Posted by: salamandercandy | January 22, 2007

Amphibian Radiations

The fossil record for amphibians is fairly spotty, apparently, and hasn’t provided much data for scientists to answer questions about what has happened to amphibians during the Earth’s major extinction events (e.g. at the ends of the Permian and Cretaceous). If worldwide extinctions are associated with major changes in climate, the expectation is that amphibians should have been hit hard in the past, due to their sensitivities to temperature, chemicals in the environment, etc. Modern day climate change is thought to be an important factor in the acceleration of amphibian extinctions. Have amphibian lineages diversified gradually since the good ol’ Permian, or, as we might expect given the delicate nature of amphibians, are the groups existing today the descendants of a lucky few lineages that survived the last global extinction event? If you were to consult the amphibian fossil record for an answer, you would have a tough time finding one.

Molecular Phylogenetics to the rescue! A recent study published in PNAS used DNA sequences from representatives of most of the extant amphibian taxa to show that, when paired with the available fossil data, the molecular data tell a story of amphibian extinctions and subsequent diversification over the last several hundred million years. Mass extinctions in amphibians have occurred at roughly the same times as the extinctions of amniote vertebrates. Some amphibian groups went through adaptive radiations–sort of like what happened to mammals after the dinosaurs bit it. The most diverse and widespread groups today are mostly those that underwent rapid diversification toward the end of the Cretaceous: the Natatanura (including “true frogs” in the genus Rana), the Nobleobatrachia (including toads and treefrogs), Microhylid frogs, Plethodontid salamanders, and Salamandrid salamanders. Sorry for the sesquipedalian taxonomic jargon. 🙂

What species or lineages of modern amphibians will make it through the current extinction crisis? Hopefully most of them, if anything can be done about the depressing trend of habitat destruction and global warming. From a long-term, evolutionary perspective it seems likely that a handful of amphibian lineages will survive and diversify in the future. If I were placing bets, I would put my money on bullfrogs (Rana catesbeina), cane toads (Bufo marinus), and maybe the Pacific treefrog (Pseudacris regilla). These plucky species seem to do pretty well despite the efforts of humans to either eradicate them outright or modify their habitats beyond recognition. There are probably other pest-like amphibians around the world that for one reason or another are well-suited to coping with environmental change. I hope that the global experiment to see which amphibian lineages are capable of surviving this latest, human-caused catastrophe never takes place. Wait… I guess it’s already begun, hasn’t it? Crap!


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