World-First Crossbreeding of the Endangered Littlejohn's Tree Frog
This breeding includes world-first crossbreeding of frogs from two otherwise fragmented regions – Darawal and Cordeaux
The breeding success is a major breakthrough in the genetic rescue of a species otherwise facing imminent extinction.
Conservation organisation Aussie Ark in partnership with the University of Newcastle is celebrating a nationally significant conservation milestone; the successful breeding of the endangered Littlejohn’s Tree Frog (Littoria littlejohni) within its nation-first insurance population.
This breeding includes world-first crossbreeding of frogs from two otherwise fragmented regions – Darawal and Cordeaux - which represents a major breakthrough in the genetic rescue of a species otherwise facing imminent extinction.
Aussie Ark started Australia’s first breeding and rewilding program for this iconic amphibian in summer last year, receiving 29 adults from the University of Newcastle’s Centre of Conservation Science which were a mix of captive-born and wild-sourced frogs. These founders were transferred into specialised aquaria in the Conservation Ark facility on the Central Coast of NSW in the grounds of the Australian Reptile Park.
In a landmark effort to curb the extinction trajectory of the species, Aussie Ark then paired frogs for breeding. This included introducing males and females from the Darawal and Cordeaux regions for the very first time in history, in four dedicated breeding tanks.
In late autumn the Conservation Ark team were delighted to witness amplexus (mating) and females becoming visibly gravid (egg-bearing). Three females then produced eggs in quick succession, with another five still gravid.
University of Newcastle researchers including PhD Candidate Lily McGough, who is running the program, attended Conservation Ark to count the first batch of eggs and conduct genetic sampling and diagnostic ultrasound imaging to confirm the reproductive status of all female amphibians.
“The primary aim was to identify which females had laid eggs, allowing us to determine maternal contributions to the population and track genetic diversity within the breeding program,” Ms McGough said. “This breeding success is particularly significant because it represents the first successful cross between two previously isolated Littlejohn’s Tree Frog populations. Bringing together individuals from different populations is a major step in genetic rescue of the species. Inbreeding is a major threat to isolated populations, as it can reduce genetic diversity, decrease reproductive fitness, and limit the species’ ability to adapt to environmental change and disease.”
Aussie Ark Chief Conservation Officer Hayley Shute worked alongside the University team in assessing the frogs and is delighted with the result.
“Based on this research we’re so excited to confirm that in just this first round of egg-laying we have 526 eggs laid!” Ms Shute said. “And fertility is between 92% and 95%, which is affirmation that Aussie Ark has created the ideal captive habitat. This isn’t easy; frogs are considered barometers for a healthy environment; water quality, humidity, temperature and food all have to be perfect to get this sort of stunning result.”
This world-first conservation result for Australia’s iconic Littlejohn’s Tree Frog is a wonderful example of the success that can be achieved via collaborations between non-government and government conservation agencies.
“By combining the University’s expertise in amphibian reproduction, genetic and research with Aussie Ark’s conservation breeding facilities and species management experience, we have been able to achieve outcomes that would not have been possible independently,” concluded Ms McGough. “Aussie Ark provides a vital link between scientific research and the broader community.”
This ‘genetic rescue’ of the Littlejohn’s Tree Frog is hugely significant, especially considering the frog’s conservation status. In the wild, the species is only found in three fragmented locations, with its last stronghold the Watagans in NSW. Sadly, this breeding area is earmarked for EnergyCo’s Hunter Transmission Station which will obliterate the habitat. Aussie Ark is fighting to stop this.
This holistic breeding and rewilding program – from rescue to rehabilitation to ultimate release – is complex and expensive. This tax time Aussie Ark appeals to the public to help ensure a future for the endangered Littlejohn’s Tree Frog, by donating before June 30 at aussieark.org.au
