Morphological and genetic differentiation between allopatric populations of a freshwater amphipod

The morphological and isozyme variation in 17 populations of the freshwater amphipod genusParamelitawas investigated to see whether morphological differences were genetically based. On the whole, morphological and genetic differentiation coincided, and could be related to geographical distribution. Five distinct genetic groups, separated at Nei's (1978) genetic identity values below 0‐35, and possessing diagnostic alleles, were identified. Discriminant functions and cluster analyses confirmed that these genetic clusters were phenotypically distinct. It was concluded that these groups were sufficiently different to warrant the recognition of five species, four of which were new, and as yet, undescribed.