Monday, July 9, 2012

Evolution2012: Monday

I hope you'll indulge me as I geek out a bit about salamanders.  I used to work with them as an undergrad, and I still have a spot in my heart for the little guys.  Now I haven't really kept up with salamanders in any sort of professional way, but I talk about them in my classes, because they make such great examples of all sorts of evolutionary processes.

Why gush about salamanders?  I started the day with three talks on the red-backed salamander Plethodon cinereus, and it was great.  One of those talks was from Andrew Kraemer from Iowa State who talked about one form of P. cinereus that appears to be a Batesian mimic of the red-spotted eft.  A Batesian mimic is a species that looks a lot like a different (model) species.  The model species is generally noxious, while the mimic is not.  So the Batesian mimic is trying to take advantage of the appearance of the model, which presumably reduces predation (since predators would avoid noxious prey).  In this system, the red-spotted eft produces a neurotoxic compound called tetrodotoxin, while the P. cinereus mimic does not.  Now Kraemer did an enormous amount of work sorting through how predators would perceive these salamanders, which was very interesting, since I just expected that the mimicry would be taken for granted.  Science lesson: Never take anything for granted.

Another talk by Richard Lehtinen summarized an interesting case of ongoing hybridization between P. cinereus and P. electromorphus that is pretty high frequency.  The last talk of the three was so cool, I won't even blog about it.  I don't want to scoop that story in any way, but I'll be keeping my eyes open for the publication.

After lunch, I went to hear Peter and Rosemary Grant, because they're the Grants.  I didn't even look to see what other talks were available, because they're the Grants.  That just says it all, doesn't it?  Having followed their work pretty closely, I already knew most of what they said, but it was terrific to hear it directly from them.  Because they're the Grants.

A few points of application for creationists.  I hear often the notion that Darwin's do not provide a legitimate example of evolution because selection is cyclical and therefore there's no net change and because there have been no new species produced.  Both of those points are incorrect, and we really need to pay attention to this research.

If we're talking about selection in Geospiza fortis, there has been a net, linear change in beak shape and size despite cyclical natural selection pressure.  How?  The big drought of '77 shifted the Daphne Major population's bill size significantly greater, because only birds capable of exploiting large seeds for food survived.  We know that story.  The more recent drought of '04 had the opposite effect: fortis bills got smaller.  Why?  Because of the introduction of the extremely large-billed Geospiza magnirostris to the same island.  G. magnirostris is simply more efficient at exploiting large seeds than G. fortis, so the only fortis birds that survived were the small-billed birds that didn't have to compete with magnirostris.  Thus, despite cyclical selection by drought, the net change in fortis went from large to small.  They remain small-billed today, and they're likely to continue to be small billed unless something happens to the magnirostris population.

But that's not really a new species is it?  No, but that's where the curious case of 5110 comes into play.  That number refers to a large bird that appeared on Daphne Major probably originating from Santa Cruz way back in 1981.  It was apparently a backcrossed hybrid of fortis-scandens-fortis, but despite it's peculiar song it managed to find a mate that was also a backcrossed hybrid.  That founding pair produced a small population with a morphology somewhere between fortis and magnirostris, with all males singing the same unusual song.  Eventually they occupied a niche opened by the selection for small-billed fortis in 2004.  So there's a population that only breeds with other members of the same population, occupies a special niche, and sings a unique song unlike any other species on the same island.  It's basically reproductively isolated from other birds, which makes it a nascent species.  All in thirty years.  Amazing.  Read all about it in this free article: The secondary contact phase of allopatric speciation in Darwin's finches

So we need to learn from these new results and modify those apologetic claims.  There have been net changes in Darwin's finches as a result of selection, and a new species has indeed emerged quite rapidly (thanks in part to natural selection).

All in all, a great day!

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