Outlier SNPs show more genetic structure between two Bay of Fundy metapopulations of Atlantic salmon than do neutral SNPs

Atlantic salmon of Eastern Canada were once of considerable importance to aboriginal, recreational, and commercial fisheries, yet many populations are now in decline, particularly those of the inner Bay of Fundy (iBoF), which were recently listed as endangered. We investigated whether nonneutral SNPs could be used to assign individual Atlantic salmon accurately to either the iBoF or the outer Bay of Fundy (oBoF) metapopulations because this has been difficult with existing neutral markers. We first searched for markers under diversifying selection by genotyping eight captively bred Bay of Fundy (BoF) populations for 320 SNP loci with the Sequenom MassARRAY (TM) system and then analysed the data set with four different F-ST outlier detection programs. Three outlier loci were identified by both BayesFST and BayeScan whereas seven outlier loci, including the three previously mentioned, were identified by both Fdist and Arlequin. A subset of 14 nonneutral SNPs was more accurate (85% accuracy) than a subset of 67 neutral SNPs (75% accuracy) at assigning individual salmon back to their metapopulation. We then chose a subset of nine outlier SNP markers and used them to inexpensively genotype archived DNA samples from seven wild BoF populations using Invader (TM) chemistry. Hierarchical AMOVA of these independent wild samples corroborated our previous findings of significant genetic differentiation between iBoF and oBoF salmon metapopulations. Our research shows that identifying and using outlier loci is an important step towards achieving the goal of consistently and accurately distinguishing iBoF from oBoF Atlantic salmon, which will aid in their conservation.