http://mama.indstate.edu/angillet/Thermal%20Adaptation/Publications/Angilletta%20et%20al%20(in%20press).pdf

The evolution of thermal physiology in ectotherms

We describe a research protocol for evaluating temperature regulation from data on small field-active ectothermic animals, especially lizards. The protocol requires data on body temperatures (Tb) of field-active ectotherms, on available operative temperatures (Te, "null temperatures" for nonregulating animals), and on the thermoregulatory set-point range (preferred body temperatures, Tset). These data are used to estimate several quantitative indexes that collectively summarize temperature regulation: the "precision" of body temperature (variance in Tb, or an equivalent metric), the "accuracy" of body temperature relative to the set-point range (the average difference between Tb and Tset), and the "effectiveness" of thermoregulation (the extent to which body temperatures are closer on the average to the set-point range than are operative temperatures). If additional data on the thermal dependence of performance are available, the impact of thermoregulation on performance (the extent to which performance is enhanced relative to that of nonregulating animals) can also be estimated. A sample analysis of the thermal biology of three Anolis lizards in Puerto Rico demonstrates the utility of the new protocol and its superiority to previous methods of evaluating temperature regulation. We also discuss several ways in which the research protocol can be extended and applied to other organisms.

Evaluating temperature regulation by field-active ectotherms: the fallacy of the inappropriate question.

Some biologists embrace the classical view that changes in behavior inevitably initiate or drive evolutionary changes in other traits, yet others note that behavior sometimes inhibits evolutionary changes. Here we develop a null model that quantifies the impact of regulatory behaviors (specifically, thermoregulatory behaviors) on body temperature and on performance of ectotherms. We apply the model to data on a lizard (Anolis cristatellus) and show that ther- moregulatory behaviors likely inhibit selection for evolutionary shifts in thermal physiology with altitude. Because behavioral adjustments are commonly used by ectotherms to regulate physiological per- formance, regulatory behaviors should generally constrain rather than drive evolution, a phenomenon we call the "Bogert effect." We briefly review a few other examples that contradict the classical view of behavior as the inevitable driving force in evolution. Overall, our analysis and brief review challenge the classical view that behavior is invariably the driving force in evolution, and instead our work supports the alternative view that behavior has diverse—and some- times conflicting—effects on the directions and rates at which other traits evolve.

https://faculty.washington.edu/hueyrb/pdfs/BehavDrive.pdf

Behavioral drive versus behavioral inertia in evolution: a null model approach.

The view that behavior and physiological performance are tightly coadapted is a central principle of physiological ecology. Here, we test this principle using a comparative study of evolutionary patterns in thermal preferences and the thermal dependence of sprinting in some Australian skinks (Lygosominae). Thermal preferences (Tp ) differ strikingly among genera (range 24° to 35°C), but critical thermal maxima (CTMax) (range 38° to 45°C) and optimal temperatures for sprinting (To , 32° to 35°C) vary less. Diurnal genera have relatively high Tp , To , and CTMax. In contrast, nocturnal genera have low Tp but have moderate to high To and CTMax. Both nonphylogenetic and phylogenetic (minimum-evolution) approaches suggest that coadaptation is tight only for genera with high Tp . Phylogenetic analyses suggest that low Tp and, thus, partial coadaptation are evolutionarily derived, indicating that low thermal preferences can evolve, even if this results in reduced performance. In one instance, thermal preferences and the thermal dependence of sprinting may have evolved in opposite directions, a phenomenon we call "antagonistic coadaptation." We speculate on factors driving partial coadaptation and antagonistic coadaptation in these skinks.

/pdf/phylogenetic-studies-of-coadaptation-preferred-temperatures-1y3ft1qgwh.pdf

Phylogenetic studies of coadaptation: preferred temperatures versus optimal performance temperatures of lizards.

Body temperature (T(b)) profoundly affects the fitness of ectotherms. Many ectotherms use behavior to control T(b) within narrow levels. These temperatures are assumed to be optimal and therefore to match body temperatures (Trmax) that maximize fitness (r). We develop an optimality model and find that optimal body temperature (T(o)) should not be centered at Trmax but shifted to a lower temperature. This finding seems paradoxical but results from two considerations relating to Jensen's inequality, which deals with how variance and skew influence integrals of nonlinear functions. First, ectotherms are not perfect thermoregulators and so experience a range of T(b). Second, temperature-fitness curves are asymmetric, such that a T(b) higher than Trmax depresses fitness more than will a T(b) displaced an equivalent amount below Trmax. Our model makes several predictions. The magnitude of the optimal shift (Trmax - To) should increase with the degree of asymmetry of temperature-fitness curves and with T(b) variance. Deviations should be relatively large for thermal specialists but insensitive to whether fitness increases with Trmax ("hotter is better"). Asymmetric (left-skewed) T(b) distributions reduce the magnitude of the optimal shift but do not eliminate it. Comparative data (insects, lizards) support key predictions. Thus, "suboptimal" is optimal.

https://faculty.washington.edu/hueyrb/pdfs/MartinHuey08.pdf

Ra. Avery

Papers

Field studies of body temperatures and thermoregulation