Dehydration alters sprint speed capacity more than maximal endurance in a terrestrial lizard.

The evolution of thermo-hydroregulation is determined by a cost-benefit balance, which in terrestrial ectotherms depends on the relationship between temperature, hydration status and maximal performance capacities. Earlier studies in amphibians uncovered deleterious effects of dehydration on a range of locomotor tasks and suggested that dehydration might further constrain the benefits of thermoregulation by decreasing tolerance to extreme temperatures. Hydric performance curves have been little investigated so far in dry-skin ectotherms, such as reptiles. Further, whether dehydration differently alters locomotor performance at low versus high temperatures in these organisms remains unresolved. Here, we manipulated drinking water availability over 10 days and quantified the hydric dependence of maximum running speed at different body temperatures as well as effects on endurance capacity in the lizard Zootoca vivipara. We further assessed whether performance decline could be explained by a loss of body condition, specifically hindlimb muscle loss. Lizards provided with limited drinking water declined significantly in condition and had much higher plasma osmolality, indicating sharp physiological dehydration. Despite that, we found only modest effects of dehydration on sprint speed, even at high body temperatures, and no obvious effects on endurance. Individual mass loss was non-linearly but weakly correlated with a decrease in endurance capacity. Sprint speed decreased with hindlimb muscle loss, and we found a slight reduction of the thermal performance breadth in the most dehydrated lizards. These results suggest that locomotor performance is primarily influenced by body temperature and secondarily by hydration state and only from a high dehydration threshold.