Skin Lipids, Water Loss, and Energy Metabolism in a South American Tree Frog (Phyllomedusa sauvagei)

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Abstract
Evaporative water loss in Phyllomedusa sauvagei is very low at ambient temperatures up to 30 C but increases precipitously between 35 and 40 C. Standard metabolic rate shows a constant (ca. 2.4) between 10 and 38 C. At ambient temperatures of 38-40 C there are pulsatile releases of clear fluid on the skin, and skin and core temperatures are maintained at 35-37 C. Some skin secretions of P. sauvagei contain lipids which are mainly wax esters. A film of the lipid retards evaporation from a water surface at temperatures below 35 C but is relatively ineffective at 38 C and above. This lipid appears to have a transition temperature strategically placed to minimize evaporative losses up to the point where thermal considerations outweigh those of water conservation.