Spatiotemporal analyses reveal infectious disease-driven selection in a free-ranging ungulate

Infectious diseases play an important role in wildlife population dynamics
by altering individual fitness, but detecting disease-driven natural
selection in free-ranging populations is difficult due to complex
disease-host relationships. Chronic wasting disease (CWD) is a fatal
infectious prion disease in cervids for which mutations in a single gene
have been mechanistically linked to disease outcomes, providing a rare
opportunity to study disease-driven selection in wildlife. In Wyoming,
USA, CWD has gradually spread across mule deer (Odocoileus hemionus)
populations, producing natural variation in disease history to evaluate
selection pressure. We used spatial variation and a novel temporal
comparison to investigate the relationship between CWD and a mutation at
codon 225 of the mule deer prion protein gene that slows disease
progression. We found that individuals with the “slow” 225F allele were
less likely to test positive for CWD, and the 225F allele was more common
in herds exposed to CWD longer. We also found that in the past two
decades, the 225F allele frequency increased more in herds with higher CWD
prevalence. This study expanded on previous research by analyzing
spatiotemporal patterns of individual- and herd-based disease data to
present multiple lines of evidence for disease-driven selection in
free-ranging wildlife.