Correspondence between thermal biology and locomotor performance in a liolaemid lizard from the southeastern coastal Pampas of Argentina.

The behavioral and physiological mechanisms of thermoregulation and the morphological traits of lizards result in a particular range of body temperatures, which influence performance and ultimately fitness. We studied the thermal biology and locomotor performance of the lizard Liolaemus wiegmannii from the coastal dunes in the southeastern Pampas of Argentina. During the austral summer, we examined the link between thermoregulation and optimal locomotor performance. Liolaemus wiegmannii faced a stressful environment due to high risk of overheating; despite this, the species was able to achieve field body temperatures (Mean Tb ± SD = 35.58 ± 2.86 °C) than expected by chance (i.e., the null model) and suitable for sustaining its physiological performance. Locomotion in this species was thermally-sensitive, with lizards showing high-performance bouts at a relatively wide range of body temperatures (30-38 °C). Lizards exhibited a mean maximum running speed of 1.30 m/s at 37.3 °C (i.e., optimal temperature for locomotion) which was within the set point range of preferred temperature (Tset = 35.4-37.5 °C). Therefore, we found a correspondence between thermal optimum and preferred temperature. Our findings suggest that L. wiegmannii, like other lizard species with a broad distribution, is capable of performing well across a wide range of temperatures despite the spatiotemporal thermal fluctuations of the environment.

Latitudinal pattern of the thermal sensitivity of running speed in the endemic lizard Liolaemus multimaculatus.

Physiological performance in lizards may be affected by climate across latitudinal or altitudinal gradients. In the coastal dune barriers in central-eastern Argentina, the annual maximum environmental temperature decreases up to 2°C from low to high latitudes, while the mean relative humidity of the air decreases from 50% to 25%. Liolaemus multimaculatus, a lizard in the family Liolaemidae, is restricted to these coastal dunes. We investigated the locomotor performance of the species at 6 different sites distributed throughout its range in these dune barriers. We inquired whether locomotor performance metrics were sensitive to the thermal regime attributable to latitude. The thermal performance breadth increased from 7% to 82% with latitude, due to a decrease in its critical thermal minimum of up to 5°C at higher latitudes. Lizards from high latitude sites showed a thermal optimum, that is, the body temperature at which maximum speed is achieved, up to 4°C lower than that of lizards from the low latitude. At relatively low temperatures, the maximum running speed of high-latitude individuals was faster than that of low-latitude ones. Thermal parameters of locomotor performance were labile, decreasing as a function of latitude. These results show populations of L. multimaculatus adjust thermal physiology to cope with local climatic variations. This suggests that thermal sensitivity responds to the magnitude of latitudinal fluctuations in environmental temperature.

Seasonal shifts in the thermal biology of the lizard Liolaemus tandiliensis (Squamata, Liolaemidae).

Small lizards can accommodate to constraints imposed by temporal changes in ambient temperature through a combination of adaptive evolution and behavioral and physiological plasticity. Thermal physiology plasticity may compensate for climate variation and favor performance while minimizing behavioral costs in sub-optimal conditions. The Tandilia's lizard, Liolaemus tandiliensis, occurs in an isolated mountain range of the Argentinean temperate Pampas. In this study, we compared the thermal biology of L. tandiliensis between late spring (December) and mid-summer (February). The habitats' thermal quality was lower in late spring than in mid-summer. The lizard's field-body temperature (Tb) was 2-3 °C higher than the operative temperature (Te). Overall, the mean preferred temperature (Tsel) was 37.4 °C [preferred range (Tset): 36.2-38.7 °C], and was similar to other Liolaemus species. The Tset and Tsel of females in late spring were 1.8 °C lower than in mid-summer. In the case of males, the Tsel did not vary among seasons, while the Tset had a difference of 2.5 °C between seasons. Adults were moderate thermoregulators, but females were more efficient only in late spring (Emales = 0.69; Efemales = 0.58), compared to mid-summer (Emales = 0.68; Efemales = 0.50). Juveniles did not show temporal differences in temperature preferences and had a relatively higher efficiency in late spring (E = 0.38) compared to mid-summer (E = 0.28). An increased proportion of juveniles and adults shifted their Tb near to the Tset in late spring respect to mid-summer. The adults also matched their preferred temperatures to their current body temperature. These results suggest that seasonal shifts in the thermoregulatory parameters of L. tandiliensis may improve their thermoregulatory efficiency. Although temporal variation in ambient temperatures might influence the thermal biology of the studied lizards, other factors such as changes in the reproductive status may have also interfered.