Is a warmer environment better for a high-mountain lizard?

The global increase in temperatures threatens the survival of lizards in habitats with broad thermal oscillations. Viviparous populations in high mountains (sky islands) often exhibit a greater thermal tolerance, a trait that, according to Janzen's Hypothesis, is favored by these environments. This raises the question of whether such an adaptation can help them cope with global warming more effectively than populations at lower elevations. To investigate this, we translocated Sceloporus bicanthalis from its native habitat at 4100 m (the species occupy elevations between 2500 and 4250 m) to a lower elevation of 2060 m, simulating a temperature increase. During a 45-day acclimatisation experiment, we measured thermophysiological traits and locomotor performance in pre-acclimatisation (in their native habitat) and post-acclimatisation individuals (at the lower-elevation site). Although we found no changes in thermal limits, the effectiveness of thermoregulation (E) was greater in the pre-acclimatisation group. Translocated individuals showed an increase in maximum sprint speed (Vmax), while the optimal performance temperature (Topt) remained constant in both groups and coincided with their preferred temperature range. Our study demonstrated that, far from being a strict thermal specialist, the thermal physiology of S. bicanthalis allows it to persist in habitats with warmer thermal conditions, evidencing a greater thermal tolerance and suggesting sufficient physiological plasticity to cope with increasing ambient temperatures.