Mitochondrial DNA sequence variation and genetic stock structure of Atlantic cod (Gadus morhua) from bay and offshore locations on the Newfoundland continental shelf

Abstract

Bay cod, Atlantic cod (Gadus morhua) that over-winter in the deep-water bays of north-eastern Newfoundland, have historically been regarded as distinct in migration and spawning behaviour from offshore (Grand Bank) cod stocks. To investigate their genetic relationships, we determined the DNA sequence of a 307-base-pair portion of the mitochondrial cytochrome b gene for 236 adult cod taken from the waters off north-eastern Newfoundland, including fish found over-wintering and spawning in Trinity Bay. Although 17 genotypes were found, a single common genotype occurs at a frequency of greater than 80% in all samples, and no alternative genotype occurs at a frequency of greater than 3%. Genotype proportions did not differ significantly among samples. Measures of genetic subdivision among sampling locations are nil. Cod over-wintering in Trinity Bay are not genetically distinct from offshore cod. In combination with tagging and physiological studies, these data suggest that there is sufficient movement of cod between bay and offshore locations to prevent the development or maintenance of independent inshore stocks. Adult cod that over-winter in Trinity Bay appear to represent an assemblage of temporarily nonmigratory fish that have become physiologically acclimated to cold-water inshore environments. The pattern of genetic variation in northern cod suggests a recent population structure characterized by extensive movement of contemporary individuals superimposed on an older structure characterized by a bottleneck in the population size of cod in the north-western Atlantic.

Phylogeographic mitogenomics of Atlantic cod Gadus morhua: Variation in and among trans‐Atlantic, trans‐Laurentian, Northern cod, and landlocked fjord populations

“…(2007) claimed strong evidence of isolation by distance, but included only one Northwest Atlantic population (from the Scotian Shelf) whose closest geographic neighbor was from Greenland. Analyses with short mtDNA cytochrome b sequences (307–401 bp) alone consistently suggest an absence of genetic differentiation within regions and trans‐Atlantic differences in haplotype frequencies (Árnason, 2004; Árnason & Pálsson, 1996; Árnason et al., 1992, 1998, 2000; Carr & Crutcher, 1998; Carr & Marshall, 1991a,b; Carr et al., 1995; Hardie et al., 2006). …”

“…Whereas the majority of cod populations are migratory between inshore feeding grounds and offshore spawning locations (Lear, 1984; Templeman, 1979), a historic hypothesis is the existence of “bay cod” that remain more or less permanently inshore in deepwater bays that surround the island of Newfoundland (Carr et al., 1995). However, mitogenomes from inshore‐spawning fish near Random Island in Trinity Bay and at Gilbert Bay in southern Labrador (RAN and GIL) are not differentiated from the nearest offshore populations (NGB and HAW) and are no less diverse as might be expected in an isolated population (cf.…”

“…(2006) assigned all cod sampled in the three Baffin Island lakes to haplotypes “ A ,” “ E ,” or “ G” ( sensu Carr et al., 1995), where “ A” is the most common, widespread haplotype in Atlantic cod. Of 18 QAS samples, our data for the homologous region would assign 11 and seven mitogenomes as identical within haplotypes “ E” and “ A ,” respectively.…”

“…Trans‐Atlantic differences are evident in protein loci (Jamieson, 1967; Mork, Ryman, Ståhl, Utter, & Sundnes, 1985), mitochondrial cytochrome b (Carr & Marshall, 1991a; Sigurgíslason & Árnason, 2003), and nuclear DNA markers (Pogson, Mesa, & Boutilier, 1995), although results at local scales remain ambiguous. Extensive mtDNA analyses have found little or no structure in waters off the coasts of eastern North America (Carr, Snellen, Howse, & Wroblewski, 1995), Iceland (Árnason, Pálsson, & Arason, 1992; Árnason, Petersen, Kristinsson, Sigurgíslason, & Pálsson, 2000), the Faroe Islands (Sigurgíslason & Árnason, 2003), Norway (Árnason & Pálsson, 1996), and the Baltic Sea (Árnason, Petersen, & Pálsson, 1998). In contrast, microsatellite studies suggest range‐wide isolation by distance (O'Leary, Coughlan, Dillane, McCarthy, & Cross, 2007), and significant structure in waters off North America (e.g., Flemish cap, Bentzen, Taggart, Ruzzante, & Cook, 1996; inshore vs. offshore, Ruzzante, Taggart, Cook, & Goddard, 1996; Arctic populations, Hardie, Gillett, & Hutchings, 2006), Norway (Knutsen, Jorde, André, & Stenseth, 2003), and the North Sea (Hutchinson, Carvalho, & Rogers, 2001).…”

Phylogenetic Analysis of Hampala Fishes (Subfamily Cyprininae) in Malaysia Inferred from Partial Mitochondrial CytochromebDNA Sequences

“…A few studies have incorporated molecular phylogenetic analysis in determining the relationships among freshwater fishes ( e.g ., Dodson et al ., 1995;Chen et al ., 1998;Wang et al ., 2000). The mitochondrial cytochrome b (cyt b ) gene is perhaps the best studied DNA segment in fishes, and several studies have shown its usefulness in elucidating evolutionary patterns in fishes ( e.g ., Kocher et al ., 1989;Meyer et al ., 1990;Carr and Marshall, 1991;Block et al ., 1993;Zhu et al ., 1994;Carr et al ., 1995). It has been well demonstrated that this gene retains a history of past isolation (Avise, 1989;Bilington and Hebert, 1991).…”