COS 259-2 - Variation in microclimate preference shapes host infection with a novel fungal pathogen of bats.

Abstract: In recent history, emerging infectious diseases have caused widespread impacts to naïve wildlife host populations. However, within populations, we often observe variation in individual-level severity of infection and disease, which can scale up to population-level responses to the invading pathogen. An important potential source of individual variation is microhabitat selection, which can theoretically influence infection severity. However, mechanistic links between host microclimate preferences and infection severity are poorly understood, despite implications for the conservation of species threatened by emerging infectious diseases. In this study, we investigate how variation in individual temperature preferences of little brown bats (Myotis lucifugus) influence the severity of their infection with Pseudogymnoascus destructans, the fungal pathogen that causes white-nose syndrome. To accomplish this objective, we deployed 298 temperature data loggers on individual bats across seven hibernacula to record body temperature throughout the hibernation season. These data allowed us to characterize the microhabitat selection of each individual over the course of hibernation. We paired individual bat microclimate data with established pathogen growth curves to construct an individual-based model of pathogen growth over the course of hibernation. We compared model results to those of simulations of pathogen growth on data from fixed temperature stations and mean bat temperatures overwinter. We hypothesized that, given the strong temperature-dependence of pathogen growth, individuals that used cold roosting environments more frequently throughout hibernation would have lower infection severity. Correspondingly, we predicted that pathogen growth simulations using data from individual bats would more closely predict on-host pathogen loads than simulations from stationary temperature data loggers, illustrating the capacity of microclimate selection to influence host infection severity. We found that bats that moved to colder roosting locations and used them for longer amounts of time had slower rates of pathogen growth. Reduced pathogen growth rates were further accompanied by additional reductions in weight loss and tissue invasion by the pathogen. Ultimately, this study illustrates that the infection severity of bats with white-nose syndrome can be modified by the microclimate selection of its host. More broadly, our findings demonstrate the important contribution of microclimate selection to infection dynamics with potential to scale up to population-level impacts, important considerations for the conservation of host species.