Cryptic species diversity and evolution in the amphipod genus Hyalella within central glaciated North America: a molecular phylogenetic approach

Many benthic freshwater invertebrates are strong candidates for diversifica tion as a result of their short generation times, the divergent selection p ressures that they encounter across habitat gradients, and the insular natu re of aquatic environments. We analysed populations of the amphipod crustac ean Hyalella azteca s.l. from habitats in Ontario, Wisconsin, New Brunswick , and the Yukon Territory. Combined analysis of allozymes and the mitochond rial cytochrome c oxidase I gene revealed that H. azteca is a complex of at least seven species showing marked genetic, but little morphological diver gence. Two or more co-occurring species were detected in at least 15 of the 24 habitats. Evidence suggests that diversification has arisen as a conseq uence of both isolation in different glacial refugia and habitat specializa tion. A recent origin for the subgenus Hyalella, following the formation of the Isthmus of Panama, is improbable; the subgenus appears to have origina ted as early as the mid-Miocene.