Population genetic structure and postglacial colonization of Atlantic salmon (Salmo salar) in the Baltic Sea area based on microsatellite DNA variation

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Abstract
The genetic structure and phylogeography of Atlantic salmon (Salmo salar) across the Baltic Sea basin and neighbouring areas (eastern Atlantic Ocean, North Sea, Barents Sea, White Sea, and two Russian lakes, Onega and Ladoga) were studied to resolve the partly contradictory hypotheses of the species' postglacial colonization history. Thirty-eight populations (total of 2180 individuals) were studied for nine DNA microsatellite loci. Within the Baltic Sea, the anadromous populations formed three clear groups, corresponding to the northern (Gulf of Bothnia), eastern (Gulf of Finland and eastern Baltic Main Basin), and southern regions (western Baltic Main Basin). The genetic differences among these three groups were clearly greater (GGB5.6%; GGBbeing the proportion of diversity components between regions within basins) than were those among population groups in the eastern Atlantic Ocean (GGB2.2%) from Ireland to the White Sea. The isolation-by-distance model explained part of the differentiation within, but not between, the regions. The results strongly indicate colonization of the Baltic Sea by at least three glacial lineages. Potential refugium areas for each lineage are proposed.