EVOLUTION OF LAKE WHITEFISH (COREGONUS-CLUPEAFORMIS) IN NORTH-AMERICA DURING THE PLEISTOCENE - GENETIC DIFFERENTIATION BETWEEN SYMPATRIC POPULATIONS

We use electrophoretic data on dehydrogenase enzymes to examine the relatedness of sympatric populations of lake whitefish (Coregonus clupeaformis) and provide evidence for the existence of a glacial refuge race of lake whitefish in eastern North America. This Acadian race is presently found in New England, the Gaspe peninsula of Quebec, and New Brunswick. It probably survived glaciation in a refugium on the exposed coastal plain of northeastern North America. In areas of contact, most glacial races appear to introgress and do not coexist in sympatry. However, sympatric pairs of populations occur (or occurred) within the ranges of all races of lake whitefish. Allele frequencies for at least one enzyme system examined for most sympatric pairs were significantly different, indicating that these sympatric populations are wholly or substantially isolated reproductively from each other. Both members of the population pairs examined in the Yukon Territory, Ontario, and Labrador were genetically characteristic of the glacial races of their region. This suggests that they are not the result of speciation due to geographic isolation in different glacial refugia. Thus, their origin appears to be postglacial, but may be older if present genetic similarities are due to recent gene flow between sympatric forms.