FRESHWATER FISH SET LIMITS TO THE AGE OF THE PANAMA ISTHMUS

We will use the biogeographic history of primary freshwater fish to test alternate ages of the completion of the Panama land bridge connecting the South and North American continents. The timing and pattern of colonization of freshwater fish in Mesoamerica from their source in South America will be modeled using molecular clocks and phylogenetic hypotheses based on mitochondrial and nuclear DNA sequences. Given that the biogeographic spread of primary freshwater fishes is constrained by their physiological intolerance to sea water, freshwater fish provide a strong signal of the geographic development of terrestrial landscapes. Although the phylogenetic history of freshwater fish in Mesoamerica establishes a complex colonization history for the region, it is noteworthy that the freshwater fish fauna is donimated by young taxa that have most probably dispersed north from northwestern South America since the Pliocene.