Fifteen tadpoles belonging to rare species of Victorian frog have grown legs in a milestone for a critical conservation program days after they were officially declared a distinct subspecies.
The “mysterious” giant burrowing frog is a threatened species found in New South Wales and remote parts of Central and East Gippsland.
Little is known about the “rare and cryptic” species and until now they have never been held or bred in captivity.
This means amphibian specialist Adam Lee, who oversees the Zoos Victoria conservation program, has no clear guide for the species.
“I was definitely a helicopter dad for a bit at the start,” Lee said. “Checking on them daily. Making sure the water conditions were right, making sure we weren’t having issues with water quality and making sure they were feeding well and no signs of disease.
“We got over 100 tadpoles in the initial collection. In the wild, there’s a certain level of mortality but so far we’ve been doing really well and getting all of them through. To have no mortalities so far is good, and you expect it going through the different developmental stages.”
Lee said roughly 15 tadpoles have “metamorphosed” so far – the process by which tadpoles grow legs and become adult frogs – and is hopeful more will soon follow.
“Their tadpole stage can last from three to 11 months and within the next three to four months we’d expect them to go through metamorphosis,” Lee said.
“The main goal at the moment is to establish captive husbandry and make sure we can rear them through the entire life cycle. Metamorphoses into frogs, and then breeding the frogs to lay eggs.”
The species grows to the size of a cricket ball and the young frogs are already larger than other comparable species that have been involved in similar conservation programs such as the critically endangered southern corroboree frog.
Dr Jodi Rowley, a frog biologist at the Australian Museum, said every success in the program should be welcomed, especially since the southern population of the giant burrowing frog has been recognised as a genetically distinct subspecies.
“It was thought they were a bit distinctive before but now it’s official,” Rowley said. “The giant burrowing frog has been officially split into two subspecies. That means the southern populations of the species, which are I believe are involved in the program, are now even more significant.”
The distinction was confirmed in a paper published in the journal Zootaxia on Monday that found the southern and northern populations were genetically distinct.
The Victoria Zoos program began in March when field researchers found the tadpoles in a remote area of Gippsland following higher than average rainfall.
The frog’s numbers have been affected by logging, land-clearing, predation from feral cats and dogs, and diseases such as chytrid fungus that attacks their skin.
The species was further threatened during the 2019-2020 Black Summer bushfires , making the individuals held at Melbourne Zoo a critical insurance population for the species.
Dr Scott Clulow, an honorary associate lecturer with the amphibian research group at Newcastle University, said the news was “fantastic” but the next stage of the process – breeding the frogs – may prove “tricky”.
“It’s a process of experimentation,” Clulow said. “We can do things to aid them like we can do with mammals and even humans. But there’s a lot of subtle environmental cues that are often involved in breeding frogs and they differ a lot between species, so it does require a lot of work to work out the conditions required.”