Thursday, April 15, 2010
Evolution you can see!
On P.135-136, Coyne described an experiment conducted in California to test the hypothesis that drought causes plants to flower earlier. The plant used was the mustard plant, Brassica rapa, and after the five year experimental period, the plant descendants of original plants in the experiment began to flower a week earlier. This is an example of evolution that can be seen within a human lifetime. What are other examples evolutions that can be witnessed within a human lifetime? What causes these evolutions? Finally, how does this relate to the biological themes?
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A great example of evolution that was seen in a human lifetime would be Richard Lenski's E. coli long-term evolution experiment. Within 22 years, the experimental E. coli had undergone 50,000 generations by 2/14/10. The idea of this experiment was to have 12 nearly identical populations of asexual E. coli reproduce in different types of settings. The reason that E. coli was such a great experimental organism was because it could produce asexually, so that there would be solely genetic mutation due to the setting the bacteria was placed in, not because genetic variation due to sexual reproduction.
ReplyDeleteOne of the most popularly noted population was the E. coli that evolved on citrate. Usually, wild type E. coli cannot transport citrate into the cell through the cell membrane; however, through 33,127 generations, the "hybrid" version of the E. coli could intake citrate, which could be used for the citric acid cycle when oxygen is present. Through thousands of generations that took only about 2 decades, humans could actually live to see evolution occur in E. coli.
This experiment is related to interdependence on nature because, though it was theoretically an "artificial" setting, E. coli populations had to adapt to the certain situations it was placed under. Due to the pressures of "nature", E. coli's genetic makeup was mutated for a more suitable form to survive in given conditions.
Source: http://en.wikipedia.org/wiki/E._coli_long-term_evolution_experiment
One of the most prominent examples of real time evolution that we can witness is the evolution of bacteria. The reason for this is that bacteria have an extremely short generation time. Some bacteria have generation times as low as around 15-20 minutes. This means a bacteria can increase its population to 8 times the original population in about an hour. Because of this rapid growth, there are many mutations that occur during binary fission. This relates to the theme of Continuity and Change. While normally, bacteria should be all the same because of asexual reproduction, random mutations in a bacteria DNA creates new strains of bacteria.
ReplyDeleteProbably one of the greatest and deadliest examples of bacterial evolution would be tuberculosis. Since ancient times, this disease, caused by Mycobacterium tuberculosis, ravished the lands, killing many. In fact, signs of TB bacteria have even been found in Egyptian mummies dating as far back as 2400 BC. However, recent breakthrough in antibiotics around 1943 finally allowed humans to fight against this disease. Starting from the first successful antibiotic against TB, streptomycin, many tuberculosis antibiotics began springing up in the markets. Although tuberculosis would eventually gain immunity to one type of drug, it was effectively treated by using a combination of drugs. By the 1980s, TB was all but eliminated. However, new cases of tuberculosis suddenly began popping up. There were two things that contributed to this. First was the AIDS epidemic, which lowered people’s immune resistance to the bacteria. The second, however, was the evolution of multi-drug resistant tuberculosis bacteria.
A mutation in some tuberculosis bacterium allowed them to acquire resistance to one drug. As stated before, though, if an immune TB was found, then a different drug was used to treat it. However, once again some of the bacteria acquired resistance through mutation and survived to reproduce again. Several chains of mutations later and TB came back to being one of the world’s top killers, this time with resistance to many known antibiotics, and it took a little less than 40 years.
Sources:
http://www.umsl.edu/~microbes/pdf/introductiontobacteria.pdf
http://www.pbs.org/wgbh/evolution/library/10/4/l_104_09.html
http://www.umdnj.edu/ntbcweb/tbhistory.htm
A main component for seeing evolution in our lifetime is having an organism that has a quick reproduction time. A quick reproduction time allows for an organism to go through many generations quickly, allowing evolution to occur rapidly. A certain species comes to mind when I think of quick reproduction, E. coli. E. coli can reproduce very quickly. Campbell writes, "In a favorable environment, an E. coli cell can copy all [its] DNA and divide to form two genetically identical daughter cells in less than an hour" (Campbell 313). When presented with a serious environmental stress, such as antibiotic, E. coli needs to evolve quickly or else the E. coli perishes at the hand of the antibiotic. Therefore, only the E. coli that are resistant to that antibiotic will survive. These surviving E. coli will reproduce themselves, and suddenly there is a whole colony of E. coli that is resistant to a certain antibiotic.
ReplyDeleteEvolution that occurs quickly in an organism is usually due to extreme environmental pressure on that organism. The pressure forces the organism to evolve, or else the organism's existence is threatened. Using Frank's example, the mustard plant was going to die if it was going to go through a drought. Therefore, the mustard plant flowered a week earlier, in an attempt to fertilize other plants before the drought occurred. This was an attempt to increase the longevity of a species.
Rapid evolution relates to the theme of evolution. The course outline book defines evolution in organismal biology as "when a population's local environment changes unfavorably, the population adapts, migrates, or dies" (COB). Essentially, that is exactly what is happening with E. coli and the mustard plant. The organism is adapting to environmental pressures. These adaptations will help ensure the well being of the organism's species in the future.