Size-fecundity relationships in the land snail Helix aspersa: preliminary results on a form outside the norm

Abstract

Summary Reproductive traits of the land snail Helix aspersa Müller were investigated under artificial conditions in a breeding population of a giant subspecies from North Africa, namely Helix aspersa maxima. The results were compared with data obtained from experiments conducted under the same experimental with the common form Helix aspersa aspersa from (1) a population from the same snail farm, which shares with Helix aspersa maxima the same environment since several generations and (2) a set of wild populations from habitats spanning environmental heterogeneity of the species range. The significantly higher egg production in Helix aspersa maxima was explained by the clutch number per snail rather than by clutch size. Moreover, an uncommon high egg weight (41.4–44.6 mg) was observed in maxima when compared with that of Helix aspersa aspersa from previous studies (28–33 mg). However, reproductive differences between the two subspecies can largely be explained by size-effects and, as a consequence, relative allocation trade-offs among components of current reproduction did not greatly differ among populations.