Analysis of coastal cod (Gadus morhua L.) sampled on spawning sites reveals a genetic gradient throughout Norway’s coastline

• Published in: BMC Genetics
• Main Authors: Geir Dahle, María Quintela, Torild Johansen, Jon-Ivar Westgaard, François Besnier, Asgeir Aglen, Knut E. Jørstad, Kevin A. Glover
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2018
• Subjects: Fishery; Otolith; Population; Fish; Outlier; NCC; Genetics; QH426-470; Arctic; Norway; Arctic cod; atlantic cod; Gadus morhua; North Atlantic
• Online Access: https://doi.org/10.1186/s12863-018-0625-8; https://doaj.org/article/648ad4ad150b44cabe1e4f677cd5eb7c

Abstract Background Atlantic cod (Gadus morhua L.) has formed the basis of many economically significant fisheries in the North Atlantic, and is one of the best studied marine fishes, but a legacy of overexploitation has depleted populations and collapsed fisheries in several regions. Previous studies have identified considerable population genetic structure for Atlantic cod. However, within Norway, which is the country with the largest remaining catch in the Atlantic, the population genetic structure of coastal cod (NCC) along the entire coastline has not yet been investigated. We sampled > 4000 cod from 55 spawning sites. All fish were genotyped with 6 microsatellite markers and Pan I (Dataset 1). A sub-set of the samples (1295 fish from 17 locations) were also genotyped with an additional 9 microsatellites (Dataset 2). Otoliths were read in order to exclude North East Arctic Cod (NEAC) from the analyses, as and where appropriate. Results We found no difference in genetic diversity, measured as number of alleles, allelic richness, heterozygosity nor effective population sizes, in the north-south gradient. In both data sets, weak but significant population genetic structure was revealed (Dataset 1: global FST = 0.008, P < 0.0001. Dataset 2: global FST = 0.004, P < 0.0001). While no clear genetic groups were identified, genetic differentiation increased among geographically-distinct samples. Although the locus Gmo132 was identified as a candidate for positive selection, possibly through linkage with a genomic region under selection, overall trends remained when this locus was excluded from the analyses. The most common allele in loci Gmo132 and Gmo34 showed a marked frequency change in the north-south gradient, increasing towards the frequency observed in NEAC in the north. Conclusion We conclude that Norwegian coastal cod displays significant population genetic structure throughout its entire range, that follows a trend of isolation by distance. Furthermore, we suggest that a gradient of genetic ...