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

Abstract

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