No abstract

Ectotherms are especially vulnerable to climate change due to their dependence on environmental thermal conditions to obtain adequate body temperatures for physiological performance. An approach to predict the impact of global warming in ectotherms is quantifying their locomotor sensitivities to temperature across the thermal performance curves (TPCs) owing to the crucial role running plays on most of their activities, like dispersion, reproduction, and foraging. Here, we have examined the relationship between body temperature (Tb) and locomotor performance in juveniles and adults of the high-mountain lizard Phymaturus palluma. We have determined the speed in long (LR) and sprint runs (SR) at five different body temperatures, and their relationship with morphological traits. In addition, we have measured the operative temperatures in the microenvironments used by P. palluma to evaluate their vulnerability to global warming. For this, we have estimated the thermal safety margin and warming tolerance. Phymaturus palluma showed a left-skewed TPCs for LR and SR. The optimal temperature (To) matched the set point of preferred temperatures and the performance breadth was correlated with the variance in Tb registered in the field, as the thermal coadaptation hypothesis predicts. The rising temperatures projected by the study site could represent a threat for the species, because currently P. palluma experiences operative temperatures that include their performance breadth and To. Moreover, we have demonstrated that the species currently exhibit negative thermal safety margins, thus an increase in ambient temperatures will reduce the amount of time in which lizards could achieve an optimal performance.

In ectotherms, temperature exerts a strong influence on the performance of physiological and ecological traits. One approach to understand the impact of rising temperatures on animals and their ability to cope with climate change is to quantify variation in thermal-sensitive traits. Here, we examined the thermal biology, the temperature dependence and the thermal plasticity of bite force (endurance and magnitude) in Diplolaemus leopardinus, an aggressive and territorial lizard, endemic to Mendoza province, Argentina. Our results indicated that this lizard behaves like a moderate thermoregulator which uses the rocks of its environment as the main heat source. Bite endurance was not influenced by head morphometry and body temperature, whereas bite force was influenced by head length and jaw length, and exhibited thermal dependence. Before thermal acclimation treatments, the maximum bite force for D. leopardinus occured at the lowest body temperature and fell sharply with increasing body temperature. After acclimation treatments, lizards acclimated at higher temperatures exhibited greater bite force. Bite force showed phenotypic plasticity, which reveals that leopard iguanas are able to maintain (and even improve) their bite force under a rising-temperature scenario.

The rising temperature predicted is of main concern for ectotherms because its direct impact on their behavior and physiology. Since physiological performance mediates a species’ resilience to warming exposure, physiological plasticity could greatly reduce the susceptibility to climate change. We studied the degree to which Diplolaemus leopardinus’ lizards are able to adjust behavioral and physiological traits in response to short periods of temperature change. We used a split cross design to measure acclimation response of preferred body temperature (Tp), and thermal performance curve of resting metabolic rate (RMR) and evaporative water loss (EWL). Our results showed that plasticity differs among traits; whereas Tp and EWL showed lower values in warm conditions, RMR increased the temperature at which its value is highest. Moreover, RMR was affected by thermal history, showing a great increase in response to cold exposure in the group initially acclimated to warm. The reduction of EWL and the increase in optimal temperature will give lizards the potential to partially mitigate the impact of rising temperatures in the energy cost and water balance. However, the decrease in Tp and the sensitivity to the warm thermal history in RMR could be detrimental to the energy net gain increasing the species vulnerability, especially considering the increase of heat waves predicted for the next fifty years. The integration of acclimation responses in behavioral and physiological traits provides a better understanding of the range of possible responses of lizards to cope with the upcoming climatic and environmental modifications expected due to climate change.