Sammendrag
Background: Selection acts strongly on individuals that colonise a habitat and have phenotypic traits that deviate
from the local optima. Our objective was to investigate the evolutionary rates in Atlantic salmon (Salmo salar) in a river
system (the Vefsna watershed in Norway), fewer than 15 generations after colonisation of two new branches of the
watercourse for spawning, which were made available by construction of fish ladders in 1889.
Methods: Differences in age and size were analysed using scale samples collected by anglers. Age and size of
recaptures from a tagging experiment were compared between the three branches. Furthermore, genetic analyses of
scale samples collected in the three river branches during two periods were performed to evaluate whether observed
differences evolved by genetic divergence over this short period, or were the result of phenotypic plasticity.
Results: We demonstrate that evolution can be rapid when fish populations are subjected to strong selection, in
spite of sympatry with their ancestral group, no physical barriers to hybridisation, and natal homing as the only reproductive
isolating barrier. After fewer than 15 generations, there was evidence of genetic isolation between the two
branches based on genetic variation at 96 single nucleotide polymorphism loci, and significant differences in several
life history traits, including size and age at maturity. Selection against large size at maturity appears to have occurred,
since large individuals were reluctant to ascend the branch with less abundant water. The estimated evolutionary rate
of change in life history traits is within the upper 3 to 7% reported in other fish studies on microevolutionary rates.
Conclusions: These findings suggest that with sufficient genetic diversity, Atlantic salmon can rapidly colonise and
evolve to new accessible habitats. This has profound implications for conservation and restoration of populations and
habitats in order to meet evolutionary challenges, including alterations in water regime, whether altered by climate
change or anthropogenic factors.
Vis fullstendig beskrivelse
