Study: Caribbean Frogs Stem From Abroad
By DAVID McFADDEN, Associated Press Writer
Sat Jun 9, 6:10 PM
SAN JUAN, Puerto Rico - More than a hundred species of tiny land-breeding frogs in the Caribbean evolved from a single South American species that probably hitched a ride on a raft of vegetation and washed up on an island beach, according to scientists who spent decades collecting tissues from the colorful hoppers.
After years of field research in dense rain forests and remote caves to catalog and collect specimens of different frogs, recent advances in genetic technology enabled researchers to compare their DNA. What they found suggests a sea voyage by an egg-laying South American frog some 30 to 50 million years ago probably led to most of the Caribbean's terrestrial frogs.
"Nothing in the anatomy of these animals told any expert who has studied them over the last century that they were actually close relatives," biologist Blair Hedges, who directed the genetic research, said Saturday from his office at Pennsylvania State University.
By lining up the genetic codes of each species of the genus Eleutherodactylus side-by-side, Hedges said he found something he'd never suspected _ the genes of almost all the 160 Caribbean frogs matched, and could be traced through thousands of generations to a single common ancestor.
Hedges and his research team sequenced and compared the DNA of roughly 300 species of frogs collected from South American, Central American and Caribbean forests to support their theory.
A previous theory proposed that frogs traveled across land bridges that linked the major Caribbean islands of Cuba, Jamaica, Hispaniola and Puerto Rico to South America until 70 million to 80 million years ago. Scientists also believed eastern and western Caribbean frogs had different ancestors.
But an analysis of the "molecular clock" in their genetic codes shows that both eastern and western Caribbean frogs diverged from a common ancestor more recently, said Hedges. A summary of his findings were published online this week in advance of Tuesday's print edition of the Proceedings of the National Academy of Sciences.
Richard Thomas, an amphibian expert from the University of Puerto Rico who was not involved in Hedges' research, described the study as "significant" and said the claim of a common ancestor for Caribbean frogs seemed "highly plausible" considering the number of genetic codes sequenced.
Understanding the frogs' ancestry and tracing their evolutionary history should help the conservation biologists who are charting their declines due to climate change, pollution and habitat destruction, Hedges said.
With some 90 percent of the Caribbean's original rain forests destroyed, biologists are racing to catalog what remains.
"Species we don't even know about are almost certainly fading away" in the Caribbean, where amphibians face rapidly diminishing habitats on some of the world's most isolated land masses, Thomas said.
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