Limited impact of chytridiomycosis on juvenile frogs in a recovered species

The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) has caused catastrophic frog declines on several continents, but disease outcome is mediated by a number of factors. Host life stage is an important consideration and many studies have highlighted the vulnerability of recently metamorphosed or juvenile frogs compared to adults. The majority of these studies have taken place in a laboratory setting, and there is a general paucity of longitudinal field studies investigating the influence of life stage on disease outcome. In this study, we assessed the effect of endemic Bd on juvenile Mixophyes fleayi (Fleay’s barred frog) in subtropical eastern Australian rainforest. Using photographic mark-recapture, we made 386 captures of 116 individuals and investigated the effect of Bd infection intensity on the apparent mortality rates of frogs using a multievent model correcting for infection state misclassification. We found that neither Bd infection status nor infection intensity predicted mortality in juvenile frogs, counter to the expectation that early life stages are more vulnerable to disease, despite average high infection prevalence (0.35, 95% HDPI [0.14, 0.52]). Additionally, we found that observed infection prevalence and intensity were somewhat lower for juveniles than adults. Our results indicate that in this Bd-recovered species, the realized impacts of chytridiomycosis on juveniles were apparently low, likely resulting in high recruitment contributing to population stability. We highlight the importance of investigating factors relating to disease outcome in a field setting and make recommendations for future studies.