Caribbean Frogs Spread After Meteor?

June 11, 2007 — The same meteor impact that wreaked havoc with dinosaurs may have been the making of 162 species of Caribbean frogs, which descended from a single South American species, according to a new study.

All of the frogs are an odd sort — having no tadpole phase, instead hatching complete out of eggs. The 800 or so species of these Eleutherodactlus frogs — make up a fifth of all living frog species and compose the largest vertebrate genus.

In the world of biological classification, however, bigger is not necessarily better, explained Blair Hedges, a biologist at Pennsylvania State University.

"The reason it's been the largest genus of vertebrates is because it's a taxonomic waste can," said Hedges. "These frogs don't give you a lot of characteristics to work with." In other words, many frog species fitting the same general description were dumped into the same genus — a level of classification just above species — simply for lack of better information.

Hedges and his coworkers have used genetic analysis to re-organize the waste can into a proper map of the Eleutherodactlus family tree.

Their study, which reveals a Caribbean branch to the family tree and supports the meteor impact connection, appears in the June 12 issue of the Proceedings of the National Academy of Sciences.

"Hedges and coworkers have tackled a vexing problem," said biologist David Wake of the University of California at Berkeley. What they found is that the very large number of frogs on Caribbean islands evolved there in the last 50 million years, after an initial invasion of a single species from South America.

"This puts a new light on this radiation (of new species), and on the history of the Caribbean area," said Wake. It's also interesting, he said, that there were no later invasions of frogs from the mainland.

That could be because the ancestral Caribbean Eleutherodactlus frogs found the islands freshly wiped clean of predators by a mile-high, meteor-made tsunami.

"That may be why we're not finding old Caribbean groups," Hedges told Discovery News. The gigantic wave, triggered by the same meteor impact which created the Chicxulub crater off Mexico's Yucatan Peninsula, is believed to have scrubbed the Caribbean islands clean of life 65 million years ago, said Hedges.

The event created a unique opportunity for the first frogs arriving afterward.

That ancestral good luck of the Caribbean frogs is now apparently running out, said Hedges, in the face of a force almost powerful as a tsunami — deforestation.

"Ninety percent of their original habitat is gone. In some cases it's 100 percent in the lowland mahogany forests that are now furniture in Europe," he said.

In fact, just as biologists are beginning to understand how the Caribbean came to be, many of the species included in the study have already been driven to extinction.