Taxonomic Implications of Meristic Variation in North Atlantic Cod Populations

Abstract

It is commonly accepted that genetic differences across populations are reinforced by environmental influences on phenotypic expression, leading to gradient variation in morphological features. We evaluated the morphological features of two Atlantic cod (Gadus mohua) populations. When nurtured in the same laboratory setting, juveniles from the two groups showed remarkable variations in shape. Nevertheless, there was no difference in the two populations' juveniles body forms grown in the wild, showing that the genetic variances between the populations were concealed by the competing influences of the varied environmental variables faced in the wild. We hypothesize that stabilizing selection for the same ideal phenotype may account for a considerable percentage of the genetic variation in fish body structure, leading to genetic divergence throughout populations under various environmental stressors. This article summarises studies on the diversity in the mitochondrial DNA sequence found in Atlantic cod (Gadus morhua) in the North Atlantic and its environs. The population genetic architecture of the Barents Sea, Northeast, and Northwest Atlantics has seen significant modifications. Compared to populations from the Northwest Atlantic, which are all dominated by a single common genotype and show little diversity in haplotype and nucleotide content, samples from Norway and the Barents Sea support many genotypes at intermediate frequencies and exhibit far more genetic variety.