Bacterial immunity traded for sperm viability in male crickets.

The notion that a trade-off exists between immunity and reproduction is now a central concept in theories of sexual selection. However, whether such a trade-off exists between immunity and gamete viability has not been established. Here we show that genetic variance for high levels of an immune response required to fight bacterial infections is associated with genetic variance for low sperm viability. These data have implications for our understanding of sexual selection mechanisms and of reproductive costs in male longevity.