Cooper C E, Withers P C
Centre for Ecosystem Diversity and Dynamics in the Department of Environmental Biology, Curtin University of Technology, PO Box U1987, Perth, Western Australia, 6845.
J Exp Biol. 2008 Sep;211(Pt 17):2759-66. doi: 10.1242/jeb.019463.
To better understand the effects of ambient relative humidity (RH) on physiological variables and the implications of RH-correcting evaporative water loss (EWL) data for marsupials, we examined the effect of RH on EWL, body temperature (Tb), metabolic rate (MR) and thermal conductance (C) of the brushtail possum (Trichosurus vulpecula), a medium-sized marsupial. Correcting EWL data for 27 species of marsupial for water vapour pressure deficit (DeltaWVP) in the chamber during measurement significantly increased, rather than decreased, the variability of the allometric relationship for EWL. For the brushtail possum, both ambient temperature (Ta) and RH significantly affected EWL. At Ta=25 degrees C, EWL was independent of RH at "63% RH, but decreased linearly at higher RH values. At Ta=30 degrees C, EWL was significantly related to RH from 26% to 92% RH. There was a significant effect of Ta on Tb and dry thermal conductance (Cdry; higher at 30 degrees C), but no effect of RH. For MR and wet thermal conductance (Cwet) there was a significant effect of Ta (MR higher and Cwet lower at 25 degrees C), and RH at Ta=30 degrees C (MR higher and Cwet lower at the lowest RH) but not at 25 degrees C. Our results indicate that brushtail possums do not necessarily show the linear relationship between ambient RH and EWL expected for an endotherm, possibly because of behavioural modification of their immediate microclimate. This may account for the failure of WVP deficit correction to improve the allometric EWL relationship for marsupials. Chamber RH is an important environmental factor to be considered when measuring standard physiological variables such as MR and Cwet.
为了更好地理解环境相对湿度（RH）对生理变量的影响，以及对有袋动物进行RH校正蒸发失水（EWL）数据的意义，我们研究了RH对袋貂（Trichosurus vulpecula，一种中型有袋动物）的EWL、体温（Tb）、代谢率（MR）和热传导率（C）的影响。对测量过程中实验箱内27种有袋动物的水蒸气压力亏缺（DeltaWVP）校正EWL数据，显著增加而非减少了EWL异速生长关系的变异性。对于袋貂，环境温度（Ta）和RH均显著影响EWL。在Ta = 25摄氏度时，EWL在“63% RH时与RH无关，但在较高RH值时呈线性下降。在Ta = 30摄氏度时，EWL在26%至92% RH范围内与RH显著相关。Ta对Tb和干热传导率（Cdry；30摄氏度时更高）有显著影响，但RH无影响。对于MR和湿热传导率（Cwet），Ta有显著影响（25摄氏度时MR更高，Cwet更低），在Ta = 30摄氏度时RH也有显著影响（最低RH时MR更高，Cwet更低），但在25摄氏度时RH无影响。我们的结果表明，袋貂不一定表现出恒温动物预期的环境RH与EWL之间的线性关系，这可能是由于它们对自身微气候的行为调节。这可能解释了水蒸气压力亏缺校正未能改善有袋动物EWL异速生长关系的原因。在测量标准生理变量如MR和Cwet时，实验箱RH是一个需要考虑的重要环境因素。
