Michael M Hansen

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European eels (Anguilla anguilla) undertake a approximately 5000-kilometer (km) spawning migration from Europe to the Sargasso Sea. The larvae are transported back to European waters by the Gulf Stream and North Atlantic Drift. However, details of the spawning migration remain unknown because tracking eels in the Atlantic Ocean has, so far, eluded study.(More)
Indigenous salmonid fish gene pools are affected by domesticated conspecifics, derived from aquaculture escapes and deliberate releases. Variability was examined at nine microsatellite loci in order to assess the long-term impact of stocking domesticated trout in two brown trout populations. The study was based on analysis of two historical samples(More)
What is the extent and scale of local adaptation (LA)? How quickly does LA arise? And what is its underlying molecular basis? Our review and meta-analysis on salmonid fishes estimates the frequency of LA to be ∼55-70%, with local populations having a 1.2 times average fitness advantage relative to foreign populations or to their performance in new(More)
Numerically small but statistically significant genetic differentiation has been found in many marine fish species despite very large census population sizes and absence of obvious barriers to migrating individuals. Analyses of morphological traits have previously identified local spawning groups of herring (Clupea harengus L.) in the environmentally(More)
Estimation of effective population sizes (N(e)) and temporal gene flow (N(e)m, m) has many implications for understanding population structure in evolutionary and conservation biology. However, comparative studies that gauge the relative performance of N(e), N(e)m or m methods are few. Using temporal genetic data from two salmonid fish population systems(More)
Muscle, liver and kidney samples of 20 species of birds, seals, whales and polar bear were analyzed for total and organic mercury. Organic mercury concentrations varied considerably between individuals. A general tendency towards age accumulation was found, together with log-linear correlations between organic mercury concentrations in the three tissues.(More)
The study of hybrid zones is central to our understanding of the genetic basis of reproductive isolation and speciation, yet very little is known about the extent and significance of hybrid zones in marine fishes. We examined the population structure of cod in the transition area between the North Sea and the Baltic Sea employing nine microsatellite loci.(More)
Knowledge of local adaptation and adaptive potential of natural populations is becoming increasingly relevant due to anthropogenic changes in the environment, such as climate change. The concern is that populations will be negatively affected by increasing temperatures without the capacity to adapt. Temperature-related adaptability in traits related to(More)
We examined polymorphism at seven microsatellite loci in 4023 brown trout (Salmo trutta) collected from 32 tributaries to the Limfjord, Denmark (approximately 200 km) and from two hatcheries used for stocking. Populations differ in their estimated sizes and stocking histories. Mean individual inbreeding coefficients do not differ among locations within(More)
Within species, individuals differ by gene expression, which may translate into remarkable phenotypic differences. Between species, gene expression levels change linearly over evolutionary time due to stochastic processes [1,2], while intraspecific evolution of transcriptional variation seems to be dominated by stabilizing selection [3]. We show that global(More)