Water relations of the burrowing sandhill frog, Arenophryne rotunda (Myobatrachidae)

Abstract

Arenophryne rotunda is a small (2-8 g) terrestrial frog that inhabits the coastal sand dunes of central Western Australia. While sand burrowing is a strategy employed by many frog species inhabiting Australia's semi-arid and arid zones, A. rotunda is unique among burrowing species because it lives independently of free water and can be found nocturnally active on the dune surface for relatively extended periods. Consequently, we examined the physiological factors that enable this unique frog to maintain water balance. A. rotunda was not found to have any special adaptation to reduce EWL (being equivalent to a free water surface) or rehydrate from water (having the lowest rehydration rate measured for 15 Western Australian frog species), but it was able to maintain water balance in sand of very low moisture (1-2%). Frogs excavated in the field were in dune sand of 4.4% moisture content, as a consequence of recent rain, which was more than adequate for these frogs to maintain water balance as reflected by their low plasma and urine osmotic concentrations. We suggest that in dry periods of the year, A. rotunda can achieve positive water balance by cutaneous water uptake by burrowing deeper into the substrate to where the percent water content is greater than 1.5%.

Biogeography and speciation of a direct developing frog from the coastal arid zone of Western Australia

“…Hopper and Gioia (2004) argue that throughout these climatic fluctuations, the Shark Bay region suffered the most severe climate change due to the massive differences in rainfall experienced in these regions during glacial maxima and minima. A. rotunda is heavily reliant on soil moisture for dermal rehydration (Cartledge et al, 2006); limited rainfall may have diminished soil moisture which thereby restricted populations to coastal areas in the west, reinforcing fragmentation via uplift of the Victoria Plateau.…”

Dryness affects burrowing depth in a semi-fossorial amphibian

“…The few studies in controlled laboratory conditions exploring dryness effects on burrowing behaviour only investigate the occurrence of emergence (Hoffman and Katz, 1989;Jansen et al, 2001). Amphibians are able to rehydrate by absorbing water from surrounding soil (Booth, 2006;Ruibal et al, 1969), so it had been suggested that burrowing anurans exposed to dry conditions would dig deeper into the substrate to seek moisture and rehydrate (Cartledge et al, 2006b). However, this hypothesis remained unconfirmed.…”

Water balance of field-excavated aestivating Australian desert frogs, the cocoon-formingNeobatrachus aquiloniusand the non-cocooningNotaden nichollsi(Amphibia: Myobatrachidae)

“…Noncocooning Australian species mostly burrow in sandy soils, e.g. Heleioporus spp., Notaden nichollsi, Arenophryne rotunda, Myobatrachus gouldii (Bentley et al, 1958;Packer, 1963;Slater and Main, 1963;Tyler et al, 1980;Tyler et al, 2000;Paltridge and Nano, 2001;Thompson et al, 2005;Cartledge et al, 2006). As a burrowing medium, sand has the advantage for non-cocooning species of high water potential at relatively low moisture content, facilitating water absorption by a burrowed frog.…”

“…As a burrowing medium, sand has the advantage for non-cocooning species of high water potential at relatively low moisture content, facilitating water absorption by a burrowed frog. For example, the sandhill frog Arenophryne rotunda can maintain water balance in sand with a gravimetric water content of only 1-2% (Cartledge et al, 2006). Scaphiopus couchii burrow in soil consisting of a higher proportion of fine particles, which correspondingly requires higher moistures to generate water potentials favourable for water uptake by the frog (McClanahan, 1972).…”