High Northern latitudes are predicted to change considerably in forthcoming climate scenarios, and empirical evidence detailing a species\u27 capacity to cope with extreme variability is needed. Tundra plants make for an excellent study because their genetic histories were impacted by the dramatic transitions of historic glacial and interglacial ages. Here, thousands of restriction site-associated DNA (RAD) markers from geographically isolated Alaskan (Arctic) and Coloradan (Alpine) Bistorta vivipara (Polygonaceae) populations are compared in an investigation of evolutionary response to rapid climate change. Non-coding nuclear markers were analyzed in a coalescent framework to estimate an effective ancestral population size (Na) and divergence date (t) of the two populations of ~23 000 individuals and ~140 000 years before present. Nucleotide substitutions per synonymous site (dS) and nonsynonymous site (dN) were calculated for putative orthologous protein-coding sequences to determine the form of selection acting on the subsampled genome in the context of t. Most sequences were either 100% conserved or exhibited dS \u3e dN, suggesting purifying selection. The few sequences suggesting positive selection (dS \u3c dN) were identified as retroelements, which are expected to escape purifying selection. There were two exceptions: a putative protein phosphatase and a kinase involved with steroid signaling. The results suggest genetic adaptation is not a readily apparent option for B. vivipara’s response to climate change. This, and other organisms whose habitats will shift quickly or disappear, may depend on demographic and plastic responses as alternatives to extinction
