Life cycle of the South American apple snail Asolene platae (Maton, 1811) (Caenogastropoda: Ampullariidae) under laboratory conditions

摘要

Reproductive mode, life cycle and fecundity are relevant to understand and predict the spread and impacts of invasive freshwater molluscs. Ampullariids or apple snails have been intensively studied in recent decades due to the fast global expansion and severe impacts of two species of Pomacea, a genus with a peculiar reproductive mode (aerial egg masses). We investigated the life cycle and fecundity of Asolene platae, an apple snail with a different reproductive mode (aquatic egg masses) from the Rio de la Plata basin by following three cohorts from hatching to death under laboratory conditions. Growth of A. platae remained continuous during the 4-year lifespan and the snails reached 80% of their asymptotic size at an age of 1 year. In terms of the von Bertalanffy model, females attain higher asymptotic sizes (26.02-25.72 mm) than males (23.01-24.89 mm), but males grow to their asymptotic sizes at slightly higher rates than females (0.047-0.054 vs 0.050-0.057 week 21). Males matured at a smaller size (21.16 vs 24.53 mm) and much earlier (55.02 vs 84.88 weeks) than females. The survivorship curves showed 63% mortality during the first 2-8 weeks, almost no mortality for the following 2 years and finally a steady decline in the number of survivors, with at least 7% of the snails still alive after 3 years. The lifespan fecundity of females included 20.61 egg masses and 1429.9 eggs. The tertiary sex ratio of the three cohorts was balanced, but varied from 0.25 to 0.76 among egg masses. Our laboratory data indicated that, in temperate environments, A. platae males would mature in their second summer and females during their second or third summer, and that the survivors would reproduce again during the three following summers. Several attributes of the life cycle of A. platae (slow growth, high posthatching mortality, late maturation and relatively low fecundity) indicate lower invasive potential and population resilience than those of invasive apple snails.