Crocker Daniel E, Kofahl Nathan, Fellers Gary D, Gates Natalie B, Houser Dorian S
Department of Biology, Sonoma State University, Rohnert Park, California 92948, USA.
Physiol Biochem Zool. 2007 Nov-Dec;80(6):635-42. doi: 10.1086/521204. Epub 2007 Sep 5.
We measured water flux and energy expenditure in free-ranging Point Reyes mountain beavers Aplodontia rufa phaea by using the doubly labeled water method. Previous laboratory investigations have suggested weak urinary concentrating ability, high rates of water flux, and low basal metabolic rates in this species. However, free-ranging measurements from hygric mammals are rare, and it is not known how these features interact in the environment. Rates of water flux (210+/-32 mL d(-1)) and field metabolic rates (1,488+/-486 kJ d(-1)) were 159% and 265%, respectively, of values predicted by allometric equations for similar-sized herbivores. Mountain beavers can likely meet their water needs through metabolic water production and preformed water in food and thus remain in water balance without access to free water. Arginine-vasopressin levels were strongly correlated with rates of water flux and plasma urea : creatinine ratios, suggesting an important role for this hormone in regulating urinary water loss in mountain beavers. High field metabolic rates may result from cool burrow temperatures that are well below lower critical temperatures measured in previous laboratory studies and suggest that thermoregulation costs may strongly influence field energetics and water flux in semifossorial mammals.
我们采用双标水法测量了自由放养的雷耶斯岬山地河狸（Aplodontia rufa phaea）的水通量和能量消耗。先前的实验室研究表明，该物种的尿浓缩能力较弱、水通量较高且基础代谢率较低。然而，对喜湿哺乳动物的自由放养测量很少见，并且尚不清楚这些特征在自然环境中是如何相互作用的。水通量（210±32 mL d⁻¹）和野外代谢率（1488±486 kJ d⁻¹）分别是根据体型相似的食草动物的异速生长方程预测值的159%和265%。山地河狸可能能够通过代谢水的产生以及食物中的预制水来满足其水分需求，因此在无法获取自由水的情况下仍能保持水平衡。精氨酸加压素水平与水通量速率以及血浆尿素:肌酐比值密切相关，表明该激素在调节山地河狸的尿水流失中起重要作用。较高的野外代谢率可能是由于洞穴温度较低，远低于先前实验室研究中测得的下限临界温度，这表明体温调节成本可能对半穴居哺乳动物的野外能量学和水通量产生强烈影响。
