Taxon diversity in the genus Holopedium (Crustacea: Cladocera) from the lakes of eastern North America

Abstract

Although the genus Holopedium contains only two recognized species, the taxonomic status of many North American populations has been uncertain. By exploiting allozyme analysis to clarify taxonomic assignments, this study shows that Holopedium populations in the lakes of eastern North America are separated into two genetically distinct lineages. Component populations of each group show both low levels of genetic polymorphism and high genetic similarity. Aside from their genetic divergence, morphological and ecological differences among the groups support their recognition as distinct species. Holopedium gibberum is broadly distributed in the cool temperate regions of North America, while H. amazonicum occurs in the southern and eastern portions of the continent. The latter pair of species co-occur at some sites without hybridization, confirming their reproductive isolation.