Environmental variables
To characterize the climate conditions at the sampling sites and identify putative drivers of environment-associated selection, we downloaded monthly data on 19 bioclimatic variables and average solar radiation from WorldClim2 (Fick & Hijmans, 2017). A global aridity index (Aridity) was added to our analysis of evapotranspiration processes and rainfall deficits underlying vegetative growth (Trabucco & Zomer, 2018). We excluded highly correlated variables with variance inflation factors (VIF) > 10 and Pearson correlation coefficients (r ) > |0.7|, leaving eight climate factors for inclusion in the subsequent analyses: BIO2, BIO4, BIO5, BIO6, BIO17, BIO18, Solar9, and Aridity.