Variation in sperm swimming behaviour and its effect on fertilization success in the serpulid polychaete Galeolaria caespitosa

Summary Established models of fertilization kinetics in free-spawning marine invertebrates predict that fertilization success is dependent upon sperm swimming velocity. Despite the prevalence of these models, there are very few published tests of this assumption. To test this, the effects of sperm swimming characteristics on fertilization success were studied in Galeolaria caespitosa (Polychaeta, Serpulidae). Both sperm activity (% motility) and sperm swimming velocities were highly variable within this species. Sperm were motile for up to 6–7 h after activation; however, mean motility, swimming velocity and fertilization success decreased after 4 h. Eggs of G. caespitosa were fertilizable up to 10 h after spawning; however, the number of embryos resulting from fertilization by fresh sperm also decreased after 4 h. Sperm motility and velocity were not affected by water-soluble egg extracts. When gamete concentration, contact time, and age were held constant, fertilization success in G. caespitosa remained...