Wednesday, April 1, 2009
environemntal effects
Selective advantage is one of the major reasons of evolution and adaptations in allowing for survival. In accordance to the ecosystem of a species, adaptations occur in correlation to certain threats that may be present. The surrounding environment or other species that are present in the ecosystem may both play roles in selective advantage. Give examples from the text of both the effects of environment and other species of the ecosystem. Also discuss how selective advantage and survival of the fittest play roles in certain characteristics that each organism portrays. Discuss the effects that humans may play on the survival of each of these animals.
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Selective advantage in a species can be measure using two factors, time and numbers of measurements, or data sample size. The period of time over which a species adapts must be measurable, or least must be measured previously. A large data sample size is important as well because “if the relative fitness of two forms of a species differs by a small percentage, one must count a large number of individuals over time in order to overcome the random effects of sampling error” (Carroll 51). Generally, even slight selection is easy to detect where “selection is very strong and therefore very fast” (Carroll 52).
ReplyDeleteAn example where selection occurred as a result of the environment was of the case of melanism in peppered moths (Carroll 52). During the Industrial Revolution, pollution modified the color and growth of lichen on trees where the peppered moth rested. The moths altered as well and the frequency of darker, melanic form of the moth increased while the lighter form of the moth decreased; as seen on figure 2.2 on page 53, as certain selective conditions changed in the environment, the melanic moth frequency decreased. Clearly, as the environment became more polluted, the melanic moth population increased and vice versa when the environment’s air quality became less polluted. Humans played a role in the increasing and decreasing population of the melanic moth due to the Industrial Revolution at the time and its aftermath. The industrial revolution had a profound change in the agriculture, manufacturing, mining, and transportation of humans; however, it also severely polluted the environment. When effort began to improve air quality, the melanic moth population probably decreased because the better air quality probably changed the coloration and growth of lichen as well. Moth color may also have protected them from predators. Another example of human intervention in natural selection was in that of the bighorn sheep (254); females favored larger horns in male rams but so did hunters; eventually, male rams were seen to have shorter horn lengths with each passing generation due to artificial selection caused by humans.
Besides moth, natural selection of animal coloring was studies in land snails, ladybird beetles, desert mice and other species. In a study about pigeon coloration selection in the wild, scientists in Davis, California studied six different plumage color schemes and the predation of pigeons from the peregrine falcon. Falcons attacked the white-rumped pigeons (figure 2.3; left) less often than other pigeons; the pigeon “made up 20 percent of all pigeons in the area. . . [and] accounted for only 2 percent of all pigeons captured by the falcons” (55). The scientists suggested that this was due to an evasive roll that the pigeon executed while attacked in midair. The human intervention in the study was when the scientists purposely switched the rump feathers of the white-rumped pigeon and the blue-barred pigeon. The previous results were reversed. The selection of white rumps in pigeons were favored over any other coloring because it improved their chances of survival.
In the Campbell text, changes in coloration in a species was a way for a species to be protected by predation. A form of passive protection from predators in animals is called “adaptive coloration” and can evolve repeatedly in a single species over generations (chapter 52); the environment can continually change and thus, so do certain organisms in order to ensure survival of their species. The process is specifically called “Camouflage, or cryptic coloration, [which] is a passive defense that makes potential prey difficult to spot against its background” (Campbell).
Influence on natural selection from another species can also inspire coevolution, such as the case of the TTX-infused Oregon rough-skinned newt and the garter snake, which was generally immune to the TTX poison. Natural selection favored high amounts of TTX in the newts and high resistance of TTX in the garter snake. Those who did not have the selective advantage (in respect to each species) died from starvation or were eaten. This is true for all the species mentioned above. Humans can intervene in the selection process by artificially changing the environment quickly so that the species will be extinct or otherwise because not enough time was provided for the species to adapt.
Selection happens amongst a species in order to ensure survival and thus, reproduction of that species. This is due to the environment, artificial or otherwise. Sean Carroll, in an interview, referenced the influence of the environment on a species by saying, “Let's say animals start living in caves, where their ancestors lived out in open air. That changes the selective conditions and certain traits – their body pigmentation or vision. They are no longer maintained because there is no selective pressure to maintain that and the genes encoding those traits for vision or for body pigmentation, those genes decay and we find them as the fossil genes. But, there are all sorts of examples for this. We humans are carrying almost 900 fossil genes and about 70 of those have evolved just since our evolution from our common ancestor with chimpanzees” (source: http://www.sciam.com/podcast/episode.cfm?id=0005BABA-81CC-153E-811383414B7F00FF)
The Antarctic ice fish is an example of selective advantage and evolutionary changes due to the environment. When the temperature in the southern ocean dropped from 68°F to less than 30°F and the ice fish were isolated in Antarctica due to changes in the ocean currents and continental drift, the Antarctic ice fish were forced to either adapt or die. The freezing water temperature became an environmental stimulus to genetic mutation and resulted in today’s ice fish’s evolutionary change of no red blood cells to decrease the blood viscosity, low metabolic rate for less energy loss, well-perfused gills for more efficient gas exchange, increased blood volume for increased cardiac output, uptake of oxygen through the skin, enlarged capillaries, large heart, and increased skin vascularity. By having greater vessels around the skin, the ice fish have greater uptake of oxygen through the skin due to scaleless skin (Carroll 24). Since the Antarctic ice fish were isolated in a cold environment that required a more efficient and selective advantage for survival, the ice fish further adapted to have no myoglobin in all ice fish and the hearts of five species, invention of “antifreeze” proteins, and changes in microtubules to be very stable at temperatures below freezing. The long-term changes in ocean temperature and currents caused necessity and opportunity for the dramatic rejection of the way of life that serves every other vertebrate on the planet (Carroll 23). The mutations that gave the ice fish species its selective advantage allowed the ice fish to survive and reproduce, showing the survival of the fittest. Humans do not play a big role in the survival of the Antarctic ice fish, since humans do not live under freezing water. However, the carbon dioxide and green house gases emitted by the 6.7 billion people in the world can cause global warming and further changes in the ocean temperature and currents. This environmental factor increasingly becoming a threat to the natural environment may become a new environmental stimulus in the future for the Antarctic ice fish to evolve and have new selective advantages and have natural selection over long periods of time.
ReplyDeleteThe fossilization of the blue/purple-promoting enzymes in the morning glory species Ipomoea quamoclit is an example of an evolutionary adaptation due to other species of the ecosystem. The species adapted to produce red flowers instead of blue or purple in order to attract hummingbirds better. Hummingbirds, the species’ pollinators, provided a stimulus for the morning glory species to evolve to attract the pollinators more, increasing their reproductive rate and thus survival of the fittest. The mutations in the genes that produce the red-promoting enzymes are naturally selected for the increased attraction to the pollinators, increasing their chance of pollination and reproduction. The pathway for the production of blue and purple pigments degenerated due to random mutations, and this became a selective advantage to the flowers that had to rely on the enzymes that produce red pigments to attract their pollinators. This shows the elimination of genes due to natural selection. The elimination of this gene proved to be more successful in the survival of the species, and the natural selection of the inactivation of the blue/purple-promoting enzymes may have led to the evolution of the red pigmentation of the flowers (Carroll 133-134).
student.ccbcmd.edu/~sschmit4/BIOL%20111/Evolution/The%20Ice%20Fish%20of%20Anarctica.ppt
http://www.pnas.org/content/94/7/3420.full.pdf+html?sid=b216d109-7ec4-4f7c-99ab-1fff2e00498a
http://www.fortunecity.com/greenfield/rattler/46/blood2.htm
An example of a species affected by the environment and other species of the ecosystem is the Atlantic Cod (page 256-257). Due to the “tragedy of the commons”, a dilemma where individuals use up resources for their own benefit until the point where there is none left, the human population in the nearby areas overfished the codfish, depleting the numbers in the ocean. In addition to fishing excessively, the fishermen had selectively chosen the oldest and biggest codfish. As a result, maturation that resulted in a large size and occurred at an older age became disadvantageous traits within the codfish population. As the large and old were overfished, the fisherman “unnaturally selected” smaller and younger fish. Due the environmental pressures implemented by human interest, being a small and young codfish became a selective advantage that prevented them from being hooked by a fishing line/net. The fisherman had created a selective advantage but at the same time, created a disadvantage. The codfish acted as a keystone species; with the great population displacement, the crustaceans and pelagic fish that the codfish preyed on experienced a population boom. The codfish also faced a “role reversal” where they became the prey,, further decimating the codfish. While a selective advantage contributes to the “survival of the fittest”, as Carroll says, “the ‘fittest’ is a matter of reproduction and survival”(258). In regards to the codfish, the fisherman selected the codfish that are young and small, deeming them “fit” for having this selective advantage in one aspect of the environment, but left them vulnerable and weak to other environmental and species pressure.
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