Affiliation:
1. Department of Ecology and Evolutionary Biology, University of California at Irvine, Irvine, CA 92697, USA
Abstract
SUMMARY
Monitor lizards (Varanus exanthematicus) were used to examine the prioritization or additivity of the metabolic responses associated with exercise and digestion, either of which can elevate metabolic rate independently. Rates of oxygen consumption (V̇.O2) and ventilation (V̇.E) were measured in lizards during fasting exercise, postprandial rest and postprandial exercise. In fasting animals, V̇.O2 increased with walking speed to a maximal value of 15.9mlO2kg−1min−1 at 1.25kmh−1. Postprandial resting metabolic rate was elevated significantly above fasting levels (4.1 versus 2.0mlO2kg−1min−1). During postprandial exercise, V̇.O2 increased to a maximal value of 18.8mlO2kg−1min−1 at 1.25kmh−1. At every level of exercise, V̇.O2 was significantly higher in postprandial animals by a similar increment; the maximal rate of oxygen consumption was significantly increased by 18% in postprandial individuals. Maximal V̇.E did not differ in fasting and postprandial animals and, therefore, the greater V̇.O2max of postprandial animals cannot be attributed to a higher ventilation rate. Air convection requirement (V̇.E/V̇.O2) is significantly lower in postprandial animals at rest and at all levels of exercise, indicating a relative hypoventilation and increased pulmonary oxygen extraction efficiency. We suggest that this increased oxygen extraction may be due to decreased cardiopulmonary shunts and/or to lower mixed venous oxygen content. The data unequivocally support an additivity model rather than prioritization models for the allocation of elevated metabolic rate: the postprandial metabolic increment is not suspended during exercise, but rather is added onto the cost of exercise. It is clear that fasting exercise did not elicit truly maximal levels of cardiopulmonary oxygen transport in these animals, indicating problems for design models that make this assumption.
Publisher
The Company of Biologists
Subject
Insect Science,Molecular Biology,Animal Science and Zoology,Aquatic Science,Physiology,Ecology, Evolution, Behavior and Systematics
Reference23 articles.
1. Benedict, F. G. (1932). The Physiology of Large Reptiles. Washington: Carnegie Institute Washington Publication 425.
2. Bennett, A. F. (1991). The evolution of activity capacity. J. Exp. Biol. 160, 1–23.
3. Bennett, A. F. (1994). Exercise performance of reptiles. Adv. Vet. Sci. Comp. Med. 38B, 113–138.
4. Bennett, A. F., Hicks, J. W. and Cullum, A. J. (2000). An experimental test of the thermoregulatory hypothesis for the evolution of endothermy. Evolution54, 1768–1773.
5. Gleeson, T. T., Mitchell, G. S. and Bennett, A. F. (1980). Cardiovascular responses to graded activity in the lizards Varanus and Iguana. Am. J. Physiol. 239, R174–R179.
Cited by
31 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献