ALLOZYME EVIDENCE OF GENETIC DIFFERENTIATION BETWEEN POPULATIONS OF HEDISTE DIVERSICOLOR (POLYCHAETA, NEREIDIDAE) FROM THE WESTERN MEDITERRANEAN

The occurrence of genetic differentiation among western Mediterranean Hediste diversicolor (Polychaeta: Nereididae) populations was assessed by allozyme electrophoresis on cellulose acetate. Seventeen loci were analysed in four populations. The level of the genetic variability wa s markedly low (mean H-L range: 0 . 014-0 . 034), but comparable to th at of other brackish water nereidids. The values of Nei genetic distan ce index (D) confirm the existence of genetic differentiation between the geographically isolated populations at Venice, Elba, Navicelli and Serchio D range: 0 . 128-0 . 356). However, the two samples from Serc hio and Navicelli, similar to 15 km apart, were not genetically differ ent (D=0 . 00005). The level of genetic differentiation in H. diversic olor populations followed the isolation-by-distance model. Reduced gen e flow among H. diversicolor populations may be explained by its limit ed dispersal capacity and the eco-physiological barriers that occur be tween different brackish habitats.