Differentiation of rainbow trout (Oncorhynchus mykiss) populations in Lake Ontario and the evaluation of the stepwise mutation and infinite allele mutation models using microsatellite variability

Microsatellites, comprising (GT)\dn6 n tandemly repeated arrays, were isolated from a size-selected genomic library of rainbow trout (Oncorhynchus mykiss) DNA. Primers were designed for five microsatellite loci, four of which were variable. Primers for two of these loci were used in conjunction with primers for three microsatellite loci from a related species, Salmo salar, to investigate patterns of differentiation in freshwater migratory populations of rainbow trout in Lake Ontario. The five loci used revealed high levels of polymorphism with heterozygosity estimates ranging from 0.740 to 0.956. Significant differences in allele frequencies among populations were observed for all loci. Heterozygosity and allele number values, at each locus for each population, were used to test two alternative mutation models, the infinite allele model (IAM) and the stepwise mutation model (SMM). The predictions of the IAM proved to be more accurate for the majority of the data and this model was used to calculate estimates of effective population size.