The role of oxidative stress in postcopulatory selection.

Two decades ago, von Schantz et al. (von Schantz T, Bensch S, Grahn M, Hasselquist D, Wittzell H. 1999 Good genes, oxidative stress and condition-dependent sexual signals. Proc. R. Soc. B 266, 1-12. (doi:10.1098/rspb.1999.0597)) united oxidative stress (OS) biology with sexual selection and life-history theory. This set the scene for analysis of how evolutionary trade-offs may be mediated by the increase in reactive molecules resulting from metabolic processes at reproduction. Despite 30 years of research on OS effects on infertility in humans, one research area that has been left behind in this integration of evolution and OS biology is postcopulatory sexual selection-this integration is long overdue. We review the basic mechanisms in OS biology, why mitochondria are the primary source of ROS and ATP production during oxidative metabolism, and why sperm, and its performance, is uniquely susceptible to OS. We also review how postcopulatory processes select for antioxidation in seminal fluids to counter OS and the implications of the net outcome of these processes on sperm damage, sperm storage, and female and oocyte manipulation of sperm metabolism and repair of DNA to enhance offspring fitness. This article is part of the theme issue 'Fifty years of sperm competition'.