Figure 1.

How oxidative stress, an overproduction of ROS that cannot be managed by protective mechanisms, can reveal mate quality. ROS are produced from a number of different sources and their production has the potential to cause oxidative stress. However, animals have a variety of different protective mechanisms that protect against such damaging effects and often work in concert with ROS production to maintain homeostasis. Under some conditions, however, there is a breakdown in homeostasis and oxidative stress results. This can correlate with negative physiological states that in many circumstances would be undesirable in a mate. Arrows indicate causal directions, with the large arrow indicating the key factor influencing oxidative stress.