The ability of an organism to tolerate seasonal temperature changes, such as extremely cold temperatures during the winter, can be influenced by their pathogens. We tested how exposure to a virulent fungal pathogen, Batrachochytrium dendrobatidis (Bd), affected the critical thermal minimum (CTmin) of two frog species, Hyla versicolor (gray treefrog) and Lithobates palustris (pickerel frog). The CTmin is the minimum thermal performance point of an organism, which we estimated via righting response trials. For both frog species, we compared the righting response of Bd-exposed and Bd-unexposed individuals in either a constant (15ºC) environment or with decreasing temperatures (-1°C/2.5 min) starting from 15°C. The CTmin for both species was higher for Bd-exposed frogs than unexposed frogs, and the CTmin of H. versicolor was higher than L. palustris. We also found that Bd-exposed frogs of both species righted themselves significantly fewer times in both decreasing and constant temperature trials. Our findings show that pathogen exposure can reduce cold tolerance and limit the thermal performance range of hosts, which may lead to increased overwintering mortality.
Keywords: Batrachochytrium dendrobatidis; Hyla versicolor; Lithobates palustris; amphibians; chytrid; chytridiomycosis.
© 2021 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.