Evidence of adaptation of oxidative stress dynamics among desert rattlesnake populations.

The maintenance of body temperature (Tb) and hydration state within tolerable ranges is crucial for effective physiological functioning and thus survival. It is well established that deviations in Tb and hydration state can have immediate effects on organismal health, and recent work has demonstrated that, despite surviving the initial impacts of such challenges, individuals may experience profound long-term impacts on fitness, though the mechanisms driving these long-term impacts remain unclear. One potential mechanism underlying detrimental long-term effects is oxidative stress, yet the relationships among increased Tb, dehydration, and oxidative stress dynamics, as well as whether these relationships can be altered through adaptation, are mostly unexplored. Accordingly, we conducted complementary field and lab experiments to investigate seasonal, behavioral, thermal, and hydric effects on oxidative stress in two species of arid-adapted Crotalus rattlesnakes representing three populations from two xeric locations with differing aridity. Regardless of experiment or treatment, we found that C. pyrrhus, the most abundant species in the more arid location, had consistently lower reactive oxygen metabolite (ROM) concentrations than did C. atrox from the same and the less arid locations. Furthermore, the C. atrox population from the more arid site had ROM concentrations intermediate and often significantly different from the other two populations. Interestingly, when Tb and activity were similar between the C. atrox populations (e.g., in Spring), ROM concentrations were similar. Contrary to our hypotheses, we found no consistent patterns relating antioxidant capacity to any environmental or phylogenetic variable. Lastly, hydration state did not influence either ROM concentration or antioxidant capacity. Overall, our study demonstrates that while water deprivation and increased temperatures don't necessarily induce oxidative stress in species tolerant of these conditions, results are consistent with the hypothesis that species that are more specialized for extremely arid environments have reduced ROM concentrations. Such insight is critical as we attempt to understand how species have adapted to arid conditions and how species may respond to a warming and drying globe.