Genetic evaluation of translocation in artificially isolated populations of white-spotted charr (Salvelinus leucomaenis)

Genetic population structure of artificially isolated white-spotted charr (Salvelinus leucomaenis) populations before and after translocation were examined using polymorphic microsatellite loci. We released 20 migrant females of below-dam populations in the Kame and Hitozuminai rivers, Japan, into small above-dam sites of each river, and also collected juveniles (0+ fish) of the pre-translocation and the post-translocation cohorts for DNA analyses. Reduced genetic diversity, expressed as the number of alleles and expected heterozygosity, was observed in all above-dam populations before translocation relative to below-dam populations. Highly significant genetic differentiation was also found between above- and below-dam populations. After translocation, on the other hand, genetic diversity of above-dam populations was restored to the levels of below-dam populations. Differences in gene frequencies between above- and below-dam populations were not detected after translocation. These results, in turn, suggest that the translocations in our survey had an immediate effect on the restoration of genetic diversity, and that the translocated individuals strongly introgressed into above-dam populations.