Mutational load and adaptive variation are shaped by climate and species range dynamics in Vitis arizonica.

Abstract

Genetic load can reduce fitness and hinder adaptation. While its genetic underpinnings are well established, the influence of environmental variation on genetic load is less well characterized, as is the relationship between genetic load and putatively adaptive genetic variation. This study examines the interplay among climate, species range dynamics, adaptive variation, and mutational load - a genomic measure of genetic load - in Vitis arizonica, a wild grape native to the American Southwest. We estimated mutational load and identified climate-associated adaptive genetic variants in 162 individuals across the species' range. Using a random forest model, we analyzed the relationship between mutational load, climate, and range shifts. Our findings linked mutational load to climatic variation, historical dispersion, and heterozygosity. Populations at the leading edge of range expansion harbored higher load and fewer putatively adaptive alleles associated with climate. Climate projections suggest that V. arizonica will expand its range by the end of the century, accompanied by a slight increase in mutational load at the population level. This study advances understanding of how environmental and geographic factors shape genetic load and adaptation, highlighting the need to integrate deleterious variation into broader models of species response to climate change.