Nearly all of the 162 land-breeding frog species on Caribbean islands, including the coqui frogs of Puerto Rico, originated from a single frog species that arrived on a sea voyage from South America. They came 30 to 50 million years ago, according to DNA-sequence analyses by scientists at Penn State.
Similarly, the scientists found that the Central American relatives of these Caribbean amphibians also arose from a single species that arrived by raft from South America.
"This discovery is surprising because no previous theories of how the frogs arrived had predicted a single origin for Caribbean terrestrial frogs, and because groups of close relatives rarely dominate the fauna of an entire continent or major geographic region," said Blair Hedges of Penn State, an evolutionary biologist who directed the research. "Because connections among continents have allowed land-dwelling animals to disperse freely over millions of years, the fauna of any one continent is usually a composite of many types of animals."
The results will be published in the June 12, 2007 issue of the Proceedings of the National Academy of Sciences and posted in the journal's online early edition this week.
The field work for the study required nearly three decades to complete because many of the species are restricted to remote and isolated mountain tops or other inaccessible areas. Some species included in the study are believed to be extinct because of habitat degradation and other causes.
"This study is a valuable contribution to our understanding of the evolutionary and biogeographic history of one of the world's most complicated places geographically, the Caribbean," said Patrick Herendeen, program director in the National Science Foundation's division of environmental biology, which funded the research. "The research presents strong evidence that this group of frogs reached the Caribbean islands by dispersal."