Placing the Floridian Genetic Break for Nearshore Taxa into a Regional Phylogenetic Perspective Using Three Lineages of Marine Mussels

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Understanding spatio-temporal patterns of biotic diversity represents one of the central challenges facing ecologists and systernatists. This challenge is particularly acute in the marine environment where we are only just now beginning to comprehend the evolutionary processes which have produced the epic diversity evident in tropical nearshore faunas. A central paradox in marine evolution is how speciation rates in many clades are sufficiently high to produce large sibling species complexes on geographic scales that are dwarfed by the dispersal potential of their planktonic larval stages. The aim of this project is to address how the Gulf-Atlantic genetic disjunction for regionally distributed Caribbean morphospecies scales relative to the genetic structuring experienced over the rest of their collective geographic ranges. Three distinct phylogenetic trajectories are hypothesized that hinge on whether the Gulf--Atlantic genetic disjunction for individual study taxa originated early in the history of the Miocene Suwannee Seaway, or postdated it's Pliocene closure, and whether or not genetic cohesiveness has been maintained across oceanic barriers to dispersal. These hypotheses will be tested using three exemplar mytilid morphospecies chosen on the basis of their appropriate geographic ranges, ecological abundance in distinct coastal habitats, availability of reference congeners on the Pacific side of the isthmus of Panama, and possession of rapidly evolving paternally -transmitted mitochondrial lineages. Mitochondrial and nuclear gene trees will be generated for population samples spanning the southeastern Florida genetic break, the oceanic dispersal barrier to Bermuda, and representative locations in the Caribbean Basin. Sampling of Caribbean/eastern Pacific congeners will allow the identification of transisthmian reference geminate species and provide a meaningful temporal perspective for the intraspecific gene tree topologies. The project promises to yield important new insights into the nature and origin of biotic diversity in both this regional fauna and in the broader marine environment.