Texas Researchers Compile Largest Genetic Data Set For Most Accurate Frog Family Tree Ever

AUSTIN, TX — New research from University of Texas at Austin scientists shows a mass extinction 66 million years ago sparked an explosion of new frog species—a finding that will aid in reconstructing a long-sought accurate family tree for the amphibians.

Scientists have long struggled to build the amphibious family tree, researchers noted. Based on fossils and limited genetic data, it's long been believed that most modern frog species popped up at a slow and steady pace from about 150 million to 66 million years ago.

But now, scientists from The University of Texas at Austin, the University of California, Berkeley, the Florida Museum of Natural History and Sun Yat-Sen University in China have compiled the largest set of frog genetic data ever evaluated for evolutionary relationships to draw the most accurate frog family tree to date. They found evidence of not one but three explosions of new frog species, on different continents, and all concentrated in the aftermath of the mass die-off of most dinosaurs and many other species about 66 million years ago, according to a university advisory on the findings.

The findings suggest a mass extinction event at the end of the Cretaceous—largely caused by an asteroid striking the Earth—also wiped out most of the frog species that were alive then, leaving behind only a few survivors. "With many other species also wiped out, the slate was wiped clean," scientists said. There were many new ecological niches that the remaining frogs could spread into, providing a sort of evolutionary rocket fuel for their rapid diversification, scientists noted.

“We know that the mass extinction event wiped out most of the dinosaurs, except for a few bird species, which then exploded in diversity and became one of the dominant groups of land animals,” David Hillis, professor of integrative biology at UT Austin and co-author of a paper appearing this week in the journal Proceedings of the National Academy of Sciences said. “As we look at more and more groups of life, we see the same pattern, and that turns out to be the case for frogs as well.”

The research reinforces earlier findings, also by UT Austin scientists, that provide heft to the argument that mass extinction events can lead to unusual spurts of evolutionary activity, scientists noted.

The new paper’s corresponding authors are David Cannatella at UT Austin, David Wake of the University of California, Berkeley, and Peng Zhang of Sun Yat-Sen University. Other authors include Yan-Jie Feng and Dan Liang of Sun Yat-Sen; and David Blackburn of the Florida Museum of Natural History.

The researchers gathered genetic samples from 156 frog species and combined it with previously published data on 145 more species to build the most complete frog family tree yet, scientists eplained. In the new samples, they studied variations in 95 genes—compared with past studies that used only 5 to 12 genes—to get a much higher-resolution view of how individual species relate to one another, scientists added.

Today, there are more than 6,700 known frog species, representing 55 families and living in a wide range of habitats from trees to aquatic environments to underground. This study significantly tightens the time frame in which this diversity came about, according to the findings.

Support for the research was provided by the U.S. National Science Foundation, the National Natural Science Foundation of China and the National Youth Talent Support Program and National Science Fund for Excellent Young Scholars of China.

>>> Photo: A tree frog (genus Boophis) found on Madagascar and Mayotte Island, off the Southeast coast of Africa.Brian Freiermuth/Univ. of Florida