Prevalence of the Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis) in Populations of Two Frog Species in the Australian Alps

David Hunter1, Rod Pietsch1, Nick Clemann2, Michael Scroggie2, Gregory Hollis3 and Gerry Marantelli 4
1 – NSW Department of Environment & Climate Change
2 – Arthur Rylah Institute for Environmental Research
3 – Department of Sustainability and Environment
4 – Amphibian Research Centre

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Summary

Over the past three decades, many amphibian species along the eastern ranges of Australia have been declining at an alarming rate. The Australian Alps region has been no exception, with all endemic frog species declining to a level warranting listing as nationally threatened. There is considerable evidence implicating a disease (chytridiomycosis) as the cause of these declines.This disease is caused by infection with the amphibian chytrid fungus (Batrachochytrium dendrobatidis), which is believed to have been introduced into the Australian environment a few decades ago.

We screened for amphibian chytrid fungus infection in two frog species across the Australian Alps; the common eastern froglet (Crinia signifiera), and the alpine tree frog (Litoria verreauxii alpina). We were particularly interested in identifying the extent to which the common eastern froglet, a species that has not declined in recent years, is a reservoir host for the amphibian chytrid fungus in the Australian Alps. We were also interested in identifying rates of infection in populations of the alpine tree frog, a subspecies that has disappeared from much of its historic range, to infer the likely susceptibility of this subspecies to this pathogen.

This study found that apparently robust populations of both the common eastern froglet and the alpine tree frog carry high infection rates (typically > 80%) of the amphibian chytrid fungus, suggesting that for both taxa, many extant populations currently have a high level of population resilience to this pathogen, at least for the populations that we sampled. This result also identifies both frog taxa as substantial reservoir hosts for the amphibian chytrid fungus in the Australian Alps, which has implications for the management of other threatened frog species in this region.

We did not detect the amphibian chytrid fungus on either species at one site sampled in Kosciuszko National Park, suggesting that this site may be pathogen free. Owing to the relative isolation of this site, it is possible that the amphibian chytrid fungus has not reached this site. The presence of ‘naïve populations’ offers a valuable opportunity to understand the impact of the amphibian chytrid fungus and develop management actions aimed at recovering species such as the southern corroboree frog (Pseudophryne corroboree) and Baw Baw frog (Philoria frosti) that continue to be threatened by this pathogen.