Emerging infectious diseases have caused dramatic declines in wildlife populations, altered species communities, and changed ecosystem function. Recently, years following the invasion of novel and virulent pathogens, populations of some host species have persisted despite having been predicted to be driven to extinction. Understanding the mechanisms mediating host population response and persistence following pathogen invasion can provide insight into the long-term coevolutionary dynamics between hosts and pathogens. Here, we investigate how characteristics of the host, environment, and their interaction facilitate host population persistence. Utilizing a common garden experiment, we explore the mechanisms of persistence in little brown bats (Myotis lucifugus) impacted by white-nose syndrome (WNS). We hypothesize that characteristics of the host conducive to their survival (i.e. host resistance or tolerance) were positively selected for by disease-induced population declines, but that host traits interact with environmental characteristics to drive colony persistence.
Results/Conclusions
Our data suggest that WNS has positively selected for host traits favorable to survival, but that environmental characteristics within hibernacula interact strongly with these traits to determine disease outcome. We found that infection severity and bat survival remained sensitive to temperature and humidity conditions within hibernacula. Increases in roosting temperature and reductions in relative humidity both increased disease severity and decreased bat survival, suggesting that persisting bat populations may be surviving in part due to climatic conditions of hibernacula. However, in all sites, survival was higher in our experiment than during the initial epidemic, suggesting that little brown bats surviving with WNS also have host traits conducive to surviving disease. Our work shows that the protection afforded by host traits appears to operate most effectively under specific environmental conditions and helps explain heterogeneity in bat population persistence with WNS. Ultimately, our results demonstrate the environmental dependence of host-pathogen coevolutionary dynamics following pathogen invasion.