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The Cocoon of the Fossorial Frog Cyclorana australis Functions Primarily as a Barrier to Water Exchange with the Substrate

Reynolds, Stephen J., Christian, Keith A. and Tracy, Christopher R. (2010). The Cocoon of the Fossorial Frog Cyclorana australis Functions Primarily as a Barrier to Water Exchange with the Substrate. Physiological and Biochemical Zoology,83(5):877-884.

Document type: Journal Article

IRMA ID 81704288xPUB178
Title The Cocoon of the Fossorial Frog Cyclorana australis Functions Primarily as a Barrier to Water Exchange with the Substrate
Author Reynolds, Stephen J.
Christian, Keith A.
Tracy, Christopher R.
Journal Name Physiological and Biochemical Zoology
Publication Date 2010
Volume Number 83
Issue Number 5
ISSN 1522-2152   (check CDU catalogue  open catalogue search in new window)
Scopus ID 2-s2.0-77956020099
Start Page 877
End Page 884
Total Pages 7
Place of Publication United States of America
Publisher University of Chicago Press
HERDC Category C1 - Journal Article (DIISR)
Abstract Studies of evaporative water loss using streams of dry air in the laboratory have demonstrated reduced rates in various taxa of cocooned frogs. However, because the cocoon is formed in subterranean burrows with humid microclimates and no air flow, loss of water by evaporation is likely to be negligible. In contrast, although potentially important, the influence of the cocoon on water exchange with the soil surface has not been characterized. In dry soils, there is a sizable water potential gradient between the frog and the soil; hence, we hypothesized that cocoons would play a role in reducing liquid water loss to dry substrates. Individuals of the burrowing frog Cyclorana australis (Hylidae: Pelodryadinae) were induced to form cocoons in the laboratory. On semisolid agar‐solute substrates across a range of water potentials, the hygroscopic cocoon absorbed small but similar amounts of moisture. With the cocoon removed, the frogs gained or lost water, depending on the direction of the frog‐substrate water potential difference. Plasma osmolality of cocooned frogs was significantly higher than in hydrated frogs. Because cocooned frogs did not exchange significant amounts of water at either high (wet) or low (dry) substrate water potentials, we conclude that the cocoon of fossorial frogs acts as a physical barrier that breaks the continuity between frog and substrate. We contend that the primary function of the cocoon is to prevent liquid water loss to drying clay and loam soils, rather than to prevent subterranean evaporative water loss.
DOI http://dx.doi.org/10.1086/656218   (check subscription with CDU E-Gateway service for CDU Staff and Students  check subscription with CDU E-Gateway in new window)
 
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