Sperm of the Shrimp Sicyonia ingentis Undergo a Bi-Phasic Capacitation Accompanied by Morphological Changes

Sperm removed from seminal receptacles of female Sicyonia ingentis can be induced to undergo a bi-phasic acrosome reaction (AR), acrosomal exocytosis followed by filament formation, using egg water (EW). Sperm removed from males will not undergo any phase of the AR when incubated with EW, indicating that these sperm undergo a capacitation process after insemination. Freshly molted females (functional virgins) were placed in aquaria with males and monitored for copulation. Mated females were isolated and allowed to carry sperm for specific periods of time. At these time points, sperm were removed and assayed for the ability to undergo the AR using EW. The results indicate that sperm are competent to undergo acrosomal exocytosis after approximately 25 hr, while competency to form acrosomal filaments is not achieved until around 145 hr post-insemination. Morphological examination of sperm removed from males and sperm removed from females revealed dramatic differences. Microscopic evidence indicates that some of the morphological changes seen during capacitation are necessary for the successful completion of the AR.