Heike Reise

A review of mating behavior in slugs of the genus Deroceras (Pulmonata: Agriolimacidae)*

The genus Deroceras Rafinesque, 1820 (the largest genus of terrestrial slugs) shows a high diversity of penis morphologies and mating behaviors. The function of most of the appending external and internal penial structures, some of them truly bizarre, is largely unknown. This paper reviews mating behavior and reproduction, based on data on 16 species from the literature and from unpublished observations. I analyze patterns common to all Deroceras species and differences among species. The general mating pattern consists of a long courtship with mutual stroking with a sarcobelum, a sudden penis eversion, and external sperm exchange (copulation). I distinguish also precourtship and withdrawal phases. Sperm exchange is usually very quick but, in a few species, occupies a considerable proportion of the total mating duration. Mutual sperm exchange is the rule. Species differences involve the durations of certain mating phases, presence and nature of initial trail following, nature and intensity of stroking (including the degree of contact with the sarcobelum), aggressiveness of courtship behavior, and the timing of the penial gland eversion. I hypothesize that the radiation of mating behaviors and associated structures has been driven by an arms race resulting from conflicting interests of mating partners over sperm donation and use. This could also have increased the rate of speciation in Deroceras. There are indications of the presence of sperm competition and conflicting interests between mating partners: individuals mate repeatedly, can store and digest sperm, and simultaneously use sperm from different mating partners for fertilization. Some details of mating behavior also indicate conflict. The timing of the penial gland eversion after sperm exchange suggests a manipulation akin to the role of love darts in helicid snails. Finally, some recommendations for studying mating behavior in Deroceras are given.

Cutaneous application of an accessory-gland secretion after sperm exchange in a terrestrial slug (Mollusca : Pulmonata)

Competition for fertilisation in hermaphroditic animals seems to have led to many odd behaviours and complex morphologies involved in the transfer of accessory-gland products to the partner. Terrestrial slugs of the genus Deroceras show remarkably elaborate and interspecifically diverse penis morphologies and mating behaviours. Most species have an appending penial gland, which in Deroceras panormitanum consists of a few long fingers that are everted after sperm exchange and laid onto the partners back. To investigate whether this gland transfers a secretion onto the partners skin, we killed slugs at different mating stages and studied their penial glands and skin histologically. Two types of secretion granules appeared at a very early stage of courtship, and the penial gland was already filled 15min into the courtship. At copulation, the gland everted this secretion onto the partners body, where it remained for at least 50min. No lysis of skin tissue or other effects on the skin were observed. The slugs tried to lick the received secretion off their own body, and some droplets were observed to be shed with the body mucus. Our results indicate the external application of a glandular substance that could function as either a pheromone or allohormone. The behaviours of the recipients suggest sexual conflict, although mutual interest cannot be ruled out.

Life cycles and adult sizes of five co-occurring species of Arion slugs

Five species of Arion slugs were collected repeatedly at a woodland site in southern England and all individuals weighed. Selected samples of these were dissected so as to weigh components of the reproductive tract. The relative weights of the gonad, spermoviduct and albumen gland provided the basis to categorize individuals into adult, subadult or immature classes, or as juvenile if the sum of these weights was below a threshold. This procedure was validated by raising A. subfuscus in captivity and killing at a range of known ages before and after egg laying. In the other species, organ weights from individuals observed to have laid eggs or mated also helped to calibrate the divisions. Such data from two species demonstrated that, following the production of an egg clutch, the albumen gland took days gradually to regrow. There was little evidence of much variation in life cycle from year to year and the broad patterns, although not precise timings, agreed with studies elsewhere. No species produced more than one generation per year and in all there was a season (brief in A. subfuscus) when adults were absent. The life cycles were predominantly annual, although in some species a minority of individuals might take 18 months to mature. The time of year at which individuals matured into adults varied between species: A. intermedius in August and September, A. distinctus mostly in December and January, A. circumscriptus mostly January to April, A. subfuscus April to early October and A. rufus July to September. The largest two species thus dominated in summer, but at other times the species overlapped considerably in size. In four species, individuals maturing later in the season did so at a smaller size; the possible exception was A. intermedius, in which maturation was highly synchronized. The coefficients of variation in adult size were compared against a collection of such data from other terrestrial molluscs. The smallest species, A. intermedius, had disproportionately large hatchlings.

Terrestrial molluscs of the Province of Newfoundland and Labrador, Canada. Part 1: Boettgerillidae

The family Boettgerillidae, represented by the Eurasian slug Boettgerilla pallens Simroth, 1912, is first recorded for Newfoundland and Labrador, Canada—a range extension of almost exactly 5000 km within the Americas. Compiled, within an appendix, to provide a national perspective for the Newfoundland and Labrador record, are 13 previously unpublished B. pallens records from British Columbia, Canada. Incidentally recorded is the second eastern Canadian outdoor occurrence of the European slug Deroceras invadens. This paper is the first in a series that will treat all of the terrestrial molluscs of Newfoundland and Labrador.