Recovery of Sperm Activity After Osmotic Shock in the Three-Spined Stickleback: Implications for Pre-Oviposition Ejaculation

Pre-oviposition ejaculation is known to occur in the three-spined stickleback and may help to determine fertilisation success when sperm competition occurs as a consequence of males adopting alternative mating tactics. However, fish sperm typically show a rapid reduction in motility after exposure to fresh water, which would appear to limit the utility of such a strategy. Here, we use computer-assisted sperm analysis (CASA) to examine changes in stickleback sperm motion over time in fresh water, showing for the first time that this reduction in motility can be reversed by an increase in osmolality. We consider the possibility that ovarian fluid may have the same effect, and suggest that pre-oviposition ejaculation may be associated with higher fertilisation success than might otherwise be the case.