LOW-TEMPERATURE AND EXERCISE RECOVERY IN THE DESERT IGUANA

We examined the effects of variable body temperature on exercise recov ery in the desert iguana, Dipsosaurus dorsalis, because both temperatu re and nonsustainable activity play an important role in the life hist ory of ectothermic tetrapods. We measured the rate of oxygen consumpti on (V over dot (O2)), the cost of nonsustainable locomotion (C-ns), bl ood and muscle lactate concentrations, and muscle glycogen concentrati ons of Dipsosaurus at 20 degrees C and 40 degrees C before, during and after exhaustive activity. We expected that low recovery temperatures would retard most aspects of metabolic recovery Animals that exercise d and recovered at 40 degrees C maintained significantly higher V over dot (O2)'s and returned to temperature-appropriate resting V over dot (O2)'s more rapidly than did animals that exercised and recovered at 20 degrees C. Animals that exercised and recovered at 20 degrees C als o had a greater average C-ns than did animals that exercised and recov ered at 40 degrees C (4.6 vs. 2.5 mu L O-2/(g X m)). The Q(10) values for V over dot (O2) were highly variable and ranged from 1.3 to 1.9 th roughout recovery. In contrast, Dipsosaurus that exercised at 40 degre es C and recovered at 20 degrees C returned to temperature-appropriate resting V over dot (O2)'s more rapidly than animals that exercised an d recovered at 40 degrees C. The C-ns was lower in animals that exerci sed at 40 degrees C and recovered at 20 degrees C than in animals that exercised and recovered at 40 degrees C (1.1 vs. 3.7 mu L O-2/(g X m) ). In contrast to those that exercised and recovered at 40 degrees C, animals that exercised and recovered at 20 degrees C did not remove a significant fraction of blood or muscle lactate during 120 min of reco very and did nor replenish a significant portion of their muscle glyco gen. Ultimately, it took animals that exercised at 40 degrees C and re covered at 20 degrees C 480 min to remove all of the exercise-generate d lactate from their blood, but animals that exercised and recovered a t 40 degrees C only required 120 min. The results of this study indica te that recovery temperature has different effects on different aspect s of exercise recovery and that, unlike the net cost of sustainable lo comotion, C-ns is thermally sensitive.