Why are some groups of animals s...( A new study of finger-sized Austral...),Health

A new study of finger-sized Australian lizards sheds light on one of the most striking yet largely unexplained patterns in nature: why is it that some groups of animals have evolved into hundreds, even thousands of species, while other groups include only a few?

The study takes a look at Australias most diverse group of vertebratesmore than 252 species of lizards called skinks. Researchers at the Cornell Lab of Ornithology have found evidence that the drying up of Australia over the past 20 million years triggered this explosive diversification. The results were published in the September 19 online edition of the Proceedings of the Royal Society B.

Lead author Dan Rabosky, a Cornell graduate student, spent many months in the remote Australian outback, trapping skinks as they skittered from one prickly clump of grass to another. By documenting where the various skink species occur and using their DNA to define their evolutionary tree, he found that the groups with the most species are the ones that live in the driest parts of Australia. Theres something about colonizing the desert that caused these skinks to diversify at an incredibly high rate, says Rabosky.

An unusual finding of this study is that these skinks upend the usual pattern of species diversity found in other parts of the world. We typically think of lush tropical rainforests as being the worlds major centers of diversity, says coauthor Irby Lovette, director of the Cornell Lab of Ornithologys Fuller Evolutionary Biology Program. With the skinks, just the opposite has happened: the rainforest skinks in Australia have much lower diversity, and a lot of the evolutionary action in this system is taking place in the deserts.

Over the last 20 million years, most of Australia changed from humid and tropical to bone-dry desert. Living in the desert is stressful for animals that are adapted for wetter habitats, says Rabosky. But somewhere in the distant past, a few skinks developed th
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