Why are our frogs disappearing, and is it too late to save them?
The deadliest pathogen ever known is wiping out our frogs. Can it be stopped?
At 7am on January 13, 1984, ranger Keith McDonald was driving along a dirt road deep in the rainforest of Eungella National Park, 80km west of Mackay, when one of the most implausible events in the natural world occurred on the passenger seat beside him.
Inside a container of water, a female frog he had collected from a stream the night before opened her mouth and spat out a fully formed juvenile frog. Over the next half-hour, 14 more froglets were born through their mother’s mouth. As any child will tell you, frogs don’t give birth through their mouth. They don’t give birth at all. They lay eggs, which hatch into tadpoles and metamorphose into frogs underwater. It was the first and last time anyone would see the unique birthing approach of the northern gastric-brooding frog. By March of 1985 the frogs, endemic to this one area on Earth, were gone, never to be seen again.
It wasn’t the only species to go. Since 1979, scientists had reported that frogs in south-east Queensland were declining. The Mount Glorious day frog was the first to go missing in action, and the southern gastric-brooding frog — like its northern cousin, it gestated young in its stomach and gave birth through the mouth — vanished in 1981, just seven years after its discovery. It wasn’t just Australia. Once abundant frogs of South, Central and North America were vanishing. More worryingly, no one could figure out why.
Worse was to come. In 1993, suspecting that whatever was killing the frogs was marching north, McDonald engaged the services of a pioneering wildlife veterinarian, Rick Speare, and the pair raced to the Atherton Tablelands near Cairns.
“We had a bad feeling about what we’d find,” says McDonald. But it was more what they didn’t find. The rainforest streams didn’t croak at night with the calls of frogs anymore. Once plentiful species of frogs had disappeared. “We couldn’t do anything about it — it was gut-wrenching. We didn’t know what was going on.”
There was no obvious cause. Nothing appeared to have changed in the environment. Rainfall was average, the streams were pristine and other animals bountiful. It was a complete mystery. Determined to find the answer, McDonald and Speare assembled what would prove to be a remarkable and groundbreaking wildlife research team. Speare had noticed that the pattern of sudden decline in Queensland was consistent with what you’d expect from an infectious disease. In 1997 his PhD student, Lee Berger, finally identified the culprit as an insidious fungus that attacked the skin of frogs. The fungus was named Batrachochytrium dendrobatidis, or chytrid fungus. Others call it the doomsday fungus.
Berger cracked the case by approaching it as you would a disease outbreak. In a CSIRO lab in Geelong, Victoria, healthy frogs were infected with the fungus and swiftly died. A few months after that experiment, Berger received news of another mass frog die-off, this time in Panama. She received a fax. It was their fungus. They knew then that it was global. During the mid-2000s, Panama would lose two-fifths of its amphibian species. Other outbreaks have devastated populations in Africa and Europe. Some experts are now calling chytrid fungus the “worst pathogen in the world”.
The fungus is a finely tuned killer that targets a biological weak spot. Amphibians’ permeable skin performs a vital role in sustaining water balance, by moving sodium and potassium back and forth. Once the skin is damaged, the frogs lose potassium and their hearts fail, leading to death. Some species fare better than others, and not all frogs die. But what makes it catastrophic on a global scale is the unusually broad number of amphibian species that are susceptible to it. A close relative of the pathogen has decimated salamander species in north-west Europe.
Chytrid fungus is an ancient organism that has thrived in the modern world. It’s thought to have originated in Asia, where it co-evolved to live benignly with native frogs that had developed resistance to it over millions of years. Its spread from the 1970s onwards coincided with the advent of mass air-travel and globalisation. Frogs became accidental stowaways, or were shipped overseas as part of the lucrative pet trade. The fungus hopped on for the ride, likely arriving in Brisbane in 1978; once loose, it spread quickly through amphibian populations that had no inbuilt resistance to it. It favours wet, cool temperate or subtropical climates; stream-dwelling frogs are particularly vulnerable, while resistant frog species can become reservoirs of the disease, hastening its spread.
Yet when Berger published her paper in 1998 postulating the fungus as the cause of the declines, her idea was largely dismissed. It wasn’t thought possible that a disease could be responsible for such catastrophic declines, scientific convention being that environmental forces such as climate change or habitat degradation must be the main drivers. Twenty years after her discovery, Berger — who is currently the Frank Fenner Life Scientist of the Year for solving the mystery of frog extinctions — now thinks she may be onto another major breakthrough in saving the frogs from chytrid fungus, this time using tools from animal breeding. And again, she says, Australia is looking the other way.
In March this year, Australian scientists revealedjust how devastating this fungus has been on a world scale. It is now known to have decimated global biodiversity more than any other pathogen ever recorded, implicated in the extinction of more than 90 amphibian species worldwide and the severe decline of at least 400 more. In Australia, up to seven species of frogs are thought to be extinct due to the fungus and 43 more are in decline — nearly a fifth of all our native amphibians. Six species — the northern and southern corroboree frog, the Baw Baw frog, the spotted tree frog, the kroombit tinker frog and the armoured mistfrog — are in critical danger of extinction.
Wildlife disease is only now beginning to be accepted as a global problem. “People didn’t want to know,” says Berger of her initial discovery. “It took 10 years after our discovery to stop arguing about it. People had invested so much in looking at the environment that they weren’t going to stop just because some young woman from Australia said the most likely thing was a disease.”
“If you’re on to a novel thing in science people typically don’t believe it,” says Berger’s husband Lee Skerratt, a leading wildlife epidemiologist and head of the research group that published the paper detailing the extent of the carnage. “Anything that challenges a prior belief, scientists will find ways to reject.”
The northern and southern corroboree frogs living in the sphagnum moss of Kosciuszko National Park were once so plentiful there are reports of fishermen using them as bait. Today there are fewer than 50 in the wild. Michael McFadden is supervisor of herpetofauna at Sydney’s Taronga Zoo. Here, the highly susceptible frogs have been given a lifeline in the form of a captive assurance breeding colony. The only reason these frogs exist in the wild at all is because they’re continually released from this colony, and similar ones at Tidbinbilla Nature Reserve near Canberra, Melbourne Zoo and Melbourne’s Healesville Sanctuary. If it wasn’t for them, these frogs would already be extinct.
McFadden pulls at the heavy door of a converted shipping container; we don sterile gumboots and step inside a bland room crawling with colour. There are 350 southern corroboree frogs in this container. Frogs can divide opinion but everyone who sees a corroboree frog immediately falls in love. They are adorably small — about 3cm long — with bright yellow stripes the shade of crime scene barricade tape. McFadden holds one in his glove and it lethargically crawls round, looking vaguely helpless but hypnotically beautiful.
The eggs of the corroboree frogs bred here are released into fenced enclosures within Kosciuszko National Park, designed to keep out other species of frogs that transmit the disease. Within these artificial arks the frogs thrive, but they don’t stand much chance in the wild until they can cope with chytrid fungus. It’s not going anywhere so the frogs need to find a way to live with it. That’s where gene resistance technology comes in.
Kyall Zenger, deputy director of the Australia Research Council’s Research Hub for Advanced Prawn Breeding and a professor at Townsville’s James Cook University, has been enlisted by Skerratt and Berger to investigate whether selective breeding technology used in aquaculture is transferable to frogs, to breed chytrid-resistant genes into vulnerable species. “Basically I’m an animal breeder,” says Zenger. “In my game you try to identify animals that carry favourable genes — disease resistance for example — and select those animals to breed. That way you end up with the healthiest and most resilient animals. It’s the same with crops. They’ve been doing this for hundreds of years. What has changed is the technology to speed it up.” Zenger thinks we may be able to use genomic technology to identify certain genes in frogs that are resistant to the effects of chytrid fungus, then use selective breeding to build a sustainable, healthy population and release those frogs back into the wild, where their offspring would carry the same disease resistance, and so on through future generations. “We’re doing it across prawns, barramundi, pearl oysters, a whole variety of animals,” says Zenger.
It’s hardly groundbreaking science; selective breeding is a standard, proven methodology used all over the world. But this approach has never been used for wildlife conservation, and so has not received anywhere near the same amount of funding. Across aquaculture in Australia the private sector has poured money into breeding disease-resistant animals, often teaming with universities and government. But when it comes to wildlife, Skerratt and Berger say they’re hitting a brick wall. They’ve seen one grant application after another turned down. It’s a different story in the US and Canada, where substantial grants have recently been awarded to work on genetic modification of frogs and RNA interference technology for controllers of chytrid.
“This is a blue sky scientific program,” says Zenger. “The really exciting thing for me is, all this technology is proven over decades. We know it works, we know the statistics, we know what we need to do. We’ve got the genomic tools and we can really make a difference to conservation now.” It’s a question of who is going to pay. For direct conservation action Skerratt and Berger estimate $15 million will be needed to fund recovery interventions for the six most endangered frog species. “It’s simple, really,” says Skerratt. “Procrastination will lead to more extinction.”
The house movers are descending on the couple’s Townsville home. Unable to secure funding to continue their gene resistance work at James Cook University, they’re packing up their possessions and their three children and moving to Victoria, where Melbourne University has taken the opportunity to acquire their research group. For Berger, who had to wait a decade for her initial discovery of chytrid fungus to gain wide acceptance, leaving James Cook University is frustrating, but she remains hopeful. After having six grant applications in a row rejected, they’re pinning their hopes on a $1 million Future Fellowship grant with the ARC being successful later this year.
“This shouldn’t be our responsibility,” she says. “It should be government co-ordinating the action. But they’re not, so we have to do it ourselves.”
“It’s a great idea,” says Taronga Zoo’s McFadden. “If we can identify where resistant genes are and selectively breed for that in captivity, or if we can utilise those genes through gene editing, then that could definitely work not just here but all over the world. If we can breed frogs that are resistant then I have no doubt we’ll be able to get them back up there in their former numbers.”
Up in the New England Tablelands of northern NSW, near thetown of Glen Innes, Jodi Rowley, curator of amphibian and reptile conservation biology at the Australian Museum, is in the midst of a search almost certain to end in disappointment. She’s trying to find a frog that hasn’t been sighted since the 1970s and is believed by some to be extinct due to chytrid fungus: the peppered tree frog. Being about the size of a fingernail and coloured mottled brown, Rowley admits it’s the ultimate needle in the haystack. So why bother? Because, she says, the richness of life is worth fighting for. Every species lost punches another hole in the ecosystem. Often we don’t know what we’re losing, or what we could stand to gain. “Frogs are actually beneficial to crops and farming, but that’s a lot harder to quantify for your average Joe,” she admits.
Past experience has taught Rowley you can’t always write off a frog. In October 2017 she was surveying a stream near here in the dead of night when her torch lit up a clutch of brown frogs sitting on a rock. It was a species Rowley had never seen before but she knew only too well what it was: the Booroolong frog, not seen in the area for more than 40 years. It wasn’t the only species to be rediscovered. Back in 2008, the northern Queensland armoured mistfrog was spotted after not being seen since 1991. A year later the yellow spotted bell frog was rediscovered in NSW’s Southern Tablelands, all areas where chytrid is present. The discoveries have given Rowley hope.
“Now we’ve found where the Booroolong frog can survive we’re hoping maybe in some of these places we may also find the peppered tree frog hanging in there. I’m not ready to give up just yet.” Rowley says about 20 per cent of Australia’s frogs are undescribed. “It’s kind of insane! For a lot of frogs we don’t have any records, don’t know where they’re distributed or how many species we have.”
To combat that knowledge gap, while at the same time engaging the public, Rowley has led an Australian Museum initiative through a smartphone app called FrogID. Launched in 2017, the app gives the public a chance to contribute to the scientific database by recording frog calls, which are then GPS location-stamped and uploaded to be identified and scrutinised by experts. “It’s a citizen science tool,” she says. “I’ve listened to tens of thousands from across the country because of FrogID.” Without public engagement Rowley knows there is less chance of obtaining meaningful funding. Part of her job is to get people enthused about frogs. “This one app has made such a difference. People say they’ve never seen or heard or even thought about a frog before, and now it’s all they see and hear.”
Data collected from FrogID recently confirmed the decline of Sydney’s green tree frog, the once common backyard frog that’s now effectively gone. In this case the culprit is probably human manipulation of suburban landscapes; we’re inadvertently destroying suitable breeding habitat by building gutters and efficient drainage, eliminating the areas of natural flooding favoured by the frogs.
FrogID has also revealed some species moving far outside their natural range, such as the eastern dwarf tree frog, detected 400km away from its native range on the NSW-Victoria border. Rowley says FrogID has been a real success in providing previously unknown data on threatened frog species such as the Black Mountain boulder frog and the southern bell frog. In just 18 months the app has generated nearly 20 per cent of total frog records ever collected in Australia.
Rowley admits chytrid fungus is the new reality and says disease is one of the biggest threats to our native species, but she’s cautious about endorsing research into gene resistance as a priority. “Habitat loss is still the biggest threat facing amphibians around the world,” she says. “I think this gene resistance technology could be beneficial for a few species but it’s not practical on a world scale and certainly not in the time frame we are going to need it. It’s a trade-off and we have to make some horrible decisions. Unless there’s more funding for biodiversity we’re going to be constantly competing. But there’s no doubt that not having Lee [Berger] working in the field is a massive blow for the frogs.”
There are signs that certain frog species are developing a level of resistance themselves. The alpine tree frog that lives in the southern alps of NSW and Victoria was found to be maturing quicker, in order to churn out more offspring at a faster rate, to replace the adult population dying of chytridiomycosis. A study from Panama has shown that some wild frogs are producing skin secretions that ward off the fungus. Certain rainforest stream species in northern Queensland are beginning to bounce back, too, moving back upstream to the cooler climates where they were knocked out by chytrid fungus years ago. Often the reason for the recoveries isn’t clear.
Rowley says that’s all the more reason to focus attention on protecting those habitats, so that the frogs have somewhere to live as they learn to tackle the disease themselves. One thing all experts agree on is that more effort is needed if we’re to have any chance of stopping the rot.
“Unless there’s massive overhaul in political will and public engagement then we’ll continue to lose biodiversity in Australia,” says Rowley. “We’ve got a terrible track record. We’re not looking after this country and its wildlife like we can.”
There’s one last frog I feel I need to visit. It’s destined to spend eternity in a jar on a shelf at the Australian Museum, in the aptly named spirit room. Herpetology technical officer Stephen Mahony carefully passes me a jar containing a specimen of Rheobatrachus vitellinus, the northern gastric-brooding frog. It lies on its back in a formalin solution like it’s floating in space, the unmistakeable crook of frogs’ legs splayed out, mouth slightly open, bulging eyes fixed on nothing. This frog is special to Mahony, and not just because it’s probably the most special frog to ever exist on our planet. Mahony’s father Michael discovered it on New Year’s Eve 1983, less than two weeks before Keith McDonald saw that most astounding regurgitation. I ask the young Mahony what he feels when he sees this frog. He pauses with emotion. “Yeah… a lot of things. We don’t really know what could or couldn’t have been done.”
Maybe the frogs have a right to exist regardless of their value to us. Or maybe they have value we’ll never see. The frog in this jar is a Gondwanaland relic that evolved in Australian streams over more than 30 million years, with reproductive biology not seen anywhere else in the animal kingdom, an animal far more outlandish in design than even the platypus. We’ll never know how it turned its stomach into a uterus, or why, and what we could learn from that.
Mahony replaces the jar on the shelf. We leave the aisle of amphibian archives and he spins a wheel to roll the rack along. His father’s frog is swallowed among the 180,000 other amphibian and reptile specimens that will float forever here in the spirit room. The last thing I notice is a new order of empty jars awaiting filling, and plenty of room on the rack.