Early events in seminal fluid and sperm storage in the female blue crab Callinectes sapidus Rathbun: Effects of male mating history, male size, and season

Male blue crabs, Callinectes sapidus Rathbun, transfer sperm and seminal fluid to their mates. The quantity of both of these components can vary, and may be particularly reduced in the ejaculate of males that have recently mated. While the potential consequences for fitness of receiving less sperm are obvious, the same is not true of seminal fluid; its role in the blue crab, other than as a sperm plug, is not known. We documented the changes in seminal fluid over time following controlled matings in the laboratory. By allowing males to mate repeatedly in quick succession, we were able to manipulate both the amount of sperm and of seminal fluid that females received. We measured the initial amount of seminal fluid and sperm transferred, and followed the number and viability of sperm, and condition of the spermathecal organs and ovaries, in cohorts of females held for various times post-mating. Females whose mates had mated recently received only about 33% as much ejaculate as those whose mates had full sperm stores. Sperm viability was unaffected, and regardless of male mating history, sperm number declined nearly 50% prior to brood production. We found that all seminal fluid is gone by 5 weeks post-mating, making it unlikely that it plays a role during long-term storage of sperm. The amount of ejaculate was independent of the size of the mate. The spermathecal organs themselves lose 86% of their mass prior to brood production, and this allowed us to develop a staging system for spermathecal condition that was useful for estimating reproductive timing in a field population in North Carolina. Essentially all field-caught females had mated, but sperm viability, sperm number, and ejaculate weight varied with season.