Alpine tree frogs infected with chytrid fungus breed more, study finds

Australia Broadcast Center

27-05-2025

An endangered frog from the Australian alps is not letting a deadly infectious disease interfere with its love life.
University of Melbourne research has found male alpine tree frogs infected with chytrid fungus breed more often.
The study found the infection could make male frogs more attractive to females.
"Our research shows infected animals are increasing their breeding effort and ultimate output," lead researcher Laura Brannelly said.
Alpine tree frogs inhabit eight known spots in the New South Wales and Victorian alps, but the population size at each of these sites is unknown.
Dr Brannelly has been studying the creatures for 12 years.
"The alpine tree frog is really adorable and such a dramatic frog," she said.
Alpine tree frogs are considered endangered in NSW, critically endangered in Victoria and vulnerable by the Commonwealth.
Chytrid fungus is a major threat to the species because it is highly infectious and attacks parts of the frog's skin, affecting its breathing ability.
The disease, which was detected in the late 1990s, has impacted frog populations around the world, including spotted tree frogs and southern corroboree frogs which also live in alpine country.
University of Melbourne researchers studied alpine tree frogs at Mount Hotham and found males produced more sperm at a higher quality when infected.
The study found infected males participated in 31 per cent more breeding events than uninfected frogs.
"The frogs are actually producing more offspring when they're infected," Dr Brannelly said.
"These animals are able to persist in some way due to increased reproduction which is weird and counterintuitive."
The study found infected male frogs also increased their colour display, appearing with brighter yellow throats, likely making them more desirable to females.
Researchers believe their stronger colouring and ability to produce higher quality sperm suggests the species is putting more effort into boosting its population than developing immunity.
"When they're infected, they're not putting a tonne of effort into fighting the disease," Dr Brannelly said.
However, a higher breeding rate does not necessarily equate to a growing population.
Rather, researchers believe the population is plateauing.
The peer-reviewed study, published in Open Biology, found that increased breeding was not a silver bullet for other threats such as climate change, bushfires and drought.
"All of their eggs are in this one basket, literally," Dr Brannelly said.
"That pond is where all of their eggs are and if a fire rips through or the pond dries out before the frogs are able to come out, that can be very detrimental to the population.
"So while breeding seems to be helping them persist and survive right now, it's probably not a long-term strategy."
The new research has excited others in the field, including Zoos Victoria's senior biologist herpetology, Nick Clemann, who has been studying frogs since the late 1990s.
He said the alpine tree frog used to exist in many more sites between Mount Baw Baw and Kosciuszko National Park, but the disease "changed the game in all the wrong ways".
"It's been lost from a large part of its range, particularly in Victoria, so there's barely a handful of sites left where it persists," Mr Clemann said.
Mr Clemann said the new "fascinating" research may help explain why some frog populations could persist despite the disease, while others could not.
"Any information that can help us understand is something we can potentially weaponise against the fungus to try and keep the animals in the landscape," he said.
"It's another piece to this puzzle."