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ABSTRACT: A key question in many genetic studies on marine organisms is how to interpret a low but statistically significant level of genetic differentiation. Do such observations reflect a real phenomenon, or are they caused by confounding factors such as unrepresentative sampling or selective forces acting on the marker loci? Further, are low levels of differentiation biologically trivial, or can they represent a meaningful and perhaps important finding? We explored these issues in an empirical study on coastal Atlantic cod, combining temporally replicated genetic samples over a 10-year period with an extensive capture-mark-recapture study of individual mobility and population size. The genetic analyses revealed a pattern of differentiation between the inner part of the fjord and the open skerries area at the fjord entrance. Overall, genetic differentiation was weak (average F(ST) = 0.0037), but nevertheless highly statistical significant and did not depend on particular loci that could be subject to selection. This spatial component dominated over temporal change, and temporal replicates clustered together throughout the 10-year period. Consistent with genetic results, the majority of the recaptured fish were found close to the point of release, with <1% of recaptured individuals dispersing between the inner fjord and outer skerries. We conclude that low levels of genetic differentiation in this marine fish can indeed be biologically meaningful, corresponding to separate, temporally persistent, local populations. We estimated the genetically effective sizes (N(e) ) of the two coastal cod populations to 198 and 542 and found a N(e) /N (spawner) ratio of 0.14.
Molecular Ecology 02/2011; 20(4):768-83. · 5.52 Impact Factor
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ABSTRACT: Abstract – Sea trout (Salmo trutta) originating from small coastal streams can be found at sea throughout the year, in contrast to conspecifics from larger rivers, which typically spend the autumn and winter in fresh water. Such an extended marine stay has been observed in coastal Skagerrak. We studied the seasonal variation in marine growth of Skagerrak sea trout based on scale increment patterns and body lengths of 563 individuals captured at sea. Growth, measured as increased body length, was rapid during summer while there was no evidence for continued growth during autumn and winter. Growth decreased with increasing age of the fish. Our results suggest that coastal Skagerrak is an important feeding area for sea trout during summer, and that an extended marine stay during autumn and winter may have trade-off benefits other than somatic growth. Alternative benefits might be increased winter survival and decreased migratory costs of juvenile fish.
Ecology of Fresh Water Fish 11/2006; 15(4):446 - 452. · 1.57 Impact Factor
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ABSTRACT: The food of migratory Salmo trutta in coastal marine waters along the Norwegian Skagerrak coast varied significantly with age, season and habitat of the fish. The main prey categories in terms of frequency of occurrence were fishes followed by crustaceans, surface insects and polychaetes. Seasonal variation in diet and within habitats was found, supporting the view that brown trout is an opportunistic feeder. An ontogenetic niche shift was observed with post-smolts feeding on inshore and shallow water prey communities, while larger brown trout fed mainly on pelagic fishes.
Journal of Fish Biology 04/2005; 59(3):533 - 543. · 1.68 Impact Factor
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ABSTRACT: Juvenile and adult anadromous trout Salmo trutta utilize the sea for feeding during the winter in the Skagerrak. This finding conflicts with the traditional view that anadromous trout overwinter in fresh water. Adults, just prior to spawning, were captured at sea in October to December, and spent fish were caught at sea from October to April, showing that the fish may leave the stream and move to sea just after spawning and spend the winter there. During mid-winter (January to February), the feeding probability (chance of finding a fish with food in its stomach) increased markedly with increasing body length, with no similar effect during early and late winter (October to December and March to April). Among individuals with food in their stomach (72·5%), there was no evidence for variation in feeding intensity [stomach fullness = (mass of stomach content)(fish body mass)−1] among early, mid-, and late winter.
Journal of Fish Biology 01/2004; 64(1):89 - 99. · 1.68 Impact Factor
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ABSTRACT: Compared with many terrestrial and freshwater environments, dispersal and interbreeding is generally much less restricted in the marine environment. We studied the tendency for a marine species, the Atlantic cod, to be sub-structured into genetically differentiated populations on a fine geographical scale. We selected a coastal area free of any obvious physical barriers and restricted sampling to a 300-km region, well within the dispersal ability of this species. Screening 10 polymorphic microsatellite loci in 6 samples we detected a weak, but consistent, differentiation at all 10 loci. The average FST over loci was small (0.0023) but highly significant statistically, demonstrating that genetically differentiated populations can arise and persist in the absence of physical barriers or great distance. We found no geographical pattern in the genetic differentiation and there was no apparent trend of isolation by distance along the coastline. These findings lend support to the notion that low levels of differentiation are due to passive transport of eggs or larvae by the ocean currents rather than to adult dispersal, the latter being strongly dependent on distance.
Molecular Ecology 03/2003; 12(2):385-94. · 5.52 Impact Factor
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ABSTRACT: Both the salmon louse Lepeophtheirus
salmonis and its close relative Caligus
elongatus are ectoparasitic on Salmonidae in salt water in the northern hemisphere. In this study we monitored population dynamics of these parasites on anadromous brown trout, i.e. sea trout, on the Norwegian Skagerrak coast in the winters of 1998–1999 and 1999–2000. The low salinity was expected to reduce sea lice populations as lice do not tolerate sojourns of more than a few weeks, at most, in freshwater. Results confirmed the presence of both parasite species on estuarine sea trout in winter, and showed that the lice populations go through a bottleneck in this period. Prevalences of infection of both parasite species were very different in the two sampling periods, but fell below 10% in March in both winters. Median infection intensity was 1–2 fish−1. Salinity was statistically related to the presence of C.
elongatus both winters, and to L.
salmonis in 1999–2000. Temperature appeared to be less important for the abundance of lice.
Journal of the Marine Biological Association of the UK 09/2002; 82(05):887 - 892. · 1.00 Impact Factor
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ABSTRACT: Anadromous brown trout along the Norwegian Skagerrak coast are genetically differentiated among streams, and there are indications of further substructuring within some streams. Among presumably long-standing populations there is a pattern of increased genetic differentiation with distance, indicating an isolation-by-distance effect. For trout that inhabit streams that have recently been recolonized after the extinction of trout because of acidification, we find evidence for a mixed origin of the recolonizing trout. Both the high levels of gametic phase disequilibrium and the clear deviation from the general pattern of increased genetic differentiation with distance that are seen in recolonized streams, are consistent with recent population admixture, and confirm the loss of the original populations of these acid streams.
Heredity 09/2001; 87(Pt 2):207-14. · 4.60 Impact Factor
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ABSTRACT: The effect of habitat fragmentation on genetic differentiation among local populations of the fungivorous beetle Bolitophagus reticulatus (Coleoptera: Tenebrionidae) was studied in two contrasting landscapes: one heavily fragmented with forest fragments of variable size surrounded by inhabitable agricultural fields, the other an old forest providing a continuous habitat. The genetic structure of the beetle within each of the two contrasting areas was investigated by means of protein electrophoresis, screening four polymorphic loci in 20 populations from each area. In both areas there were significant genetic differences among local populations, but on average differentiation in the fragmented area was three times greater than in the continuous one, strongly indicating a genetic isolation effect of habitat fragmentation. These genetic results are in accordance with previous studies on dispersal in this species.
Heredity 07/2000; 84 ( Pt 6):667-76. · 4.60 Impact Factor
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ABSTRACT: The effect of ethanol [1 g/kg per orally (p.o.) during 1 hr] after thyrotropin-releasing hormone (TRH) pretreatment (five doses of 20 mg p.o. during 30 hr preceding ethanol intake) was studied in a placebo-controlled, double-blind design in 11 healthy subjects. Computerized reaction tests measuring errors and reaction time, as well as clinical testing and a self evaluation (modified Osgood test) were performed before, 75, 150, and 225 min after ethanol intake. TRH treatment did not influence blood ethanol concentrations. The effect of ethanol to produce errors was substantially reduced in all three reaction tests after TRH treatment compared to placebo treatment. The reaction times were slightly increased in simple and four choice reaction tests and up to 20% increased in a complex test in the TRH-ethanol situation compared to the placebo-ethanol situation. The effects caused by ethanol were also significantly reduced in three clinical tests and in two subjective tests of inebriation by TRH treatment compared to placebo treatment. In conclusion the study demonstrated that several acute effects of ethanol intake in humans were reduced by TRH pretreatment which did not interfere with the blood ethanol concentration versus time curve.
Alcoholism Clinical and Experimental Research 07/1989; 13(3):365-70. · 3.34 Impact Factor
