Low Temperature and Exercise Recovery in the Desert Iguana

Abstract

We examined the effects of variable body temperature on exercise recovery in the desert iguana, Dipsosaurus dorsalis, because both temperature and nonsustainable activity play an important role in the life history of ectothermic tetrapods. We measured the rate of oxygen consumption (V̇o2), the cost of nonsustainable locomotion (Cns), blood and muscle lactate concentrations, and muscle glycogen concentrations of Dipsosaurus at 20° C and 40° C before, during, and after exhaustive activity. We expected that low recovery temperatures would retard most aspects of metabolic recovery. Animals that exercised and recovered at 40° C maintained significantly higher V̇o2's and returned to temperature-appropriate resting V̇o2's more rapidly than did animals that exercised and recovered at 20° C. Animals that exercised and recovered at 20° C also had a greater average Cns than did animals that exercised and recovered at 40° C (4.6 vs. 2.5 μL O₂/(g × m)). The Q10 values for V̇o2 were highly variable and ranged from 1.3 to 1.9 throughout recovery. In contrast, Dipsosaurus that exercised at 40° C and recovered at 20° C returned to temperature-appropriate resting V̇o2's more rapidly than animals that exercised and recovered at 40° C. The Cns was lower in animals that exercised at 40° C and recovered at 20° C than in animals that exercised and recovered at 40° C (1.1 vs. 3.7 μL O₂/(g × m)). In contrast to those that exercised and recovered at 40° C, animals that exercised and recovered at 20° C did not remove a significant fraction of blood or muscle lactate during 120 min of recovery and did not replenish a significant portion of their muscle glycogen, Ultimately, it took animals that exercised at 40° C and recovered at 20° C 480 min to remove all of the exercise-generated lactate from their blood, but animals that exercised and recovered at 40° C only required 120 min. The results of this study indicate that recovery temperature has different effects on different aspects of exercise recovery and that, unlike the net cost of sustainable locomotion, Cns is thermally sensitive.