Physiological and Environmental Correlates of Snake Fungal Disease in a Field-active Pitviper

Lind, Craig M.

Department of Natural Science and Mathematics

Stockton University, Galloway, NJ 08205 USA

Farrell, Terence M.

Department of Biology

Stetson University, DeLand, FL 32723 USA

Snake fungal disease (SFD) is an emerging threat to snake populations in the Unites States. The disease is often associated with hibernation or cool winter temperatures, but little detailed information exists to describe the environmental and physiological correlates of infection severity or individual outcomes of infection in field-active populations. To address these gaps in knowledge, we studied a population of Pigmy Rattlesnakes afflicted with SFD over the course of two years. We describe the severity of infection in relation to seasonal variation in three physiological variables (stress hormones, innate immune function, and energetic status) and two environmental variables (food abundance and temperature). We also examine the individual outcomes of infection in snakes that were recaptured repeatedly over the course of the study. Seasonal peaks in the severity of clinical signs of SFD were related to low temperature, high stress hormone levels, low body condition, and low foraging success. Seasonal declines in innate immune function in the population preceded seasonal peaks in the severity of clinical signs. Individuals identified as severely infected at the onset of the study were often recaptured at later dates with no visible signs of infection, and infection severity was unrelated to the probability of recapture over the two-year study. Results indicate multiple potential factors associated with underlying within and among individual variation in SFD severity and highlight important mechanistic relationships that are in need of further experimental investigation.