Intrapopulation variation of the esterase-2 polymorphism in the serum of anadromous arctic charr, salvelinus-alpinus, from a northern labrador river

Intrapopulation variation of the diallelic Esterase-2 (serum esterase) polymorphism in the Arctic charr, Salvelinus alpinus, was studied in an anadromous population from the Ikarut River in northern Labrador. Differences in genotype frequencies observed between two sampling years, between sexes, and between juvenile and mature fish were not significant. However, considerable variation was found in the allele frequencies among year-classes. Furthermore, the allele frequency variation was associated with temperature; the frequency of the fast allele, F, was positively correlated with the mean summer temperatures in the year of hatching. The same type of association has been found in a Swedish population. Temperature-dependent selection in late incubation or post-hatching in the fry or fingerling stage could explain the observed association. The nonrandom distribution of the variation within populations has important implications for the use of the polymorphism in stock discrimination work and for the interpretation of interpopulation variation.