Disturbances in an environment can cause physiological traits to shift in organisms. Physiological trait shifts allow organisms to adjust to new conditions in their environment but changes can have serious effects on survival. Small mammals are particularly susceptible to disturbances. Their relatively large surface area to volume ratios leads to rapid heat loss to the environment incurring high metabolic energy costs to maintain body temperature. Disturbances in an environment challenge this balance and compound metabolic costs. Pseudogymnoascus destructans (Pd) is the fungal pathogen that causes white-nose syndrome in North American bats. Pd infection increases temperate bat energy expenditures during hibernation and subsequent starvation leads to death. Persisting bat populations with chronic Pd exposure may decrease surface area to volume ratios and thus, increase survival over time. Since Pd has optimal growth at colder temperatures, we predict changes to forearm length (a proxy for surface area) and/or mass (volume proxy) vary across latitude with greater shifts at northern latitudes. We collected summer mist net capture data for big brown bats in the eastern US. We then created linear mixed effects models for forearm length divided by mass as functions of pre- to post-Pd introduction, latitude and capture site.
Results/Conclusions
Adult female big brown bats’ surface area to volume ratios decreased with increasing latitude prior to Pd introduction (pre-Pd) but lost that latitudinal decline after Pd introduction (post-Pd; F1, 2920 = 7.752, P = 0.0054, R2 = 0.41). Further, in northern latitudes post-Pd, adult females had a greater surface area to volume ratio than pre-Pd. Adult males (F1, 2930 = 8.738, P = 0.0031, R2 = 0.41) and juveniles (F1, 1532 = 5.267, P = 0.0218, R2 = 0.42) also lost declines in surface area to volume ratios as latitude increased following Pd introduction. Adult males and juveniles in northern latitudes post-Pd also had a greater surface area to volume ratio than pre-Pd. Based on our results, we think persisting bat species may experience long-term physiological impacts from chronic exposure to Pd. Big brown bats are less susceptible to Pd infection and white-nose syndrome relative to other bat species; therefore, physiological responses to pathogen interactions in less susceptible hosts may only be recognizable with long-term exposure rather than upon initial impact. Thus, our results support the need for more research into long-term host-pathogen interactions with less susceptible species in order to holistically evaluate wildlife disease impacts.