Abstract
The cold-adapted polar cod Boreogadus saida, a key species in Arctic ecosystems, is vulnerable to global warming and ice retreat. In this study, 1257 individuals sampled in 17 locations within the latitudinal range of 75–81°N from Svalbard to East Siberian Sea were genotyped with a dedicated suite of 116 single-nucleotide polymorphic loci (SNP). The overall pattern of isolation by distance (IBD) found was driven by the two easternmost samples (East Siberian Sea and Laptev Sea), whereas no differentiation was registered in the area between the Kara Sea and Svalbard. Eleven SNP under strong linkage disequilibrium, nine of which could be annotated to chromosome 2 in Atlantic cod, defined two genetic groups of distinct size, with the major cluster containing seven-fold larger number of individuals than the minor. No underlying geographic basis was evident, as both clusters were detected throughout all sampling sites in relatively similar proportions (i.e. individuals in the minor cluster ranging between 4 and 19% on the location basis). Similarly, females and males were also evenly distributed between clusters and age groups. A differentiation was, however, found regarding size at age: individuals belonging to the major cluster were significantly longer in the second year. This study contributes to increasing the population genetic knowledge of this species and suggests that an appropriate management should be ensured to safeguard its diversity.
Highlights
Polar cod, Boreogadus saida, Lepechin, 1774 is a small gadid fish whose ability to synthesize antifreeze glycoproteins (Chen et al 1997) enable survival in the freezing environments of the Arctic Ocean and surroundings seas
This study aims to characterize the population genetic structure of polar cod in the geographic region ranging from Svalbard to the East Siberian Sea using a panel of developed single-nucleotide polymorphic loci (SNP) markers
Each genotype was assigned to the two inferred clusters based on the individual proportion of membership using a threshold of ancestry of q > 0.8, which allowed the identification of a major cluster hosting 1098 individuals and a minor cluster hosting 151, leaving out eight admixed individuals
Summary
Boreogadus saida, Lepechin, 1774 is a small gadid fish whose ability to synthesize antifreeze glycoproteins (Chen et al 1997) enable survival in the freezing environments of the Arctic Ocean and surroundings seas. In the Atlantic Ocean, it occurs as far south as the Gulf of St Lawrence (Canada), whereas in the Pacific Ocean, it is found as far south as the Sea of Okhotsk and Norton Sound (Western Alaska) This species performs a crucial role in the Arctic food web where it is estimated to funnel 75% of lower trophic energy to upper marine and near-shore predators including birds, seals, beluga whales and eventually polar bears and humans (Ponomarenko 1968; Bradstreet et al 1986; Crawford and Jorgenson 1996; Hop and Gjøsæter 2013). The revision of Russian historical data (1935–2020) combined with literature published in English reported large abundance of polar cod in the eastern Barents Sea and adjacent waters and revealed crucial knowledge gaps including the uncertainty as to what degree the species is dependent on sea ice, its genetic structure or the distribution of the age 0-group in the NE Barents Sea (Aune 2021)
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