Ostrowski Stéphane, Williams Joseph B, Ismael Khairi
National Wildlife Research Center, PO Box 1086, Taif, Saudi Arabia.
J Exp Biol. 2003 May;206(Pt 9):1471-8. doi: 10.1242/jeb.00275.
To test the idea that large, free-living, desert ungulates use heterothermy to reduce water loss, we measured core body temperature (T(b)) of six free-ranging, adult Arabian oryx (Oryx leucoryx) during 2 years in the arid desert of west-central Saudi Arabia. We report the first case of heterothermy in a free-living ruminant in a desert environment: T(b) varied by 4.1+/-1.7 degrees C day(-1) during summer (June to September) and by 1.5+/-0.6 degrees C day (-1) during winter (November to March). Over both seasons, mean T(b) was 38.4+/-1.3 degrees C. During the day in both summer and winter, T(b) increased continually, suggesting that oryx store heat instead of dissipating it by evaporation, whereas at night T(b) decreased. The minimum T(b) was lower in summer (36.5+/-1.16 degrees C) than in winter (37.5+/-0.51 degrees C) despite the fact that the temperature gradient between T(b) and air temperature (T(a)) was larger and solar radiation was lower in winter. Throughout the year, daily variation in T(b) appeared to reflect thermal load (T(a,max)-T(a,min)) rather than an endogenous rhythm. Behavioural thermoregulation was used by oryx to cope with thermal stress during summer: animals lay down in shade in the morning shortly before T(a) exceeded T(b) and remained there until evening when T(b)-T(a) became positive. The use of heterothermy by oryx resulted in storage of 672.4 kJ day(-1) animal(-1) in summer and 258.6 kJ day(-1) animal(-1) in winter, if heat storage is based on calculations involving mean T(b). To dissipate this heat by evaporation would require 0.28 litres H(2)O day(-1) animal(-1) and 0.11 litres H(2)O day(-1) animal(-1) in summer and winter, respectively. Without heat storage in summer, we estimated that oryx would have to increase their water intake by 19%, a requirement that would be difficult to meet in their desert environment. If heat storage was calculated based on the daily change in T(b) rather than on heat storage above mean T(b) then we estimated that oryx saved 0.538 litres H(2)O day(-1) animal(-1) during summer.
为了验证大型、自由放养的沙漠有蹄类动物利用异温性来减少水分流失这一观点，我们在沙特阿拉伯中西部干旱沙漠地区对6只自由放养的成年阿拉伯羚羊（阿拉伯大羚羊，Oryx leucoryx）的核心体温（T(b)）进行了为期两年的测量。我们报告了沙漠环境中自由生活反刍动物的首例异温性案例：夏季（6月至9月）T(b)每日变化4.1±1.7摄氏度，冬季（11月至3月）每日变化1.5±0.6摄氏度。在两个季节中，平均T(b)为38.4±1.3摄氏度。在夏季和冬季的白天，T(b)持续上升，这表明羚羊储存热量而非通过蒸发散热，而在夜间T(b)下降。尽管冬季T(b)与气温（T(a)）之间的温度梯度更大且太阳辐射更低，但夏季的最低T(b)（36.5±1.16摄氏度）低于冬季（37.5±0.51摄氏度）。全年T(b)的每日变化似乎反映的是热负荷（T(a,max)-T(a,min)）而非内源性节律。夏季时，羚羊通过行为体温调节来应对热应激：在T(a)超过T(b)之前不久，动物们会在早晨卧于阴凉处，一直待到傍晚T(b)-T(a)变为正值。如果基于涉及平均T(b)的计算来确定热量储存，那么羚羊利用异温性在夏季可储存672.4千焦/天·只，冬季可储存258.6千焦/天·只。通过蒸发来消散这些热量，夏季和冬季分别需要0.28升/天·只和0.11升/天·只的水。如果夏季不进行热量储存，我们估计羚羊的需水量将增加19%，而在它们的沙漠环境中这一需求很难满足。如果根据T(b)的每日变化而非高于平均T(b)的热量储存来计算热量储存，那么我们估计夏季羚羊每天每只可节省0.538升水。
