Analysis of gene associated tandem repeat markers in Atlantic salmon (Salmo salar L.) populations:: implications for restoration and conservation in the Baltic Sea

Patterns of genetic diversity and differentiation among five wild and four hatchery populations of Atlantic salmon in the Baltic Sea were assessed based on eight assumedly neutral microsatellite loci and six gene-associated markers, including four expressed sequence tag (EST) linked and two major histocompatibility complex (MHC) linked tandem repeat markers (micro- and mini-satellites). The coalescent simulations based on the method of Beaumont and Nichols (1996, Proc. R. Soc. Lond. Ser. B - Biol. Sci., 263, 1619-1626) indicated that two loci (MHCII alpha and Ssa171, with the lowest and highest overall F-ST estimates, respectively) exhibited significant departures (P < 0.05) from the neutral expectations. Another coalescent-based test for selective neutrality (Vitalis et al. 2001, Genetics, 158, 1811-1823) further supported the outlier status of the Ssa171 microsatellite locus but not of the MHCII alpha linked minisatellite. In addition, actin related protein linked microsatellite locus was identified with this test as an outlier in six pairwise population comparisons. All genetic diversity estimates revealed more genetic variation in hatchery stocks than in the small wild salmon populations from the Gulf of Finland. However, the wild populations possessed alleles at gene-associated markers (e.g. MHCI and IGF) not found in the hatchery stocks, which together with moderate genetic differentiation and distinctive environmental conditions justifies the special conservation measures for the last remaining native salmon populations in the Gulf of Finland.