Searching for a seriously secretive frog species

We have been searching for some of Australia’s most poorly known frog species in order to find out more about them and threats to their survival. In particular, we want to know if they are impacted by the amphibian chytrid fungus (Batrachochytrium dendrobatidis; Bd), a pathogen responsible for a potentially deadly disease. One species we have been searching for is the Green-thighed Frog (Litoria brevipalmata), a species that is considered threatened but for which very little is known, including whether or not it is impacted by Bd. We set out to try and locate the notoriously elusive Green-thighed frog and report the first data on Bd in the species.

Many of Australia’s frogs are in trouble, partly due to the disease chytridiomycosis, which is caused by the amphibian chytrid fungus (Batrachochytrium dendrobatidis; Bd). Currently, we don’t have a full understanding of where Bd is, what frog species are infected by it and whether or not they get sick or die from it. Having such information would help us determine which frogs could be in the most danger from Bd and how best to help conserve them, making research on amphibian diseases like Bd a focus for the Australian Museum herpetology team.

Detecting Bd means first finding the frogs themselves, and then swabbing their skin, which the fungus is capable of infecting. However, frogs are not the easiest animals to find- they are typically nocturnal, often hidden or camouflaged, and most are pretty small. We often rely on finding frogs by listening out for their calls, but some species call very rarely. The difficulty in finding some frog species is a key reason for why there are still so many gaps in our understanding of frogs and the threats facing them.

The Green-thighed Frog takes the detection difficulty to a whole new level. Not only is it mostly brown, the same colour as the leaf litter under which it shelters, but it also calls only one or two nights of the year, immediately after extremely heavy rain. If there’s not enough rain, then they won’t make a sound- good luck noticing a silent brown frog under brown leaf litter in the middle of a forest!

Not deterred by this knowledge, we set out to discover whether Bd might be a problem for this highly elusive frog. Weather forecasts must have been our most visited websites during this project; any night there was a hint of decent rain, we’d prepare our gear and make the hour and a half drive out to the field site. You would be amazed at how much rain was deemed not enough by these particularly picky frogs. On many a night we wandered through puddles over 10 metres across, emerging from the forest so drenched you’d have thought we’d fallen in the puddles! Between the bouts of torrential rain, it was quiet on these nights; the other local frogs were presumably seeking shelter. Even then, there was no sign of the Green-thighed Frog.

Then one night, after three years of searching and more mosquito bites than bear thinking about, our persistence finally paid off! Opening the doors and stepping out of the four-wheel drive, we heard a distant droning – too far to identify, but probably a frog and maybe one we hadn’t heard calling during our previous surveys. We walked down the dirt road that led to the sound, slowly at first but picking up pace as we got closer until the sound became recognisable. We’d done it, arriving at a flooded ditch on the side of the road, we saw a Green-thighed Frog! And then another and another. We’d actually turned up for a big Green-thighed Frog breeding event, with a bunch of calling males and a few females surrounding the pond!

After containing our excitement for finding the frogs, we swabbed them for Bd, a harmless process where a cotton swab is run along the frog’s skin, picking up the DNA of Bd along the way if it is present.

Our lab tests showed that the individuals we swabbed were free from Bd! But while this initial result is encouraging, we need to expand our research from this single survey to know for certain if the Green-thighed Frog is truly free from Bd or, if Bd is detected on individuals in the future, whether it poses a threat to the species. For now, we’re hopeful that Bd might be something that we don't have to worry about for the Green-thighed Frog. But to be sure, we'll just have to find this frog again!

Christopher Portway, Research Assistant, Herpetology, Australian Museum Research Institute.

Timothy Cutajar, Research Assistant, Herpetology, Australian Museum Research Institute.

Dr Jodi Rowley, Curator, Amphibian & Reptile Conservation Biology, Australian Museum Research Institute & UNSW Sydney.

More information

Portway, C.D., Cutajar, T.P. & Rowley, J.J.L. (2020). Preliminary survey for amphibian chytrid fungus infection in the enigmatic Green-thighed Frog. Herpetological Review. 51 (2), 252-253.

Acknowledgements

Thanks to Jordann Crawford-Ash, Josie Stokes, Harry Leung, Chi Phan, Victoria Graham, and Siobhan Dennison for their assistance in the field, and to Cameron Slatyer, Michael Mahony, and Frank Lemckert for field work advice. This project has been assisted by the New South Wales Government through its Environmental Trust.