The study of ontogenetic trajectory reveals the timing of reproductive events in Ancylus fluviatilis (Gastropoda: Planorbidae)

Abstract

We analysed ontogenetic shape change in the planorbid limpet Ancylus fluviatilis (Müller, 1774) in two rivers in Southern Italy. We developed a new method to discriminate among different cohorts in Ancylus, based on principal component analysis. The method is useful when shape change during growth is allometric, as in our study model. We discovered that bivoltinism occurs in Ancylus in Southern Italy, contrary to previous accounts, which invariably describe A. fluviatilis as a semelparous and univoltine species, although acknowledging difficulty in discriminating among cohorts. The methods presented here may potentially help research in reproductive traits in many other mollusc populations where shape change during ontogeny is demonstrated to be allometric.

Keywords:

• Hygrophila
• life cycle
• bivoltinism
• allometric growth
• limpet
• Pulmonata
• Europe
• Italy

Acknowledgements

We are especially indebted to Pietro Battaglini for his critical reading and insightful comments on earlier versions of the manuscript. Winston Ponder and two anonymous reviewers kindly offered important advice that improved the quality of this manuscript.