Wednesday, February 8, 2012

How Important Is Geographical Isolation in Speciation?

Genetic Tests for Ecological and Allopatric Speciation in Anoles on an Island Archipelago Thorpe RS, Surget-Groba Y, Johansson H (2010) . PLoS Genet 6(4)

Over the last 150 years, since Darwin's study of islands and his “Origin of Species,” island archipelagos have played a central role in the understanding of evolution and how species multiply (speciation). Islands epitomise the conventional view of geographic (allopatric) speciation, where genomes diverge in isolation until accumulated differences result in reproductive isolation and the capacity to coexist without interbreeding. Current-day Martinique in the Lesser Antilles is composed of several ancient islands that have only recently coalesced into a single entity. The molecular phylogeny and geology show that these ancient islands have had their own tree lizard (anole) species for a very long time, about six to eight million years. Now they have met, we can genetically test for reproductive isolation. However, when we use selectively neutral markers from the nuclear genome, on this naturally replicated system, we can see that these anoles are freely exchanging genes and not behaving as species. Indeed, there is more genetic isolation between adjacent populations of the same species from different habitats than between separate putative allospecies from the ancient islands. This rejects allopatric speciation in a case study from a system thought to exemplify it, and suggests the potential importance of ecological speciation.

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