsa).
The University of California-Berkeley's evolution webpage has an article on MRSA, detailing the evolution of the "superbug"
The first mechanism is vertical transmission of the antibiotic-resistant genes. This is the random mutation and passing-on of the genes through generations. This process is especially quick in bacteria because of the bacteria's short generation times and long population sizes.
However, the mechanism that has truly made MRSA deadly is horizontal transfer. This is the transfer between bacteria of DNA. This occurs through conjugation. Campbell describes this process as when a donor cell uses a sex pilus to attach to a recipient cell. The pilus retracts, the cells are pulled together, and a mating bridge forms to create a pathway for DNA (Campbell 562). According to the Berkeley site, horizontal transfer speeds up evolution because the bacteria do not have to wait for random mutation. The bacteria can simply receive the genes for drug resistance from another strain (http://evolution.berkeley.edu/evolibrary/news/080401_mrsa).
MRSA's adaptation of drug resistance definitely does not benefit humans, but this resistance to antibiotics that was developed by natural selection definitely helps the bacteria survive and reproduce. No longer can the bacteria be killed by antibiotics; MRSA is resistant to all of our medicine, which is definitely useful in the fight for survival.
as an addition, this adaptation of drug-resistance relates to our theme of continuity and change. Bacteria are constantly changing in response to humans' use of antibiotics. The antibiotic-resistant genes of MRSA have been passed down as well as transferred to other bacteria.
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