Abstract
BackgroundThe walleye pollock (Theragra chalcogramma) and Norwegian pollock (T. finnmarchica) are confined to the North Pacific and North Atlantic Oceans, respectively, and considered as distinct species within the family Gadidae. We have determined the complete mtDNA nucleotide sequence of two specimens of Norwegian pollock and compared the sequences to that of 10 specimens of walleye pollock representing stocks from the Sea of Japan and the Bering Sea, 2 specimens of Atlantic cod (Gadus morhua), and 2 specimens of haddock (Melanogrammus aeglefinus).ResultsA total number of 204 variable positions were identified among the 12 pollock specimens, but no specific substitution pattern could be identified between the walleye and Norwegian pollocks. Phylogenetic analysis using 16.500 homologous mtDNA nucleotide positions clearly identify the Norwegian pollock within the walleye pollock species cluster. Furthermore, the Norwegian pollock sequences were most similar to mitochondrial genotypes present in walleye pollock specimens from the Sea of Japan, an observation supported both by neighbor-joining, maximum parsimony, and maximum likelihood analyses.ConclusionWe infer that walleye pollock and Norwegian pollock represent one single species and that Norwegian pollock has been recently introduced from the Pacific to the Atlantic Oceans.
Highlights
The walleye pollock (Theragra chalcogramma) and Norwegian pollock (T. finnmarchica) are confined to the North Pacific and North Atlantic Oceans, respectively, and considered as distinct species within the family Gadidae
In the present study we have performed analysis that includes the complete mitochondrial genome sequences from multiple individuals of Norwegian pollock (T. finnmarchica), walleye pollock (T. chalcogramma), Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) in order to resolve the controversial relationship of the Theragra species
The complete mitochondrial genome sequence was determined for two individuals of Norwegian pollock (T. finnmarchica), as well as one new individual each of Atlantic cod (G. morhua) and haddock (M. aeglefinus) (Table 1)
Summary
The complete mitochondrial genome sequence was determined for two individuals of Norwegian pollock (T. finnmarchica), as well as one new individual each of Atlantic cod (G. morhua) and haddock (M. aeglefinus) (Table 1). The mtDNAs were approximately 16.6 kb in length with identical gene content and organization (13 protein coding genes, 2 ribosomal RNA genes, and 22 transfer RNA genes; Fig 1A) compared to previously published sequences in Atlantic cod, walleye pollock and haddock [13,14,15]. A total of 16.500 nucleotide positions were unambiguously aligned from 16 specimens representing Norwegian pollock (2 specimens), walleye pollock (10 specimens), Atlantic cod (2 specimens), and haddock (2 specimens). The p-distances between genera are about 10 fold higher This observation in the mitochondrial DNA sequence is consistent with the conclusion that Norwegian pollock and walleye pollock are not genetically distinct. This work This work [14] [14] [14] [14] [14] [14] [14] [14] [14] [14] [13] This work [15] This work
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