Skin Lipids and Cutaneous Water Loss Among Larks Along an Aridity Gradient

主要研究人员：俄亥俄州立大学进化、生态学和组织生物学系约瑟夫·B·威廉姆斯博士，俄亥俄州立大学，哥伦布，俄亥俄州43210。塑造当前脊椎动物生命的一个重大进化事件是从水到陆地的转变。在这一转变过程中，动物进化出减少水分流失的皮肤。随着保持较高体温的能力的发展，称为吸热，水分流失的问题加剧了，因为高代谢率与呼吸道和排泄的水分流失增加有关。由于能量消耗和水分损失率高，吸热植物不适合生活在沙漠、环境温度高、降雨量少和植物生长缓慢的地区。然而，尽管如此，鸟类占据了世界上最干燥的沙漠。最近的研究表明，与同一家族的近亲相比，适应干旱的百灵鸟的总蒸发水损失，即呼吸损失和通过皮肤的损失之和，都有所减少。沙漠鸟类可以通过减少它们皮肤的水分损失来减少它们的总蒸发水分损失。这项建议概述了一项综合研究，旨在促进我们对环境、通过皮肤的水分损失、皮肤结构、表皮外层的脂肪成分以及增加的皮肤水分损失对行为和/或自然环境中生存的影响之间的相互作用的理解。通过改变温度、空气中水蒸气含量和水合状态的对比方法和对照实验，将检验鸟类皮肤对沙漠条件的适应情况，以及可逆表型可塑性在通过皮肤失水方面的作用。生理表型的差异也可能是发育过程中环境差异的结果。描述种群内短期和进化变化的可能性，对于预测随着全球变暖导致的地球温度上升而发生的分布变化和物种灭绝的可能性至关重要。

Title of Proposal: Skin lipids and cutaneous water loss among larks along an aridity gradient.Principal Investigator: Dr. Joseph B. Williams, Dept Evolution, Ecology, and Organismal Biology, Ohio State University, Columbus, OH 43210.A major evolutionary event that shaped current vertebrate life was the transition from water to land. During this transition, animals evolved skin that reduced water loss. With the later development of the ability of maintain high body temperature, called endothermy, problems of water loss were exacerbated because high metabolic rates are associated with increased water losses from respiratory passages and by excretion. With high rates of energy expenditure and water loss, endotherms make poor candidates for living in deserts, regions of high ambient temperature, low rainfall, and low plant growth. Yet despite this, birds occupy the driest deserts in the world. Recent work has indicated that arid-adapted larks have a reduced total evaporative water loss, the sum of respiratory water loss and water loss through the skin, compared with mesic relatives within the same family. Desert birds could reduce their total evaporative water loss by decreasing their water loss through their skin. Research suggests that the barrier to water vapor diffusion in vertebrates resides in the non-living outer layer of the epidermis. This proposal outlines an integrated study designed to advance our understanding of the interplay between environment, water loss through the skin, skin structure, lipid composition of the outer layer of the epidermis, and the effect that increased cutaneous water loss has on behavior and/or survival in a natural setting. The comparative method and controlled experiments varying temperature, water vapor content of the air, and hydration state will be used to examine adaptation of the avian skin to desert conditions and the role of reversible phenotypic plasticity on water loss through the skin. Variation in physiological phenotype may also result from differences in environment during development. Experiments are planned that shed light on how variation in the water content of the air during development influences cutaneous water loss in adults. Characterization of the potential for both short-term and evolutionary change within populations will be of crucial importance in predicting changes in distribution and the probability of extinction with the rise in temperature of the earth as a result of global warming.