Thermal tolerance,selected body temperature and thermal dependence of food assimilation and locomotor performance in the Qinghai toad headed lizard,Phrynocephalus vlangalii
Thermal tolerance,selected body temperature and thermal dependence of food assimilation and locomotor performance in the Qinghai toad headed lizard,Phrynocephalus vlangalii
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作者：
Ji Xiang
温度是影响生物体许多生物过程的最重要的环境因素。变温动物可以在很宽的体温范围内生存，但它们的生理过程和行为表现通常在中等到相对较高的体温下达到最大。2005年8月，我们在青海省一个种群中采集了青海蟾蜍头蜥（Phrynocephalus vlangalii;Agamidae），并利用成虫研究了其选择体温（Tsel）、热耐性（临界热最小值（CTmin）和临界热最大值（CTmax））以及食物同化和运动性能的热依赖性。Tsel在实验室温度梯度范围从18℃到60℃（高于玻璃饲养箱地板20 mm）上测量；CTmin和CTmax在28℃的培养箱中以0.25℃/分钟的速度冷却或加热，当培养箱内温度低于5℃或高于40℃时速度减慢。我们没有发现Tsel、CTmin和CTmax的性别差异，因此合并了两性的数据。Tsel、CTmin和CTmax的平均值分别为33.3℃、0.9℃和46.9℃。在27 ~ 35℃范围内，体温对日摄食量有影响，但对表观消化系数和同化效率影响不大。在17 ~ 39℃范围内，随着体温的升高，在跑道上停留的次数减少，在41℃时，停留的次数增加。在17 ~ 39℃范围内，冲刺速度随体温的升高而升高，在41℃时下降。总体而言，高体温（29-41℃）下连续运动长度的平均值大于低体温（17-27℃）下的平均值。总体而言，33-41℃的体温范围是运动的最佳温度。当将我们的数据与温带和温暖气候蜥蜴的数据进行比较时，我们发现，在P.vlangalii中，最大化运动性能的体温相对较高。我们的数据支持这样的观点，即Tsel代表了许多过程在相对较高水平上运行的体温，正如事实所揭示的那样，Tsel处于P.vlangalii运动性能的最佳温度范围内。种间比较表明，不同生境和地理（气候）区域的蜥蜴CTmin和CTmax存在差异。总体而言，生活在温暖栖息地或生活在温暖地区的蜥蜴CTmin更大，而生活在开放栖息地的蜥蜴CTmax更大。青海蟾蜍蜥通常生活在干旱或半干旱地区植被稀疏的空旷地带。P.vlangalii所占据的区域气候恶劣，环境温度的日波动和季节波动非常明显。因此，在P.vlangalii中看到的对极端温度的增强耐受能力可能是进化决定的，作为适应当地热条件的结果。
Temperature is the single most important environmental factor affecting many biological processes in organisms.Ectotherms are viable under a wide range of body temperatures,but their physiological processes and behavioral performances are usually maximized at moderate to relatively high body temperatures.We collected Qinghai toad-headed lizards(Phrynocephalus vlangalii;Agamidae) in August 2005 from a population in Qinghai(northwestern China) and used adults to study selected body temperature(Tsel),thermal tolerance [critical thermal minimum(CTmin) and critical thermal maximum(CTmax)]and the thermal dependence of food assimilation and locomotor performance.Tsel was measured on a laboratory thermal gradient ranging from 18 ℃ to 60 ℃(20 mm above the terrarium floor);CTmin and CTmax were determined in an incubator,with lizards being cooled or heated from 28 ℃ at the rate of 0.25 ℃ per minute and more slowly when temperatures inside the incubator were lower than 5 ℃ or higher than 40 ℃.We did not find between-sex differences in Tsel,CTmin and CTmax,and thus pooled data for both sexes.The mean values for Tsel,CTmin and CTmax were 33.3 ℃,0.9 ℃ and 46.9 ℃,respectively.Within the range from 27 ℃ to 35℃,body temperature affected daily food intake but had no important role in influencing apparent digestive coefficient and assimilation efficiency.Thus,consistent with the results reported for a wide range of lizard taxa,our data show that digestive performance is less sensitive to variation in body temperature in P.vlangalii.The number of stops in the racetrack decreased with increase in body temperature within the range from 17 ℃ to 39 ℃,and then increased at 41 ℃.Sprint speed increased with increase in body temperature within the range from 17 ℃ to 39 ℃,and then decreased at 41 ℃.The mean values for the length ofcontinuous locomotion were overall greater at higher body temperatures(29-41℃) than at lower temperatures(17-27 ℃).Overall,body temperatures within the range of 33-41 ℃ were optimal for locomotion.When comparing our data with those reported for temperate and warm-climate lizards,we found that body temperatures maximizing locomotor performance are relatively high in P.vlangalii.Our data support the idea that Tsel represents the body temperature at which numerous processes function at a relatively high level,as revealed by the fact that Tsel fell within the range of temperatures optimal for locomotor performance in P.vlangalii.Inter-specific comparisons reveal that lizards using different habitats and occupying different geographic(climatic) regions differ in both CTmin and CTmax.Overall,CTmin is greater in lizards using warmer habitats or living in warmer localities,and CTmax is greater in lizards using opened habitats.Qinghai toad-headed lizards are typically found in open spaces in arid or semi-arid regions covered sparse vegetation.The region occupied by P.vlangalii is climatically severe,where daily and seasonal fluctuations in ambient temperature are very pronounced.Thus,the enhanced ability to tolerate temperature extremes seen in P.vlangalii is likely determined evolutionarily as a consequence of adaptation to local thermal conditions.