Hydration state does not influence dormancy during dry subtropical winter in the tegu lizard Salvator merianae

Water supply is essential for most physiological processes, making its efficient use vital for the organism, especially in hot and dry periods. The tegu lizard Salvator merianae, which is abundant in regions characterized by cool and dry winters, exhibits temperature-independent dormancy. Dehydration is known to affect physiological-behavioural performance, but the role of water availability in dormancy in tegus remains uncertain. This is particularly important in the current context of climate change, marked by more frequent heat waves and longer dry seasons. Thus, we investigated whether hydration state influences winter metabolic and behavioural reductions in male and female tegus. From April to September, we measured plasma osmolality, haematocrit, plasma ammonia concentration, body temperature (Tb), activity rate (overall dynamic body acceleration via triaxial accelerometry), specific behaviours (exploration, sheltering and resting), body mass and body condition factor in control and dehydrated individuals during pre-dormancy (April-May), dormancy (June-July) and post-dormancy (August-September) phases. Dehydrated tegus exhibited higher plasma osmolality and Tb compared with controls, whereas haematocrit, plasma ammonia concentration, body mass, body condition factor, activity rate and specific behaviours were similar between groups throughout the experimental months. Both control and dehydrated animals showed coordinated reductions in activity rate and behavioural expression during the pre-dormancy and dormancy phases, followed by increases during the post-dormancy phase. These results indicate that hydration state does not play a role as a driver of dormancy in tegus during moderately cold and dry winters; however, dehydration may be a risk factor for superheating during prolonged dry seasons and frequent heat waves.