The genetic structure of Atlantic cod (Gadus morhua) around Iceland: Insight from microsatellites, the Pan I locus, and tagging experiments

Allelic variation at nine microsatellite loci and the Pan I locus provides evidence that Atlantic cod (Gadus morhua) around Iceland is genetically structured (F_ST = 0.003 and F_ST = 0.261, respectively). A total of 2534 cod were sampled at 22 spawning locations. For both types of markers, most of the significant pairwise F_ST resulted from northeastern-southwestern comparisons. A multidimensional scaling analysis based on F_ST, a spatial hierarchical analysis of molecular variance (SAMOVA) and a hierarchical analysis of molecular variance (AMOVA), conducted on both types of markers confirmed a genetic differentiation between cod from the northeastern and southwestern regions. Genetic discontinuities were revealed across two main current fronts in the southeast and northwest, where the cold and warm water masses meet. The AMOVA also detected genetic differences with depth. Expected and observed heterozygosity of microsatellite loci significantly decreased with depth, whereas the B allele frequency at the Pan I locus increased. A tagging experiment of spawning fish conducted during the same years as the genetic work revealed that tagged individuals released in the southwestern region seldom migrated to the northeastern region and vice versa, suggesting that the southwestern and northeastern populations of Atlantic cod around Iceland represent two distinct spawning components.