COLLEGE STATION, - Forty million years ago, rodents from Africa may have colonized South America by rafting or swimming across the Atlantic, Texas A&M University biologists theorize by studying the evolution of rodents, looking at their genes instead of their fossils - an approach that promises to revolutionize the field of evolutionary biology.
"We have good evidence that suggests that South America was founded by a single ancestral stock of caviomorph relatives from Africa," says Rodney Honeycutt, a Texas A&M professor of biology who has been studying the evolution of rodents for the last eight years.
"The radiations of these rodents to South America are too young for continental drift to have played a role in their colonization by African ancestors. This presents a dilemma, because either caviomorph ancestors dispersed to South America from Africa over water (e.g., by rafting) or the caviomorph radiations are considerably older than suggested by the paleontological evidence. We're seeking answers by using molecular data to address these questions."
Honeycutt, his Ph.D. student, Diane Rowe, and a former student, Ron Adkins from the University of Massachusetts, are using genetics to study the evolution of South American and African rodents. The approach has been to sequence specific genes from several diverse rodent species and then use changes in these genes to reconstruct the evolutionary history of these rodents.
Scientists sequenced genes of several rodents and looked at the changes - or mutations - among the genes. Then they compared the number of changes between the genetic sequences of the rodents and constructed the rodents' evolutionary tree.
"We found that the South American and African radiations were unique but they do share a common ancestry," Honeycutt says, adding that the time when the two groups diverged may be considerably older (45 million years) than what the fossils are suggesting (36 million years).
Contact: Judith Whtie
Texas A&M University