COS 193-5 - Investigating the seasonal dynamics of Snake Fungal Disease in free-ranging eastern copperheads

Abstract: Snake Fungal Disease (SFD) is an emerging wildlife disease impacting free-ranging snakes across eastern North America. Snake Fungal Disease has been implicated in the decline of multiple imperiled snake populations, including timber rattlesnakes (Crotalus horridus) in New Hampshire and eastern massasaugas (Sistrurus catenatus) in Illinois. However, both individual and population-level impacts of SFD are highly variable, and we lack the monitoring techniques necessary to understand the temporal progression of the disease. Because infected snakes do not always present clinical signs, reliance on visual symptoms alone may overlook valuable information about seasonal dynamics. Most previous studies only used clinical signs to diagnose SFD, such as skin lesions and disfigured scales, and did not repeatedly sample individuals to follow disease progression across the active season. To address this knowledge gap, we combined molecular techniques and standard tracking approaches to monitor the disease histories of snakes over multiple active seasons to determine the individual- and population-level impacts of SFD. Our focal species was the eastern copperhead (Agkistrodon contortrix), a species of special concern in New Jersey that is unrepresented in the SFD literature. During the snake active season (April-September) of 2020 and 2021, we radio-tracked to repeatedly capture individuals from a population of eastern copperheads in New Jersey. During each recapture, we visually assessed individuals for clinical signs of SFD and sampled for fungal DNA. qPCR analysis of samples suggested low prevalence of SFD (8/30 snakes). While individual disease histories and responses varied greatly, overall infection severity remained low, and we observed no SFD-related mortalities. Although population-level fungal loads exhibited a slight decrease over the course of both the 2020 and 2021 active seasons, this seasonality was not statistically significant. We found the lack of a definitive trend surprising because previous studies almost unanimously report that snakes exhibit the worst SFD symptoms in the spring and recover as the active season progresses. Although we cannot rule out secondary and long-term effects of infection on individual fitness, the copperheads in this population appear to be coping with SFD.