Allele frequence variation at the EST-2 locus in Arctic charr: Is it clinal?

Abstract

The geographical distribution of allele frequencies at the EST-2 locus in Arctic charr (Salvelinus alpinus (L.)) was studied by examining literature data for 209 Arctic charr populations from most of the species range. A non-significant positive correlation was demonstrated between the frequency of the EST-2 (100) allele and latitude. This result is contrary to the suggestion by Nyman and Shaw (1971; Comp. Biochem. physiol. 40B: 563–566) that these variables are negatively correlated as a result of selection against the EST-2 (100) allele at low temperatures. Three observations suggest that genetic drift may often override possibly existing temperature-dependent selection in determining esterase allele frequencies in the Arctic charr. Firstly, esterase allele frequencies show considerable variation within restricted geographical areas. Secondly, fixation for either of the esterase alleles is common in small populations. Thirdly, the proportion of populations fixed for one allele varies with the regional average frequency of that allele. On this background, selection appears to be of less importance in determining esterase allele frequencies in the Arctic charr than has hitherto been suggested.