University of Texas at Austin

Tuesday, March 24, 2009

Follow data, find frogs

Dendrobates mysteriosus is from the transition between the Andes Mountains to Amazonia in northeastern Perus.

Dendrobates mysteriosus is from the transition between the Andes Mountains to Amazonia in northeastern Perus.

Detectives follow the evidence. Reporters follow the money. Scientists follow the data.

They might not know where these things will lead, but, one way or another, it should be the truth—or at least as close to it as they can get.

Juan Santos, a Ph.D. student in integrative biology, followed the data from the Amazon River basin up into the Andes Mountains and back to the Amazon to show that a major portion of the Amazon’s poison frogs were mountain grown.

Santos published the study in study published in PLoS Biology. His adviser David Cannatella, a professor of integrative biology, was a co-author.

Poison frogs are widespread across northern South America and very diverse in Amazonia and Choco, a region along the Pacific Coast, Santos said.

It had been thought that the Amazon’s frogs started out there and spread to other parts of South and Central America.

That seemed reasonable enough, but to Santos those frogs up in the Andes were a puzzle.

“They seem to be very restricted in their distribution and very diverse genetically,” Santos said. Those are two things that wouldn’t be expected if frogs had hopped up from the Amazon.

Santos said the study’s results reshape the understanding of the origins of the amazing diversity of the New World Tropical region.

“They strongly suggest that the terrestrial diversity is highly dynamic and involves the geological history of South America,” he said.

Santos and a team of researchers created an evolutionary tree, or phylogeny, using 223 of the 353 species of poison frogs known from throughout this region.

In analyzing the evolutionary relationships among the poison frogs, they discovered that Amazonian diversity is the result of at least 14 dispersals of ancestral frogs into the region beginning about 23 million years ago.

Since then a large inland system of water covering the Amazon Basin has come and gone, the Andes Mountains started their uplift (about 15 million years ago) and the Amazon River was formed (about nine million years ago).

Santos said the researchers knew they were onto something unusual as the tree of the relationships between the frogs filled out.

“I think that we had a hunch after we saw the phylogeny (tree of evolutionary relationships) among the poison frogs,” Santos said. “This gave us a strong feeling that the Andean poison frogs were actually much older than those of the lowlands and this led to our analysis that helped us to reconstruct the ancestral distributions of the entire family.”

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