Genetic differentiation and biogeography in southern European populations of the genus Scardinius (Pisces, Cyprinidae) based on allozyme data

Levels of genetic differentiation and variability were assessed in several populations and species belonging to the primary freshwater fish genus Scardinius by means of electrophoretic analyses of 28 enzymatic loci. We studied one population of S. acarnanicus and one of S. graecus, both endemic to Greece, seven populations of S. erythrophthalmus from Greece, Slovenia, northern and central Italy, and the single extant population of S. scardafa, a species endemic to central Italy. Patterns of genetic relationships placed the Greek species basal in the neighbour-joining (NJ) and maximum parsimony (MP) trees, S. scardafa and S. erythrophthalmus are sister species. Based on the molecular clock, the split between S. acarnanicus and S. graecus occurred around 4.3 Myr ago and the split between (S. acarnanicus, S. graecus) and (S. scardafa, S. erythrophthalmus) around 3.5 Myr ago, both after the Messinian lacustrine 'Lago Mare' phase of the Mediterranean. The separation between S. scardafa and S. erytbrophthalmus was more recent (0.5 Myr ago) and was probably the result of confluences between adjacent river basins during the Pleistocene. Within S. erythrophthalmus, the Greek population showed a certain degree of genetic differentiation, whereas northern and central Italian populations were nearly indistinguishable. These findings demonstrate the impact of the artificial introduction of this species into central Italy, leading to the near extinction of the endemic S. scardafa.