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Biomedical subjects

Sigurd Einum

Publications and source records attributed to Sigurd Einum.

4 recordsLinked to original sources
PubMed2006

Rapid parallel evolutionary changes of gene transcription profiles in farmed Atlantic salmon.

Farmed salmon strains have been selected to improve growth rates as well as other traits of commercial interest but the 2 million farmed salmon escaping annually may enhance the risk of extinction of wild populations through genetic and ecological interactions. Here, we compare the transcription profiles of 3557 genes in the progeny of farmed and wild Atlantic salmon from Norway and Canada grown in controlled conditions, and demonstrate that five to seven generations of artificial selection led to heritable changes in gene transcription profiles, the average magnitude of the differences being 25% and 18% for at least 1.4% and 1.7% of the expressed genes in juvenile salmon from Norway and Canada, respectively. Moreover, genes showing significant transcription profile differences in both farmed strains (16%) all exhibited parallel changes. These findings, along with the identification of several genes whose expression profiles were modified through artificial selection, provide new insights into the molecular basis of parallel evolution, and suggest how gene flow from farmed escapees may affect the genetic integrity of wild populations.

Analysis of Variance↗
PubMed2005

Local-scale density-dependent survival of mobile organisms in continuous habitats: an experimental test using Atlantic salmon.

For organisms with restricted mobility, density dependence may occur on spatial scales much smaller than that of the whole population. Averaging densities over whole populations in such organisms gives a more or less inaccurate description of the real variation in competitive intensity over time and space. The potential for local density dependence in more mobile organisms is less well understood, particularly for organisms living in continuous habitats. To test for local density-dependent processes in such an organism, we manipulated egg density (the number of eggs nest(-1)) among ten artificial nests of Atlantic salmon along an 1,848-m long river during two consecutive years. Eggs in different nests were given unique thermal otolith-banding patterns to allow identification of juvenile nest origin. At capture, 1-2 months after emergence, the spatial distribution of juveniles reflected nest locations, with the median absolute dispersal distance being 92 and 41 m in the 2 years. Estimated nest-specific survival rates were strongly negatively related to hatched-egg density in both years (r(2)=0.72 and 0.62), despite dramatic differences in overall mean survival (0.22 and 0.02). Thus, density-dependent survival following emergence in Atlantic salmon juveniles occurs on spatial scales much smaller than that of whole populations. The consistency across years suggests that the phenomenon is likely to occur over most environmental conditions. Our observation of local-scale density dependence is consistent with strong juvenile territoriality, which forces individuals emerging in high-initial density areas to disperse farther, and a high cost (metabolic or predation) of dispersal. We conclude that for mobile organisms with patchy distributions of propagules and constrained juvenile dispersal, increased emphasis on local-scale dynamics should enable a more mechanistic understanding of population regulation even in continuous habitats, and hence increase the predictive power of population models.

Analysis of Variance↗
PubMed2002

Egg-size evolution in aquatic environments: does oxygen availability constrain size?

Selection against large eggs has been proposed for aquatic environments, putatively because large eggs should have more difficulty obtaining the required oxygen. Here, we use brown trout (Salmo trutta) eggs to provide an experimental test of this hypothesis. At high levels of dissolved oxygen (14 mg l(-1)), egg survival was high and independent of egg size. At low oxygen levels (2.3 mg l(-1)), survival decreased overall, and was higher for large-egged than small-egged siblings. Thus, contrary to conventional expectation, low oxygen levels selected for large rather than small eggs. A second experiment using Atlantic salmon (S. salar) eggs indicated that oxygen consumption increases relatively slowly with increasing egg mass (allometric constant = 0.44). The failure of the conventional 'bigger is worse during incubation' hypothesis may thus be due to the erroneous assumption that oxygen consumption increases at a greater rate with increasing egg mass than does the egg surface area that is available for oxygen diffusion. We also demonstrate, using data from Atlantic salmon, that nest-specific oxygen consumption decreases with increasing egg size, but that this effect is more pronounced for large than for small females. This may help to explain the positive correlation between adult body size and egg size observed in fishes that cluster their eggs.

Animals↗