New James Cook University research has used highly sensitive environmental DNA (e-DNA) techniques to find two species of threatened frogs in places they've never been seen before - and find another still struggling to recover from past disease outbreaks.
Queensland's rainforest frogs were hit hard by chytrid fungus in the 1980s and 1990s - an aquatic pathogen that infects the skin of frogs, destroying its structure and function - causing the likely extinction of six species and significant declines of others.
Introduced to Australia through the international trade in frogs, outbreaks of the chytrid fungus disease began here in the late 1970s. The fungus is now recognised as having had one of the biggest impacts on global biodiversity in recent decades.
"The fungus has had its greatest impact on frogs in cool wet areas. The upland frogs that hang around streams were hardest hit," said one of the research paper's co-authors, JCU Professor Conrad Hoskin.
"The Waterfall and Lacelid Frogs were largely knocked out of the uplands of North Queensland's Wet Tropics rainforests by the early 1990s, and we lacked survey data to assess persistence and recovery on many creeks.
"In this study we detected them on many creeks, including in areas we hadn't found them since the chytrid fungus outbreak."
JCU TropWATER's Dr Cecilia Villacorta-Rath led the research and explained that it was good news that the frogs were more widespread than previously thought.
"They're bouncing back," she said.
Another upland frog - the Critically Endangered Armoured Mistfrog - was thought to be extinct in the early 1990s until it was rediscovered at a single site in 2008.
"Our eDNA results now confirm that the only population that survived the catastrophic impacts from chytrid disease was at that single site," said Prof Hoskin.
"When we sampled historic creeks and other likely creeks we didn't find any evidence of them."
In the past, surveying for frogs has involved trekking into extremely remote and inaccessible locations - such as upland waterfalls buried deep within the rainforests of Far North Queensland.
This time, the team of researchers sampled water from more accessible lowland locations in creeks and streams of the Daintree Rainforest - before analysing for genetic traces or DNA fragments of the three different endangered frog species.
"Our eDNA techniques can successfully detect frog populations using water samples collected as far as 22km downstream from where they live," said Dr Villacorta-Rath.
"Environmental DNA helps us find endangered populations without having to check every river and stream to spot individuals directly."
Dr Villacorta-Rath explained that eDNA techniques have opened the door to engaging with a wide range of end-users, including Indigenous rangers, government agencies, industry and citizen science groups.
"The eDNA field sampling protocol is very user-friendly. But guidance on interpretation of results is needed - given that there are many factors that affect eDNA detectability," she said.
"In another project we are asking citizen scientists to collect eDNA samples of waterways in Far North Queensland to better understand fish diversity."
TropWATER is leading advances in eDNA science to address ecological challenges in the Australian Tropics. Projects like this are a valuable first step to identify where at-risk populations may be found.
The research study was supported with funding from the Australian Government under the National Environmental Science Program and has been published in Conservation Science and Practice.
