TAXON DIVERSITY IN THE GENUS HOLOPEDIUM (CRUSTACEA, CLADOCERA) FROM THE LAKES OF EASTERN NORTH-AMERICA

Although the genus Holopedium contains only two recognized species, th e taxonomic status of many North American populations has been uncerta in. By exploiting allozyme analysis to clarify taxonomic assignments, this study shows that Holopedium populations in the lakes of eastern N orth America are separated into two genetically distinct lineages. Com ponent populations of each group show both low levels of genetic polym orphism and high genetic similarity. Aside from their genetic divergen ce, 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. a mazonicum occurs in the southern and eastern portions of the continent . The latter pair of species co-occur at some sites without hybridizat ion, confirming their reproductive isolation.