Population decline of a leaf frog coincident with recurrent ranavirosis outbreaks in the Atlantic Forest

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Abstract Amphibian populations are increasingly threatened by emerging pathogens, yet robust evidence linking disease outbreaks with population-level impacts remains scarce in the Neotropics. We investigated a mortality event affecting endemic treefrogs in the Brazilian Atlantic Forest by integrating field observations, molecular characterisation, histopathology, and long-term monitoring. Ranavirosis infection was the confirmed primary cause of mortality, with phylogenetic analyses placing the virus lineage within a globally distributed Ranavirus rana1 (FV3) clade. Outbreak probability was negatively associated with short-term relative humidity, suggesting that drier conditions facilitate disease progression. The outbreaks coincided with a > 80% decline in reproductive output of the population, indicating a severe collapse in recruitment. Strikingly, model comparisons revealed that none of the climatic variables showed consistent trends over the past > 25 years, with the long-term decline better explained by the epizootic shift than by climatic variation. Together, these findings provide rare evidence consistent with recurrent ranavirosis outbreaks contributing to population decline in Neotropical amphibians and highlight the need to integrate disease surveillance into conservation strategies.

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