DIVERGENCE IN PROTEINS, MITOCHONDRIAL-DNA, AND REPRODUCTIVE COMPATIBILITY ACROSS THE ISTHMUS OF PANAMA

It is widely believed that gene flow connected many shallow water popu lations of the Caribbean and eastern Pacific until the Panama seaway c losed 3.0 to 3.5 million years ago. Measurements of biochemical and re productive divergence for seven closely related, transisthmian pairs o f snapping shrimps (Alpheus) indicate, however, that isolation was sta ggered rather than simultaneous. The four least divergent pairs provid e the best estimate for rates of molecular divergence and speciation. Ecological, genetic, and geological data suggest that gene flow was di srupted for the remaining three pairs by environmental change several million years before the land barrier was complete.