Ostrowski Stéphane, Williams Joseph B
National Wildlife Research Center, Taif, Saudi Arabia.
J Exp Biol. 2006 Apr;209(Pt 8):1421-9. doi: 10.1242/jeb.02151.
To test whether free-living desert ungulates employ heterothermy to reduce water loss, we measured core body temperature (T(b)) of six free-living Arabian sand gazelles (Gazella subgutturosa marica), a small desert antelope (12-20 kg) that lives in the deserts of Saudi Arabia, where air temperature (T(a)) often exceeds 40 degrees C. We found that the mean daily T(b) varied by 2.6+/-0.8 degrees C during summer (June-July) and 1.7+/-0.3 degrees C during winter (January-February); over both seasons, mean T(b) was 39.5+/-0.2 degrees C. During the day, in summer, T(b) increased by more than 2 degrees C when T(a)>T(b) and declined at night when T(a)<T(b), suggesting that gazelles stored heat during day and dissipated it by non evaporative means during night. The minimum T(b) was lower in summer (38.2+/-0.5 degrees C) than in winter (38.6+/-0.3 degrees C) despite the fact that the gradient between T(b) and T(a) was larger and solar radiation was lower in winter. Correlation between daily variation of T(b) and mean, maximal T(a)s were significant in summer, but not in winter. To dissipate the amount of heat stored by gazelles would require an evaporative water loss of 33.5 ml H(2)O day(-1) in summer and 23.2 ml H(2)O day(-1) in winter. We tested whether the amplitude of daily variation in T(b) was influenced by the level of water provided to six captive sand gazelles maintained under controlled conditions in summer. The daily amplitude of T(b) was increased by 1.4 degrees C when gazelles were denied drinking water but supplied with pre-formed water in food, and by 1.1 degrees C when they were denied both water and food. Gazelles denied only drinking water increased the amplitude of variation in T(b), whereas when denied both food and water, they seemed to undergo a dehydration-hyperthermia, with increased mean and maximal T(b) values but no decrease of minimal T(b). Free-ranging and captive gazelles surviving on pre-formed water in natural food used heterothermy during summer with no elevation of plasma osmolality, indicating that they were not in a state of dehydration. Our data on variation in T(b) of gazelles provide an example of a small desert ungulate employing heterothermy to reduce evaporative water loss that would otherwise be required to maintain normothermic T(b).
为了测试自由生活的沙漠有蹄类动物是否采用异温性来减少水分流失，我们测量了六只自由生活的阿拉伯沙瞪羚（Gazella subgutturosa marica）的核心体温（T(b)），这是一种生活在沙特阿拉伯沙漠的小型沙漠羚羊（体重12 - 20千克），那里的气温（T(a)）经常超过40摄氏度。我们发现，夏季（6月至7月）平均每日T(b)变化2.6±0.8摄氏度，冬季（1月至2月）变化1.7±0.3摄氏度；在两个季节中，平均T(b)为39.5±0.2摄氏度。在夏季白天，当T(a)>T(b)时，T(b)升高超过2摄氏度，而在夜间当T(a)<T(b)时则下降，这表明瞪羚在白天储存热量，并在夜间通过非蒸发方式散热。尽管冬季T(b)与T(a)之间的梯度更大且太阳辐射更低，但夏季的最低T(b)（38.2±0.5摄氏度）低于冬季（38.6±0.3摄氏度）。夏季T(b)的每日变化与平均、最高T(a)之间的相关性显著，而冬季则不显著。为了散发瞪羚储存的热量，夏季需要蒸发失水33.5毫升H₂O/天，冬季需要23.2毫升H₂O/天。我们测试了夏季在受控条件下饲养的六只圈养沙瞪羚，其T(b)每日变化幅度是否受提供的水量影响。当不给瞪羚饮水但在食物中提供预先形成的水时，T(b)的每日变化幅度增加1.4摄氏度；当既不给水也不给食物时，增加1.1摄氏度。只被剥夺饮水的瞪羚增加了T(b)的变化幅度，而当既被剥夺食物又被剥夺水时，它们似乎经历了脱水热，平均和最高T(b)值增加，但最低T(b)没有降低。以天然食物中预先形成的水为生的自由放养和圈养瞪羚在夏季采用异温性，血浆渗透压没有升高，这表明它们没有处于脱水状态。我们关于瞪羚T(b)变化的数据提供了一个小型沙漠有蹄类动物采用异温性来减少蒸发失水的例子，否则维持正常体温的T(b)就需要这种蒸发失水。
