Gene Flow and Genetic Differentiation among California Coastal Rainbow Trout Populations

Abstract

Present levels of genetic variability and estimates of historical rates of gene flow were obtained by analyses of allele frequency data from 31 California coastal rainbow trout populations. Genetic variability was higher than seen in most salmonid species. Seventy-one electrophoretic alleles were segregating at 24 loci. Seven loci were monomorphic. Between-population genetic indentities were high and there was only a weak relationship between geographic proximity of populations and genetic identity. Average within-population heterozygosity and percent polymorphic loci were 0.092 and 35.1, respectively. Estimated total heterozygosity was 0.106; therefore, 86.8% of the total gene diversity could be ascribed to within-population genetic variation. The remaining 13.2% of the total gene diversity represented genetic differences between rainbow trout populations. Both qualitative and quantitative methods of analyses suggested that historical rates of gene flow were high; realized gene flow was estimated to be at least 1.7 migrants per population per generation. It is argued that each population's allele frequencies may simply be expression of temporal fluctuations around the panmictic allele frequencies of the greater global population.