"That's lightning-fast," said co-author Craig Moritz, professor of integrative biology at UC Berkeley and director of the Museum of Vertebrate Zoology. "To find a recently evolved species like this is exceptional, at least in my experience."

The yet-to-be-named species arose after two isolated populations of the green-eyed tree frog reestablished contact less than 8,000 years ago and found that their hybrid offspring were less viable. To avoid hybridizing with the wrong frogs and ensure healthy offspring, one group of females preferentially chose mates from their own lineage. Over several thousand years, this behavior created a reproductively isolated population - essentially a new species - that is unable to mate with either of the original frog populations.

This example suggests that rapid speciation is often driven by recontact between long-isolated populations, Moritz said. Random drift between isolated populations can produce small variations over millions of years, whereas recontact can amplify the difference over several thousands of years to generate a distinct species.

"The overarching question is: Why are there so many species in the tropics?" Moritz said. "This work has led me to think that the reason is complex topography with lots of valleys and steep slopes, where you have species meeting in lots of little pockets, so that you get all these independent evolutionary experiments going on. Perhaps that helps explain why places like the Andes are so extraordinarily diverse."

Moritz; lead author Conrad Hoskin, a graduate student at the University of Queensland in St. Lucia, Australia; and colleagues Megan Higgie of the University of Quee
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Contact: Robert Sanders
rsanders@berkeley.edu
510-643-6998
University of California - Berkeley
28-Oct-2005