Meeting Abstract
48.10 Jan. 6 Why sub-optimal is optimal: a model of ectotherm thermal preferences MARTIN, T.L.; HUEY, R.B.*; Harvard Univ.; Univ. Washington, Seattle hueyrb@u.washington.edu
Body temperature profoundly affects the fitness of ectotherms, and many ectotherms use behavioral adjustments in an attempt to control body temperatures within narrow, species-specific levels. Biologists have long assumed that such �preferred body temperatures� are optimal and thus correspond with the body temperatures (Tr-max) that maximize Darwinian fitness (r). We develop a simple model of optimal behavioral thermoregulation and find that thermal preferences should in fact be centered not at Tr-max, but at a temperature lower than Tr-max. This finding may seem paradoxical, but is an inevitable consequence of two considerations. First, ectotherms aren�t perfect thermoregulators and so experience a range of body temperatures. Second, thermal fitness curves of ectotherms are asymmetric (Tr-max is much closer to the upper than to the lower lethal temperature), such that a body temperature higher than Tr-max will depress fitness much more than will a body temperature displaced an equivalent amount below Tr-max. This model makes several predictions. Ectotherms should maximize total fitness by centering thermal preferences below Tr-max and the magnitude of the optimal deviation below Tr-max should increase with the degree of asymmetry of the thermal fitness curves as well as with the variance in body temperature. Moreover, deviation should be relatively large for thermal specialists, but should be insensitive to whether fitness increases with Tr-max (�warmer is better�). We challenge some of these predictions primarily with a large comparative data set on the thermal dependence of sprint speed of lizards. Thermal preferences are indeed generally below the optimum temperature for sprinting. As predicted, the magnitude of the deviation increased with the degree of asymmetry of the thermal performance curve and with the degree of thermal specialization (standardized independent contrasts). Thus, suboptimal is optimal.
