Allelic variation at nine microsatellite loci and the Pan I locus provides evidence that Atlantic cod (Gadus morhua) around Iceland is genetically structured (F ST = 0.003 and F ST = 0.261, respectively). A total of 2534 cod were sampled at 22 spawning locations. For both types of markers, most of the significant pairwise F ST resulted from northeastern-southwestern comparisons. A multidimensional scaling analysis based on F ST , a spatial hierarchical analysis of molecular variance (SAMOVA) and a hierarchical analysis of molecular variance (AMOVA), conducted on both types of markers confirmed a genetic differentiation between cod from the northeastern and southwestern regions. Genetic discontinuities were revealed across two main current fronts in the southeast and northwest, where the cold and warm water masses meet. The AMOVA also detected genetic differences with depth. Expected and observed heterozygosity of microsatellite loci significantly decreased with depth, whereas the B allele frequency at the Pan I locus increased. A tagging experiment of spawning fish conducted during the same years as the genetic work revealed that tagged individuals released in the southwestern region seldom migrated to the northeastern region and vice versa, suggesting that the southwestern and northeastern populations of Atlantic cod around Iceland represent two distinct spawning components.Résumé : La variation allélique de neuf microsatellites et du locus Pan I met en évidence une structure génétique chez la morue Atlantique (Gadus morhua) dans les eaux islandaises (F ST respectifs, F ST = 0,003 et F ST = 0,261). Un total de 2534 morues a été échantillonné sur 22 sites de ponte. Pour les deux marqueurs génétiques utilisés, la majorité des valeurs significatives de F ST par paires de populations est due à des comparaisons nord-est et sud-ouest. Une analyse multidimensionnelle basée sur les F ST par paires de populations, une analyse spatiale hiérarchique de variance molécu-laire (SAMOVA) et une analyse hiérarchique de variance moléculaire (AMOVA), réalisées sur les deux types de marqueurs génétiques, révèlent une différenciation significative entre les échantillons du nord-est et du sud-ouest. La recherche de discontinuités génétiques indique la présence de deux barrières au flux génique correspondant aux principaux fronts de courants océaniques localisés dans le nord-ouest et le sud-est du pays aux points où les masses d'eaux chaudes et froides entrent en contact. L'analyse AMOVA détecte aussi des différences génétiques en fonction de la profondeur. Une analyse approfondie montre que les hétérozygoties observées et attendues des microsatellites diminuent significativement avec la profondeur, alors que la fréquence de l'allèle B du locus Pan I augmente. Une expérience de « capture-recapture » réalisée sur les sites de pontes en même temps que les études génétiques révèle que des individus marqués et relâchés dans la région du sud-ouest migrent rarement vers la région du nord-est et vice versa, ce qui confirme que les population...

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Pampoulie, C., Skirnisdottir, S., Hauksdottir, S., Olafsson, K., Eiríksson, H., Chosson, V., Hreggvidsson, G. O., Gunnarsson, G. H., and Hjorleifsdottir, S. 2011. A pilot genetic study reveals the absence of spatial genetic structure in Norway lobster (Nephrops norvegicus) on fishing grounds in Icelandic waters. – ICES Journal of Marine Science, 68: 20–25. Stock structure of Norway lobster off southern Iceland was investigated using 12 microsatellite loci. No genetic method detected significant genetic differentiation among the locations sampled, even among Icelandic samples and an out-group from Scotland. Testing the power of resolution of microsatellite loci, the loci and sample sizes used were sufficient to detect significant genetic differentiation with confidence. The lack of genetic structure is discussed in terms of the level of gene flow, recent isolation of populations, and the statistical power of the experimental design.

Biodiversity in the oceans has dramatically declined since the beginning of the industrial era, with accelerated loss of marine biodiversity impairing the ocean's capacity to maintain vital ecosystem services. A few organisms epitomize the damaging and long‐lasting effects of anthropogenic exploitation: Some whale species, for instance, were brought to the brink of extinction, with their population sizes reduced to such low levels that may have caused a significant disruption to their reproductive dynamics and facilitated hybridization events. The incidence of hybridization is nevertheless believed to be rare, and very little information exists on its directionality. Here, using genetic markers, we show that all but one whale hybrid sample collected in Icelandic waters originated from the successful mating of male fin whale and female blue whale, thus suggesting unidirectional hybridization. We also demonstrate for the first time the existence of a second‐generation adult (male) hybrid resulting from a backcross between a female hybrid and a pure male fin whale. The incidence of hybridization events between fin and blue whales is likely underestimated and the observed unidirectional hybridization (for F1 and F2 hybrids) is likely to induce a reproductive loss in blue whale, which may represent an additional challenge to its recovery in the Atlantic Ocean compared to other rorquals.

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