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Coastal Atlantic cod (Gadus morhua) in the Northeast Atlantic has seen a continuous decline since the industrialization of the coastal fishery, and management needs to address the spatial and temporal complexities of coexisting cod stocks. Toward that end, genetic analyses and oceanographic modelling of coastal and oceanic cod larval drift patterns were combined to elucidate the mechanisms responsible for an observed genetic cline over a >1500 km stretch along the coast of Norway. The results indicate that the north-south cline in coastal cod represents an extended contact zone between genetically divergent North Sea and Northeast Arctic cod and is maintained by two-way gene flow: by northward drift of pelagic eggs and larvae and by southward spawning migrations of Northeast Arctic cod. Computer simulations verify that the genetic cline can be established rapidly if gene flow into coastal populations is substantial. The shape of the cline, on the other hand, was found to be largely insensitive to the total amount of gene flow and therefore carries little information on extent of gene flow into and among coastal populations. La morue (Gadus morhua) cotiere dans le nord-est de l'ocean Atlantique connait un declin soutenu depuis l'industrialisation de la peche cotiere, et sa gestion doit tenir compte des complexites spatiales et temporelles associees aux stocks de morues coexistants. A cette fin, des analyses genetiques et la modelisation oceanographique des motifs de derive cotiere et oceanique de larves de morue ont ete combinees dans le but d'elucider les mecanismes a l'origine d'un cline genetique observe sur une etendue de >1500 km le long de la cote norvegienne. Les resultats indiquent que le cline du nord au sud de la morue cotiere represente une vaste zone de contact de morues de la mer du Nord et de morues du nord-est de l'ocean Arctique, divergentes sur le plan genetique, qui est maintenue par un flux genetique bidirectionnel produit par la derive vers le nord d'oeufs et de larves pelagiques et par les migrations de frai vers le sud de morues du nord-est de l'ocean Arctique. Des simulations informatiques confirment que l'etablissement du cline genetique peut etre rapide si le flux genetique entrant dans les populations cotieres est important. La forme du cline, par contre, s'avere largement insensible a la quantite totale du flux genetique et offre donc peu d'information sur l'ampleur du flux genetique entrant dans les populations cotieres et entre ces dernieres. [Traduit par la Redaction], Introduction A major role for genetic analyses of commercially important species is to uncover population structuring and aid management by providing information on the appropriate geographic partitioning of the resource [...]

The International Union for Conservation of Nature (IUCN) Red List identifies threatened and endangered species and is a key instrument in global biodiversity conservation efforts. Our understanding of the structure and value of genetic biodiversity below the species level is rapidly increasing. Nonetheless, the IUCN assessment criteria overlook genetic variation within species. Here, we address this blind spot and discuss the principles of species conservation status classification relative to intraspecific biodiversity. We focus on coastal species, which thrive in heterogeneous environments known to drive genetic differentiation. The focal example species, Atlantic cod and sugar kelp, have contrasting life histories, are ecologically and economically important constituents of the coastal ecosystem, and are currently not classified as threatened in Norway and Canada. We expose important variation in population structure, the presence of ecotypes and genetic-environment covariation, as well as loss of ecotypes that threatens the conservation of these species. Because the genetic makeup of species directly influences their resilience, omitting this information from conservation status assessments can result in loss of adaptive capacity to future stressors, such as climate change. Consequently, recognizing and preserving intraspecific variation emerges as vital for species' abilities to adapt to and survive in future ocean conditions. [ABSTRACT FROM AUTHOR]

Knowledge of functional dispersal barriers in the marine environment can be used to inform a wide variety of management actions, such as marine spatial planning, restoration efforts, fisheries regulations, and invasive species management. Locations and causes of dispersal barriers can be studied through various methods, including movement tracking, biophysical modeling, demographic models, and genetics. Combining methods illustrating potential dispersal, such as biophysical modeling, with realized dispersal through, e.g., genetic connectivity estimates, provides particularly useful information for teasing apart potential causes of observed barriers. In this study, we focus on blue mussels (Mytilus edulis) in the Skagerrak—a marginal sea connected to the North Sea in Northern Europe—and combine biophysical models of larval dispersal with genomic data to infer locations and causes of dispersal barriers in the area. Results from both methods agree; patterns of ocean currents are a major structuring factor in the area. We find a complex pattern of source‐sink dynamics with several dispersal barriers and show that some areas can be isolated despite an overall high dispersal capability. Finally, we translate our finding into management advice that can be used to sustainably manage this ecologically and economically important species in the future. [ABSTRACT FROM AUTHOR]

As human exploration and harvesting moves to the high seas, ecological understanding of the deep sea has become a priority, especially in those commercially exploited species whose life cycle, habitat use, and demographic structure remain poorly understood. Here we combine otolith trace element and stable isotope analyses with microsatellite data to investigate population structure and connectivity in the migratory deep-sea black scabbardfish (Aphanopus carbo), sampled along a latitudinal gradient spanning much of the known species range in the Northeast Atlantic. In each sampled life stage, otolith trace element and oxygen isotope compositions are similar among fish from different capture locations, but otolith compositions vary greatly between life stages. Oxygen isotope compositions indicate ontogenetic migrations from relatively warm water conditions during larval growth to cooler waters with increasing age. Analysis of microsatellite DNA also suggests lack of genetic structure among the areas sampled. The multidisciplinary approach employed collectively suggests that A. carbo individuals undergo an ocean-scale ontogenetic migration, beginning with spawning in southern, warm-water Macaronesian areas (potentially dominated by Madeira), followed by a large proportion of immature fish moving to and feeding on the continental slope in northern areas. The results lend the first conclusive evidence for defining the life-history circuit of this species and the perception of its stock structure across the North Atlantic. L'exploration humaine vers la haute mer et l'exploitation de cette derniere font en sorte que la comprehension ecologique des profondeurs marines devient prioritaire, particulierement en ce qui concerne les especes exploitees a des fins commerciales dont les cycles biologiques, les habitudes d'utilisation de l'habitat et les structures demographiques demeurent mal compris. Nous combinons l'analyse des elements en traces et des isotopes stables des otolites a des donnees de microsatellites pour etudier la structure et la connectivite des populations de sabres noirs (Aphanopus carbo), une espece demersale migratrice, echantillonnees le long d'un gradient couvrant une bonne partie de l'aire de repartition connue de l'espece dans le nord-est de l'Atlantique. Pour chaque etape du cycle de vie echantillonnee, les poissons captures dans des lieux differents presentent des concentrations semblables d'elements en traces et d'isotopes stables dans les otolites, alors que la composition des otolites varie grandement d'une etape du cycle de vie a l'autre. Les concentrations d'isotopes d'oxygene indiquent l'existence de migrations ontogeniques a partir de lieux caracterises par des eaux relativement chaudes durant la croissance des larves, vers des eaux plus froides a mesure que les poissons vieillissent. L'analyse de microsatellites d'ADN semble egalement indiquer une absence de structure genetique entre les differents lieux echantillonnes. L'approche multidisciplinaire employee donne collectivement a penser que les individus d'A. carbo effectuent une migration ontogenetique d'echelle oceanique qui commence par le frai dans des regions meridionales d'eau chaude de la Macaronesie (potentiellement dominees par la region de Madere), suivi du deplacement d'une grande partie des poissons immatures vers les pentes continentales de regions septentrionales, oU ils s'alimentent. Nos resultats constituent les premieres donnees concluantes permettant de circonscrire le circuit emprunte par cette espece au cours de son cycle de vie et d'entrevoir la structure du stock a l'echelle de l'Atlantique Nord. [Traduit par la Redaction], Introduction For most deep-sea fish, there is rather limited information on general ecology, life cycles, and population structure (Begg et al. 1999). In particular, the extent of large-scale migrations in [...]

Amounts of genetic drift and the effective size of populations can be estimated from observed temporal shifts in sample allele frequencies. Bias in this so-called temporal method has been noted in cases of small sample sizes and when allele frequencies are highly skewed. We characterize bias in commonly applied estimators under different sampling plans and propose an alternative estimator for genetic drift and effective size that weights alleles differently. Numerical evaluations of exact probability distributions and computer simulations verify that this new estimator yields unbiased estimates also when based on a modest number of alleles and loci. At the cost of a larger standard deviation, it thus eliminates the bias associated with earlier estimators. The new estimator should be particularly useful for microsatellite loci and panels of SNPs, representing a large number of alleles, many of which will occur at low frequencies.

Abstract: We report statistically significant genetic structure among samples of Greenland halibut (Reinhardtius hippoglossoides), rejecting the null hypothesis of panmixia in the North Atlantic. The species appears instead to be [...]

Mixed origins of recolonized sea trout populations are discussed based on genetic evidence. A study was carried out to find out whether extinctions caused by acid precipitation in southern Norway and the recovery after deacidification have had an effect on the genetic constitution of anadromous brown trout. No samples from the period before the acidification are available, so genetic differentiation patterns among established and recently recolonized sea trout streams are compared.

Genetic differentiation for populations of the beetle Bolitophagus reticulatus (Coleoptera: Tenebrionidae) has been studied in a European landscape with agricultural areas surrounding forest fragments and a continuous old-forest one. Significant genetic differences were seen among local populations. On average, however, differentiation in the fragmented area was three times that of the continuous one. A genetic isolation effect of habitat fragmentation is strongly suggested.

We studied temporal allele frequency shifts over 15 years and estimated the genetically effective size of four natural populations of brown trout (Salmo trutta L.) on the basis of the variation at 14 polymorphic allozyme loci. The allele frequency differences between consecutive cohorts were significant in all four populations. There were no indications of natural selection, and we conclude that random genetic drift is the most likely cause of temporal allele frequency shifts at the loci examined. Effective population sizes were estimated from observed allele frequency shifts among cohorts, taking into consideration the demographic characteristics of each population. The estimated effective sizes of the four populations range from 52 to 480 individuals, and we conclude that the effective size of natural brown trout populations may differ considerably among lakes that are similar in size and other apparent characteristics. In spite of their different effective sizes all four populations have similar levels of genetic variation (average heterozygosity) indicating that excessive loss of genetic variability has been retarded, most likely because of gene flow among neighboring populations.

The mechanism of allele frequency variation in finite population is investigated for determining the effective size from observing the temporal frequency changes in the selectively neutral alleles. The allele frequency variation reveals the effective population size is not the only factor which determines the frequency changes. The age-specific survival and birth rates also influence the changes in the frequency.

The relationship between physiology and temperature has a large influence on population‐level responses to climate change. In natural settings, direct thermal effects on metabolism may be exaggerated or offset by behavioural responses influencing individual energy balance. Drawing on a newly developed proxy, we provide the first estimates of the thermal performance curve of field metabolism in a wild fish. We investigate the thermal sensitivity of field metabolic rate in two sympatric, genetically distinct ecotypes of Atlantic cod from the Skagerrak coast of southern Norway. The combined ecotype median of field metabolic rate increased with increasing temperature until around 16°C, coincident with the thermal optimum for growth for juvenile Atlantic cod. Individual cod experienced temperatures in excess of the thermal optimum for field metabolic rate, indicating some degree of thermal limitation of field metabolism in a complex natural environment with the potential for thermal refugia. The two cod ecotypes showed different thermal performance curves for field metabolic rate, revealing that genetic components to temperature sensitivity persist beyond acclimation effects. The cold‐adapted fjord ecotype maintained higher field metabolic rates at cooler temperatures than the warm‐adapted North Sea ecotype, which showed clear preference for warmer waters around the thermal optimum. Field metabolic rates of the two ecotypes were strongly influenced by year and location of sampling, implying more complex behavioural responses to environmental conditions. We emphasise that the energy uses reflecting physiological conditions in the field should be considered in the evaluation of the effect of climatic variables on fish population dynamics and demonstrate that otolith isotopes provide an analytical framework to answer this question. [ABSTRACT FROM AUTHOR]

Understanding the biological processes involved in genetic differentiation and divergence between populations within species is a pivotal aim in evolutionary biology. One particular phenomenon that requires clarification is the maintenance of genetic barriers despite the high potential for gene flow in the marine environment. Such patterns have been attributed to limited dispersal or local adaptation, and to a lesser extent to the demographic history of the species. The corkwing wrasse (Symphodus melops) is an example of a marine fish species where regions of particular strong divergence are observed. One such genetic break occurred at a surprisingly small spatial scale (FST ~0.1), over a short coastline (<60 km) in the North Sea‐Skagerrak transition area in southwestern Norway. Here, we investigate the observed divergence and purported reproductive isolation using genome resequencing. Our results suggest that historical events during the post‐glacial recolonization route can explain the present population structure of the corkwing wrasse in the northeast Atlantic. While the divergence across the break is strong, we detected ongoing gene flow between populations over the break suggesting recent contact or negative selection against hybrids. Moreover, we found few outlier loci and no clear genomic regions potentially being under selection. We concluded that neutral processes and random genetic drift e.g., due to founder events during colonization have shaped the population structure in this species in Northern Europe. Our findings underline the need to take into account the demographic process in studies of divergence processes. [ABSTRACT FROM AUTHOR]