Hibernation Activity and the Susceptibility of Southeastern Bats to Pseudogymnoascus destructans, the Causal Agent of White-Nose Syndrome

Past research in the southeastern United States suggests that bats are regularly leaving hibernacula throughout winter. Of the bats captured during winter outside of cave hibernacula more than 50% of bats were negative for Pseudogymnoascus destructans (Pd), the causal agent of white-nose syndrome (WNS). In addition, of the bats we captured that were Pd positive, pathogen load and prevalence varied considerably among species. Episodic activity and foraging during winter raises body temperature, which should activate the immune system, possibly retarding fungal growth, and resulting in repeated low-level exposures to the Pd pathogen that could lead to disease immunity. Although it is established that bats in the southeastern U.S. are active outside cave hibernacula during winter, the possible impacts on susceptibility to infection by Pd and the epizootiology of WNS both within and among species have not been investigated. Differences in winter activity that may account for species-specific differences in WNS disease susceptibility, particularly in more southern latitudes, require further investigation. To investigate these issues, we captured active bats outside of hibernacula for five winters (2012/13, 2013/14, 2015/16, 2016/17, and 2017/18) to track capture rates and dynamics of Pd from initial invasion through establishment in five cavernicolous bat species ranging in Pd susceptibility. Additionally, we monitored the winter activity of four of these bat species throughout the hibernation seasons of 2016/17, 2017/18, and 2018/19 to delineate similarities and differences in winter activity regimes within and among species. We found that capture rates declined starkly in three out of five study species, which were the three species most susceptible to WNS included in my study. Dynamics of Pd shifted as time passed, although species maintained similar levels to susceptibility to Pd from initial invasion into early establishment. Lastly, various characteristics of activity of hibernating bats (i.e. torpor and arousal skin temperatures, torpor bout and arousal frequency, activity length, and activity frequency) in the southeast U.S. varied significantly and could likely explain some variation of susceptibility to Pd observed in target species.