Conservation Management of the Mountain Chicken Frog
Global biodiversity is being lost at an unprecedented rate, such that we have entered the sixth mass extinction in the history of the earth with emerging infectious diseases (EID) recognised as an important contributor to this loss. Amphibian chytridiomycosis is an EID that has driven very rapid declines in, or even extinctions of, hundreds of amphibian species. Infectious diseases such as chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), often persist in biological and non-biological reservoirs making them difficult to eradicate. In turn, this makes reintroductions of target species challenging due to the risk of infection. This thesis investigates the critically endangered mountain chicken (Leptodactylus fallax) as a case study of the population impacts of a chytridiomycosis epidemic and to test the effectiveness of strategies to mitigate the effects of the disease. Specifically, this research (1) charts the decline of the mountain chicken on the only two islands on which it exists, and determines the impact on genetic diversity; (2) tests whether anti-fungal treatment can improve the survival of mountain chickens with Bd infection in the wild; (3) examines the role of Bd reservoir species in causing Bd infections of reintroduced mountain chickens; and (4) determines habitat features that are predictors of infection at release sites. Chytridiomycosis drove the mountain chicken to near extinction on Dominica in 2002 and Montserrat in 2009, in one of the fastest recorded vertebrate species declines, leading to a significant loss of genetic diversity. On Montserrat, treating mountain chickens with an anti-fungal drug (itraconazole) during the chytridiomycosis epidemic improved survival rates and reduced Bd infection rates in the short term, but did not provide long-term protection. Although mountain chickens have been driven to near-extinction by Bd infection on Montserrat, the pathogen persists in two sympatric reservoir species which are not impacted by Bd infection, the most prolific of which (Eleutherodactylus johnstonei) displays strong seasonality in Bd infection prevalence and load. Timing mountain chicken reintroduction to occur during the period when tree frog Bd infection was at its lowest was tested to determine the impact on reintroduction success. Multi-state mark-recapture modelling applied post-release showed that optimising the timing of release reduced Bd infection rates and increased survival. Radio-tracking was utilised with geographic profiling to determine that release site water bodies were likely sources of Bd infection in reintroduced mountain chickens. This could inform targeted mitigation of the pathogen and improve future reintroduction success. Where species have been extirpated in the wild, and an irreversible threat such as an EID persists, novel reintroduction strategies are required. These include optimising the timing and conditions of release in order to minimise the impact of the threat along with targeted mitigation measures such as individual level treatments.