GENETIC DIFFERENTIATION IN HEDISTE DIVERSICOLOR (POLYCHAETA, NEREIDIDAE) FOR THE NORTH-SEA AND THE BALTIC SEA

Genetic differentiation between North Sea and Baltic Sea Hediste diver sicolor (O.F. Muller, 1776) (Polychaeta: Nereididae) populations was s tudied by allozyme electrophoresis on starch gel. Thirteen loci were a nalyzed in eight populations. The level of genetic variation was very low (mean H-o = 0.000 to 0.015). Differentiation between H. diversicol or populations is quite high (F-ST = 0.892) and reflected by three enz yme loci (MDH-I, MDH-II*, IDH-I*). The reduced gene flow (N-m < 1) ma y be explained by the limited dispersal capacity of the species. Regar dless of whether found in the North Sea or Baltic Sea, there appear to be two different genetic types which are parapatric or sympatric in s ome places. The two types hybridize at three localities, but no signs of hybridization have been found at one (Tallinn).