Thermal stability vs. variability: Insights in oxidative stress from a eurytolerant fish

Climate change will increase the frequency, intensity, and duration of heatwaves. This thermal volatility will challenge to the oxidative homeostasis of aquatic ectotherms through many temperature-dependent environmental factors. In this study, we examined the effects of chronic exposure of sheepshead minnows (Cyprinodon variegatus) to multiple thermal regimes on the oxidative physiology of white muscle in these eurytolerant fish. The thermal treatments included stable (15 °C and 30 °C) and cycling regimes (between 21 and 29 °C at 6, 8 and 10-h intervals). The effect of these thermal treatments on oxidative stress during an acute thermal challenge (12 h at 32 °C) was also examined. Enzymatic activity of catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx), scavenging capacities of hydroxyl and peroxyl radicals, and lipid peroxidation (LPO) damage were quantified. We found no differences between or across treatments in any of the enzymatic antioxidants or LPO damage. We found that peroxyl radical scavenging was greatest at the peak of the 8- and 10-h thermal cycles. Peroxyl scavenging after an acute thermal challenge was greater than before the challenge for the steady 15 °C and 8-h cycle treatments, greater before the acute challenge for the steady 30 °C and 6-h cycle, and equivalent in the 10-h cycle. These findings demonstrate that even the most tolerant of marine ectotherms must engage oxidative defenses when presented with thermal variability and heighten concerns about the impact of climate change on less tolerant species.