Exposure to low doses of Batrachochytrium dendrobatidis reveals variation in resistance in the Critically Endangered southern corroboree frog

Emerging infectious diseases, such as chytridiomycosis caused by Batrachochytrium dendrobatidis (Bd), pose a significant extinction threat to amphibians, including the Critically Endangered southern corroboree frog ( Pseudophryne corroboree ). Understanding phenotypic variation in Bd susceptibility is important for developing and applying novel conservation strategies, such as selective breeding, to enhance disease resistance and support population recovery. In one of the largest experimental Bd challenge studies to date, we exposed 972 juvenile P. corroboree bred to represent the extant genetic diversity of the species, encompassing all 15 historical populations. Across three replicate experiments, survival rates ranged from 44 % to 74 %, with frogs from one zoo exhibiting higher mortality. Notably, 21–47 % of Bd-exposed frogs remained uninfected, suggesting significant phenotypic variation in disease resistance in this population. Among infected frogs, disease progression varied, with most reaching terminal stages within 69 days (range: 33–97 days), though a few individuals maintained stable infection loads without developing clinical chytridiomycosis. Experimental factors, such as age, size, and body condition, did not consistently predict survival or infection rates across experiments. While younger and smaller frogs were generally more susceptible, the effects of these factors varied across replicates, highlighting the importance of large sample sizes and repeated experiments to capture phenotypic variation in susceptibility. These findings suggest that a subset of P. corroboree may possess the capacity to resist or tolerate low-dose Bd exposure, offering potential for selective breeding programs to improve conservation outcomes. The dataset generated from this study will be instrumental in guiding breeding strategies that strengthen conservation efforts for this critically endangered, iconic amphibian.