The River Eira in Norway. Photo Eva B. Thorstad
This new study provides clear evidence of unintentional human-induced evolution in a natural salmon population, in which the species managed to adapt to the altered environment after hydropower regulation.
Many ecosystems are altered by human activity. To survive, affected populations must respond to these changes by means of adaptive plasticity or adaptive trait evolution. Allele frequency changes at functional loci provide evidence of evolutionary response, but such documentation is scarce in wild populations.
Using concordant temporal genetic and phenotypic data from a wild population of Atlantic salmon impacted by hydropower development, this new study presents one of the largest evolutionary changes reported on the decadal timescale. Modeling the dynamics revealed a rapid adaptive response to the reduced waterflow in the River Eira, Norway. The results provide clear evidence of human-induced evolution mediated by large-effect loci in a wild population.
Time series data spanning nearly a century were used to investigate how the body mass of Atlantic salmon adapted to river regulation. The change in body mass followed the change in waterflow, both decreasing to ∼1/3 of their original values. Allele frequency changes at two loci in the regions of vgll3 and six6 predicted more than 80% of the observed body mass reduction.
Modeling the adaptive dynamics revealed that the population mean lagged behind its optimum before catching up approximately six salmon generations after the initial waterflow reduction. The results demonstrate rapid adaptation mediated by large-effect loci and provide insight into the temporal dynamics of evolutionary rescue following human disturbance.
Jensen, A.J., Hagen, I.J., Czorlich, Y., Bolstad, G., Bremset, G., Finstad, B., Hindar, K., Skaala, Ø. & Karlsson, S. 2022. Large-effect loci mediate rapid adaptation of salmon body size after river regulation. PNAS 119(44) e2207634119.