Do freshwater ecoregions and continental shelf width predict patterns of historical gene flow in the freshwater fish Poecilia butleri?

We examined historical patterns of gene flow in the freshwater fish Poecilia butleri in western Mexico. We tested the hypothesis that the boundaries between four freshwater ecological communities (ecoregions) might have limited the movement of P. butleri because changes in species compositions might restrict establishment between adjacent ecoregions, even in situations where a physical barrier is absent. Hence, we predicted that boundaries between ecoregions should correspond to phylogeographical breaks in P. butleri. We also tested the hypothesis that the width of the continental shelf affected historical gene flow in P. butleri because a broad continental shelf provides a greater opportunity for rivers to coalesce during historical episodes of low sea levels as opposed to a narrow continental shelf that should restrict the potential for gene flow among adjacent rivers. Hence, we predicted greater amounts of historical gene flow among neighbouring river basins in the region of western ...