The Oxidative Cost of Reproduction: Theoretical Questions and Alternative Mechanisms

The role of reproduction in increasing oxidative stress may be fundamental to understanding aging and the evolutionary trade-off between survival and fecundity. However, contradictory results among experimental studies have challenged the oxidative cost of reproduction. Limitations in experimental design may explain inconsistent findings. Nonetheless, some authors have argued that the hypothesis is founded on the faulty assumptions of an energy-based allocation trade-off and a direct positive link between metabolic rates and the production of reactive oxygen species (ROS) by the mitochondria. We propose that evolutionary trade-offs do not require the allocation of limiting resources and that reproduction may result in ROS-induced oxidative stress without increased mitochondrial ROS. We discuss the previously published oxidative-shielding hypothesis and propose two new hypotheses: hormesis and extortion for reproduction. These hypotheses aim to explain the counterintuitive results indicating that there is less oxidative damage in animals allowed to breed compared with those prevented from reproducing.