BERMINGHAM, E.; Smithsonian Tropical Research Institute, Republic of Panama: Evolutionary assembly of the Mesoamerican freshwater fish fauna

Over the past 2-7 million years there has been extensive intercontinental exchange of flora and fauna between North and South America across the isthmian bridge of Panama, a phenomenon known as the Great American Interchange because of its importance for New World biogeography. Although freshwater fishes participated in the Great American Interchange, biogeographic studies of this group are few in comparison to the detailed and instructive studies of mammals. Yet, because the dispersal of primary freshwater fishes depends on direct connections between drainage basins, historical biogeographic analysis of freshwater fishes permits strong inference regarding the biotic and geologic evolution of Mesoamerica. Using molecular systematic approaches, we have taken advantage of the unique isthmian experiment to investigate the modern assembly and diversification of a biota. We show that the primary freshwater fish fauna of Mesoamerica assembled in a relatively brief period of time, and posit several distinct, but relatively recent waves of invasion from putative source populations in northwestern Colombia. In subsequent colonization episodes the geographic scale of the dispersion of lineages was progressively more limited, a pattern we attribute to both biological contingency and landscape evolution. Thus, the fish eye view of Mesoamerica suggests a complex biogeographic history of overlaid cycles of colonization, diversification, sorting and extinction of lineages.