When Froggy Goes a Courtin'
Females don't fall for the same old song when distant groups reconnect
Distance can be hard on relationships--especially if you are a 2.5- inch frog. So, after a million years, when geographically isolated green-eyed tree frogs (Litoria genimaculata) reconnected with their former group, the females exercised a newfound mate selectivity based on a unique male mating call. This ensured the finicky females paired only with males from their new group and generated a distinct frog species in just 8,000 years or so.
"That's lightning-fast," for species development, said University of California, Berkeley researcher Craig Moritz.
Moritz and Australian colleague Conrad Hoskin studied the impact of geographic changes that began several million years ago and caused a single population of green-eyed tree frogs in Australia's rainforest to split into distinct northern and southern groups. About 8,000 years ago, another environmental change allowed the two groups to intermingle. By then, frogs produced from a northern male-southern female pairing didn't survive well. As a result, a crossbreeding southern female was at a reproductive disadvantage.
The selection pressure led to a mating strategy in which southern female frogs preferentially selected southern males by virtue of his distinctive call. The behavior of the females therefore sped up, or reinforced, the normal speciation process. In a few thousand years a new species that could no longer mate successfully with either the northern or southern frogs developed.
This type of reinforcement of natural selection has been controversial since Darwin's time, but Moritz and Hoskin provided data to support the concept in the Oct. 27 issue of Nature.
The U.S. National Science Foundation and the Australian Cooperative Research Centre for Tropical Rainforest Ecology and Management sponsored this research.
For the complete story, see the University of California, Berkeley news release.
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