Thermoregulatory behavior varies with altitude and season in the sceloporine mesquite lizard

Abstract

In ectothermic animals, body temperature is the most important factor affecting physiology and behavior. Reptiles depend on environmental temperature to regulate their body temperature, so geographic variation in environmental temperature can affect the biology of these organisms in the short and long term. We may expect physiological and behavioral responses to temperature change to be especially important in ectotherms inhabiting temperate zones, where different seasons present different thermal challenges. High-mountain temperate systems represent a natural laboratory for studies of evolutionary and plastic variation in thermal biology. The aim of the present study is to evaluate operative temperature with biophysical models, active body temperature under field conditions, preferred temperature in a thermal gradient in the laboratory, and thermal indexes in Sceloporus grammicus lizards along an elevational gradient. We measured these traits in three populations at 2500, 3400, and 4100 m elevation at different seasons of the year (spring, summer and autumn). Our results showed that operative temperature varied with season and elevation, with greater variation at middle and high elevations than at low elevations. Body temperature and preferred temperature varied with altitude and season but did not differ between sexes. Thermal quality was lowest in the high-altitude population and in the summer season. Thermoregulatory efficiency was highest in the three populations in the autumn. Our results suggest that thermoregulatory strategies vary with elevation and season, allowing individual lizards to confront annual fluctuations in the thermal environment and conflicting with some previous descriptions of Sceloporus lizards as thermally conservative.