In a fascinating new study from the November/December 2006 issue of
Physiological and Biochemical Zoology, researchers from the University
of Florida explore wiping behaviours in a tree frog that waxes itself,
and test whether these frogs become dormant to conserve energy during
dehydration. Many amphibians have skin that offers little resistance to
evaporative water loss. To compensate, these and some other arboreal
frogs secrete lipids and then use an elaborate series of wiping motions
to rub the waxy secretions over their entire bodies.
"This self-wiping is a complex behaviour involving the use of all
four limbs to stroke or rub all dorsal and ventral body surfaces,
including the limbs," explains Nadia A. Gomez (University of Florida,
Gainesville) and her coauthors. They continue: "Thus, the animal is
protected from dehydration, provided the external film of lipids is not
physically disrupted by movements or other disturbance."
Tree frogs characteristically go into a resting posture after wiping
themselves, tucking their limbs tightly against or beneath their body
and closing their eyes. The researchers found that this series of
actions following "waxing" allows tree frogs (Phyllomedusa
hypochondrialis) to limit rates of surface evaporation to as little as
4 percent of that from a free water surface in the same environment.
To examine the question of dormancy, the researchers found that
waxed and inactive frogs had about the same metabolic rate as unwaxed,
dehydrating frogs. This suggests that waxed frogs are not in a
hibernation-like dormant state, as was previously thought. (Some frogs,
however, showed moderate reductions of metabolic rate as dehydration
advanced, suggesting that they might become dormant during, for
example, a prolonged drought.)
"Our data do not provide strong evidence that P. hypochondrialis
routinely depress metabolic rates and enter a deep dormant state during
quiescent behaviours following wiping," explain the authors. "Moreover,
quiescent Phyllomedusa remain responsive to [the] presence of insects
and eat readily."
Since 1928, Physiological and Biochemical Zoology has presented
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Nadia A. Gomez, Michelle Acosta, Frederic Zaidan III, and Harvey B.
Lillywhite. "Wiping Behavior, Skin Resistance, and the Metabolic
Response to Dehydration in the Arboreal Frog Phyllomedusa
hypochondrialis." Physiological and Biochemical Zoology 79:6.
University of Chicago Press Journals. October 2006.