A note on oviposition by Lymnaea stagnalis (Linnaeus, 1758) (Gastropoda: Pulmonata: Lymnaeidae) on shells of conspecifics under laboratory conditions

Abstract

Oviposition by Lymnaea stagnalis (L.) on shells of conspecifics has been reported anecdotally from laboratory observations. In order to gain the first quantitative insight into this behaviour, we have quantified the proportion of individuals bearing egg clutches in a long-term monospecific outdoor laboratory culture of L. stagnalis during two consecutive late-summer months. The snails were assigned to size classes based on shell height. Differences between the size class composition of clutch-bearers and of the general population were statistically compared by means of Pearson's distance χ² P analysis. Egg clutches were laid on snails of shell height >15 mm (i.e. reproductive-age individuals), with significant selection for the larger size classes (shell height 25-40 mm). While the mechanisms of and reasons behind such behaviour remain unknown, selection of larger adults as egg-carriers may have ecological implications at the population level.