Thursday, April 8, 2010
Divergent Evolution
On page 173, Coyne writes that "two species of the monkeyflower Mimulus live in the same area of the Sierra Nevada, but rarely interbreed because one species is pollinated by bumblebees and the other by hummingbirds" (Coyne 173). Coyne later explains a hypothesis of how one monkeyflower species diverged from the other on page 175-176. Explain the mechanism that caused this evolution. Also, name other related species that cannot interbreed for some reason. Explain why they cannot interbreed. Consult outside sources to support your examples.
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On page 175, Coyne describes the mechanism that caused divergent evolution of the monkeyflower species through Mayr's hypothesis that members of the ancestral species at one point faced a geographic barrier. When isolated, each portion of the species had to adapt to its new environment; where there were more hummingbirds, flowers evolved to attract hummingbirds as pollinators, and where there were more bees, flowers evolved to attract bees as pollinators (demonstrating an interdependence in nature). From there, natural selection and evolution continued to adjust each type to its proper setting, creating further differences between the two. When the barrier vanished and the two divisions of the species were geographically reunited, their new adaptations inhibited interbreeding, and instead of the geographic barrier, they now faced a reproductive barrier.
ReplyDeleteAnother species that diverged similarly was the Galapagos finch. Due to adaptive radiation, the island's geographic barrier caused speciation after groups of the species formed different niches and evolved to better fit those niches.
http://my.uen.org/mydocuments/downloadfile?userid=54611&documentid=6171875
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ReplyDeleteCoyne mentions on 173 that a species of flies (Drosophila--supposed to be italicized)cannot create hybrid offspring because the pheromones of this fly species doesn't appeal to other fly species.
ReplyDeleteIf closely related species breed then their offspring would be sterile and thus the goal of surviving and reproducing would not be reached. Most likely the hybrid fetus will die before birth.
The BSC or the biological species concept explains that "'reproductively isolated'" or geographically isolated, species act differently and look differently, and even secrete different chemicals; making them unappealing, so that even if two species share many similarities, they will not interbreed due to things like different mating seasons (Coyne 171). This helps prevent unfruitful reproduction.
I agree with Eilrayna that geographic barriers forced each species to develop to their new environments, therefore creating reproductive isolation, which later became a reproductive barrier, when the monkeyflower species was no longer geographically isolated.
Sources:
wikipedia.org
http://oak.cats.ohiou.edu/~jm703496 /es-reinforce.html