Reise - Mating and reproduction in Deroceras slugs

Mating and reproduction in Deroceras slugs

Heike Reise

State Museum of Natural History Görlitz, PF 300 154, D-02806 Görlitz, Germany, Heike.Reise@smng.smwk.sachsen.de

Deroceras is the largest genus of terrestrial slugs with a high diversity of penis morphologies and mating behaviors. The function of most of the appending external and internal penis structures, sometimes truly bizarre, is largely unknown. I review mating behavior and reproduction based on 18 species from the literature and my own observations. I analyze patterns common to all Deroceras, and differences between species. The general mating pattern consists of a long courtship with mutual stroking with a stimulator, a sudden penis eversion and external sperm exchange (copulation). Sperm exchange is usually very quick, but in a few species is 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 stimulator, aggressiveness of courtship behavior, and the timing of flagellum eversion. I hypothesize that the radiation of mating behaviors and associated structures may have been driven by an arms race resulting from conflicting interests of mating partners over sperm donation and usage. This could also have increased the rate of speciation in Deroceras. There are indications for the presence of sperm competition and conflicting interests between mating partners: individuals mate repeatedly, can store and digest sperm, lay many egg clutches over a long period, simultaneously use sperm from different mating partners for egg fertilization, and some details of mating behavior also suggest conflict.