Rapid evolution of reproductive isolation in the wild: Evidence from introduced salmon

Colonization of new environments should promote rapid speciation as a bypro duct of adaptation to divergent selective regimes. Although this process of ecological speciation is known to have occurred over millennia or centurie s, nothing is known about how quickly reproductive isolation actually evolv es when new environments are first colonized. Using DNA microsatellites, po pulation-specific natural tags, and phenotypic variation, we tested for rep roductive isolation between two adjacent salmon populations of a common anc estry that colonized divergent reproductive environments (a river and a lak e beach). We found evidence for the evolution of reproductive isolation aft er fewer than 13 generations.