Molecular taxonomy finally catches up with the growling grass frog

The growling grass frog (aka southern bell frog) is one of the most iconic wetland species across western Victoria and south-east South Australia. Their call is part of the seasonal soundtrack, signalling wetland filling and heralding in the beginning of the dry down. The species is threatened nationally and, during drier periods like the millennium drought, their distribution shrinks back to a limited number of core refuge areas. Like many Australian frogs, they have been knocked around by disease (specifically chytridiomycosis – amphibian chytrid fungus disease), habitat loss, predation by invasive fish and and poor catchment management. Yet they are a species capable of explosive breeding when conditions are right.

The wetter than average conditions experienced during spring and summer of 2022 have allowed frogs in western Victoria to move far and wide in search of new wetland homes. If ever there were a year to hear growlers in a new location, or one where they haven’t been recorded for a while, the summer of 2022 has been it. Have a listen to them calling at Mt Burr Swamp here. I was particularly happy to hear them calling from some wetlands we have only recently rehabilitated, not to mention their deafening chorus at several “older” project sites. It’s part of our motivation because we know, that by keeping water around for longer, we help maximise the chance that tadpoles of this species will survive through to adult frog-hood and with more hydrologically resilient wetlands in the landscape, the opportunities for frogs to re-establish and persist across the landscape improves.

Growling grass frogs at Walker Swamp (Litoria raniformis major)

A recent scientific publication now confirms what has been suspected since some early insights in 2008. The species as we know it, Litoria raniformis, actually exists as a complex of two genetically distinct lineages. The split occurs geographically, i.e. one lineage occurs in the Murray Darling Basin (Litoria raniformis raniformis), with another occupying south-east New South Wales, southern Victoria, south-east South Australia and Tasmania (Litoria raniformis major).

There are however some subtle anomalies, which the authors conclude are most likely a result of humans moving the species around, probably as tadpoles. because of the species’ popularity in the pet trade. For example, the study reports a Tasmanian individual exhibiting genetic signals of a backcross between the two subspecies, and museum specimens from the Mount Lofty Ranges, near Adelaide yield genetic signatures for both subspecies. Populations that have been introduced to New Zealand appear likely to have come from the southern subspecies, L. l. major.

So it looks like humans have been the culprits in mixing up some of the growler’s genetics – an interesting insight into the species! It’s also important to note that anyone keeping these threatened frogs as pets should have the appropriate permit. But for now let’s hope the the recent wetter than average season gives this iconic species a much needed boost!

Lachlan Farrington


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