Study reveals why some groups of animals are so diverse

Scientists seem to have finally solved the mystery why some groups of animals evolve into hundreds, sometimes even into thousands of species, while other groups include only a few.

Washington, Sept 23 : Scientists seem to have finally solved the mystery why some groups of animals evolve into hundreds, sometimes even into thousands of species, while other groups include only a few.

For his research, lead author Dan Rabosky, from the Cornell lab of Ornithology picked up more than 252 species of lizards known as skinks from the Australian outback.

He documented where the various skink species occurred and used their DNA to define their evolutionary tree.

Findings revealed that the groups with the most species were the ones that lived in the driest parts of Australia.

"There's something about colonizing the desert that caused these skinks to diversify at an incredibly high rate," said Rabosky.

He said an unusual finding of this study was that these skinks upended the usual pattern of species diversity found in other parts of the world.

"We typically think of lush tropical rainforests as being the world's major centres of diversity. 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," said co-author Irby Lovette, director of the Cornell Lab of Ornithology's Fuller Evolutionary Biology Program.

According to the researchers, over the last 20 million years, most of Australia changed from humid and tropical to bone-dry desert.

Living in the desert proved more stressful for animals that were adapted for wetter habitats, but with the passage of time, few skinks developed the ability to survive in their increasingly arid world, Rabosky said in his study in the September 19 online edition of the Proceedings of the Royal Society B.

"Australian skinks are really fascinating. Two groups in particular have gone evolutionarily crazy, each splitting into as many as 100 different species. In contrast to skinks on other continents, and even some other groups in Australia, the diversity of these particular groups has really exploded," said Rabosky.

He said the drying of the "drying up" of Australia over the past 20 million years triggered this explosive diversification, adding that it is the descendents of these few early desert colonists that evolved into amazingly large numbers of skink species.

The study included skinks with spots, skinks with stripes, skinks with four legs, or two - or none.

ANI