Oxidative stress and condition-dependent sexual signals: more than just seeing red

Abstract

The links between fitness, health, sexual signals and mate choice are complex and subject to ongoing study. In 1999, von Schantz et al. made the valuable suggestion that oxidative stress may be an important missing piece of this complex puzzle. Their suggestion has been enthusiastically tested, with over 300 studies citing their paper, but most effort has concerned carotenoid-based (and to a lesser extent melanin-based) visual signals, predominantly in birds and fishes. Today, we know a great deal more about oxidative stress and related physiology, in both a pathological and regulatory sense, than we did in 1999. We revisit von Schantz et al.'s predictions and, more importantly, highlight novel mechanisms that could link oxidative stress with a range of energetically demanding signals, greatly increasing the scope from visual signalling systems that are usually discussed and nearly always tested. In particular, we argue that differences between individuals in their ability to regulate physiology related to oxidative stress may be an important factor influencing the production of sexual signals and the costs that are incurred from investment.

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.