Pantophysin (Pan I) locus divergence between inshore v. offshore and northern v. southern populations of Atlantic cod in the north‐east Atlantic

Abstract

More than 6000 cod Gadus morhua, sampled in coastal and offshore waters stretching from the Barents Sea down to the North Sea, were analysed for frequencies of alleles at the scnDNA pantophysin locus (Pan I) [formerly called synaptophysin (Syp I)]. The significant allele frequency difference between the two major stocks of cod in Norway, north-east Arctic cod (NEAC) and Norwegian coastal cod (NCC), was upheld in all years of the investigation (1993 to 2001), and applied both to larval cod and post-juveniles of various ages. On a north-south axis, the appearance of a latitudinal cline of post-juvenile (!1 year) allele frequencies was exposed. The intermediate allele frequencies in coastal areas of northern Norway, seem to a large extent to be caused by intermingling of the two stocks, although the existence of populations of coastal cod with alternative Pan I frequencies could not be ruled out. The role of selection is yet unresolved. Depth of the sampling location seemed to have an effect on the allele frequencies and their temporal stability, while there was no indication of seasonal variation in the frequencies. Breeding structure was the most likely cause for upholding the extreme divergence in Pan I frequencies between NEAC and NCC. # 2005 The Fisheries Society of the British Isles

Fine-scale spatial and temporal genetic structure of Atlantic cod off the Atlantic coast of the USA

“…Variation in PanI has been correlated with environmental factors, including water temperature, salinity, depth, latitudinal gradients and inshore/offshore migrations (Beacham et al 2002, Case et al 2005, Sarvas & Fevolden 2005, with potential fitness effects reported (Otterlei et al 1999, Case et al 2006, Jónsdóttir et al 2008. The patterns are not consistent across studies and geographic regions, however, indicating that the selective pressures may be complex (Jónsdóttir et al 2008).…”

Extreme male-skewed sex ratios on spawning grounds for Atlantic cod Gadus morhua with typical coastal cod signatures of the Pan I (pantophysin) locus

“…This possibility cannot be dismissed, but the major reason for variable Pan I allele frequencies in catches of cod from these waters, both spatially and temporally, is probably attributable to varying proportions of NEAC and NCC in the catches. This holds true for both adult fish (Sarvas & Fevolden 2005a,b, Westgaard & Fevolden 2007) and 0-group juveniles (Fevolden et al 2012).…”

“…Sarvas & Fevolden 2005a). The innermost known spawning site of that fjord, Bergneset, displayed sex ratios that were at least as skewed as in Malangen (9 of 10 fish on average over all study years were males) but the Pan I A frequencies were lower, down to 57% one year, as compared to the steady 90% in Malangen.…”

“…Sarvas & Fevolden 2005a, Fevolden et al 2012. A complicating factor in nearshore waters in northern Norway, even within fjords, is that the migratory NEAC may intermingle with NCC, giving the impression that populations with intermediate Pan I allele frequencies exist.…”

“…Two major features have emerged from these studies: (1) the 2-allelic class system of Pan I (Pogson & Fevolden 2003) is dominated in NCC by the Pan I A class (≈80%) and in NEAC with correspondingly high or even higher frequencies of the Pan I B allelic class (e.g. Sarvas & Fevolden 2005a, Fevolden et al 2012, and (2) whereas the Pan I frequencies over the years are stable in NEAC, they tend to vary both over time and space in fjords, an attribute claimed to be due to variable intermingling of NEAC and NCC within the coastal/fjord system (Sarvas & Fevolden 2005a,b, Westgaard & Fevolden 2007.…”