The invader mudsnail<i>Potamopyrgus antipodarum</i>in the Tiber River basin (Central Italy)

Abstract

Although the New Zealand mudsnail Potamopyrgus antipodarum has been observed in Italy since 1961, no investigations have gone beyond recording its presence. In this study, populations from three Italian watercourses with different environmental features were comparatively analysed with a view to shedding light on the relationships between habitat type and reproduction. At the study sites, populations were exclusively composed of females. Ultra‐structural details showed that egg growth takes place through the accumulation of stored materials, which are essentially constituted by translucent vesicles (lipids) and by electron‐dense granules with a darker rim (proteins), the latter deriving from the confluence of smaller granules of the same type. The egg surface displays numerous microvilli, which interdigitate with those emerging from both adjacent eggs and bordering cells. Our comparative analysis shows that the populations differ slightly in fecundity, whereas the number of brooded embryos/female markedly decreases, in parallel with the mean density, in running‐water habitats lacking aquatic vegetation. Statistical analysis confirms that P. antipodarum positively selects biological substrates, such as beds of Vaucheria sp. and even, on occasion, dead leaves and wood floating on the water surface. The results suggest that biological substrates constitute one of the key factors favouring the massive spread of P. antipodarum in watercourses.