Evaporative water loss and skin lipids of anuran amphibians

Abstract

Abstract African reed frogs ( Hyperolius spp) and tree frogs ( Chiromantis spp), an Australian tree frog ( Litoria gracilenta ) and a South American tree frog ( Phyllomedusa azurae ) have much lower rates of evaporative water loss from their dorsal skin (0.2 to 2 mg g −1 h −1 ) than most anuran amphibians, which evaporate water at a rate equivalent to a free water surface. Evaporative water loss rates of Chiromantis, Hyperolius , and Litoria are considerably higher when their ventral skin is exposed. Other anuran amphibians, Hylagratiosa, Agalychnis callidryas , and Afrixalus spp, appear to be moderately waterproof. The mechanism for reduction of evaporative water loss from the skin of the waterproof frogs is unclear, but it appears to involve a lipid barrier. This barrier is disrupted by treatment with a chloroform‐methanol mixture. Thin layer chromatographic analysis of lipids extracted from the dorsal and ventral skin of waterproof and nonwaterproof amphibians revealed a considerable variety of neutral and polar lipids. However, few of the lipid components were unique to the dorsal skin of waterproof frogs. We conclude that the presence per se of many of the intradermal lipids (including cholesterol, cholesterol esters, fatty acids, triglycerides, and phospholipids) is not correlated with a waterproofing barrier, although these lipids might contribute to a structural lipid barrier.