‘The chytrid fungus devastated amphibians globally — frog spas and saunas can help’

What is the core of your research?■ My research tries to tackle global environmental challenges. I’ve worked particularly on invasive species and I’ve been involved for two decades now on emerging diseases, especially the chytrid fungus which has swept the world, wreaking havoc on amphibian biodiversity. Many global problems are difficult to eradicate, so a lot of my work focuses on how we can mitigate impacts, so native species can survive.

Over 40 frog species in Australia have declined heavily due to the disease linked to the chytrid fungus. Seven went extinct completely. This is a worldwide problem but the story starts in Australia because it was only due to the disappearance of the unique gastric brooding frog that triggered people to realise there was a global problem of declining frog species. The cause was chytrid fungus, this microscopic invasive fungal pathogen that lives in water and infects frogs. This emerged in the 1970s, swept the world and sent 100 species completely extinct, with another 400 facing huge population declines. '

Can you tell us about the green and golden bell frogs you’re working on now?
■ The green and golden bell frog used to be one of the most common species on the eastern seaboard of Australia — it’s now disappeared from over 90% of its range, occurring only in a very small number of scattered locations along the East Coast. It’s disappeared entirely in the Australian Capital Territory (ACT) region, which is inland and has a slightly higher elevation. Now, some frogs managed to just hang on in lowland areas towards the coast, where the climate is milder, temperatures slightly warmer through winter and wetlands have more saline influences. I’ve spent 15 years researching this species and found that slightly elevated water salinity can be detrimental to the fungal pathogen while the frogs do fine — wet, cold conditions favour the pathogen. At 25 degrees, it starts to get suboptimal for the fungus — above 27 degrees can be lethal.

Now, our research showed the green and golden bell frog prefers to be in 28 to 30 degrees. Those observations have led us to the approaches we trialed in my lab and in mesocosms at the university — we’ve shown that if you can create small pockets of habitat with these environmental stressor conditions, like temperature and salinity, the pathogen is harmed. These environmental stressors give frogs the upper hand potentially over the infection — rather than mass perishing, frogs might get sick but they’re able to clear themselves of the infection. Alongside, those conditions could make the pathogen less able to infect hosts.

We call these ‘disease refugia’ — we’ve been developing simple, low-tech, affordable and scalable ways to manipulate the environment to hopefully return the green and golden bell frog. After 50 years of it being extinct in the ACT, we’ve released it at 15 wetlands, creating small pockets of disease refugia.

Can you tell us about your frog spas and saunas?■ Our strategy is multi-pronged and the frog spas and saunas are an important part. Too much stress is bad for any organism and we thought we’d flip that paradigm — the fungal pathogen is also a multicellular organism. So, if we could deliberately create additional stress for it, we could tip the balance — slightly elevated salinity and temperatures above a certain threshold do exactly that. Our little saunas are literally just piles of house bricks that the frogs love to get into because they provide nice refuges and have little holes and cracks in them, so frogs feel snug and safe there. If you paint these black and put little greenhouses over them, they heat up well in the sun, even when it’s very cold — in winter here, when the temperature can be close to 0 degrees, these can heat up to 25 degrees or more. Those conditions favour frogs over the pathogen.

For the saline influence, we didn’t want to go and tip truckloads of salt into giant wetlands — so, we developed small satellite ponds, digging in cattle troughs which are cheap and easy. They’re little ponds around big wetlands and we can manipulate the salinity there easily without affecting anything else. The frogs love to use them — and they get a healthy dose of that slightly elevated salinity which the pathogen hates.

Another prong is a human health approach — we and other researchers developed a way to immunise some frogs against the disease. That’s enabled us to release a few hundred such frogs into the wild. They should be protected, at least for that generation, so hopefully, they live long and breed — the offspring, of course, are not immunised but they’re hopefully afforded protection by our spas and saunas. So, we aim to create this roll-away effect of basically self-immunising over generations.

How will you monitor the frogs you’ve released?■ We’ve actually tagged them with a little microchip just under their skin. We go out at night now and call out to them — it’s a wonderful call and it sounds a bit like a motorbike revving up. If you walk around the swamp doing that, they call back to you, so you can spot them with torches and check them, using ‘capture, mark, recapture’ surveys — we then use mathematical models to work out the population size relative to what we released.
We are in the Australian summer now — we’ll soon head into autumn, then winter. When we come out the other side into next spring, and all the frogs reemerge, we’ll have a very good idea about whether they have survived better in the 15 wetlands we have made across the ACT.

Can you discuss your frog names?■ Certainly — one aspect at the heart of this project is to engage community and local citizens in research, monitoring and conservation. There is an old history of believing conservation is best done behind locked gates — I believe the opposite. The more we engage community, the more they become custodians and the more people care helps to protect species. We’ve leveraged that in the incredible work of digging these ponds. Local people are passionate about this — a small part of the reward is how we’ve got 400 green and golden frogs now finally hopping around on ACT soil. They each have a microchip and number but we thought it’s more fun to attach an actual name as people relate to that — some community volunteers came up with creative names like Dua Leaper and James Pond.

Skeptics will ask, why should humans even worry about the fate of frogs?■ Humans couldn’t survive without frogs — it’s that simple. Frogs are an incredibly important part of our ecosystems. They eat huge numbers of invertebrates and control insect populations, which would otherwise cause plagues and diseases like malaria. We’d be overrun with insects without frogs. Tadpoles are one of the most important aquatic nutrient cyclers — wetlands, streams and waterways would not function without them. Frogs are also a crucial source of medical tech and innovation.

Also, frogs are just incredible animals, as amazing as whales, pandas or mammals we are perhaps more drawn to. Frogs are very beautiful, extremely interesting and incredibly diverse. We have two species in Australia called hip pocket frogs — the males have little pouches, a bit like a kangaroo’s pocket, on their hips. The female lays eggs on a forest floor and the male comes up just when they’re ready to hatch. The tadpoles hatch and wriggle inside his pockets. Now, he’s the size of your thumbnail and he has those tadpoles living entirely in his pockets where they metamorphose into froglets, coming out about the size of a match head — then, they’re off on their own journeys into the rainforests of southeast Australia.

Frogs have seen millions of years of evolution that other animals haven’t achieved — they are vital to the existence of the world as we know it.