Speciation in Freshwater Fishes

The extraordinary species richness of teleost fishes has attracted much research on mechanisms and modes of speciation. We here review research on speciation in freshwater fish in light of speciation theory, and place this in a context of knowledge about broad-scale diversity patterns in freshwater fishes. We structure our review around the major axes of divergence during speciation in freshwater fishes. These include transitions between marine and freshwater habitats, transitions between lake and stream habitats, and ecological transitions within habitats, as well as allopatric differentiation without distinct niche shifts. Major research directions in the years to come include integrating genomics with evolutionary ecology in studies of freshwater fish speciation, understanding the transition from extrinsic environment-dependent to intrinsic reproductive isolation and its influences on species persistence, and understanding the extrinsic and intrinsic constraints to speciation and how these relate to broad-scale diversification patterns through time.