Rahul Somvanshi
Scientists at the University of Newcastle have bred the endangered Littlejohn’s tree frog in captivity for the first time, producing around 90 healthy tadpoles from laboratory tanks. The breakthrough comes as a proposed transmission line threatens to cut through habitat restoration work spanning nearly a decade.
Two separate pairs bred, producing about 200 eggs each in carefully controlled tanks. The timing creates urgency – the Hunter Transmission Project environmental impact statement remains open for public submissions until 5pm on September 24, 2025.
“It’s incredibly difficult to replicate the natural habitat in the lab. Tadpoles are extremely sensitive, with temperature and water chemistry all needing to be carefully balanced,” said Dr Kaya Klop-Toker, the University of Newcastle conservation scientist who led the breeding program.
The brown tree frogs from the Watagans required precise conditions to trigger reproduction. “This is a species that has been declining for the last 20 to 30 years, very little was known about this species before we started working on them,” Dr Klop-Toker said.
Adults reach 60mm in length with orange coloring in armpits and thighs that distinguishes them from similar species. The species was listed as Endangered under the EPBC Act from February 18, 2022.
The captive breeding forms part of integrated conservation combining habitat creation with laboratory techniques. Working with NSW agencies, the team created more than 40 new breeding ponds in the Watagans ranges, similar to habitat protection efforts for amphibians in other regions.
“We discovered there are two sub-populations living two kilometres apart. By building aquatic stepping stones, we’ve connected frog populations that were previously cut off,” explained Dr Alex Callen, Assistant Director for the Centre for Conservation Science.
Genetic analysis proved the habitat corridor improved gene flow between separated groups. The approach reflects the “One Plan” conservation model recently endorsed by the International Union for Conservation of Nature.
Beyond habitat work, the team developed reproductive technologies for threatened amphibians. Dr Rose Upton leads research into sperm cryopreservation and in vitro fertilization for genetic management.
“Sperm cryopreservation has the potential to boost genetic diversity within both captive and wild populations of threatened frogs. It can even help reintroduce genetic diversity that has been lost,” Dr Upton said.
The techniques allow combining genetics from different populations without moving frogs between small, vulnerable wild groups.
The conservation gains now face pressure from energy infrastructure. “The Hunter Transmission Line project is currently proposing to clear a 60m wide corridor alongside the new breeding habitat, with a proposed switching station to be built on top of key breeding ponds,” Dr Klop-Toker said.
The 110-kilometre, 500-kilovolt transmission line between Bayswater and Olney forms part of NSW’s renewable energy transition as coal stations close. Construction would commence in 2027, subject to approvals.
The conservation program also runs “head-starting” where wild eggs are raised in controlled lab conditions. “This gives the eggs a much better chance to reach maturity by shielding them from predators and disease,” Dr Klop-Toker said.
For monitoring, “we insert a tiny polymer tag under the skin that glows under UV light and lasts a few days to monitor newly released frogs,” since the species rejects microchips.
The captive-bred frogs will go to the Woronora Plateau, with some tadpoles going to Aussie Ark’s Reptile Park. Global statistics show 41% of amphibian release programs achieve multi-generation breeding success in the wild.
The integrated approach demonstrates how small, specialized programs can achieve results through multiple intervention strategies. The work is conducted through the University’s Amphibian Integrated Conservation Unit, with funding secured after the 2019-2020 bushfires.
Littlejohn’s tree frog populations remain small and inbred across their range from Watagan State Forest to the Woronora Plateau. The captive breeding milestone provides new tools for managing genetic diversity in one of Australia’s least-known amphibian species.
The environmental impact statement for the Hunter Transmission Project remains open until 5pm September 24, 2025. Submissions can be made through the NSW Planning Portal at planningportal.nsw.gov.au/major-projects/have-your-say.
