Many species of pulmonate land snails are equipped with one or more so-called "love darts". Even though the number and shape of these calcareous darts vary considerably between species, dart use has only been investigated in very few species. Here, we redescribe the mating behaviour of Polymita muscarum because previous reports did not include the use of the dart apparatus. Mating in this hermaphroditic land snail can be divided into three stages: courtship, copulation and post-copulatory activity. During courtship, full eversion of the genital atrium is reached, thus exposing the sensitive zone, genital lobes and dart apparatus. We observed that P. muscarum pushes the everted dart apparatus repeatedly onto different parts of the partner's body and does not lose its dart after stabbing. Dissected specimens had a single, slender dart with a round base, a broad corona and a circular cross-section. We propose that the morphology of P. muscarum 's dart is consistent with the idea of simple darts needing to be stabbed more often in order to increase the transfer of mucus, which contains a biologically active substance (i.e. allohormone) that enhances the chances of paternity. Besides adding to the growing diversity in the use of love darts in land snails, these findings contribute to the understanding of the evolution of this peculiar reproductive act.
Promiscuity, sperm storage and internal fertilization enhance sperm competition, which leads to sexual conflict whenever an advantageous trait for sperm donors is harmful to recipients. In separate-sex species, such conflicts can severely impact the evolution of reproductive characteristics, physiology and behaviours. For simultaneous hermaphrodites, the generality of this impact remains unclear and underlying mechanisms remain largely unexplored. In the hermaphrodite Lymnaea stagnalis several previous studies showed that investment in eggs differs depending on semen receipt, but these were inconsistent about the direction of change. We investigated whether the change in egg laying is caused by a seminal fluid component. By intravaginally injecting animals, we here reveal that a component of the seminal fluid inhibits egg laying, thus providing the first direct evidence for involvement of such components in competition for fertilization in hermaphrodites. We discuss the broad implications that this finding has on a number of previous studies performed in the same species.
Post-copulatory sexual selection research tends to focus on the numerous adaptations that have evolved to increase the chances of donated spermatozoa fertilizing oocytes. Even though fertilization obviously directly depends on the presence of sufficient, viable spermatozoa, the quantification of the sperm transfer process itself has not received the attention it deserves. Here, we present experimental work on a simultaneously hermaphroditic snail in combination with a review of the literature focussing on the relationship between the duration of copulation and the number of sperm that are transferred. Based on classical work, this relationship is often assumed to be linear, but as we show here this need not be the case. Both our experimental data and the reviewed literature indicate that there are clear instances where the process of sperm transfer is not a linear process, i.e., longer copulation duration does not necessarily imply more transfer of sperm. As we point out, there seems to be a bias in the literature towards investigating this in insects, but other animal groups in which this has been investigated do show similar relationships. To conclude, we discuss how the specific patterns of sperm transfer that have been reported can be biologically interpreted and we caution that simply using copulation duration as a proxy for the number of sperm transferred can be misleading.
Body size can be a good indicator of the quality of a potential mate in terms of fecundity. In many hermaphrodites, egg production is positively correlated with body size. Especially when donating sperm is costly, a preference for larger partners might be expected. Here we test this prediction for the great pond snail Lymnaea stagnalis. As expected, we find a clear effect of body size on egg production, and show that shell height can be used as a reliable predictor of body size. Additionally, behavioural observations reveal that these snails are not physically limited in mating with a much larger or smaller partner. Nonetheless, both in a choice experiment as well as in spontaneous copulations, we find no evidence of mate choice based on body size. These results contribute to a growing field of research which attempts to understand the evolution of the wide variation in the ways that hermaphroditic species respond to the size of potential mating partners.
Anthropogenic environmental change is leading to changes in distribution for many organisms. While this is frequently discussed for prominent organisms of high conservation value, the same is true for the many cryptic species that rarely figure in debates on the human impact. One such cryptic taxon is the European Ptomaphagus sericatus () and related forms. During a citizen science expedition in the Vondelpark, Amsterdam, the Netherlands, we obtained two forms of this species complex. We placed the examination of these specimens in the context of a re-analysis of the species group, and, using DNA barcoding and genital study on material collected thoughout Europe, found that the P. sericatus species complex consists of three distinct, partly sympatric species, one of which was previously undescribed. On the basis of collection data, at least two species, P. medius and P. thebeatles sp. n., show signs of having recently undergone (possibly anthropogenic) range changes, with P. medius even reaching North America. We describe P. thebeatles sp. n.; we raise two subspecies, viz. P. sericatus sericatus (Chaudoir, 1854) and P. sericatus medius () to the level of species, and designate a neotype for the former; we identify P. dacicus
and P. pyrenaeus
as junior synonyms of P. sericatus, and P. compressitarsus () as a junior synonym of P. subvillosus Goeze, 1777; we identify P. septentrionalis
and P. miser () as junior synonyms of P. medius; we designate lectotypes for P. medius and P. miser.