Cod, Gadus morhua L., populations identified by mitochondrial DNA

Abstract

Isozyme and haemoglobin analysis has shown that the cod, Gadus morhua L., in the NE Atlantic can be regarded as two populations: Arctic and coastal cod. One hundred and one individual cod from nine different locations were sampled and restriction fragment analysis uncovered 14 different mtDNA clones. Calculation of sequence divergence between localities displayed large divergence between samples from coastal and Arctic areas (1.77-5.62%), as opposed to the low intrapopulation divergence (z 0.10%) and the divergence between localities along the coast (=0,17%)andin the BarentsSea(z 1.00Y0).

Macro- and micro-geographic variation in pantophysin (PanI) allele frequencies in NE Atlantic cod Gadus morhua

“…Considerable differences in haplotype diversity also exist among some geographically proximate Icelandic populations, though there is no evidence of any overall geographic pattern (Árnason et al 2000). The divergence between Norwegian Arctic and coastal cod described by Dahle (1991), together with the patterns seen in Icelandic cod are consistent with the data presented here and may suggest that the transition zones between Pan I allelic groups are due to historical isolation and subsequent secondary contact. Such a possibility is further substantiated by Fevolden & Pogson (1997), who found evidence of mixing between genetically divergent populations, indicated by an increase in F IS from 0.002 at the head of Ullsfjorden, to 0.275 near the mouth of the fjord, as the Pan I B allele becomes more prevalent.…”

“…Fevolden & Pogson (1997) detected highly significant Pan I allele frequency differences between populations of Norwegian coastal and northeast Arctic cod at the Pan I locus. In contrast, mitochondrial DNA studies on these populations are equivocal, revealing evidence for differentiation between coastal and northeast Arctic cod in Dahle's (1991) study but not in that by Árnason & Pálsson (1996). In a Pan I study of cod in a Norwegian fjord, Karlsson & Mork (2003) proposed that significant deviations from Hardy-Weinberg equilibrium may be due to contemporary selection.…”

“…Hybrid zones have been described in Atlantic cod (Nielsen et al 2003), but evidence for secondary contact along Pan I transition zones from mtDNA is equivocal. Árnason & Pálsson (1996) found little differentiation at the mtDNA cytochrome b gene between the proposed Arctic and coastal cod stocks while Dahle (1991) detected major divergence between these 2 groups. The discordance between these studies may be due to the sampling and assignment of fish into Arctic and coastal groups; Árnason & Pálsson (1996) assigned individuals purely on the basis of their capture location, thus potentially sampling mixed populations, while Dahle (1991) differentiated between Arctic and coastal cod using haemoglobin polymorphism.…”

“…Árnason & Pálsson (1996) found little differentiation at the mtDNA cytochrome b gene between the proposed Arctic and coastal cod stocks while Dahle (1991) detected major divergence between these 2 groups. The discordance between these studies may be due to the sampling and assignment of fish into Arctic and coastal groups; Árnason & Pálsson (1996) assigned individuals purely on the basis of their capture location, thus potentially sampling mixed populations, while Dahle (1991) differentiated between Arctic and coastal cod using haemoglobin polymorphism. Considerable differences in haplotype diversity also exist among some geographically proximate Icelandic populations, though there is no evidence of any overall geographic pattern (Árnason et al 2000).…”

Population genetic structure of the glacier lanternfish,Benthosema glaciale(Myctophidae) in Norwegian waters

“…1998; cod Gadus morhua: Jørstad & Naevdal 1989, Dahle 1991; blue whiting Micromesistius poutassou : Giaever & Stien 1998). These studies also implicated a restricted gene flow between the fjords and the offshore waters.…”