Sadowski-Fugitt Leslie M, Tracy Christopher R, Christian Keith A, Williams Joseph B
Department of Evolution, Ecology, and Organismal Biology, 318 West 12th Avenue, Aronoff Laboratory, Ohio State University, Columbus, Ohio 43210, USA.
Physiol Biochem Zool. 2012 Jan-Feb;85(1):40-50. doi: 10.1086/663695. Epub 2011 Dec 14.
For amphibians to survive in environments that experience annual droughts, they must minimize evaporative water loss. One genus of Australian hylid frogs, Cyclorana, prevents desiccation by burrowing in the soil and forming cocoons composed of alternating layers of shed epidermis and glandular secretions. Previous data are inconclusive about the role that lipids play in reducing evaporative water loss through skin (cutaneous water loss [CWL]) when Cyclorana spp. are within cocoons. In this study, we measured CWL and lipids in the epidermis and in cocoons of five species of Cyclorana. CWL was significantly lower in frogs within cocoons than in frogs without cocoons. Surface-area-specific CWL for the three small species was significantly higher than that of the two larger species of Cyclorana, but this difference was not apparent in frogs within cocoons. Although lipids were responsible for more of the dry mass of the epidermis (approximately 20%) than of the cocoons (approximately 7%) we found that cerebrosides and ceramides, two polar lipid classes, were almost exclusively found in cocoons. This suggests that these lipid classes are in the glandular secretions rather than in the epidermis. Because these polar lipids are the types that reduce water loss in birds (cerebrosides and ceramides) and mammals (ceramides), we conclude that they are important not only for holding together the shed layers of skin but also for contributing to the barrier against water loss.
为了在每年都会经历干旱的环境中生存，两栖动物必须尽量减少水分蒸发损失。澳大利亚雨蛙属（Cyclorana）的一类蛙通过在土壤中挖掘洞穴并形成由脱落的表皮和腺体分泌物交替层组成的茧来防止脱水。关于Cyclorana属蛙类在茧内时脂质在减少通过皮肤的水分蒸发损失（皮肤水分损失 [CWL]）中所起的作用，先前的数据尚无定论。在本研究中，我们测量了五种Cyclorana蛙表皮和茧中的CWL及脂质含量。有茧的蛙的CWL显著低于无茧的蛙。三种小型Cyclorana蛙的单位表面积CWL显著高于两种大型Cyclorana蛙，但这种差异在有茧的蛙中并不明显。尽管脂质在表皮干物质中所占比例（约20%）高于茧（约7%），但我们发现脑苷脂和神经酰胺这两种极性脂质几乎只存在于茧中。这表明这些脂质类别存在于腺体分泌物中而非表皮中。由于这些极性脂质是鸟类（脑苷脂和神经酰胺）和哺乳动物（神经酰胺）中减少水分流失的类型，我们得出结论，它们不仅对于将脱落的皮肤层黏合在一起很重要，而且对于形成防水屏障也有作用。
