Acclimation to elevated emersion temperature has no effect on susceptibility to acute, heat-induced lipid peroxidation in an intertidal mussel (Mytilus californianus)

Abstract

Organisms inhabiting the rocky intertidal zone must tolerate both aquatic and terrestrial stresses encountered over the tidal cycle, particularly those that occur during emersion such as desiccation, hypoxia, and thermal stress. We tested whether episodic exposure to elevated body temperatures that are possible in future climate scenarios leads to up-regulation of the antioxidant defense system or, alternatively, to accumulation of oxidative damage. We quantified antioxidant capacities against peroxyl and hydroxyl radicals, catalase enzymatic activity, and lipid peroxidation—a form of oxidative damage—in gill, mantle, and adductor muscle from mussels (Mytilus californianus) exposed to three treatments for 4 weeks: immersed continuously in seawater (15 ± 1 °C), exposed to moderate temperature air (21.8 ± 0.1 °C) for 4 h per day, or exposed to warm air (30 ± 0.1 °C) for 4 h per day. We quantified antioxidants and oxidative damage under both baseline conditions and following a common, acute heat stress challenge. Gill tissue accumulated lipid peroxidation damage during the acute thermal challenge independent of acclimation history, and this tissue expressed the lowest baseline levels of defense against peroxyl radicals that promote lipid peroxidation. There was no up-regulation of measured components of the antioxidant system in any tissue following the acclimation regimes. There was also no evidence for chronic accumulation of lipid oxidative damage. Based on these patterns, we hypothesize that the costs of repairing lipid peroxidation are less than the costs of mounting a constitutive, baseline antioxidant defense against extreme events that tend to be rare and relatively unpredictable in nature.