Frequent Arousal from Hibernation Linked to Severity of Infection and Mortality in Bats with White-Nose Syndrome

White-nose syndrome (WNS), an emerging infectious disease that has killed over 5.5 million hibernating bats, is named for the causative agent, a white fungus (Geomyces destructans (Gd)) that invades the skin of torpid bats. During hibernation, arousals to warm (euthermic) body temperatures are normal but deplete fat stores. Temperature-sensitive dataloggers were attached to the backs of 504 free-ranging little brown bats (Myotis lucifugus) in hibernacula located throughout the northeastern USA. Dataloggers were retrieved at the end of the hibernation season and complete profiles of skin temperature data were available from 83 bats, which were categorized as: (1) unaffected, (2) WNS-affected but alive at time of datalogger removal, or (3) WNS-affected but found dead at time of datalogger removal. Histological confirmation of WNS severity (as indexed by degree of fungal infection) as well as confirmation of presence/absence of DNA from Gd by PCR was determined for 26 animals. We demonstrated that WNS-affected bats aroused to euthermic body temperatures more frequently than unaffected bats, likely contributing to subsequent mortality. Within the subset of WNS-affected bats that were found dead at the time of datalogger removal, the number of arousal bouts since datalogger attachment significantly predicted date of death. Additionally, the severity of cutaneous Gd infection correlated with the number of arousal episodes from torpor during hibernation. Thus, increased frequency of arousal from torpor likely contributes to WNS-associated mortality, but the question of how Gd infection induces increased arousals remains unanswered.

Physiological Consequences Of White-Nose Syndrome

White-nose syndrome (WNS) is a disease that has caused the mass mortality of hibernating bat species. Since its first discovery in the winter of 2006-2007, an estimated five million bats or more have been killed. Although infection with Pseudogymnoascus destructans (Pd, the causative agent of WNS) does not always result in death, bats that survive Pd infection may experience fitness consequences. To understand the physiological consequences of WNS, I measured reproductive rates of free-ranging hibernating bat species of the Northeastern United States. In addition, captive little brown myotis (Myotis lucifugus) bats that were infected by Pd but survived (¿WNS survivors¿) and uninfected bats were studied in order to understand the potential consequences (e.g., lower reproductive rates, decreased ability to heal wounds, degradation of wing tissue, and altered metabolic rates) of surviving WNS. No differences in reproductive rates were found between WNS-survivors and uninfected bats in either the field or in captivity. In addition, wound healing was not affected by Pd infection. However, wing tissue degradation was worse for little brown myotis 19 days post-hibernation, and mass specific metabolic rate (MSMR) was significantly higher for those infected with Pd 22 days post-hibernation. While it is clear that these consequences are a direct result of Pd infection, further research investigating the long-term consequences for both mothers and pups is necessary.