Chromosomal inversions in the Atlantic cod genome: implications for management of Canada’s Northern cod stock
Following stock collapse and over twenty years of moratoria, the state of Canada’s Northern Atlantic cod (Gadus morhua) remains precarious. To test if recent stock growth was of endogenous or exogenous origin, we performed a whole genome scan (ddRAD) on 135 adults captured in 2015 at three offshore spawning locations spanning the range of the offshore stock along the northeastern Newfoundland and Labrador shelf (Hawke Channel, Notre Dame Channel and Bonavista Corridor), with an additional 105 adults from three more southern locations (St. Anns Bank, Browns Bank and Bay of Fundy). Population structure analysis using 5,077 single nucleotide polymorphisms (SNPs) detected a distinct genetic break off the coast of Nova Scotia near 45 °N. Gene flow between groups north and south of this divide appears to be limited despite the presence of several northern-type and admixed individuals present in the southern area. North of the genetic divide, allele frequencies of neutral loci were indicative of a panmictic population. Several outlier SNPs were found to be associated with ecologically relevant physical characteristics (visual pigments, fin development, response to hypoxia, and various metabolic processes), which may be indicative of different ecological niches.