An alpine plant shows no decrease in genetic diversity associated with rapid post-glacial range expansion

While range expansion is hypothesized to be a mechanism for species persistence under climate change, many eco-evolutionary models describe demographic and genetic processes during range expansion that may decrease genetic variation and increase genetic load at the leading edge (i.e., expansion load). These predictions are related to dispersal limitation at the leading edge driving colonization dynamics, a scenario common in post-glacial range expansion at the continental scale (≈20,000 years ago). However, post-glacial range expansion can also occur on contemporary time scales, such as alpine glacier recession following the end of The Little Ice Age (≈150 years ago) and our understanding of dispersal limitation structuring these instances of rapid range expansion are relatively understudied. Here, we test whether there is evidence supporting the role of dispersal limitation during range expansion following alpine glacier retreat using the native alpine plant Erythranthe ( Mimulus ) lewisii by examining patterns of neutral genetic diversity (single nucleotide polymorphisms) across the history of glacier recession (i.e., glacier chronosequence) across two glacier forelands in Garibaldi Provincial Park, BC. We find weak support for the prediction of increasing clines in genetic differentiation towards the range edge, and no support for decreasing clines in genetic diversity, suggesting dispersal limitation is not characterizing colonization during range expansion, with the implication that the accumulation of expansion load at the range edge is likely not applicable on these spatiotemporal scales. Together, our results suggest that loss of genetic diversity for range-shifting species in the alpine is likely not a key contributing factor to any decreased fitness over time.