The chytrid fungus Batrachochytrium dendrobatidis has been implicated in the decline and extinction of numerous frog species worldwide. In Queensland, Australia, it has been proposed as the cause of the decline or apparent extinction of at least 14 high-elevation rainforest frog species. One of these, Taudactylus eungellensis, disappeared from rainforest streams in Eungella National Park in 1985–1986, but a few remnant populations were subsequently discovered. Here, we report the analysis of B. dendrobatidis infections in toe tips of T. eungellensis and sympatric species collected in a mark-recapture study between 1994 and 1998. This longitudinal study of the fungus in individually marked frogs sheds new light on the effect of this threatening infectious process in field, as distinct from laboratory, conditions. We found a seasonal peak of infection in the cooler months, with no evidence of interannual variation. The overall prevalence of infection was 18% in T. eungellensis and 28% in Litoria wilcoxii/jungguy, a sympatric frog that appeared not to decline in 1985–1986. No infection was found in any of the other sympatric species. Most importantly, we found no consistent evidence of lower survival in T. eungellensis that were infected at the time of first capture, compared with uninfected individuals. These results refute the hypothesis that remnant populations of T. eungellensis recovered after a B. dendrobatidis epidemic because the pathogen had disappeared. They show that populations of T. eungellensis now persist with stable, endemic infections of B. dendrobatidis.

Summary1. Emerging infectious diseases can have serious consequences for wildlife populations, ecosystem structure and biodiversity. Predicting the spatial patterns and potential impacts of diseases in freeranging wildlife are therefore important for planning, prioritizing and implementing research and management actions. 2. We developed spatial models of environmental suitability (ES) for infection with the pathogen Batrachochytrium dendrobatidis, which causes the most significant disease affecting vertebrate biodiversity on record, amphibian chytridiomycosis. We applied relatively newly developed methods for modelling ES (Maxent) to the first comprehensive, continent-wide data base (comprising >10000 observations) on the occurrence of infection with this pathogen and employed novel methodologies to deal with common but rarely addressed sources of model uncertainty. 3. We used ES to (i) predict the minimum potential geographic distribution of infection with B. dendrobatidis in Australia and (ii) test the hypothesis that ES for B. dendrobatidis should help explain patterns of amphibian decline given its theoretical and empirical link with organism abundance (intensity of infection), a known determinant of disease severity. 4. We show that (i) infection with B. dendrobatidis has probably reached its broad geographic limits in Australia under current climatic conditions but that smaller areas of invasion potential remain, (ii) areas of high predicted ES for B. dendrobatidis accurately reflect areas where population declines due to severe chytridiomycosis have occurred and (iii) that a host-specific metric of ES for B. dendrobatidis (ES for Bd species ) is the strongest predictor of decline in Australian amphibians at a continental scale yet discovered. 5. Synthesis and applications. Our results provide quantitative information that helps to explain both the spatial distribution and potential effects (risk) of amphibian infection with B. dendrobatidis at the population level. Given scarce conservation resources, our results can be used immediately in Australia and our methods applied elsewhere to prioritize species, regions and actions in the struggle to limit further biodiversity loss.

The chytrid fungus Batrachochytrium dendrobatidis (Bd ) is likely the cause of numerous recent amphibian population declines worldwide. While the fungus is generally highly pathogenic to amphibians, hosts express a wide range of responses to infection, probably due to variation among hosts and environmental conditions, but possibly also due to variation in Bd. We investigated variation in Bd by exposing standardized host groups to 2 Bd strains in a uniform environment. All exposed frogs became infected, but subsequent lethal and sub-lethal (weight loss) responses differed among groups. These results demonstrate variation in Bd and suggest variation occurs even at small geographical scales, likely explaining some of the variation in host responses. With lower than expected mortality among infected frogs, we continued our study opportunistically to determine whether or not frogs could recover from chytridiomycosis. Using heat, we cleared infection from half of the surviving frogs, leaving the other half infected, then continued to monitor mortality and weight. Mortality ceased among disinfected frogs but continued among infected frogs. Disinfected frogs gained weight significantly more than infected frogs, to the point of becoming indistinguishable from controls, demonstrating that at least some of the effects of sub-lethal chytridiomycosis on hosts can be non-permanent and reversible.