Effect of activity duration on recovery and metabolic costs in the desert iguana ( Dipsosaurus dorsalis)

Abstract

The majority of elevated O 2 consumption associated with short and vigorous activity occurs during recovery, thus an assessment of associated metabolic costs should also examine the excess post-exercise oxygen consumption (EPOC). This study examined O 2 uptake during exercise, EPOC and distance traveled during 5-, 15-, 60- and 300-s sprints at maximal treadmill intensity in Dipsosaurus ( N=10; 74.3±2.1 g). EPOC (0.08, 0.14, 0.23 and 0.18 ml O 2 g −1, respectively) was large (80–99% of total elevated O 2 consumption) and increased significantly between 5 and 60 s. The cost of activity ( C act; ml O 2 g −1·km −1), intended to reflect the total net costs associated with the activity, was calculated as the total elevated O 2 consumption per unit distance traveled. C act decreased with activity duration due to proportionally larger increases in distance traveled relative to EPOC volume, and is predicted by the equation C act=14.7×activity duration (s) −0.24. The inclusion of EPOC costs provides an ecologically relevant estimate of the total metabolic cost of locomotor activity. C act exceeds standard transport costs at all durations examined due to the addition of obligate recovery costs. The differences are large enough to impact energy budget analyses for ectotherms.