North American temperate bats are threatened by the introduced fungal pathogen, Pseudogymnoascus destructans (Pd) which causes white-nose syndrome. Pd infects bat wing membranes, causing increased torpid metabolic rates and mortality from energy depletion during hibernation. Surviving bats emerging from hibernation expend additional energy healing from infection. Because of this, populations of persisting and less-susceptible species could see cumulative damaging effects from annual Pd exposure. In areas where Pd is established, repeated host-pathogen interactions may leave less-susceptible females with fewer energy stores to invest in reproduction. Thus, repeated exposure to Pd could negatively affect reproduction, even in species and populations with low white-nose syndrome mortality rates. To examine if energy stores of persisting, less-susceptible female bats is decreasing, we collected summer capture data of less-susceptible species, Eptesicus fuscus, from NY and IN between 1994 and 2018. We used a linear mixed effects model to evaluate female mass as a function of year and site to quantify changes to body mass over time. Residuals from this model were subject to an interaction between the number of years exposed to Pd and reproductive status (i.e. pregnant, lactating, post-lactating and non-reproductive) to determine if mass variation was converging as years of Pd exposure increased.
Results/Conclusions
We found no change in average mass across adult female captures between 1994 and 2018 (P = 0.13). However, when residuals from this model were subject to an interaction between the number of years exposed to Pd and reproductive status, E. fuscus mass diverged from the mean (P < 0.001), suggesting a growing variation in adult female energy stores with more years of Pd exposure. This was driven by an increased variation in pregnant female mass (P = 0.009). Chronic Pd exposure on less-susceptible species could have population level impacts due to the increased variation in pregnant female energy stores. To better understand if an annual energetic disadvantage upon hibernation emergence could be impacting the fitness of less-susceptible species long-term, more E. fuscus capture data from other states are needed. Further investigation within the variation of these data, such as time and relative location of capture, is warranted to reveal the source of this striking variation.