GENETIC-DIVERGENCE, BETWEEN SIBLING SPECIES LITTORINA-MARIAE SACCHI AND RASTELLI AND LITTORINA-OBTUSATA (L) (MOLLUSCA, GASTROPODA) FROM THEWHITE-SEA

Genetic comparison of two sibling species of marine gastropods, Littor ina marine Sacchi and Rastelli and L. obtusata (L.), was conducted usi ng electrophoresis of proteins encoded by 29 loci. Three loci were fix ed for different alleles, and in eight polymorphic loci allele frequen cies differed in sympatric samples. This supports earlier findings tha t these taxa are reproductively isolated and, therefore, good species. Nei's standard genetic distance between L. mariae and L. obtusata was 0.25 +/- 0.094, which is in the range normally found for congeneric s pecies. The amount of genetic variation present in both species was ve ry similar. The proportion of polymorphic loci was 0.24: +/- 0.08 in L . mariae and 0.28 +/- 0.08 in L. obtusata using the 0.95 criterion of polymorphism. The mean heterozygosity of L. mariae was 0.097 +/- 0.035 and that of L. obtusata was 0.117 +/- 0.037. Description of variation in polymorphic loci suitable for population studies and description o f diagnostic loci for species identification are given.