Genetic similarity among zebra mussel populations within North America and Europe

The zebra mussel Dreissena polymorpha has rapidly established both contiguous and disjunct populations during its spread through eastern North America. If new colonies are founded by small numbers of individuals, populations with markedly different genetic and phenotypic characters could arise (founder effect); this possibility could confound ecological comparisons of populations from different geographic locations. We analyzed genetic differentiation among 18 populations of mussels from the Great Lakes and seven populations from Europe using starch-gel electrophoresis. Analysis of 27 proteins yielded data from 15 polymorphic loci and one monomorphic locus. The data indicated that zebra mussels in North America have the same high genetic variability (Ho = 0.30–0.43) that is found in European populations (Ho = 0.27–0.35) and is typical of molluscs. Little variation appears to have been lost when zebra mussel were transported to North America. Nei's genetic distances between populations were small (0.004–0.028) compared with distances among populations of other mollusc species (0.023–0.184). Like populations from Europe, populations within North America were not highly differentiated, which suggests that founder populations have not been small and (or) frequent genetic mixing has occurred. European populations clustered seperately from North American populations (Nei's distance = 0.058).