Amphibian survival compromised by long-term effects of chytrid fungus

Abstract

Chytridiomycosis, the disease caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), has been unambiguously implicated in the decline of amphibian populations worldwide. However, the impact of this devastating infectious disease can be difficult to gauge without empirical data on the population-level effects of Bd. Often, assessments of the amphibian chytridiomycosis panzootic are based primarily on expert opinions; as a result, declines in tropical areas are promptly attributed to Bd while its impact on temperate species not suffering from adult mass mortalities is frequently overlooked. Here, we investigated the survival probability in an amphibian species from a temperate area that until now has not been considered to be severely impacted by the disease. Specifically, we related individual survival to Bd infection status using long-term capture-mark-recapture data of male spiny common toads (Bufo spinosus) in Sierra de Guadarrama National Park in central Spain. Even though the study population has demonstrated potential for adaptation to Bd and die-offs of adult individuals have not been recorded, our results clearly indicated that the probability of survival was lower for Bd-positive individuals. Moreover, the probability of becoming Bd-positive was higher than the probability of clearance, driving the population to a slow but certain decline. These results are consistent with other indicators of a negative population trend and suggest that the impact of Bd on temperate species of less concern may be greater than previously thought.