The aquatic pathogenic fungus, Batrachochytrium dendrobatidis (Bd), infects amphibians and is a leading factor in recent global amphibian declines. Bd infections in North America often fluctuate across seasons, but few studies investigate the effects of winter conditions on infection dynamics in northern temperate climates. Investigating Bd during winter can provide unique insight into which species are sustaining infections and how Bd infection impacts overwintering amphibian hosts. We examined whether Bd infections would persist in aquatic overwintering amphibians in the field. Additionally, we explored how Bd infections would impact cold tolerance via locomotor performance trials in the laboratory. Field sampling documented Bd infection status and infection load of overwintering green frogs (Lithobates clamitans). Our laboratory study tested the effect of Bd infection on thermal tolerance of two anuran species: the pickerel frog (Lithobates palustris), and the gray treefrog (Hyla versicolor). Frogs were acclimated to 15°C, and then tested for loss of righting response at 1°C increments by decreasing temperatures by 0.4°C min-1 to measure critical thermal minimum. Righting response for each individual was also tested at a constant 15°C to calculate difference between temperature treatments.
Results/Conclusions
Field sampling showed that overwintering L. clamitans retain levels of infection prevalence in winter at 28%, which is similar to prevalence in the spring and summer of 29%. In H. versicolor, we found mean critical thermal minimum was significantly higher in infected individuals (mean = 12.7°C) than uninfected individuals (mean = 9.27°C), indicating that infected individuals could not tolerate cold temperatures as well as uninfected individuals. The effect of decreasing temperature on H. versicolor righting response was greater for uninfected than infected individuals. For L. palustris, mean critical thermal minimum was significantly higher in infected individuals (mean = 10.3°C) than uninfected individuals (mean = 6.03°C). The effect of decreasing temperature on L. palustris righting response was not different between infected and uninfected individuals. Our findings show Bd infections can be retained during winter, highlighting the importance of broader sampling for Bd across seasons. The reduced locomotor performance of infected individuals suggests amphibians may be less tolerant of colder temperatures when infected with Bd. Examining Bd infections in winter conditions will help describe a more complete understanding of seasonal Bd dynamics in northern temperate climates.