EVOLUTIONARY PATTERNS OF THE THERMAL SENSITIVITY OF SPRINT SPEED IN ANOLIS LIZARDS.

I present evidence that the thermal sensitivity of sprint speed of Anolis lizards has evolved to match the activity body temperatures (Tb ) experienced by local populations in nature. Anolis lizards from a range of altitudes in Costa Rica have limited thermoregulatory abilities and consequently have field Tb that differ substantially in median and interquartile distance (a measure of variability). Experimentally determined maximal sprint temperatures (Tb at which lizards run fastest) were positively correlated with median field Tb , and performance breadths (ranges of Tb over which lizards run well) were correlated with the variability (interquartile distance) of field Tb in the species I examined. Such correlations would be expected if the thermal sensitivity of sprint speed and field Tb had evolved together to improve the sprint performance of lizards in nature. Integration of laboratory and field studies indicates that several species of Anolis regularly experience impaired sprint speeds in the field, despite apparent evolutionary modification of their thermal physiologies. However, this impairment would have been more severe if the thermal sensitivities of sprint speed had not evolved. Data from other groups of lizards indicate that the thermal sensitivity of sprint speed has not evolved to match Tb of local populations (Hertz et al., 1983; Crowley, 1985). These lizards experience less variable Tb and less impairment of sprint speeds in the field than do the anoles. Thus, selection for modification of the thermal sensitivity of sprint speed might have been stronger for anoles than for other groups of lizards. © 1986 The Society for the Study of Evolution.