Genetic heterogeneity and growth properties of different genotypes of Atlantic cod (Gadus morhua L.) at two spawning sites off south Iceland

This study provides evidence of countergradient variations in life-history traits among coastal cod Gadus morhua off the Norwegian coast, suggesting the existence of sub-populations. One-yr-old wild-caught individuals from 70°N were smaller, grew slower, weighed less, and had a lower condition factor (CF) than southern cod from 60°N during the sampling period from June to February. In contrast, both a higher growth potential and an increase in CF were found in northern cod when offspring of northern and southern cod from the same area and of the same age as the wild cod were housed together in a 'common-garden' experiment. The rapid growth in northern cod was achieved by higher success in food competition when given a restricted amount of food. Active feeding behaviour and larger energy allocation to storage tissues, as suggested by the higher increase in condition, represents adaptations to the high-latitude environment for northern cod and countergradient variation. These differences suggest the existence of genetically distinct sub-populations along the Norwegian coast. Development of sub-populations that differ in behaviour and life-history strategies are discussed in relation to mechanisms for local retention of early life stages and local adaptation of older stages. Sub-populations with different life histories may respond differently to fisheries, and attention to this could be beneficial for improving fisheries management.

Section: Local Retention Of Early Life Stagessupporting

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Sub-populations of coastal cod with different behaviour and life-history strategies

Salvanes¹,

Skjæraasen²,

Nilsen³

2004

“…In Norwegian (Fevolden & Pogson 1995) and Icelandic waters (Jónsdóttir et al 2002, Imsland & Jónsdóttir 2003, Ja kobsdóttir et al 2011, the Pan I AA homo zygotes of post-juvenile cod have been reported to exhibit higher length at age than the Pan I BB homozygotes. Jónsdóttir et al (2008), however, suggested that the genotype that grew fastest around Iceland varied with spawning sites, rendering data on possible growth and Pan I genotype correlations for post-juvenile cod inconclusive.…”

Section: Introductionmentioning

confidence: 98%

Settling-depth vs. genotype and size vs. genotype correlations at the Pan I locus in 0-group Atlantic cod Gadus morhua

Fevolden¹,

Westgaard²,

Pedersen³

et al. 2012

We sampled 0-group juvenile Atlantic cod Gadus morhua L. within fjords and offshore in northern Norway from 1994 to 2008 using different gears for the 3 sampling depths: shore seine (0−3 m), pelagic trawl (various depths), and bottom trawl (> 80 m). Frequencies of alleles at the Pan I locus (4218 fish analysed) showed highly significant differences among samples collected in the different habitats. The Pan I A allele showed a mean frequency of ~80% in the shore seine samples, 12% in the bottom trawl samples, and between 5 and 57% in the pelagic samples. These differences are thought to reflect the co-occurrence of different populations of cod in the area with different settling regimes. Shallow-water settlers are thought to represent the stationary Norwegian coastal cod (NCC), the deep-water settlers represent the migratory Arcto-Norwegian cod (ANC), and the non-settled individuals represent a variable mixture of the 2 populations. For designated samples, we analyzed 16 microsatellites (non-neutral and neutral) that supported a genetic divergence between shallow-water and deep-water settlers. Correlations between length and Pan I genotypes within selected samples showed that the Pan I BB homozygotes (typical of ANC) were significantly longer than the Pan I AA homozygotes (typical of NCC). This could reflect differences in spawning time and growth conditions between ANC and NCC, just as well as one genotype being superior to the others in terms of growth performance. Finally, we argue that the Pan I difference between 0-group NCC and ANC is not caused by contemporary selection but reflects adaptation on an ecological post-glacial time scale.

“…Additionally, the data set of Fevolden & Pogson (1997) enabled examination of micro-geographic variation in Pan I allele frequencies in the Norwegian Fjords in relation to depth, temperature and salinity. Elucidation of genotype-environment relationships at Pan I has relevance to predictive recruitment models and aquaculture, particularly given the links between Pan I genotype and growth and condition, which support the occurrence of contemporary selection (Fevolden & Pogson 1995, Jónsdóttir et al 2002.…”

Section: Introductionmentioning

confidence: 99%

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

Case¹,

Hutchinson²,

Hauser³

et al. 2005

Using samples of Atlantic cod Gadus morhua L. from the North Sea, and previously published genetic data from the Irish and Celtic Seas, Iceland, and Norwegian fjord and offshore populations, we describe striking macro-and micro-geographic patterns in pantophysin (Pan I) allele frequencies. The relatively abrupt discontinuity in Pan I allele frequency distribution at 2 different locations is not congruent with standard patterns of isolation by distance and could arise from population admixtures, historical or contemporary natural selection, behavioural segregation or a combination of these factors. Here, we examined the relationships between the distributions of Pan I alleles and temperature, salinity and depth. In the northeast Atlantic, temperature was highly correlated with Pan I allele frequency, even when the effect of geographic distance was removed. In the Norwegian fjords, partial Mantel tests indicated that temperature, salinity and depth all had a significant effect on Pan I allele frequency in juvenile fish. However, a sample from the brackish waters of the eastern Baltic Sea suggested that salinity may be linked to Pan I allele frequency distribution and that the relationship with temperature was weaker in areas of low salinity. Strong correlations between Pan I allele frequencies and key environmental variables, together with evidence from the available literature, suggested that environmental conditions play an important role in determining the distribution of different Pan I genotypes. The combined use of environmental data, Pan I genotyping and neutral markers may provide a valuable approach to examine local adaptation, levels of gene flow and stock structuring.