We employ a battery of 33 polymorphic microsatellite loci to describe geographical population structure of the mangrove killifish ( Kryptolebias marmoratus ), the only vertebrate species known to have a mixed‐mating system of selfing and outcrossing. Significant population genetic structure was detected at spatial scales ranging from tens to hundreds of kilometres in Florida, Belize, and the Bahamas. The wealth of genotypic in...