The broad biogeographic patterns that characterize the world's oceans have been well summarized using classical analyses. The application of molecular techniques, however, can additionally provide an estimate of the time elapsed since geographically isolated sister populations or species were last in genetic contact. The purpose of this proposal is to determine the pattern of genetic relationships among the snapping shrimp (Alpheus) of the eastern Atlantic, western Atlantic, and eastern Pacific. Snapping shrimp are an ideal group with which to characterize biogeographic patterns in the tropics, because of their high diversity and well documented patterns of divergence across the Isthmus of Panama (eastern Pacific, western Atlantic). The collected data will be used to answer the following questions: 1) is there evidence of recent gene flow across the Atlantic, or is the tropical eastern Atlantic fauna endemic, at least with respect to close relatives in the western Atlantic? Understanding endemicity is fundamental to the categorization and conservation of marine biodiversity, 2) if divergence across the eastern Atlantic predated that across the Isthmus of Panama (minimally 2 3 million years), when did these faunas separate based on molecular calibrations using transisthmian data? Dating trans Atlantic divergences allows molecular data sets to be compared with reconstructions based on geological or paleoceanographic studies, to their mutual benefit, and 3) do eastern Atlantic taxa reveal evidence of extinction events associated with the Isthmus of Panama, e.g. relationships between the eastern Pacific and eastern Atlantic that are closer than transisthmian relationships? Such undetected extinctions are a possible explanation for some of the variation observed across the Isthmus and, if documented, would usefully constrain our estimates for rates of molecular evolution in this model system.
