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The spectral sensitivity of visual pigments in vertebrate eyes is optimized for specific light conditions. One of such pigments, rhodopsin ( RH1), mediates dim-light vision. Amino acid replacements at tuning sites may alter spectral sensitivity, providing a mechanism to adapt to ambient light conditions and depth of habitat in fish. Here we present a first investigation of RH1 gene polymorphism among two ecotypes of Atlantic cod in Icelandic waters, which experience divergent light environments throughout the year due to alternative foraging behaviour. We identified one synonymous single nucleotide polymorphism (SNP) in the RH1 protein coding region and one in the 3′ untranslated region (3′-UTR) that are strongly divergent between these two ecotypes. Moreover, these polymorphisms coincided with the well-known panthophysin ( Pan I) polymorphism that differentiates coastal and frontal (migratory) populations of Atlantic cod. While the RH1 SNPs do not provide direct inference for a specific molecular mechanism, their association with this dim-sensitive pigment indicates the involvement of the visual system in local adaptation of Atlantic cod. [ABSTRACT FROM AUTHOR]

Inferring the number of genetically distinct populations and their levels of connectivity is of key importance for the sustainable management and conservation of wildlife. This represents an extra challenge in the marine environment where there are few physical barriers to gene-flow, and populations may overlap in time and space. Several studies have investigated the population genetic structure within the North Atlantic minke whale with contrasting results. In order to address this issue, we analyzed ten microsatellite loci and 331 bp of the mitochondrial D-loop on 2990 whales sampled in the North East Atlantic in the period 2004 and 2007–2011. The primary findings were: (1) No spatial or temporal genetic differentiations were observed for either class of genetic marker. (2) mtDNA identified three distinct mitochondrial lineages without any underlying geographical pattern. (3) Nuclear markers showed evidence of a single panmictic population in the NE Atlantic according STRUCTURE's highest average likelihood found at K = 1. (4) When K = 2 was accepted, based on the Evanno's test, whales were divided into two more or less equally sized groups that showed significant genetic differentiation between them but without any sign of underlying geographic pattern. However, mtDNA for these individuals did not corroborate the differentiation. (5) In order to further evaluate the potential for cryptic structuring, a set of 100 in silico generated panmictic populations was examined using the same procedures as above showing genetic differentiation between two artificially divided groups, similar to the aforementioned observations. This demonstrates that clustering methods may spuriously reveal cryptic genetic structure. Based upon these data, we find no evidence to support the existence of spatial or cryptic population genetic structure of minke whales within the NE Atlantic. However, in order to conclusively evaluate population structure within this highly mobile species, more markers will be required. [ABSTRACT FROM AUTHOR]

Growth and condition (both somatic and hepatosomatic index) of Atlantic cod spawning at different locations around Iceland was studied in relation to the Pan I locus. South of Iceland cod carrying the Pan IAB and Pan IBB genotypes were more frequent while cod carrying the Pan IAA genotype was more frequent north of Iceland. Differences in growth were detected between cod spawning at different areas around Iceland. Cod spawning south of Iceland grew faster than cod spawning north of Iceland. Differences in growth rate were also observed among cod carrying different Pan I genotypes within a spawning area. The least frequent Pan I genotype expressed the highest growth in both south and north of Iceland. Cod carrying the Pan IAA grew fastest at spawning locations south of Iceland, while cod carrying the Pan IBB genotype grew fastest in north of Iceland. A consistent relationship between condition and the different Pan I genotypes was also observed in all the areas. Cod carrying the Pan IAA expressed the highest somatic condition and the lowest hepatosomatic index. Together, these results indicate that the relation of growth and condition with the Pan I locus is more complicated than earlier thought and is likely to be influenced by other factors, like size-selective fishing and food supply. [ABSTRACT FROM AUTHOR]

Throughout their geographic distribution, marine fish species often form subpopulations with limited connectivity, among which individuals display a variety of migratory behaviours. Fish behaviour experiments using Data Storage Tags (DSTs) have been useful to define the natural movement of individuals. In Icelandic waters, such experiments have indicated the presence of two distinct behaviour types of the Atlantic cod Gadus morhua, related to vertical migrations and habitat choice in feeding migrations. Some individuals have been shown to stay most of the time in shallow waters characterised by the seasonal trend in temperature for the shelf waters, while other migrate to deeper and colder waters where most of them forage in temperature fronts characterized by highly variable temperatures. The analysis of the pantophysin locus ( Pan I) of the same individuals revealed that individuals carrying the Pan IAA genotype are likely to display a shallow water feeding migrations while individuals carrying the Pan IBB genotype preferred deeper waters and forage near thermal fronts. The heterozygote exhibited both type of behaviours. This study therefore suggests that further research need to be done on the pantophysin locus and its potential effects on cod phenotypes to assess the potential relationship between this locus and the behavioural types described. [ABSTRACT FROM AUTHOR]

Abstract: Microsatellite DNA loci and the Pantophysin locus (Pan I) were used to investigate levels of genetic diversity within farmed strains of Atlantic cod Gadus morhua and to compare them with the wild source population. A total of 282 farmed samples originating from a spawning ground off the south-west coast of Iceland were sampled in the years 2002 and 2003, and 258 wild cod were collected at the same spawning ground in the same years. The farmed strains exhibited a lower mean number of alleles and allelic diversity than the wild samples at the microsatellite loci. Significant differences were observed between wild and farmed samples both in allele and genotype frequencies at the Pan I locus. We argue that the genetic divergence of wild and farmed samples of Atlantic cod may be due to a small number of effective founding breeders contributing to the genetic variation of the farmed strains, inducing a reduction in allelic diversity. We discuss the potential effect of breeding practices on the genetic diversity of Atlantic cod. [Copyright &y& Elsevier]

Eighteen new microsatellite loci consisting of 10 di-, 5 tri-, 2 tetra- and 1 heptanucleotide repeats are introduced for the Atlantic cod ( Gadus morhua L.). All loci were co-amplified in two polymerase chain reactions (plus two previously published microsatellites) and all products were typed clearly. The number of alleles per locus ranged from six (PGmo130) to 45 (PGmo76) and the observed heterozygosity ranged from 0.356 (PGmo130) to 0.957 (PGmo95). All loci except one followed Hardy–Weinberg expectations. Genetic linkage disequilibrium analysis between all pairs of loci did not yield any significant values. [ABSTRACT FROM AUTHOR]

Nine out of 22 microsatellite primers tested were successfully amplified on three samples of cod Gadus morhua L. (two contemporary and one archived otolith samples). All loci were polymorphic (5–23 alleles/locus). The average observed heterozygosity across loci and samples was 0.625, ranging from 0.294 to 0.895 at each locus. All loci were under Hardy–Weinberg equilibrium, except PGmo56 that showed significant excess of heterozygotes in all studied samples. The isolated loci were suitable for degraded DNA and therefore useful for conducting a long-term temporal study with DNA obtained from archived otoliths of cod. [ABSTRACT FROM AUTHOR]