Gene-Enzyme Variation in Three Sympatric Species Oflittorina. Ii. The Roscoff Population, With a Note on the Origin of North Americanl. Littorea

Gene-enzyme variation was examined at ten to fifteen loci in three sympatric species of Littorina collected from Cape Cod, Massachusetts and Roscoff, Brittany. The North American and French populations of L. saxatilis and L. obtusata were, in general, quite similar in allele content and frequency. In contrast, the North American and French populations of L. littorea were genetically differentiated at a majority of their loci. This pattern of heterogeneity in the three species, along with calculated values of average heterozygosity, suggests that North American specimens of L. littorea are not recent colonists from Europe and have passed through a severe population bottleneck on the North American continent. Survey studies carried out over a four year period revealed a general pattern of temporal constancy in allele frequency in all three species.