How did two tiny brown frogs end up on islands off the coast of West Africa when their closest known relative lives in East Africa? That's one of the questions Academy scientist Bob Drewes and graduate student Josef Uyeda asked themselves when they examined the DNA sequences of two frogs from the islands of São Tomé and Principé this summer. They had originally sequenced the DNA to determine whether or not the frogs were correctly assigned to the same species. The data demonstrated that São Tomé’s frogs were substantially different from those on Principé and should be reclassified as a new species. More surprising, the DNA sequences also indicated that the two species were much more closely related to East African frogs than to their neighbors on the West African mainland. The key to understanding this puzzle, Drewes explained, may be the old age of the islands. "The islands are much older than most of the mountain chains that now function as barriers in central Africa. In the late Pliocene, the entire Congo Basin was most likely a lake. The ancestors of these frogs may have floated out to the islands on large rafts of land that broke off from the banks of the Congo River and followed the currents to the west."
