6 results on '"Westgaard, Jon-Ivar"'
Search Results
2. "Real-time" genetic monitoring of a commercial fishery on the doorstep of an MPA reveals unique insights into the interaction between coastal and migratory forms of the Atlantic cod.
- Author
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Johansen, Torild, Westgaard, Jon-Ivar, Seliussen, Bjørghild B., Nedreaas, Kjell, Dahle, Geir, Glover, Kevin A., Kvalsund, Roger, and Aglen, Asgeir
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FISHERY management , *AQUATIC resource management , *FISH population thinning , *ATLANTIC cod behavior , *MARINE parks & reserves - Abstract
With the decline of many of the world's fisheries, increased regulation, including marine protected areas (MPA), forms an increasingly important role in promoting sustainable resource use. Here, we present a novel "real-time" genetic monitoring programme used to protect the depleted Norwegian coastal cod stock (NCC) in an MPA during the spawning season, while a fishery targeted at the sustainable Northeast Arctic cod stock (NEAC) operates immediately outside. In the period 2009-2016,>6800 cod from the fishery were genotyped with the PanI locus that is discriminatory between these two stocks. The estimated fraction of NEAC increased during the study period until 2014; however, it did not exceed 70% for any sustained period. Therefore, the MPA remained closed for commercial harvest. Genetic analysis of eggs revealed a distinctly lower fraction of NEAC than in the catch from the adult stock, both immediately outside and within the MPA itself. We suggest that this discrepancy is likely to reflect differences in spawning areas used by NCC and NEAC. Estimated fractions of NEAC/NCC using PanI, otolith classification, and 39 single nucleotide polymorphisms were similar, thus validating the use of PanI to estimate NEAC/NCC composition. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
3. Geographic extent of introgression in Sebastes mentella and its effect on genetic population structure.
- Author
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Saha, Atal, Johansen, Torild, Hedeholm, Rasmus, Nielsen, Einar E., Westgaard, Jon-Ivar, Hauser, Lorenz, Planque, Benjamin, Cadrin, Steven X., and Boje, Jesper
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INTROGRESSION (Genetics) ,SEBASTES mentella ,POPULATION genetics ,BIOLOGICAL variation ,BIOLOGICAL divergence - Abstract
Genetic population structure is often used to identify management units in exploited species, but the extent of genetic differentiation may be inflated by geographic variation in the level of hybridization between species. We identify the genetic population structure of Sebastes mentella and investigate possible introgression within the genus by analyzing 13 microsatellites in 2,562 redfish specimens sampled throughout the North Atlantic. The data support an historical divergence between the 'shallow' and 'deep' groups, beyond the Irminger Sea where they were described previously. A third group , 'slope,' has an extended distribution on the East Greenland Shelf, in addition to earlier findings on the Icelandic slope. Furthermore, S. mentella from the Northeast Arctic and Northwest Atlantic waters are genetically different populations. In both areas, interspecific introgression may influence allele frequency differences among populations. Evidence of introgression was found for almost all the identified Sebastes gene pools, but to a much lower extent than suggested earlier. Greenland waters appear to be a sympatric zone for many of the genetically independent Sebastes groups. This study illustrates that the identified groups maintain their genetic integrity in this region despite introgression. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
4. Genetically distinct populations of northern shrimp, Pandalus borealis, in the North Atlantic: adaptation to different temperatures as an isolation factor.
- Author
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Jorde, Per Erik, Søvik, Guldborg, Westgaard, Jon‐Ivar, Albretsen, Jon, André, Carl, Hvingel, Carsten, Johansen, Torild, Sandvik, Anne Dagrun, Kingsley, Michael, and Jørstad, Knut Eirik
- Subjects
PANDALUS borealis ,POPULATION genetics ,SHRIMP populations ,WATER temperature ,BIODIVERSITY - Abstract
The large-scale population genetic structure of northern shrimp, Pandalus borealis, was investigated over the species' range in the North Atlantic, identifying multiple genetically distinct groups. Genetic divergence among sample localities varied among 10 microsatellite loci (range: F
ST = −0.0002 to 0.0475) with a highly significant average ( FST = 0.0149; P < 0.0001). In contrast, little or no genetic differences were observed among temporal replicates from the same localities ( FST = 0.0004; P = 0.33). Spatial genetic patterns were compared to geographic distances, patterns of larval drift obtained through oceanographic modelling, and temperature differences, within a multiple linear regression framework. The best-fit model included all three factors and explained approximately 29% of all spatial genetic divergence. However, geographic distance and larval drift alone had only minor effects (2.5-4.7%) on large-scale genetic differentiation patterns, whereas bottom temperature differences explained most (26%). Larval drift was found to promote genetic homogeneity in parts of the study area with strong currents, but appeared ineffective across large temperature gradients. These findings highlight the breakdown of gene flow in a species with a long pelagic larval phase (up to 3 months) and indicate a role for local adaptation to temperature conditions in promoting evolutionary diversification and speciation in the marine environment. [ABSTRACT FROM AUTHOR]- Published
- 2015
- Full Text
- View/download PDF
5. Analysis of coastal cod (<italic>Gadus morhua</italic> L.) sampled on spawning sites reveals a genetic gradient throughout Norway's coastline.
- Author
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Dahle, Geir, Quintela, María, Johansen, Torild, Westgaard, Jon-Ivar, Besnier, François, Aglen, Asgeir, Jørstad, Knut E., and Glover, Kevin A.
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ATLANTIC salmon ,MICROSATELLITE repeats ,FISH populations ,POPULATION genetics ,ATLANTIC cod - Abstract
Background: Atlantic cod (
Gadus morhua L.) has formed the basis of many economically significant fisheries in the North Atlantic, and is one of the best studied marine fishes, but a legacy of overexploitation has depleted populations and collapsed fisheries in several regions. Previous studies have identified considerable population genetic structure for Atlantic cod. However, within Norway, which is the country with the largest remaining catch in the Atlantic, the population genetic structure of coastal cod (NCC) along the entire coastline has not yet been investigated. We sampled > 4000 cod from 55 spawning sites. All fish were genotyped with 6 microsatellite markers and Pan I (Dataset 1). A sub-set of the samples (1295 fish from 17 locations) were also genotyped with an additional 9 microsatellites (Dataset 2). Otoliths were read in order to exclude North East Arctic Cod (NEAC) from the analyses, as and where appropriate. Results: We found no difference in genetic diversity, measured as number of alleles, allelic richness, heterozygosity nor effective population sizes, in the north-south gradient. In both data sets, weak but significant population genetic structure was revealed (Dataset 1: global FST = 0.008,P < 0.0001. Dataset 2: global FST = 0.004,P < 0.0001). While no clear genetic groups were identified, genetic differentiation increased among geographically-distinct samples. Although the locus Gmo132 was identified as a candidate for positive selection, possibly through linkage with a genomic region under selection, overall trends remained when this locus was excluded from the analyses. The most common allele in loci Gmo132 and Gmo34 showed a marked frequency change in the north-south gradient, increasing towards the frequency observed in NEAC in the north. Conclusion: We conclude that Norwegian coastal cod displays significant population genetic structure throughout its entire range, that follows a trend of isolation by distance. Furthermore, we suggest that a gradient of genetic introgression between NEAC and NCC contributes to the observed population genetic structure. The current management regime for coastal cod in Norway, dividing it into two stocks at 62°N, represents a simplification of the level of genetic connectivity among coastal cod in Norway, and needs revision. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
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6. Climate-induced range expansions of marine fauna into the Arctic – what is the most likely colonisation route?
- Author
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Andrews, Adam Jon, Præbel, Kim, Christiansen, Jørgen Schou, and Westgaard, Jon-Ivar
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climate change ,Atlantic cod ,Barents Sea ,range expansion of fishes ,population genetics ,VDP::Mathematics and natural science: 400::Zoology and botany: 480::Marine biology: 497 ,BIO-3950 ,VDP::Matematikk og Naturvitenskap: 400::Zoologiske og botaniske fag: 480::Marinbiologi: 497 - Abstract
As a result of climate change, the Arctic faunas of the Northeast Atlantic have begun to shift in an Atlantic direction. One system exposed to such a change is the Northeast Greenland (NEG) Shelf. However, the colonisation route taken by boreal fauna to the NEG shelf is unknown. This knowledge is essential to predict to what extent boreal fauna will dominate Arctic habitats, and alter ecosystems in the future. For the species under study here, colonisation is possible from either the Barents Sea via a northern route, or via southern expansion from Iceland and Jan Mayen Island. Here, we used microsatellite markers and established reference population genetic data from Atlantic cod (Gadus morhua), beaked redfish (Sebastes mentella) and deep-sea shrimp (Pandalus borealis) to determine the most likely origin of specimens of these species recently collected at the NEG shelf. We demonstrate that all three species originate from the Barents Sea, and suggest that a likely colonisation route is via advection across the Fram Strait. Our results show that the species composition of Arctic habitats can be shaped by the dispersal of pelagic larvae, and that the fauna of the Barents Sea can project on to adjacent Arctic habitats with unknown consequences to the structure and function of putatively isolated Arctic communities.
- Published
- 2018
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