Response of wild caught American bullfrogs (Lithobates catesbeianus) to different strains of the fungal pathogen Batrachochytrium dendrobatidis
Invasive species and emerging infectious diseases contribute to the current biodiversity crisis. Invasive American bullfrogs (Lithobates catesbeianus) are extremely successful invaders and considered to be one of the factors affecting populations of native amphibians due to predation, competition and they can carry diseases that can infect native amphibians. L. catesbeianus has been reported to be a tolerant carrier of the amphibian chytrid fungus Batrachochytrium dendrobatidis(Bd), a pathogen that has contributed to worldwide amphibian population declines. Some suggested that bullfrogs harbor the pathogen across their native and invaded distributional range without experiencing mortality or morbidity. However, recent evidence suggests that bullfrog susceptibility to Bd may be strain specific. Here, we examined the effects of Bd exposure on survival of newly metamorphic bullfrogs using two different Bd strains. One Bd strain was isolated from bullfrogs within their native range (JEL 627, ME referred as native strain) and another strain (JEL 630, OR referred as invasive strain) was isolated from bullfrogs from the invasive range Oregon. We evaluated if Bd exposure affects survival of newly metamorphic individuals exposed to the pathogen and if the responses of exposed animals change depending on the strain to which they were exposed.
We found a differential response of wild caught American bullfrogs from Oregon when exposed to the two Bd strains. Survivorship of animals exposed to the native strain was lower than animals exposed to the invasive strain. Our results suggest American bullfrogs can resist or tolerate their sympatric Bd strain but be susceptible to a novel Bd strain. Our research provides insight to how invasive species respond to different strains isolated from conspecifics from native and invasive distributional ranges.