Genetic structure of immunologically associated candidate genes suggests arctic rabies variants exert differential selection in arctic fox populations

Abstract

Patterns of local adaptation can emerge in response to the selective pressures diseases exert on host populations as reflected in increased frequencies of respective, advantageous genotypes. Elucidating patterns of local adaptation enhance our understanding of mechanisms of disease spread and the capacity for species to adapt in context of rapidly changing environments such as the Arctic. Arctic rabies is a lethal disease that largely persists in northern climates and overlaps with the distribution of its natural host, arctic fox. Arctic fox populations display little neutral genetic structure across their North American range, whereas phylogenetically unique arctic rabies variants are restricted in their geographic distributions. It remains unknown if arctic rabies variants impose differential selection upon host populations, nor what role different rabies variants play in the maintenance and spread of this disease. Using a targeted, genotyping-by-sequencing assay, we assessed correlations of arctic fox immunogenetic variation with arctic rabies variants to gain further insight into the epidemiology of this disease. Corroborating past research, we found no neutral genetic structure between sampled regions, but did find moderate immunogenetic structuring between foxes predominated by different arctic rabies variants. FST outliers associated with host immunogenetic structure included SNPs within interleukin and Toll-like receptor coding regions (IL12B, IL5, TLR3 and NFKB1); genes known to mediate host responses to rabies. While these data do not necessarily reflect causation, nor a direct link to arctic rabies, the contrasting genetic structure of immunologically associated candidate genes with neutral loci is suggestive of differential selection and patterns of local adaptation in this system. These data are somewhat unexpected given the long-lived nature and dispersal capacities of arctic fox; traits expected to undermine local adaptation. Overall, these data contribute to our understanding of the co-evolutionary relationships between arctic rabies and their primary host and provide data relevant to the management of this disease.