Abstract
Understanding disease dynamics during the breeding season of declining amphibian species will improve our understanding of how remnant populations persist with endemic infection, and will assist the development of management techniques to protect disease-threatened species from extinction. We monitored the endangered Litoria verreauxii alpina (alpine treefrog) during the breeding season through capture-mark-recapture (CMR) studies in which we investigated the dynamics of chytridiomycosis in relation to population size in two populations. We found that infection prevalence and intensity increased throughout the breeding season in both populations, but infection prevalence and intensity was higher (3.49 and 2.02 times higher prevalence and intensity, respectively) at the site that had a 90-fold higher population density. This suggests that Bd transmission is density-dependent. Weekly survival probability was related to disease state, with heavily infected animals having the lowest survival. There was low recovery from infection, especially when animals were heavily infected with Bd. Sympatric amphibian species are likely to be reservoir hosts for the disease and can play an important role in the disease ecology of Bd. Although we found 0% prevalence in crayfish (Cherax destructor), we found that a sympatric amphibian (Crinia signifera) maintained 100% infection prevalence at a high intensity throughout the season. Our results demonstrate the importance of including infection intensity into CMR disease analysis in order to fully understand the implications of disease on the amphibian community. We recommend a combined management approach to promote lower population densities and ensure consistent progeny survival. The most effective management strategy to safeguard the persistence of this susceptible species might be to increase habitat area while maintaining a similar sized suitable breeding zone and to increase water flow and area to reduce drought.
Highlights
The amphibian disease chytridiomycosis is a major cause of amphibian declines globally and has been called the most devastating threat from disease to biodiversity [1]
In-depth ecological studies are important for determining disease impact in the wild because many factors can affect disease dynamics
The population estimate for Oglivies Dam (0.17 hectares) was 2725 males; and the estimated population density was 16,031 males per hectare (Table 2)
Summary
The amphibian disease chytridiomycosis (caused by the fungal pathogen Batrachochytrium dendrobatidis, Bd) is a major cause of amphibian declines globally and has been called the most devastating threat from disease to biodiversity [1]. In-depth ecological studies are important for determining disease impact in the wild because many factors can affect disease dynamics. Breeding habitat plays an important role in the prevalence of Bd infection, with higher prevalence more often associated with permanent water bodies [2,3]. Bd infection tends to peak seasonally [7,8,9,10,11], and the peak is often attributed to optimal temperature conditions for Bd. other factors might play a role [12]. Intensive population monitoring throughout the breeding season can shed light on the ecological impact of Bd on declining species and can inform management decisions
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