Exploring diversity in Australia’s banjo frogs or ‘pobblebonks’

The Australian banjo frogs or ‘pobblebonks’ are a spectacular group of four medium to large (3–9 cm) burrowing frog species, recognisable by their distinctive ‘bonk’ and ‘tok’ mating calls (which sound similar to the pluck of a banjo string).

The Western Banjo Frog (Limnodynastes dorsalis) occurs in south-west Western Australia, while the remaining three species: the Giant Banjo Frog (Limnodynastes interioris), Northern Banjo Frog (Limnodynastes terraereginae) and Eastern Banjo Frog (Limnodynastes dumerilii), are found in southern and eastern Australia. The Eastern Banjo Frog is currently considered to include five subspecies.

The Northern Banjo Frog has the largest distribution of all species in the group, encompassing a range of wet to semi-arid habitats from central New South Wales to the northernmost tip of Queensland. Remarkably, some populations even thrive in the acidic coastal ‘wallum’ swamplands of eastern Australia, earning them a title as one of the most acid-tolerant animals in the world.

In a recent study, we explored phylogeographic diversity within the Northern Banjo Frog and its close relatives, by analysing variation in genetic structure, body shape and appearance (morphology) throughout the species range. We also used a comprehensive analysis of call recordings submitted by citizen scientists to the Australian Museum’s FrogID project to investigate geographic variation in mating calls.

Our study found some key differences between geographically isolated populations in far north Queensland. Interestingly, the Northern Banjo Frogs from Cape York Peninsula appeared to grow much larger and have more vivid patterns than populations further south. We also found that the length and pitch of the Northern Banjo Frog call is highly variable throughout the species’ range, with populations from Cape York Peninsula typically calling with a much lower pitch than populations further south.

Our genetic analyses confirmed the Cape York population as distinct from the southern populations. In our new paper, we redescribe the Cape York population as the Superb Banjo Frog (Limnodynastes terraereginae), while reclassifying the population covering the remainder of their southern range as the Scarlet-sided Banjo Frog (Limnodynastes grayi).

Our study also confirmed that one of the subspecies of the Eastern Banjo Frog (formerly known as Limnodynastes dumerilii grayi – a taxonomic error), is highly distinctive and shares a closer evolutionary relationship with the Superb and Scarlet-sided Banjo Frogs, than to the Eastern Banjo Frog which it was previously grouped with. We reclassify this species as the Coastal Banjo Frog (Limnodynastes superciliaris), resurrecting the first scientific name applied to a specimen collected in Sydney more than 160 years ago!

The Coastal Banjo Frog is the smallest of the three re-classified species and has the most restricted distribution, occurring largely within lowland sandy heath and wallum swamplands from Sydney to the mid-north New South Wales coast. Because of its restricted distribution and the overlap of its habitat with areas of intensive coastal urban development, care will be needed to ensure that this species isn’t pushed towards extinction.

Much is still left to be learned about the distribution and ecology of these species, particularly the Superb Banjo Frog. Due to the remoteness of their habitat in Cape York Peninsula, relatively few records of the species exist on public databases. With that in mind, we send a call-out to any FrogID users who live or travel in Cape York Peninsula – listen out for the distinctive banjo-like “bonk” of a Superb Banjo Frog and be sure to record it with the app. Every recording adds to our knowledge of Australia’s incredible frog diversity!

Superb Banjo Frog (Limnodynastes terraereginae) call

Tom Parkin, Research Assistant, Herpetology, Australian Museum

Dr Jodi Rowley, Curator, Amphibian and Reptile Conservation Biology, Australian Museum

Grace Gillard, Research Assistant, Amphibian and Reptile Conservation Biology, Australian Museum

Professor Stephen Donnellan, Honorary Researcher, South Australian Museum

Acknowledgements

We thank the Australian Biological Resources Study (ABRS) National Taxonomy Research Grant program for providing the funding required to conduct this research. We also thank the dedicated citizen scientists of Australia whose submissions to FrogID are helping us better understand and conserve Australia’s Frogs.