Genetic differentiation between Tasmanian cultured Atlantic salmon (Salmo salar L.) and their ancestral Canadian population:: comparison of microsatellite DNA and allozyme and mitochondrial DNA variation

Atlantic salmon (Salmo salar) were imported to Australia from the River Philip, Nova Scotia, in the mid-1960s. A population was established in New South Wales, and in the mid-1980s ova from this population were used to found the Tasmanian salmon aquaculture industry. An allozyme and mitochondrial DNA examination of the Tasmanian and parent Canadian populations in 1993 showed some small but significant allele frequency differences between the two samples for one of seven polymorphic allozymes and for mitochondrial DNA haplotypes. However, there was no evidence of reduced genetic variability in the Tasmanian sample. The same individual fish from both populations have now been examined for eight polymorphic microsatellite loci. Small but significant differences in allele frequencies between the two samples were found for four of the eight loci, and there was evidence of a small overall loss of genetic variation (both heterozygosity and alleles) in the Tasmanian sample. Mean heterozygosity per microsatellite locus was more than twice that per allozyme locus: for the Tasmanian fish 0.434 (n = 63) (0.207 for allozymes) and for the Canadian fish 0.509 (n = 63) (0.182 for allozymes). Estimates of per-generation effective population sizes were calculated to be 65.2 +/- 19.7 (s.d.) from the microsatellite data, 106.1 +/- 74.4 for the allozymes data and 70.1 +/- 19.4 for the combined data set, assuming allele frequencies in the River Philip sample represent those in the progenitor population and ten generations of isolation. Microsatellite loci, with higher numbers of alleles and higher heterozygosities, are more sensitive than allozyme loci to changes in effective population size. (C) 1999 Elsevier Science B.V. All rights reserved.