Constraint and cost of oxidative stress on reproduction: correlative evidence in laboratory mice and review of the literature

A significant increase in oxidative damage over time was only observed in females caring for offspring, whereas antioxidant defences increased over time regardless of reproductive status. Interestingly, oxidative damage measured prior to reproduction was negatively associated with litter size at birth (constraint), whereas damage measured after reproduction was positively related to litter size at weaning (cost).Globally, our correlative results and the review of literature describing the links between reproduction and oxidative stress underline the importance of timing/dynamics when studying and interpreting oxidative balance in relation to reproduction. Our study highlights the duality (constraint and cost) of oxidative stress in life-history trade-offs, thus supporting the theory that oxidative stress plays a key role in life-history evolution.A central concept in evolutionary ecology is that fitness-related traits, which allow organisms to produce many offspring over many reproductive attempts (i.e. fecundity and survival), are traded-off amongst themselves due to a ubiquitous constraint: a limited available pool of resources to share between all biological functions [1]. Hence, current parental investment in reproduction is expected to result in decreased survival and future reproductive value known as the so-called cost of reproduction [1,2]. It has been established for some time that life-history trade-offs are the bedrock of evolutionary biology, and in recent years attention has turned towards examining the nature of the mechanisms underlying trade-offs. In this context, the production of reactive oxygen species (ROS), by-products of oxidative metabolism, appears to be a corner-stone factor both by its universal and inevitable nature [3].Oxidative stress is defined as an imbalanced situation where deleterious production of ROS (mainly by the mitochondria during normal energy processing) exceeds the capacity of the various anti-oxidant systems to deal with t