Saturday, March 27, 2010
Speciation Is...
On page 169, Coyne brings up the point that discrete clusters, or species, evolve in all organisms that reproduce sexually. Why are discrete and discontinuous clusters exhibited only in sexually reproductive organisms as opposed to asexually reproductive organisms? Note the significance of mutations, with regards to meiosis, mitosis and/or different types of asexual reproduction as we've previously learned in class. On pages 170-172, Coyne continues to describe the concept of species as a whole. While certain humans may have obviously different characteristics, they are part of the same species. On the other hand, certain Drosophila fruit flies are identical - down to the last microscopic detail - yet, they are different species. Clearly, species are not distinct based on "looks". According to Coyne, what distinguishes whether organisms are the same species or not? How does this relate to any theme in biology? And finally, why do you think Coyne puts such emphasis on how a species arises - in other words, what is the evolutionary significance of speciation?
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Surviving species are mostly seen to be sexual because the asexual can be killed very easily. We’ve learned in class that although asexual reproduction may increase a population’s numbers very quickly, the population’s genome may be filled with harmful mutations that could decimate the population. That’s why genetic variety is good.
ReplyDeleteWe’ve seen how inbreeding families leads to children that may have bad genomes. The Daily Herald actually released some information saying how, prior to his murder, King Tut was already infected by brain malaria, a disease that is genetically inherited. If mummies did not inbreed like asexual populations do, then there would be chance that King Tut would have survived.
To see whether organisms are the same species, scientists employ the BSC concept, which defines a species as “a group of interbreeding natural populations that are reproductively isolated from other such groups” (Coyne 172). An animal from one species can’t successfully breed with another species and expect to have a surviving line of animals. Even though farmers cross horses and donkeys, the mule offspring cannot reproduce; the mule is infertile.
One person studying species could relate the concept to interdependence in nature. Sometimes, scientists see symbiotic relationships in nature that have grown stronger after a long period of time.
For example, in a journal article I read in the beginning of the year, Colletes cunicularius bees and the Ophrys exaltata orchid are dependent on each other for their survival. Without the orchids, the bees would die, and without the bees, the flowers would die. It if weren’t for evolution and speciation that has allowed the flower to mimic a bee’s mate (Pouyannian mimicry, as the article explains, is a species imitating another specie’s mate so the imitator will be copulated), then the relationship between these two species wouldn’t have been so intricate, and this relationship would not be a selective advantage.
I think that Coyne puts a heavy influence on speciation not only to emphasize that evolution is true (that is the title of the book, believe it or not), but to also show how our world is comprised of a whole variety of species. An individual organism may belong in one genus, but Coyne wants to show that genus means even more than one type of organism, but rather a whole huge array of them, each with its own selective advantages, geographical home, food, and the like.
As we all know, sexual reproducers attain genetic diversity through "crossing over" during meiosis. However, asexual reproducers such as bacteria are able to mutate their DNA using transformation, transduction, and conjugation. Because crossing over only occurs during meiosis, and because sexual reproduction takes much more time and energy than asexual reproduction, asexual reproducers such as bacteria are able to diversify their DNA much more rapidly than complex sexual reproducers. The quick diversification of DNA, then, allows for a much more diverse set of genes within a species, and makes possible continua of different types of organisms as opposed to ostensibly distinct species. In other words, the more genetic variation within a taxon, the less clear the boundaries between species, and since asexual bacteria are able to attain much greater genetic diversity than complex sexual reproducers, the clusters among bacteria are much more continuous than the clusters among complex sexual reproducers.
ReplyDeleteAccording to Jerry Coyne, the German biologist Ernst Mayr "defined a species as a group of interbreeding natural populations that are reproductively isolated from other such groups" (172). In other words, a species is a group of individuals who are able to reproduce with one another and produce fertile offspring. While two individuals of different species of the genus Drosophila may appear identical, one must remember that physical appearance is only one out of myriad features of an organism. Ultimately, some characteristic other than appearance is present within the two individuals that is caused by a gene different enough within the two individuals as to prevent the genome of one individual from being compatible with the genome of the other individual for sexual reproduction.
One of the most important concepts of evolution is the idea that all life evolved from a single universal common ancestor. Surely, the universal common ancestor comprised only one species. Therefore, speciation, the forming of multiple species from a single species, is an important part of evolution, as without speciation the vast number of diverse species present in our world today could not have evolved from the single universal common ancestor.