Spermatophore formation in the simultaneously hermaphroditic land snail Arianta arbustorum (Pulmonata : Stylommatophora : Helicidae)

In helicid gastropods including Arianta arbustorum (LINNAEUS, 1758) sperm a re reciprocally exchanged during copulation through spermatophores. A. arbu storum has been extensively investigated with respect to sexual selection a nd a considerable amount of data on sperm and spermatophore transfer are av ailable. However, nothing is known about spermatophore formation and its po ssible influence on sperm exchange. As a contribution to the very limited k nowledge on spermatophore formation in stylommatophoran gastropods in gener al and in order to complement the existing behavioural studies from a funct ional-anatomical point of view, we investigated spermatophore formation in A. arbustorum. Spermatophores were collected at certain intervals from 2 to 90 min after the onset of copulation either through forceful separation of the pairs (after which spermatophores were expelled by the snails) or thro ugh dissection of electrocuted and fixed animals. We found that spermatopho re formation was initiated more or less synchronously in mating partners a few minutes after the onset of copulation and continued until shortly befor e transfer, which occurred after more than 60 min. Growth of the sperm cont ainer, which is probably mediated through the incoming ejaculate dilating t he viscous, workable material secreted by the epiphallus, followed a satura tion curve where the final length was reached slightly earlier than the fin al volume. However, growth and final size were not adjusted among partners confirming earlier findings that there is no sperm trading in A. arbustorum . Spermatophores collected from separated snails Were larger than those fro m fixed individuals indicating that spermatophore formation is not immediat ely stopped after separation. This means that the former protocol is less p recise for the investigation of spermatophore formation than a treatment in volving rapid fixation. In A. arbustorum, spermatophore formation differs l argely from that in the only other investigated helicid snail, Helix pomati a Linnaeus 1758. in which the container is assembled and the spermatophore transferred in less than 10 min.