Genetic differentiation of white-spotted charr (Salvelinus leucomaenis) populations after habitat fragmentation:: Spatial-temporal changes in gene frequencies

Freshwater fishes that have been isolated by artificial dams have become models for studying the effects of recent barriers on genetic variation and population differentiation. In this study, we examined the genetic structure of 11 populations of white-spotted charr ( Salvelinus leucomaenis) by using polymorphic microsatellite loci. Reduced genetic diversity, expressed as the number of alleles and the expected heterozygosity, was observed in all above-dam relative to below-dam populations. Highly significant genetic differentiation ( F-ST) was found for all pairwise comparisons among populations, with F-ST-values ranging from 0.023 to 0.639. Both multiple regression analysis and a randomization test revealed that genetic differentiation above and below dams was negatively related to the habitat size of above-dam populations, and was positively related to the time period of isolation. This study is one of the few attempts to predict the population genetic structure of such variable spatial - temporal scales. We conclude that differences in genetic structure above and below dams are related to recent historical population size, whereby sites with a lower effective number of adults are more prone to temporal stochasticity in gene frequencies.