Spatiotemporal genetic structure of anadromous Arctic char (Salvelinus alpinus) populations in a region experiencing pronounced climate change

We examined spatio-temporal genetic variation at 53 single nucleotide polymorphisms in anadromous Arctic char populations from Western Greenland, a region experiencing pronounced climate change. The study was based on contemporary and historical samples, the latter represented by DNA extracted from otoliths and scales from the 1950s–1960s. We investigated whether genetic population structure was temporarily stable or unstable, the latter due to relatively small spawning and nursery areas combined with a harsh Arctic environment. Furthermore, in order to evaluate the potential for adaptive responses and local adaptation we estimated effective population size (Ne) and migration rate (m). Temporal stability of genetic population structure was suggested, based on a hierarchical analysis of genetic differentiation showing much higher differentiation among samples from different populations (FCT = 0.091) than among temporal samples from the same populations (FSC = 0.01). This was further supported by a neighbor-joining tree and assignment of individuals that showed high contingency between historical and contemporary samples. Estimates of Ne were high (> 500) in three out of four populations, with a lower estimate in one population potentially reflecting fishing pressure or suboptimal environmental conditions. Estimates of m were in most cases low, ≤ 0.01. Ne and m estimates suggest a potential for adaptive responses and local adaptation. However, long generation time may also cause adaptive responses by microevolution to be unable to track climate change, especially considering the low migration rates that reduce potential evolutionary rescue by gene flow from populations better adapted to the altered environments.