Thermoregulatory accuracy in Liolaemus lutzae: do sex and age influence thermoregulatory effectiveness?

We investigated aspects of the thermal niche of the liolaemid lizard Liolaemus lutzae, aiming to compare thermoregulatory accuracy between sexes and between juveniles and adults. We sampled body temperatures and operative environmental temperatures across a range of microhabitats potentially used by L. lutzae. Preferred body temperatures and the set-point range of individuals were estimated in a laboratory photothermal gradient. We estimated three thermoregulation indices to evaluate the efficiency of thermoregulation and compared the thermoregulatory accuracy of different sexes and ages. The accuracy of T_b was calculated using the mean of the deviations of T_b from T_set (d‾_b), the thermal quality of each microhabitat was assessed measuring the mean of the deviations of T_e from T_set (d‾_e), and the effectiveness of thermoregulation (E) calculated from the formula E=1-d‾_b/d‾_e. We found a difference between d‾_b of adults and juveniles but not between males and females. The juveniles had higher values of E compared to adults of both sexes. We observed negative values of E between 8h00 and 9h00 and after 15h00. The period between 11h00 and 13h00 showed values of E closest to 1 for both, juveniles and adults. Liolaemus lutzae is usually exposed to temperatures above its preferred range in the study area, especially between 10:00 and 15:00 (60% of its activity period), when the average operative temperature (T_e) exceeds the T_set. The lizards were exposed to extreme temperatures between 11:00 and 14:00 when the T_e exceeds the CT_max. The thermal quality of microhabitats tended to vary throughout the day, requiring L. lutzae to actively thermoregulate. Juvenile L. lutzae seemed to thermoregulate more accurately than adults. Juveniles compensate for their lower thermal inertia through careful behavioral thermoregulation, which explains the absence of differences in body temperature (T_b) between adults and juveniles.