GENETIC SIMILARITY AMONG ZEBRA MUSSEL POPULATIONS WITHIN NORTH-AMERICA AND EUROPE

The zebra mussel Dreissena polymorpha has rapidly established both con tiguous and disjunct populations during its spread through eastern Nor th America. If new colonies are founded by small numbers of individual s, populations with markedly different genetic and phenotypic characte rs could arise (founder effect); this possibility could confound ecolo gical comparisons of populations from different geographic locations. We analyzed genetic differentiation among 18 populations of mussels fr om the Great Lakes and seven populations from Europe using starch-gel electrophoresis. Analysis of 27 proteins yielded data from 15 polymorp hic loci and one monomorphic locus. The data indicated that zebra muss els in North America have the same high genetic variability (H-o = 0.3 0-0.43) that is found in European populations (H-o = 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 distance s between populations were small (0.004-0.028) compared with distances among populations of other mollusc species (0.023-0.184). Like popula tions from Europe, populations within North America were not highly di fferentiated, which suggests that founder populations have not been sm all and (or) frequent genetic mixing has occurred. European population s clustered seperately from North American populations (Nei's distance = 0.058).