Evaluating the Role of Melanic Coloration and Environmental Conditions on Heat Gain among Patagonian Lizards (Liolaemus fitzingerii Group)

Abstract

The performance of ectotherms in their environment is predominantly shaped by body temperature, which is contingent upon the interplay of environmental conditions and their capacity to regulate heat exchange. Thermoregulation involves costs (e.g., energy and fitness costs), which can be buffered by behavioral, physiological, and biophysical mechanisms (e.g., coloration) or both. Here, we evaluated how differences in heating rates of Liolaemus melanops and Liolaemus xanthoviridis of the Liolaemus fitzingerii group were correlated with phenotypic traits expected to influence heat gain (melanic coloration and body size). We also investigated whether environmental conditions were correlated with heating rates in these species. We collected adult males in coastal and plateau localities of both species. We measured heating rates, mass, and melanism in laboratory conditions, and we collected data variables from each collecting site. Our results showed that heating rates were influenced only by mass, where slender lizards heated faster than heavier lizards. Our results did not provide evidence for the color-mediated thermoregulation hypothesis, which posits that, assuming a similar body size, melanic ectothermic individuals should heat more quickly and reach higher equilibrium temperatures than lighter ones. Also, we did not find evidence that different environmental conditions of the coastal and plateau localities affected heating rate. In these species of Liolaemus, behavioral and physiological adjustments could be key mechanisms driving active thermoregulation.