Tiny Jamaican Tree Crab Made Big And Fast Evolutionary Leap, Scientist...( -are not related to crabs on theother ...)

The research team includes Hedges, Christoph D. Schubart, of the University of Southwestern Louisiana, and Rudolf Diesel, of Bielefeld University in Germany. Schubart collected 22 crab species from Jamaica and surrounding areas, including Venezuela and Panama, then brought them to Penn State for genetic research in Hedges's lab. "We sequenced two genes from each of these species, which gave us a little over a thousand base pairs--enough to say statistically that all the terrestrial Jamaican crabs form a single group," Hedges says.

The genes used in the study have accumulated mutations at a fairly constant rate relative to one another during their evolution, so the researchers could use the changes like the ticking of a molecular clock to trace the history of each species back to its origin. "The clock-like mutations in the gene sequences start ticking away as soon as a new species evolves, so the molecular clock takes you back to the actual time of origin of the species," Hedges explains.

The scientists calibrated this molecular clock to an evolutionary event well established by geological studies, the closing of the Panama land bridge between North and South America 3.1 million years ago that separated species of marine crabs into two breeding groups--those living on the Caribbean side of Panama and those living on the Pacific side. Using this date as a secure calibration point--and the mutation rate for the two genes from related crabs on either side of Panama as a timing device--the researchers were able to determine how long ago all of their 22 crab species originated.

"We found that these Jamaican land crabs began evolving only 4 million years ago, so their evolution has been quite rapid," Hedges says. "This date makes sense because it corresponds to a time in Jamaica's geologic
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Contact: Barbara K. Kennedy
science@psu.edu
814-863-4682
Penn State
27-May-1998