Bradshaw Corey J A, McMahon Clive R, Hays Graeme C
School for Environmental Research, Institute of Advanced Studies, Charles Darwin University, Darwin, Northern Territory 0909, Australia.
Physiol Biochem Zool. 2007 Mar-Apr;80(2):209-19. doi: 10.1086/511142. Epub 2007 Jan 16.
Good estimates of metabolic rate in free-ranging animals are essential for understanding behavior, distribution, and abundance. For the critically endangered leatherback turtle (Dermochelys coriacea), one of the world's largest reptiles, there has been a long-standing debate over whether this species demonstrates any metabolic endothermy. In short, do leatherbacks have a purely ectothermic reptilian metabolic rate or one that is elevated as a result of regional endothermy? Recent measurements have provided the first estimates of field metabolic rate (FMR) in leatherback turtles using doubly labeled water; however, the technique is prohibitively expensive and logistically difficult and produces estimates that are highly variable across individuals in this species. We therefore examined dive duration and depth data collected for nine free-swimming leatherback turtles over long periods (up to 431 d) to infer aerobic dive limits (ADLs) based on the asymptotic increase in maximum dive duration with depth. From this index of ADL and the known mass-specific oxygen storage capacity (To(2)) of leatherbacks, we inferred diving metabolic rate (DMR) as To2/ADL. We predicted that if leatherbacks conform to the purely ectothermic reptilian model of oxygen consumption, these inferred estimates of DMR should fall between predicted and measured values of reptilian resting and field metabolic rates, as well as being substantially lower than the FMR predicted for an endotherm of equivalent mass. Indeed, our behaviorally derived DMR estimates (mean=0.73+/-0.11 mL O(2) min(-1) kg(-1)) were 3.00+/-0.54 times the resting metabolic rate measured in unrestrained leatherbacks and 0.50+/-0.08 times the average FMR for a reptile of equivalent mass. These DMRs were also nearly one order of magnitude lower than the FMR predicted for an endotherm of equivalent mass. Thus, our findings lend support to the notion that diving leatherback turtles are indeed ectothermic and do not demonstrate elevated metabolic rates that might be expected due to regional endothermy. Their capacity to have a warm body core even in cold water therefore seems to derive from their large size, heat exchangers, thermal inertia, and insulating fat layers and not from an elevated metabolic rate.
准确估算自由活动动物的代谢率对于理解其行为、分布和数量至关重要。对于极度濒危的棱皮龟（蠵龟科），作为世界上最大的爬行动物之一，关于该物种是否表现出任何代谢性体温调节一直存在长期争论。简而言之，棱皮龟是具有纯粹的变温爬行动物代谢率，还是由于局部体温调节而升高的代谢率呢？最近的测量使用双标记水首次估算了棱皮龟的野外代谢率（FMR）；然而，该技术成本过高且在后勤方面存在困难，并且所产生的估算值在该物种的个体之间差异很大。因此，我们检查了为9只自由游动的棱皮龟在长时间（长达431天）内收集的潜水持续时间和深度数据，以根据最大潜水持续时间随深度的渐近增加来推断有氧潜水极限（ADL）。根据这个ADL指数以及棱皮龟已知的质量比氧气储存能力（To(2)），我们将潜水代谢率（DMR）推断为To2/ADL。我们预测，如果棱皮龟符合纯粹变温爬行动物的氧气消耗模型，这些推断的DMR估算值应该落在爬行动物静息和野外代谢率的预测值与测量值之间，并且也应远低于同等质量的恒温动物预测的FMR。事实上，我们通过行为得出的DMR估算值（平均值 = 0.73±0.11 mL O(2) min(-1) kg(-1)）是在不受约束的棱皮龟中测量的静息代谢率的3.00±0.54倍，是同等质量爬行动物平均FMR的0.50±0.08倍。这些DMR也比同等质量恒温动物预测的FMR低近一个数量级。因此，我们的研究结果支持了这样一种观点，即潜水的棱皮龟确实是变温动物，并且没有表现出因局部体温调节而可能预期的升高的代谢率。因此，它们即使在冷水中也能拥有温暖身体核心的能力似乎源于它们的体型大、热交换器、热惯性和绝缘脂肪层，而不是源于升高的代谢率。
