Lactic acid is a sperm motility inactivation factor in the sperm storage tubules of the domestic bird

Although successful fertilization depends on timely encounters between sperm and egg, decoupling of mating and fertilization often confers reproductive advantages to internally fertilizing animals. In several vertebrate groups, post-copulatory sperm viability is prolonged by their storage in specialized organs within the female reproductive tract. In birds, ejaculated sperm can be stored in a quiescent stage within oviductal sperm storage tubules (SSTs), thereby preventing the loss of fertility for up to 15 weeks; however, the mechanism by which once-activated spermatozoa are rendered quiescent within SSTs remains a mystery. Here, we show that quail SSTs maintain a hypoxic niche and secrete lactic acid. Sperm immobility is induced by lactic acid through cytoplasmic acidification and flagellar dynein ATPase inactivation. Our results suggested a novel physiological role of lactic acid in promoting sperm quiescence in the SSTs and open up new opportunity for technological improvement in prolonging sperm longevity at ambient or body temperature.