Bermuda. Famous for its sun. Sand. Surf. Shorts. Triangles. Lizards.
Okay, maybe not the lizards. Not yet.
Islands and lakes hold a special place in the heart of evolutionary biologists (here’s a few examples from this blog: sticklebacks, crickets). As Jerry Coyne likes to say, island biogeography provides evidence for evolution so strong that most creationists simply ignore it.
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Bermuda formed about two million years ago. It’s small and a long way from the mainland, and has almost certainly never been connected to any other landmass. That Bermuda appeared very recently (in geologic terms) and that it is so far away from potentially invasive populations means that anything that lives only in Bermuda has probably evolved pretty darn fast.
Plestiodon longirostris is a skink that is found on Bermuda and nowhere else on earth. There aren’t many animal species living on this island at all, which is not surprising, given how remote it is. There are, however, other members of the genus, many of which live on the mainland of North America.
We’ve gotten fairly good at using DNA to generate hypotheses about relationships between species, and, to a lesser degree, the time of divergence. Using that, Brandley and company found that Plestiodon longirostris split from its closest relatives...
How old would you expect the Bermuda skink lineage to be? “Well, the island’s only two million years old, so it's got to be younger than that.”
That's a perfectly sensible answer. But wrong.
Brandley and company estimate that this lizard split from its relatives about 16 million years ago. This means that the line leading to this particular skink diverged way, way before Bermuda formed.
These data don’t, alas, give many clues to when the skink’s ancestors got to the island, or how. Nor do we know how its relatives on the mainland went extinct. But what it does say is that islands are not only important centers for evolutionary experimentation, they can also act as centers for preservation. Or, as the authors put it, islands can be a “life raft” for species that make it to their shores.
Brandley, M., Wang, Y., Guo, X., Nieto Montes de Oca, A., Fería Ortíz, M., Hikida, T., & Ota, H. (2010). Bermuda as an evolutionary life raft for an ancient lineage of endangered Lizards PLoS ONE, 5 (6) DOI: 10.1371/journal.pone.0011375
Lizard picture from here.
Additional: Another take at Natural Selections.