GENETIC-VARIATION IN THE STYGOBITE AMPHIPOD NIPHARGUS-RHENORHODANENSIS - COMPARISON OF 4 HYPORHEIC POPULATIONS OF THE RHONE AND THE AIN RIVERS (FRANCE)

Electrophoretic allozyme analysis was performed on the stygobite amphi pods Niphargus rhenorhodanensis collected from the sediments of four l ocations, three on the River Rhone and one on its tributary, the River Ain. Six enzymes, encoded by seven presumptive loci, were examined. F our loci were monomorphic, while three were polymorphic, with three al leles segregating at the AO, GPI and EST loci. The four populations se em to belong to a panmictic unit, with little genetic differentiation among populations. Thus, gene flow among populations does not appear t o be impeded by either geographic distance (15 to 60 km) or the presen ce of dams on the River Rhone. At the scale of the study, and with thi s method, an ancestral genetic unit seems to have existed for the indi viduals of the Rhone and Ain Rivers, owing to recolonization after the last glaciations (12,000 years ago), but homogenization of genetic pa tterns may also have resulted from extensive migrations not expected a ccording to the biology of this stygobite species.