Hormetic effects on the development of the oxidative state and of the oxidative stress response in zebra finches

Stressful conditions are an important ecological and evolutionary force modulating adaptive responses of natural populations to environmental conditions, and external stressors can cause changes in cellular function including the generation of oxidative stress, that is an imbalance between pro-oxidants and antioxidants in favour of the former. The traditional conceptual model sees oxidative stress as having damaging consequences for living systems, potentially leading to physiological senescence and death. Recent evidence, however, suggests that early exposure to stressful circumstances might stimulate protective mechanisms, resulting in biologically beneficial effects (termed hormesis). In fact, some biological stimuli, such as physical activity or changes in temperature, have been shown to be potentially harmful when extreme, but actually beneficial at lower intensities. Whilst there has been some work on hormesis in the context of human medicine, there have been no attempts to assess the ecological relevance of such a phenomenon. Here I plan to test the hypothesis that individuals exposed to circumstances that induce a moderate level of oxidative stress early in life cope with oxidative stress in adulthood. My aim in the Fellowship is to test novel predictions that arise from this hypothesis by means of experiments on zebra finches (Taenopigya guttata) that manipulate environmental conditions faced by animals in both early and adult life. In particular, I will test the long-term effect of early exposure to two ecologically relevant stressors that have been suggested to have hormetic effects: physical activity and heat stress. In a first experiment I will test whether individuals subjected to a mild physical activity when juveniles will later in life have a better oxidative stress response to strenuous flight or to heat stress compared to those of individuals that were subjected to more intense physical activity or to no training. In a second experiment, I will test whether a mild heat stress experienced during development upregulates antioxidant defences, so improving later in life the oxidative stress response to heat stress or strenuous flight, again in comparison with individuals that experienced either no or more severe heat stress. The results of these experiments will provide an understanding of the causes and consequences of variation in the oxidative stress response and of the role that specific environmental stressors play in optimising responses of the organism to the environment.