Molecular Divergence and Evolutionary Relationships in Pontoporeia (Crustacea: Amphipoda)

Abstract

To evaluate hypotheses put forward to explain the origin of the "glacial relict" faunal element in North American and Eurasian lakes, the levels of genetic divergence among species and populations of the amphipod genus Pontoporeia were studied using enzyme electrophoresis. Genetic distances among the European fresh- and brackish-water P. affinis, the North American freshwater P. hoyi, and the marine P. femorata (from Europe) ranged D = 1.5–2.8, suggesting divergence times of the order tens of million years for all these lineages. An undescribed North American coastal species (P. "affinis") was similarly distinct from P. hoyi and P. femorata, but more closely related to the European P. affinis (D = 0.5). No further systematic subdivision within these species was revealed in the examined material. The number of expressed isozyme loci was the same in P. affinis and P. femorata for all enzymes examined; the results provide no support for the hypothesis of a recent polyploidization event in the evolution of P. affinis, as earlier suspected on karyological grounds. All speculations on the role of the late Pleistocene glaciations in molding the currently recognized systematic structure of Pontoporeia were thus dismissed.