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

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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.