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Gillespie G.R.,University of Melbourne | Hunter D.,New South Wales Office of Environment and Heritage | Berger L.,James Cook University | Marantelli G.,Amphibian Research Center
Animal Conservation | Year: 2015

The amphibian pathogen Batrachochytrium dendrobatidis (Bd) has been implicated as a leading agent of amphibian declines. However, few studies have documented the real-time host/pathogen dynamics during the arrival of Bd and the decline of an amphibian population. Diagnosing population declines is difficult because multiple factors may be involved and data are often inadequate. However, identifying the relative impact among different threatening processes is critical to understanding population declines. We report the decline and extinction of a population of a threatened temperate montane frog species Litoria spenceri in south-eastern Australia. Unlike most threatened species at the time, its ecology and population demography were well understood, and a monitoring programme was in place, enabling prompt detection of the decline and evaluation of its cause. Histology for Bd on a unique series of phalange samples showed that the decline was strongly linked to the arrival and increased prevalence of Bd, estimated to have emerged in the population within 39 days of first detection. Our study provides the first real-time observation of a mass die-off and decline in a temperate Australian species and the first tight estimate of Bd arrival in a declining population in Australia. These findings not only provide further evidence that Bd has contributed to amphibian declines but also demonstrates how Bd may work in concert with other threatening processes, resulting in extinction. © 2014 The Zoological Society of London. Source

Canessa S.,University of Melbourne | Hunter D.,NSW Office of Environment and Heritage | Mcfadden M.,Taronga Zoo | Marantelli G.,Amphibian Research Center | Mccarthy M.A.,University of Melbourne
Journal of Applied Ecology | Year: 2014

Summary: Ex situ programmes for endangered species commonly focus on two main objectives: insurance against immediate risk of extinction and reintroduction. Releases influence the size of captive and wild populations and may present managers with a trade-off between the two objectives. This can be further complicated when considering the costs of the captive population and the possible release of different life stages. We approached this decision problem by combining population models and decision-analytic methods, using the reintroduction programme for the southern corroboree frog Pseudophryne corroboree in Australia as an example. We identified the optimal release rates of eggs and subadults which maximized the size of the captive and reintroduced populations while meeting constraints. We explored two scenarios: a long-term programme for a stable age-distributed captive population and a short-term programme with non-stable age distribution and limited budget. We accounted for uncertainty in the estimated vital rates and demographic stochasticity. Assuming a stable age distribution, large proportions of individuals could be released without decreasing the captive population below its initial size. The optimal strategy was sensitive to the post-release survival of both life stages, but subadult releases were generally most cost-effective, producing a large wild population and requiring a cheaper captive population. Egg releases were optimal for high expected juvenile survival, whereas mixed releases of both life stages were never optimal. In the short-term realistic scenario, subadult releases also produced the largest wild population, but they required a large increase in the size and cost of the captive population that exceeded the available budget. Egg releases were cheaper but yielded smaller numbers in the wild, whereas joint releases of both life stages provided more wild individuals, meeting budget constraints without depleting the captive population. Synthesis and applications. Optimal release strategies for endangered species reflect the trade-offs between insurance and reintroduction objectives and depend on the vital rates of the released individuals. Although focusing on a single life stage may have practical advantages, mixed strategies can maximize cost-effectiveness by combining the relative advantages of releasing early and late life stages. Optimal release strategies for endangered species reflect the trade-offs between insurance and reintroduction objectives and depend on the vital rates of the released individuals. Although focusing on a single life stage may have practical advantages, mixed strategies can maximize cost-effectiveness by combining the relative advantages of releasing early and late life stages. © 2014 The Authors. Journal of Applied Ecology © 2014 British Ecological Society. Source

Scheele B.C.,Australian National University | Hunter D.A.,NSW Office of Environment and Heritage | Grogan L.F.,James Cook University | Berger L.,James Cook University | And 6 more authors.
Conservation Biology | Year: 2014

Wildlife diseases pose an increasing threat to biodiversity and are a major management challenge. A striking example of this threat is the emergence of chytridiomycosis. Despite diagnosis of chytridiomycosis as an important driver of global amphibian declines 15 years ago, researchers have yet to devise effective large-scale management responses other than biosecurity measures to mitigate disease spread and the establishment of disease-free captive assurance colonies prior to or during disease outbreaks. We examined the development of management actions that can be implemented after an epidemic in surviving populations. We developed a conceptual framework with clear interventions to guide experimental management and applied research so that further extinctions of amphibian species threatened by chytridiomycosis might be prevented. Within our framework, there are 2 management approaches: reducing Batrachochytrium dendrobatidis (the fungus that causes chytridiomycosis) in the environment or on amphibians and increasing the capacity of populations to persist despite increased mortality from disease. The latter approach emphasizes that mitigation does not necessarily need to focus on reducing disease-associated mortality. We propose promising management actions that can be implemented and tested based on current knowledge and that include habitat manipulation, antifungal treatments, animal translocation, bioaugmentation, head starting, and selection for resistance. Case studies where these strategies are being implemented will demonstrate their potential to save critically endangered species. © 2014 Society for Conservation Biology. Source

Brannelly L.A.,James Cook University | Berger L.,James Cook University | Marrantelli G.,Amphibian Research Center | Skerratt L.F.,James Cook University
Wildlife Research | Year: 2015

Context One of the major drivers of the current worldwide amphibian decline and extinction crisis is the spread of the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd). Captive assurance colonies may be the only lifeline for some species. Current antifungal chemotherapies can be effective for clearing infection but may have detrimental side effects. The only non-chemotherapeutic treatment that has been clinically tested is heat, which is impractical for cold-adapted species. The fungus does not survive desiccation, and therefore a plausible alternative non-chemotherapeutic treatment would be a low-humidity regimen. Aims We tested the efficacy of a low-humidity treatment regimen for treating Bd-infected animals of the critically endangered species Pseudophryne corroboree. This species has high tolerance of dry environments, and is thus an ideal candidate for this treatment trial. Methods Forty frogs were exposed to 1×106 zoospores. At three weeks after exposure access to water was reduced to once daily for 10 days for 20 animals. Ten of these animals were also rinsed daily with the aim of removing zoospores. Key results The drying regimen neither increased survival nor decreased infection load, and treatment may have hastened mortality. All infected frogs died between 21 and 80 days after exposure, except one untreated frog. Conclusions Our results suggest that a drying regimen is not a viable treatment for chytridiomycosis. Infection may decrease the host's ability to cope with water stress. Implications The failed drying treatment in P. corroboree suggests that drying is not an appropriate treatment for chytridiomycosis and treatment efforts should be focussed on chemotherapies for cold-adapted species. P. corroboree is a critically endangered species for which chytridiomycosis is the primary cause of decline, yet few experiments have been carried out on this species with regards to chytridiomycosis. All experimental information about this species and disease will benefit the management and protection of the species. Source

Hunter D.A.,Climate Change and Water | Hunter D.A.,University of Canberra | Speare R.,James Cook University | Marantelli G.,Amphibian Research Center | And 3 more authors.
Diseases of Aquatic Organisms | Year: 2010

Since the early 1980s, the southern corroboree frog Pseudophryne corroboree and northern corroboree frog P. pengilleyi have been in a state of decline from their sub-alpine and high montane bog environments on the southern tablelands of New South Wales, Australia. To date, there has been no adequate explanation as to what is causing the decline of these species. We investigated the possibility that a pathogen associated with other recent frog declines in Australia, the amphibian chytrid fungus Batrachochytrium dendrobatidis, may have been implicated in the decline of the corroboree frogs. We used histology of toe material and real-time PCR of skin swabs to investigate the presence and infection rates with B. dendrobatidis in historic and extant populations of both corroboree frog species. Using histology, we did not detect any B. dendrobatidis infections in corroboree frog populations prior to their decline. However, using the same technique, high rates of infection were observed in populations of both species after the onset of substantial population declines. The real-time PCR screening of skin swabs identified high overall infection rates in extant populations of P. corroboree (between 44 and 59%), while significantly lower rates of infection were observed in low-altitude P. pengilleyi populations (14%). These results suggest that the initial and continued decline of the corroboree frogs may well be attributed to the emergence of B. dendrobatidis in populations of these species. © Inter-Research 2010. Source

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