Partitioning of evaporative water loss in white-winged doves: plasticity in response to short-term thermal acclimation

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Abstract
We investigated changes in the relative contributions of respiratory evaporative water loss (REWL) and cutaneous evaporative water loss (CEWL) to total evaporative water loss (TEWL) in response to short-term thermal acclimation in western white-winged doves Zenaida asiatica mearnsii. We measured REWL, CEWL, oxygen consumption and carbon dioxide production in a partitioned chamber using flow-through respirometry. In doves housed for 2-4 weeks in a room heated to ca. 43°C during the day, TEWL increased from 5.5±1.3 mg g-1 h-1 at an air temperature (Ta) of 35°C to 19.3±2.5 mg g-1 h-1 at Ta=45°C. In doves housed at room temperature for the same period, TEWL increased from 4.6±1.1 mg g-1 h-1 at Ta=35°C to 16.1±4.6 mg g-1 h-1 at Ta=45°C. The CEWL of heat-acclimated doves increased from 3.6±1.2 mg g-1 h-1 (64% of TEWL) at 35°C to 15.0±2.1 mg g-1 h-1 (78% of TEWL) at Ta=45°C. Cool-acclimated doves exhibited more modest increases in CEWL, from 2.7±0.7 mg g-1 h-1 at Ta=35°C to 7.8±3.4 mg g-1 h-1 at Ta=45°C, with the contribution of CEWL to TEWL averaging 53% over this Ta range. Cool-acclimated doves became mildly hyperthermic (body temperature Tb=42.9±0.4°C) and expended 35% more energy relative to heat-acclimated doves (Tb=41.9±0.6°C) at Ta=45°C, even though TEWL in the two groups was similar. In each of the two groups, metabolic rate did not vary with Ta, and averaged 7.1±0.5 mW g-1 in cool-acclimated doves and 6.3±0.8 mW g-1 in heat-acclimated doves. The differences in TEWL partitioning we observed between the two experimental groups resulted from a consistently lower skin water vapour diffusion resistance (rv) in the heat-acclimated doves. At Ta=45°C, rv in the cool-acclimated doves was 120±81 s cm-1, whereas rv in the heat-acclimated doves was 38±8 s cm-1. Our data reveal that in Z. a. mearnsii, TEWL partitioning varies in response to short-term thermal acclimation.

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