Phenotypic Flexibility in Cutaneous Water Loss and Lipids of the                     Stratum Corneum in House Sparrows (Passer domesticus) following                     Acclimation to High and Low Humidity

Intercellular lipids of the stratum corneum (SC), the outer layer of the epidermis, form a barrier to water vapor diffusion through the skin. Previously, we measured cutaneous water loss (CWL) and lipid composition of the SC of adult house sparrows from two populations, one living in the deserts of Saudi Arabia and another living in mesic Ohio. Adult desert house sparrows had a lower CWL, a lower proportion of free fatty acids, and a higher proportion of ceramides and cerebrosides in the SC compared with mesic sparrows. In this study, we investigated developmental plasticity of CWL and lipid composition of the SC in desert and mesic nestling house sparrows reared in low and high humidity and compared our results with previous work on adults. We measured CWL of nestlings and analyzed the lipid composition of the SC using thin-layer chromatography. We showed that nestling house sparrows from both localities had higher CWL than adults in their natural environment, a result of major modifications of the lipid composition of the SC. The expression of plasticity in CWL seems to be a response to opposed selection pressures, thermoregulation and water conservation, at different life stages, on which regulation of CWL plays a crucial role. Desert nestlings showed a greater degree of plasticity in CWL and lipid composition of the SC than did mesic nestlings, a finding consistent with the idea that organisms exposed to more environmental stress ought to be more plastic than individuals living in more benign environments.

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House sparrows (Passer domesticus) increase protein catabolism in response to water restriction

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00701.2010 ◽

2011 ◽

Vol 300 (4) ◽

pp. R925-R930 ◽

Cited By ~ 16

Author(s):

Alexander R. Gerson ◽

Christopher G. Guglielmo

Keyword(s):

Water Balance ◽

Lean Mass ◽

Water Loss ◽

Passer Domesticus ◽

Composition Analysis ◽

Protein Catabolism ◽

Water Restriction ◽

House Sparrows ◽

Evaporative Water ◽

Body Protein

Birds primarily rely on fat for energy during fasting and to fuel energetically demanding activities. Proteins are catabolized supplemental to fat, the function of which in birds remains poorly understood. It has been proposed that birds may increase the catabolism of body protein under dehydrating conditions as a means to maintain water balance, because catabolism of wet protein yields more total metabolic and bound water (0.155·H2O−1·kJ−1) than wet lipids (0.029 g·H2O−1·kJ−1). On the other hand, protein sparing should be important to maintain function of muscles and organs. We used quantitative magnetic resonance body composition analysis and hygrometry to investigate the effect of water restriction on fat and lean mass catabolism during short-term fasting at rest and in response to a metabolic challenge (4-h shivering) in house sparrows ( Passer domesticus ). Water loss at rest and during shivering was compared with water gains from the catabolism of tissue. At rest, water-restricted birds had significantly greater lean mass loss, higher plasma uric acid concentration, and plasma osmolality than control birds. Endogenous water gains from lean mass catabolism offset losses over the resting period. Water restriction had no effect on lean mass catabolism during shivering, as water gains from fat oxidation appeared sufficient to maintain water balance. These data provide direct evidence supporting the hypothesis that water stress can increase protein catabolism at rest, possibly as a metabolic strategy to offset high rates of evaporative water loss.

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