THE EFFECT OF NATURAL-SELECTION ON ESTIMATES OF GENETIC-DIVERGENCE AMONG POPULATIONS OF THE ATLANTIC SALMON

The effect of natural selection on the mMEP-2 locus on measures of ge netic divergence among Atlantic salmon populations was investigated by examining the pattern of change in the level of genetic differentiati on (F-ST) averaged over loci when data on the mMEP-2 locus were eithe r included or excluded. The level of F-ST among populations at various geographic scales was estimated from allele frequencies at up to four loci ((s)AAT-4, IDDH-1*, IDHP-3*, and mMEP-2*). At smaller geographi c scales (within river systems or limited geographic regions) levels o f variance in mMEP-2 allele frequencies were reduced relative to mean levels. At larger geographic scales (across continents or the species range) variation in mMEP-2 allele frequencies was greater than mean levels. These results suggest an a priori hypothesis for the effect of selection on the mMEP-2 locus which may be applied in future studies on variation in protein coding or other (e.g. mini-and microsatellite ) loci in the Atlantic salmon. It is recommended that estimates of gen e flow among populations of the Atlantic salmon based on mean F-ST est imates which include data on the mMEP-2 locus should be viewed with c aution. (C) 1997 The Fisheries Society of the British Isles.