Evolutionary roads to rodents.

• Author: Hardman, Chris
• Position: Americas [??]Ojo! - Brief Article

SOUTH AMERICA is home to the most diverse collection of rodents in the world. They range in size from the tiny, third-of-an-ounce pygmy rice rat to the world's largest rodent, the 140-pound capybara. They climb through the trees in search of fruits and green seeds, scour the ground for grass and leaves, or prowl the water for unwary crabs and insects. What makes this group so interesting is their evolutionary history and the mystery of why they are so different from any other group of rodents in the world.

Professor Rodney Honeycutt of Texas A&M University has been studying the evolution of rodents for nearly a decade. He is particularly interested in the large South American caviomorph rodents that include more than two hundred species, such as the capybara, agouti, paca, porcupine, and spiny rat. Because rodents account for more than half of all mammal species in the world, knowledge about their evolution can provide clues to the evolution of other mammal species as well.

Honeycutt and his colleagues--Diane Rowe, also from Texas A&M, Ron Adkins, of the University of Massachusetts, and Milton Gallardo, from the Instituto de Ecologia y Evolucion, Universidad Austral de Chile--are using molecular data to construct the rodents' evolutionary history.

"We have good evidence that suggests that South America was founded by a single ancestral stock of caviomorph relatives from Africa," Honeycutt says. He proposes that forty million years ago, the rodents hitched rides on small clumps of land that had broken off of the African mainland. Powerful currents carried the rodents across the Atlantic over twelve hundred miles from Africa to South America. "There are some currents that go between Africa and South America that have been argued to be very good vehicles for transporting organisms from one continent to the other, especially historical currents and patterns," Honeycutt explains.

The timing of the African rodents' migration to South America couldn't have been better. Many of the large grazing mammals already living...