Conservation efforts for the critically-endangered Southern Corroboree Frog — of which only a handful survive and none are breeding in the wild — have received a major boost, with the long-awaited release of a complete genome.
“If you call to a Southern Corroborree Frog, it will answer back,” says lead author of a paper outlining the research, Dr Tiffany Kosch of the University of Melbourne. But now calls are going unanswered in the amphibian’s habitat at Mt Kosciusko, Australia’s tallest peak.
“The Walgalu Wiradjuri people would call to the ‘gyak’, because its Spring emergence signalled that passes were free of snow and travel was possible,” Kosch told Cosmos.
“Frogs don’t really start breeding until it’s warm enough. So, if there’s still a lot of snow remaining, or if it’s really cold, they won’t call.”
But now the high country has gone quiet. The gyak is critically endangered, functionally extinct in the wild, yet another victim of chytridiomycosis caused by the introduced chytrid fungus.
The species is only able to survive with the support of zoos.
“Only a handful of individuals remain,” says Kosch, and that’s been the case for about 15 years, but they’re only persisting because of yearly reintroductions. “They’re not really breeding in the wild. They’re just kind of hanging around.”
It lives in sphagnum bogs in the New South Wales Snowy Mountains. Its vivid colours warn potential predators that this tasty-looking morsel is poisonous, and an alternative snack might be a better idea. It can’t jump or hop like other frogs and its skin pattern is unique, like the human fingerprint
Now the conservation effort for the amphibian has taken a new turn. A complete Southern Corroboree Frog genome has been mapped.
“This is the first time the genome of this species has been sequenced, and it was not easy due to its enormous size. We discovered that Southern Corroboree Frogs have remarkably large genomes—more than three times the size of the human genome,” Kosch says.
The genome, the frog’s genetic blueprint, will be used to support its conservation and eventual return to the wild by identifying genes which confer resistance to disease.
“The research has taken almost a decade and is one of the highest-quality frog genomes ever produced.”
The research team included the Vertebrate Genomes Project at Rockefeller University, USA and the NSW Department of Climate Change, Energy, the Environment and Water, says Kosch.
A captive-bred male frog supplied the tissue for the genome map, including kidney and liver samples.
“Sadly, the survival of Southern Corroboree Frogs depends solely on conservation breeding programs such as those run at Melbourne Zoo, Healesville Sanctuary, and Taronga Conservation Society,” says Kosch.
“Mapping the genome is the critical first step in our ultimate goal to restore this unique and visually striking species to its natural place in the ecosystem. The genome allows us to understand which genes increase or decrease susceptibility to the chytrid disease.
“Our focus now turns to using what we have learned to selectively breed frogs that are resistant to chytrid fungus and able to not only survive but thrive naturally in the environment, without ongoing human intervention.”
The genome is already being put to work. A gene association study has just been completed, looking at the effect of chytrid on a range of frogs representing the full scope of genetic variability in the remaining population..
“We have their genetic data so we can identify gene regions that are associated with both susceptibility and resistance to the fungus.”
The genetic work has been extended to mapping the genome of the Common Eastern Froglet, which lives alongside the Southern Corroboree Frog, and is resistant to the fungus.
“I’ve just sequenced the Common Eastern Froglet genome and we’re going to be doing some comparisons between the two to look for any immunity genes or something else that may be driving the differences in susceptibility between the two, and if that were the case, we could use approaches like genetic engineering to knock in Chytrid resistance genes to the Corroboree Frogs.”
Kosch also says hybridisation could be possible with the more chytrid-resistant Northern Corroboree Frog.
“But at the moment, the biggest challenge is just trying to determine which genes we might want to be working with, either those that are naturally in the corroboree frogs, or those that might be in other species that could be used as good targets.”
Mapping the genome also has implications for conservation strategies for other amphibians threatened by chytridiomycosis.
“We plan to compare the genome with those of other amphibians to uncover broader patterns of resilience and improve the viability of other at-risk species,” Kosch says.
The paper is published in Wellcome Open Research.
Feature article: frogs and chytrid
