Sperm transfer, sperm storage, and sperm digestion in the hermaphroditic land snail Succinea putris (Gastropoda, Pulmonata)

Many hermaphroditic species are promiscuous, have a sperm digesting organ and an allosperm storage organ (i.e., spermatheca) with multiple compartments (i.e., spermathecal tubules) providing opportunities for sperm competition. The relative paternity of a sperm donor drives the evolution of mating behaviors that allow manipulation of the sperm receiver's reproductive behavior or physiology. We studied the relationship between sperm transfer, sperm storage, sperm digestion, and copulation duration in the hermaphroditic land snail Succinea putris, in which an active individual mates on top of a passive individual. Specifically, we examined (i) whether the entire copulation duration was required to complete reciprocal sperm transfer, (ii) sperm transfer patterns and their relationship with activity role, and (iii) the timing of sperm storage and sperm digestion. We found that reciprocal sperm transfer was completed within the first 5 h of copulation, which is ∼2–3 h before the end of copulation. Sperm transfer was mainly sequential, meaning that one individual donated all his ejaculate before its partner started to reciprocate. The initiation of sperm transfer did not depend on the activity role. The presence of allosperm in the spermatheca before sperm transfer suggests that individuals remate before they are allosperm depleted. No sperm was digested during copulation but sperm digestion took place 0–72 h after copulation. Our results suggest that contact mate guarding is a likely manipulation strategy in S. putris, because partners cannot immediately remate. In addition, staying in copula after sperm transfer is completed seems to prevent the immediate digestion of sperm and therefore may promote sperm displacement and allosperm storage.