Climatic drivers of chytrid prevalence in the critically endangered Admirable Redbelly Toad

Abstract Global warming is driving shifts in rainfall and temperature patterns, and projections indicate an increase in frequency and intensity of climate anomalies. These changes influence wildlife disease dynamics, affecting pathogen development, host behavior, physiology, and disease susceptibility. Understanding the intricate interplay between climatic anomalies and emerging pathogens in amphibian is essential to inform conservation efforts targeted towards this highly threatened vertebrate group. In-situ research is recommended as a conservation action by the International Union for Conservation of Nature (IUCN 2023) for the microendemic and Critically Endangered amphibian Melanophryniscus admirabilis (Admirable Redbelly Toad). We therefore investigated the seasonal climatic fluctuations and climatic anomalies affecting infections by the waterborne chytrid Batrachochytrium dendrobatidis (Bd) in this sole surviving population, which holds significant conservation concern. We found links between high Bd prevalence, monthly low rainfall and rainfall deficit. Additionally, an increase in Bd prevalence was associated with temperatures exceeding historical averages. These findings suggests that climatic anomalies play a crucial role in Bd transmission and infection status among toads, probably due their aggregation behavior in few available pools during drier and warmer periods. Despite the current low prevalence of Bd and infection loads, the projected escalation of climatic anomalies might render M. admirabilis uniquely susceptible to synergistic interactions between Bd and extreme climatic conditions. The insights gained from this study can improve the conservation efforts and underscore the intricate relationship between climatic anomalies and chytrid infection, shedding light on potential vulnerabilities within threatened amphibian populations.