Ca2+-dependent exocytosis of parasperm globular bodies in the strawberry conch gastropod Conomurex luhuanus.

Several animal groups produce two morphologically distinct types of sperm in the testis, including fertilizing eusperm and non-fertilizing parasperm. This phenomenon, termed sperm dimorphism, is considered to play a role in reproductive strategies such as sperm competition. In the marine gastropod Conomurex luhuanus, parasperm possess numerous globular bodies and the cilia-based undulating membranes. However, the function of the globular bodies and the motility of the undulating membranes remain unclear. Here, we describe the process and regulation of globular body exocytosis in parasperm. Upon dilution in artificial seawater, exocytosis occurs via membrane fusion between globular body membrane and the plasma membrane, followed by the release of globular body contents. Exocytosis was markedly suppressed under Ca2+ -deficient conditions but was enhanced by increases in intracellular Ca2+ induced by an ionophore A23187. In contrast, both the absence of extracellular K⁺ and high extracellular K⁺ concentrations enhanced exocytosis. On the other hand, the direction of wave propagation of the undulating membrane was reversed by high extracellular Ca2+ concentrations or by treatment with A23187, whereas it was suppressed under high extracellular K⁺ conditions. Together, these findings indicate that globular body exocytosis and changes in swimming direction are regulated by different mechanisms. This study provides novel insight into the post-ejaculatory behavior and potential function of parasperm within the female reproductive tract of gastropods.