Biodiversity is declining around the world at an unprecedented rate, threatening the health of the ecosystems on which we depend. One of the major challenges to effective biodiversity conservation is our understanding of species diversity remains incomplete, and largely unrecognised in conservation assessments.

Species discovery is often complicated by the presence of cryptic diversity – commonly defined as two or more distinct species originally classified as one due to morphological similarity.

Many species that were once considered to be geographically widespread, upon closer examination, are found to be groups of very similar-looking but genetically divergent species. These ‘cryptic’ species are often found to have much more restricted distributions and are therefore more vulnerable to extinction than previously realised.

Frogs, in particular, are considered to have high levels of undiagnosed species diversity, and are incidentally one of the most threatened animal groups on the planet. Documenting their cryptic diversity, before it disappears, is thus a key conservation priority and a focus of our research at the Australian Museum.

Cape York Graceful Tree Frog

The Cape York Graceful Tree Frog (Litoria bella) was previously confused with the more widely distributed Graceful Tree Frog (Litoria gracilenta) and was only scientifically named in 2016.

Image: Jodi Rowley
© Jodi Rowley

Part of this work involves listening carefully to frog calls across a species range. Frog calls are species-specific and can be a useful tool for identifying cryptic diversity. By necessity, a male frog’s mating call needs to be distinct from those of other species living in an area, as well as attractive enough to females of its own species.

For some frog groups, variation in their calls may even be a contributing factor driving their cryptic speciation. Female preferences for a particular sounding mating call might result in pre-mating reproductive isolation which, over time, leads to a split into two or more similar-looking species with different sounding calls.

Until recently, there has been a lack of data on variation in advertisement calls for many widespread frogs. However, the call recordings submitted by citizen scientists to the FrogID program have helped bridge this gap immensely. FrogID recordings are already contributing valuable data helping to inform the taxonomy and conservation status for several Australian frog groups.

Red Tree Frog (Litoria rubella)

Red Tree Frog (Litoria rubella).

Image: Jodi Rowley
© Australian Museum

Our research involves a lot of fieldwork ‘ground-truthing’ the recordings, and sometimes collecting specimens and tissue samples of closely-related species for closer comparisons. Back in the lab we measure and compare their morphological characters, sequence their DNA, map species distributions and analyse call recordings to formally describe any cryptic species we discover. We also seek to identify any potential threatening processes that may be impacting the species in the wild.

These studies not only reveal interesting insights into the evolutionary history of species, informing our understanding of how they have diversified over the continent through time – but it has practical applications for biodiversity conservation. By improving our knowledge of the geographic and taxonomic boundaries between species, we can be better informed about an individual species conservation and management requirements.

You can help at home by continuing to document and record the frogs you hear calling, even the seemingly common, widespread ones! It’s all useful data helping us to unravel the mysteries of Australia’s cryptic frogs.

Project leads: Tom Parkin and Jodi Rowley.

Acknowledgements: This project is supported by the Australian Biological Resources Study (ABRS) National Taxonomy Research Grant Program (NTRGP) of the Australian Government Department of Agriculture, Water and the Environment.

Using FrogID

Using the FrogID app to record calling frogs can help understand the true number of frog species in Australia.

Image: Jodi Rowley
© Australian Museum