Wednesday, January 07, 2009

After a long break... let's talk a bit more about speciation!   posted by DMI @ 1/07/2009 10:03:00 AM

...well. I took a bit longer than I had intended in getting to work on this next post, but it's okay. When I left you hanging a few weeks ago, I mentioned that the idea of reinforcement (that is, selection for increased pre-mating isolation in the presence of post-mating isolation) was out of favor for a while, but it was brought back in a big way by a certain paper. I'll spend some time talking about that paper here.

So, of course, the paper I'm talking about is Coyne and Orr 1989 (open access). Maybe it's just because of the way I was taught speciation, but this paper arguably opened the flood gates for a lot of modern research on speciation. First of all, Coyne and Orr came up with a useful way to quantify reproductive isolation. This allowed them to undertake one of the first meta-analyses of speciation ever, and they came up with some rather interesting data. The most important stuff is in figure 5:

Figure 5 shows that among both "allopatric" and "sympatric" taxa, pre-zygotic isolation increases with time, but among sympatic taxa, it increases faster! This is in contrast to the rates of increase of post-zygotic isolation, which are the same between allopatric and sympatric taxa. This definitely argues in favor of a reinforcement hypothesis.

Anyway, there are many other important points to this paper, primarily that there is a correlation between genetic distance and reproductive isolation. This is precisely what we expect under the current model of speciation, which I will hopefully talk about in the future.

As an administrative note, I figured initially that I would do a series of posts, which would build on top of each other, but I'll probably put that off. I'll just be blogging about things I find that are interesting, which can come a lot quicker! Hopefully you'll see more of me in the near future.