Roe J H, Hopkins W A, Snodgrass J W, Congdon J D
University of Georgia, Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802, USA.
Comp Biochem Physiol A Mol Integr Physiol. 2004 Oct;139(2):159-68. doi: 10.1016/j.cbpb.2004.08.005.
Measuring standard metabolic rate (SMR) and specific dynamic action (SDA) has yielded insight into patterns of energy expenditure in snakes, but less emphasis has been placed on identifying metabolic variation and associated energy cost of circadian rhythms. To estimate SMR, SDA, and identify metabolic variation associated with circadian cycles in nocturnally active African house snakes (Lamprophis fuliginosus), we measured oxygen consumption rates (VO2) at frequent intervals before and during digestion of meals equaling 10%, 20% and 30% of their body mass. Circadian rhythms in metabolism were perceptible in the VO2 data during fasting and after the initial stages of digestion. We estimated SMR of L. fuliginosus (mean mass=16.7+/-0.3 g) to be 0.68+/-0.02 (+/-SEM) mL O2/h at 25 degrees C. Twenty-four hours after eating, VO2 peaked at 3.2-5.3 times SMR. During digestion of meals equaling 10-30% of their body mass, the volume of oxygen consumed ranged from 109 to 119 mL O2 for SMR, whereas extra oxygen consumed for digestion and assimilation ranged from 68 to 256 mL O2 (equivalent to 14.5-17.0% of ingested energy). The oxygen consumed due to the rise in metabolism during the active phase of the daily cycle ranged from 55 to 66 mL O2 during digestion. Peak VO2, digestive scope, and SDA increased with increasing meal size. Comparisons of our estimates to estimates derived from methods used in previous investigations resulted in wide variance of metabolic variables (up to 39%), likely due to the influence of circadian rhythms and activity on the selection of baseline metabolism. We suggest frequent VO2 measurements over multiple days, coupled with mathematical methods that reduce the influence of undesired sources of VO2 variation (e.g., activity, circadian cycles) are needed to reliably assess SMR and SDA in animals exhibiting strong circadian cycles.
测量标准代谢率（SMR）和特殊动力作用（SDA）有助于深入了解蛇类的能量消耗模式，但在识别昼夜节律的代谢变化及相关能量成本方面的关注较少。为了估计夜行性非洲家蛇（Lamprophis fuliginosus）的SMR、SDA，并识别与昼夜周期相关的代谢变化，我们在进食相当于其体重10%、20%和30%的餐食之前及消化期间，频繁测量了耗氧率（VO2）。在禁食期间和消化初始阶段之后的VO2数据中，可察觉到代谢的昼夜节律。我们估计，在25摄氏度时，L. fuliginosus（平均体重=16.7±0.3克）的SMR为0.68±0.02（±SEM）毫升氧气/小时。进食24小时后，VO2达到峰值，为SMR的3.2 - 5.3倍。在消化相当于其体重10% - 30%的餐食期间，SMR的耗氧量范围为109至119毫升氧气，而消化和同化额外消耗的氧气范围为68至256毫升氧气（相当于摄入能量的14.5% - 17.0%）。在消化期间，由于每日活动阶段代谢升高而消耗的氧气在55至66毫升氧气之间。VO2峰值、消化范围和SDA随餐食大小增加而增加。将我们的估计值与先前研究中使用的方法得出的估计值进行比较，代谢变量存在很大差异（高达39%），这可能是由于昼夜节律和活动对基础代谢选择的影响。我们建议，对于表现出强烈昼夜节律的动物，需要在多天内频繁测量VO2，并结合数学方法来减少VO2变化的不期望来源（如活动、昼夜周期）的影响，以可靠地评估SMR和SDA。
