Cyclorana

When the going gets tough, the tough get digging
Published 5 April 2023

In most people’s minds, frogs are associated with stagnant ponds, limpid pools and sodden swamps. So you might be forgiven for thinking that the desert lands of Australia would not be welcoming to frog-kind, that the only hopping in the area would be done by kangaroos. Nevertheless, Australia is home to a wide diversity of native frog species, some of which exhibit remarkable adaptations to their harsh environment.

Water-holding frog Cyclorana platycephala, copyright Tnarg 12345.

Cyclorana has commonly been recognized as a genus containing a baker’s dozen of frog species widespread across northern and central Australia. They form part of the Australasian treefrogs or bell frogs of the Pelodryadidae (historically included in the Hylidae; Duellman et al. 2016). Some reach large sizes with the giant frog C. australis and New Holland frog C. novaehollandiae each about ten centimetres in length. Cyclorana species differ from other pelodryadids in adaptations for digging such as the absence of discs or pads on the fingers and toes and the first finger opposed to the remaining digits (Cogger 2018). However, though most authors have agreed that the Cyclorana frogs themselves form a coherent group (with the occasional exception of the striped burrowing frog C. alboguttata), they have sometimes fallen as collateral damage to shifting classifications of related pelodryadids. Duellman et al. (2016) subsumed Cyclorana within a larger genus Dryopsophus. In this post, I’m still using Cyclorana for convenience’s sake.

Main’s frog Cyclorana maini, copyright Alexandre Roux.

Species of Cyclorana are mostly found in savannah woodland and desert (Anstis et al. 2016). They are usually only seen after rainfall, during which time they call and breed in temporarily inundated pools and streams. During the intervening dry periods, they burrow underground and aestivate in buried chambers. Chambers vary from a few centimetres below the surface to at least a foot deep (Tracy et al. 2007), presumably depending on species and/or local soil conditions. The frogs adopt a ‘water-conserving’ posture, crouched with legs drawn tight against the body. Large amounts of water may be held in the bladder. Over time, the frogs become encased within a leathery cocoon that entirely covers the body except for the nostrils. Microscopic examination of the cocoon reveals a layered structure (Withers 1995) indicating its formation from shed layers of epidermis. Interestingly, there are few if any indications of overt changes in the frog’s metabolism during aestivation. Skin is not shed at a different rate from normal (one layer every few days) and cocoon formation seems as much a by-product of the immobile frog not cleaning shed layers away as anything else. The frog remains responsive to disturbance and readily breaks free from the cocoon by simply moving about (though the process does naturally become slower as the cocoon grows thicker). Nevertheless, some species of Cyclorana may remain inert for remarkable periods with up to five years recorded for the water-holding frog C. platycephala. That is indeed a long time between drinks.

References

Anstis, M., L. C. Price, J. D. Roberts, S. R. Catalano, H. B. Hines, P. Doughty & S. C. Donnellan. 2016. Revision of the water-holding frogs, Cyclorana platycephala (Anura: Hylidae), from arid Australia, including a description of a new species. Zootaxa 4126 (4): 451–479.

Cogger, H. G. 2018. Reptiles and Amphibians of Australia updated 7th ed. CSIRO Publishing: Collingwood.

Duellman, W. E., A. B. Marion & S. B. Hedges. 2016. Phylogenetics, classification, and biogeography of the treefrogs (Amphibia: Anura: Arboranae). Zootaxa 4104 (1): 1–109.

Tracy, C. R., S. J. Reynolds, L. McArthur, C. R. Tracy & K. A. Christian. 2007. Ecology of aestivation in a cocoon-forming frog, Cyclorana australis (Hylidae). Copeia 2007 (4): 901–912.

Withers, P. C. 1995. Cocoon formation and structure in the aestivating Australian desert frogs, Neobatrachus and Cyclorana. Australian Journal of Zoology 43: 429–441.

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