Selection Patterns in Geographically Separated Populations of Atlantic Salmon Reveal Biological Differences

Atlantic salmon from southern and northern regions in Norway display genetic differences, but these have remained uncharacterized. These differences may result from variation in recolonization times and patterns of salmon along the Norwegian coastline. The underlying drivers for these genetic differences are not known, but may include different environmental factors in the south and north, such as temperature, light and disease pressure. This study aims to elucidate the genetic differences between Atlantic salmon in southern and northern Norway using genome wide association studies (GWAS) to look for selection processes on genes and genomic regions in the Atlantic salmon genome.

GWAS using 4,450,990 SNPs derived from genome resequencing data from four rivers in Northern Norway and four rivers in Western Norway revealed significantly different allele frequencies between salmon from north and south of Norway. The study identified 11 selective sweeps, comprising more than 50 genes, of which 16 contained missense mutations. Genotyping salmon from 19 other rivers along the Norwegian coastline showed that these missense mutations are separating the salmon populations in the north and south of Norway. Result from this study are relevant for the aquaculture community since different selection processes can be related to relevant characteristics in aquaculture such as disease resistance, metabolism (growth) and processes regulated by photoperiod such as timing of reproduction.