Australia’s hip-pocket frogs practice one of the most distinctive breeding strategies in the amphibian world – and are actually two species, DNA analysis has revealed. Both species are highly threatened by climate change, habitat loss, and introduced species, and the newly described version is almost certainly critically endangered.
Hip-pocket frogs, also known as marsupial frogs, live in rainforests on eastern Australian mountains. Unlike almost all other amphibians, they lay eggs on the rainforest floor rather than in water. The father stays close to the eggs for around six days, then sits on the egg mass, which liquefies. The tadpoles climb up into small pouches near the top of each leg, and stay there until they grow legs of their own, at which point start their independent lives.
The frog has been scientifically described since 1933, presumably known to the Indigenous people of the area thousands of years longer. However, Professor Michael Mahony of Newcastle University led a team examining its DNA, and found the frogs living on Wollumbin (Mt Warning) are a separate species from those at the other five known locations. The discovery was reported in Zootaxa, where the new species is called Assa wollumbin. Those at other locations keep the name Assa darlingtoni.
The two frogs, both 16mm (0.6 inches) long, look so similar even herpetologists can’t tell them apart. However, with hundreds of kilometers of hot dry valleys separating A. darlingtoni’s known habitats, Mahony and co-authors thought they might have been separated long enough to divide into separate species. They took DNA samples from frogs at each location and tested for differences. Mahony told IFLScience it was surprising that frogs at some of the more distantly scattered sites remained genetically quite similar, while those at Wollumbin were different enough to deserve a new name.
Having identified the genetic differences, the team investigated again and noticed differences in their mating calls. A wollumbin has a higher dominant frequency and seldom uses more than nine notes to a call, while A. darlingtoni uses around 13 in warm weather. However, Mahony told IFLScience it would probably be hard to identify species in the wild on this basis alone without a recording of each for comparison.
There are no known differences in the two species’ approach to their really distinctive feature: the parental care provided by the fathers. “As far as we know the mother does nothing after laying the eggs,” Mahony told IFLScience. “The father doesn’t seem to supply any nutrition.” However, the protection he provides to the developing tadpoles – still feeding off the yolks of their eggs – is apparently crucial.
In a world where many male animals provide no parental care at all, and those that do usually share it with the females, Mahony said; “It’s not easy to see” how this arose. “Only four of the 4,000 [frog] species worldwide have male parental care where the male carries its developing tadpoles ,” Mahony said in a statement. The other two examples are rainforest-dwelling South-American frogs where the father carries the tadpoles to water, where they develop unsupported.
Assa’s habitat is often steep, so while the environment is wet enough not to desiccate the eggs, there are few standing bodies of water. “By freeing themselves of the need to use standing water to breed the frogs escape predators,” Mahony noted, “They can breed wherever there is wet moss or leaves.”
Being located just inside New South Wales, A. wollumbin is eligible for the state’s newly created category of protection, Assets of Intergenerational Significance, which could see it and Wollumbin National Park gain additional resources.