Saturday, March 28, 2009
Selective Advantage
The Antarctic icefish have gone through various adaptations that allow them to survive in freezing temperature such as the modification of proteins that develop microtubules stable in freezing temperature. What would happen if the icefish was removed from its environment and placed in a warmer environment? What effects would occur to the icefish's distinct cardiovascular system? How would the advantages that allowed them to survive in the Antarctic environment become a disadvantage in the warmer environment?
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Cold water has a much greater oxygen solubility than warm water. This means that there is much more oxygen in cold water than in hot water. For this reason, icefish have developed relatively large gills. They have evolved scaleless skin with large capillaries. These features developed in the icefish to increase absorption of oxygen from the environment. However, one might wonder why icefish would have to evolve to take in more oxygen if cold water has more oxygen than warm water. Wouldn’t their gills get smaller? There is already more oxygen where they live than in warm water. The reason is this: if they lived in warm water, they would have red blood cells. Red blood cells contain hemoglobin, which binds oxygen and helps circulate it to the rest of the body so the body can function. In cold water, however, body fluid like blood becomes more viscous, making it difficult to pump. Icefish got rid of red blood cells during evolution and replaced them with another way of obtaining oxygen: larger gills and larger capillaries. Myoglobin is another molecule that binds oxygen. It binds oxygen and carries it to muscles. Many icefish are pale because they don’t have myoglobin. Their cardiovascular adaptations: larger gills and capillaries, provide them with sufficient oxygen. All in all, if icefish lived in warm water, they would have red blood cells (because there would be no fear of abnormally high viscosity), and the red blood cells would have hemoglobin and myoglobin. There would be no need for larger gills and capillaries.
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ReplyDeleteIn response to Amie's questions, if the icefish was removed from the Arctic environment and placed into a warmer one, they will die (hope you laugh at that one Mr. Erdmann). Anyways, the truth of the matter is, the icefish would probably be unable to survive such a rapid change in its surroundings. First of all, since it does not hemoglobin, which transports oxygen from the lungs or gills to the rest of the body, the sudden decrease in the presence of oxygen (warm water has much less oxygen concentration than cold water) would likely cause the fish to experience hypoxia, which is the condition when the body tissues do not receive the functional amount of oxygen (Source: http://en.wikipedia.org/wiki/Hypoxia_(medical)). In addition, like Theodore stated, the icefish evolved larger gills and capillaries to make up for the lack of red blood cells. The large gills may provide some relief to the sudden drop in oxygen solubility, but since the fish has no red blood cells to carry the oxygen molecules, its large gills and large heart would probably not provide many benefits in comparison to other warm water fishes. This would answer how their distinct cardiovascular system would respond to the environmental changes, but I’m not sure what you mean by “what effects would occur to the icefish's distinct cardiovascular system?”
ReplyDeleteAs for your last question, one of the icefish’s advantages of not having hemoglobin may become disadvantageous in a warmer environment because the reason that the icefish eliminated most of their hemoglobin in their blood is because the body fluids are much more difficult to pump in a cold environment. In a warm environment however, it would be much more efficient to send oxygen throughout the body by binding the molecules to hemoglobin and allow it to be pumped to the vital organs and tissues. Therefore, the icefish’s lack of hemoglobin, which let them to survive in the colder Arctic environment, would lead it to its grave in a sudden increase of surrounding temperature. Furthermore, the icefish’s famous “antifreeze protein,” which is key to allowing its body fluids to remain liquid in subfreezing temperatures, would also be a disadvantage in a warm environment because it would act as an unnecessary burden on its cardiovascular system, as these proteins would no longer have a function in warmer temperatures.
One theme of biology, evolution, is change in the genetic material of a population of organisms from one generation to the next. These changes are caused by a combination of three main processes: variation, reproduction, and natural selection. Genes that are passed on to an organism's offspring produce the inherited traits that are the basis of evolution. These traits vary within populations, with organisms showing heritable differences in their traits. When organisms reproduce, their offspring may have new or altered traits. These new traits arise in two main ways: either from mutations in genes, or from the transfer of genes between populations and between species. In species that reproduce sexually, new combinations of genes are also produced by genetic recombination, which can increase variation between organisms. Evolution occurs when these heritable differences become more common or rare in a population. Natural selection, a process causing heritable traits that are helpful for survival and reproduction to become more common in a population, and harmful traits to become more rare. This occurs because individuals with advantageous traits are more likely to reproduce, so that more individuals in the next generation inherit these traits. Over many generations, adaptations occur through a combination of successive, small, random changes in traits, and natural selection of those variants best suited for their environment. The example of the icefish is a great connection to the theme of evolution as it shows the extraordinary power of tiny, almost unnoticeable changes of a species over a long period of time, where totally new adaptations are made to stay level with the changes in the environment. Carroll made it a very powerful point in his book, that with a little bit of luck and a basic understanding of chance, evolution will take place when appropriate. This example also demonstrates the main point that Carroll was getting to, the fact that evolution takes a very long time, and sometimes we as the human race may not live to see these changes, but it doesn’t mean that they don’t occur (Source: http://www.ucmp.berkeley.edu/history/evolution.html).