River drying influences genetic variation and population structure in an Arctic freshwater fish

Conserving biodiversity in an era of rapid climate change requires understanding the mechanisms that influence dispersal, gene flow and, ultimately, species persistence. This information is becoming critical for conserving key species in rapidly warming places such as the Arctic. Arctic freshwater fish not only face warmer conditions, but also the drying of tundra streams due to climate change. Here, we examined population structure, gene flow, and the influence of landscape features on the neutral genetic variation of the Arctic grayling on Alaska’s North Slope. We estimated the number of genetically distinct clusters and determined effective population sizes for and patterns of gene flow among geographic regions. We predicted that river distance, river drying, distance to the coast, and elevational gradient would influence genetic differentiation for Arctic grayling. Bayesian clustering and discriminant analysis of principal components found support for five or six genetic clusters roughly corresponding to downstream and headwater subwatersheds. Estimates of gene flow revealed asymmetric downstream bias. River distance and river dry zones were significantly associated with increasing genetic differentiation among sampling locations despite this species' high dispersal capability and the temporary nature of dry zones. Isolation and downstream-biased dispersal could contribute to high levels of inter-population genetic variation among the headwaters of the North Slope Arctic grayling metapopulation, which might be particularly important for species conservation during rapid climate change. More generally, small, isolated populations might drive particular alleles to higher frequencies due to selection or drift, thus promoting the genetic potential for rapid evolutionary changes under future climate change.