Abstract

Arctic Char Salvelinus alpinus have colonized northern postglacial lakes within the last few thousand years. Divergent populations have adapted to thrive in the prevailing oligotrophic environments and thus have developed morphotypes with different ecological behaviors. The morphotypes usually differ in size, morphology, coloration, feeding ecology, and/or habitat occupancy. Although morphotypes that have very divergent spawning seasons should become genetically segregated, genetic differentiation, in most cases, has been weak. Thus, results to date have suggested that Arctic Char morphotype separation has been driven largely by the environmentally mediated phenotypic plasticity of the species, with differentiation between morphotypes having commenced too recently to generate substantial genetic drift. Here we used the major histocompatibility (MH) class II genes in an attempt to isolate sympatric Arctic Char morphotypes known to be ecologically differentiated. These morphotypes are from postglacial lakes in both Siberia and eastern Canada, and differ in either diet, habitat occupancy, or both. The MH Class II allelic polymorphism was significantly different between morphotypes. This suggested there is differential heritable adaptation to the natural selection exerted by pathogens unique to each ecological niche within each lake.