Infection increases vulnerability to climate change via effects on host thermal tolerance

Unprecedented global climate change and increasing rates of infectious disease emergence are occurring simultaneously. Infection with emerging pathogens may alter the thermal thresholds of hosts. However, the effects of fungal infection on host thermal limits have not been examined. Moreover, the influence of infections on the heat tolerance of hosts has rarely been investigated within the context of realistic thermal acclimation regimes and potential anthropogenic climate change. We tested for effects of fungal infection on host thermal tolerance in a model system: frogs infected with the chytrid Batrachochytrium dendrobatidis. Infection reduced the critical thermal maxima (CTmax) of hosts by up to ~4 °C. Acclimation to realistic daily heat pulses enhanced thermal tolerance among infected individuals, but the magnitude of the parasitism effect usually exceeded the magnitude of the acclimation effect. In ectotherms, behaviors that elevate body temperature may decrease parasite performance or increase immune function, thereby reducing infection risk or the intensity of existing infections. However, increased heat sensitivity from infections may discourage these protective behaviors, even at temperatures below critical maxima, tipping the balance in favor of the parasite. We conclude that infectious disease could lead to increased uncertainty in estimates of species’ vulnerability to climate change

A project that designs and trials a pilot survey to map the distribution of chyridomycosis (caused by the amphibian chytrid fungus) in Australian frogs

[Extract] The aim of this tender was to design and trial a pilot survey to map the distribution of chytridiomycosis in Australian frogs. The project has 5 components: Scope Items 1 and 3 being desk top synthesis and evaluation activities, Scope Item 2 being a data gathering and proof of concept activity, Scope Item 4 being a field and laboratory based project testing the protocol developed in Scope Item 3, and Scope Item 5 assessing and evaluating the previous outputs and providing recommendations that need to be addressed to allow a national survey for chytridiomycosis to proceed in an effective manner. Diagnostic Tests: An analysis of published and unpublished literature identified that chytridiomycosis could be diagnosed by at least 11 tests, that can be collapsed into 5 categories; culture, microscopical examination of unstained epidermis, histology, capture ELISA and PCR. Although each diagnostic test has detection of the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), as its final outcome and could on superficial assessment appear to be competing with each other, we discovered that this was true only in part. The tests have different functions and complement, rather than exclude, one another. For example, examination of fresh tissue is an essential test when culture of B.dendrobatidis from infected skin is being attempted in the laboratory. Histology is the diagnostic test of choice for retrospective surveys of archived specimens, and the sensitivity of diagnosis is increased by immunohistochemistry using polyclonal antibodies. For the proposed mapping survey, real-time PCR is the recommended diagnostic technique owing to its increased sensitivity and non-invasiveness

Stress and chytridiomycosis: Exogenous exposure to corticosterone does not alter amphibian susceptibility to a fungal pathogen

Recent emergence and spread of the amphibian fungal pathogen, Batrachochytrium dendrobatidis (Bd) has been attributed to a number of factors, including environmental stressors that increase host susceptibility to Bd. Physiological stress can increase circulating levels of the hormone, corticosterone, which can alter a host's physiology and affect its susceptibility to pathogens. We experimentally elevated whole‐body levels of corticosterone in both larval and post‐metamorphic amphibians, and subsequently tested their susceptibility to Bd. Larvae of three species were tested ( Anaxyrus boreas , Rana cascadae , and Lithobates catesbeianus ) and one species was tested after metamorphosis ( R. cascadae ). After exposure to Bd, we measured whole‐body corticosterone, infection, mortality, growth, and development. We found that exposure to exogenous corticosterone had no effect on Bd infection in any species or at either life stage. Species varied in whole‐body corticosterone levels and exposure to corticosterone reduced mass in A. boreas and R. cascadae larvae. Exposure to Bd did not affect mortality, but had a number of sublethal effects. Across species, larvae exposed to Bd had higher corticosterone levels than unexposed larvae, but the opposite pattern was found in post‐metamorphic R. cascadae . Bd exposure also increased larval length in all species and increased mass in R. cascadae larvae. Our results indicate that caution is warranted in assuming a strong link between elevated levels of corticosterone and disease susceptibility in amphibians. The role of physiological stress in altering Bd prevalence in amphibian populations is likely much more complicated than can be explained by examining a single “stress” endpoint. J. Exp. Zool. 321A:243–253, 2014 . © 2014 Wiley Periodicals, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106976/1/jez1855.pd

Red hot frogs:Identifying the Australian frogs most at risk of extinction

More than a third of the world’s amphibian species are listed as Threatened or Extinct, with a recent assessment identifying 45 Australian frogs (18.4% of the currently recognised species) as ‘Threatened’ based on IUCN criteria. We applied structured expert elicitation to 26 frogs assessed as Critically Endangered and Endangered to estimate their probability of extinction by 2040. We also investigated whether participant experience (measured as a self-assigned categorical score, i.e. ‘expert’ or ‘non-expert’) influenced the estimates. Collation and analysis of participant opinion indicated that eight species are at high risk (>50% chance) of becoming extinct by 2040, with the disease chytridiomycosis identified as the primary threat. A further five species are at moderate–high risk (30–50% chance), primarily due to climate change. Fourteen of the 26 frog species are endemic to Queensland, with many species restricted to small geographic ranges that are susceptible to stochastic events (e.g. a severe heatwave or a large bushfire). Experts were more likely to rate extinction probability higher for poorly known species (those with <10 experts), while non-experts were more likely to rate extinction probability higher for better-known species. However, scores converged following discussion, indicating that there was greater consensus in the estimates of extinction probability. Increased resourcing and management intervention are urgently needed to avert future extinctions of Australia’s frogs. Key priorities include developing and supporting captive management and establishing or extending in-situ population refuges to alleviate the impacts of disease and climate change