Climate-associated genomic differentiation in Lemmon’s willow, an important restoration species

Kyle Rosenblad, David Ackerly

Restoration practitioners are considering assisted gene flow to promote persistence of restored vegetation under future climatic conditions. However, for many important restoration species, the extent of climate-associated genomic differentiation remains unclear. Here, we examined climate-associated genomic differentiation in Lemmon’s willow (Salix lemmonii), a key species in Sierra Nevada meadow restoration, across 40 montane meadows in California’s Tahoe National Forest (mean pairwise distance = 31 km). Using ddRADseq-derived allele frequencies and 270 m-resolution climate data, we tested for associations between climate and genomic variation, while accounting for geography and population structure. Climate explained 10% of among-population allele-frequency variation. Two complementary genotype-environment association methods identified a shared set of 15 outlier loci, which were associated with spring snowpack, actual evapotranspiration, and potential evapotranspiration. Between-site differences in potential evapotranspiration were also associated with overall pairwise genetic differentiation. Together, these results reveal climate-associated genomic differentiation in an important restoration species and highlight multiple components of hydrology as important factors shaping genomic variation. The relatively fine spatial scale of climate-associated differentiation suggests practitioners may be able to access material for climate-informed restoration plantings within tens of kilometers or less.