The Impairment of Body Condition Transiently Increases Oxidative Stress: A Dietary Restriction Experiment in Partridges.

A proper body condition determines the correct functioning of physiological processes and the optimal expression of fitness-related traits. Among these processes, maintaining the redox balance is essential to protect the organism from damage caused by oxidative stress. Yet, the causal link between an impaired body condition and a consequent increase in oxidative stress remains surprisingly far from clear. We experimentally tested such link by imposing a dietary restriction (DR), that is, decreased food availability, to nonreproductive adult red-legged partridges (Alectoris rufa) and measuring a battery of oxidative stress biomarkers. Levels of oxidative status (ratio of reduced to oxidized glutathione [GSH:GSSG] in erythrocytes), oxidative damage in plasma lipids (MDA), and plasma antioxidant capacity (OXY and TEAC assays) were quantified before the DR, twice during the DR, and once after the end of the DR. The GSH:GSSG ratio remained steady throughout the experiment. By contrast, after 19 days under DR, individuals showed an increase in MDA levels and an altered antioxidant capacity (a reduction in OXY and an increase in TEAC) with respect to controls, showing that the worsening of body condition indeed leads to an increase of the oxidative stress. However, these effects were transitory, appearing only by 19 days under DR and disappearing afterwards. These findings suggest that, despite the temporary increase in oxidative damage, individuals adapt their oxidative physiology to overcome resource restriction, possibly by reallocating resources from other physiological processes. This highlights the importance of considering dynamic changes when evaluating the impact of stressful conditions.