A genetic assessment of single versus double origin of landlocked Atlantic salmon (Salmo salar) from Lake Saint-Jean, Quebec, Canada

We assessed the genetic relationships among landlocked populations and parapatric anadromous populations of Atlantic salmon (Salmo salar) from the Saguenay River system to infer the alternative scenarios of single versus double origin of salmon in Lake Saint-Jean, Quebec, Canada. We predicted that the hypothesis of double origin would be supported by the closer relationship of some landlocked populations to anadromous ones than to other landlocked populations. Alternatively, the single-origin scenario would be supported if landlocked populations were genetically closer to each other than to anadromous populations. Contrasting results of population differentiation at microsatellite loci were obtained with statistical treatments involving allelic frequency alone (theta, D-CE) or incorporating mutational differences (R-ST, (delta mu)(2)). A closer relationship among all landlocked populations of Lake Saint-Jean compared with anadromous ones was observed in analyses that only incorporated allele frequency information. In contrast, analyses incorporating allelic size variance all supported a closer relationship between the Metabetchouane population and other populations from outside Lake Saint-Jean. We discuss the possible factors responsible for these apparently contradictory results and propose alternative historical scenarios potentially responsible for the salmon population structure in Lake Saint-Jean.