Evaluating Adaptive Capacity of Desert Bighorn Sheep to Climate Change: Identifying Genetic Links to Climate Adaptations
Natural selection may result in local adaptation to different environmental conditions across the range of a species. Understanding local adaptation, in turn, informs management decisions such as translocation to restore locally-extinct populations.
We used a landscape genomics approach to detect genetic signatures of selection related to climatic variation among desert bighorn sheep populations across their indigenous range in the western United States. This approach allowed us to investigate broad patterns of both neutral and adaptive genetic variation across very different environments. Analyses suggested that ancestry and isolation by distance were the most significant forces driving genetic variation in desert bighorn sheep, but that climate was associated with at least 1 locus (i.e., location on the genome) under directional selection. The alternate allele (i.e., variant) at this locus was associated with biologically significant increases in elevation and precipitation, decreases in temperature, and was nearly private to herds occupying the Great Basin ecosystem.
Our results suggest climate conditions at higher latitudes may have resulted in a distinct ecotype of desert bighorn sheep whose adaptations are still apparent among the few remaining indigenous populations in the Great Basin. We also found 2 highly supported candidate genes in the genomic region linked to this outlier. How the molecular function of these candidate genes may affect physiological response of desert bighorn sheep to climate is unclear, although their identification provides new insight into the genetic mechanisms potentially underlying environmental adaptation. We identified several other loci under strong directional selection not related to climate and described a previously unknown pattern of strong genetic divergence of bighorn sheep within the White Mountains compared to other populations.
Overall, these findings suggest selection from environmental factors may influence genomic variation at the ecosystem-scale in desert bighorn sheep and these results extend our understanding of how this subspecies may respond to different environmental conditions.