On the life cycle of Lymnaea stagnalis (Pulmonata: Gastropoda) in southwestern Alberta

Abstract

The life cycle of Lymnaea stagnalis, occupying shallow ponds in southwestern Alberta, was studied from 1973 through 1978. Contrary to most published studies, L. stagnalis does not display an annual life cycle in this habitat. Individual snails did not begin ovipositing until their second or third summer and continued for one or more summers thereafter. Oviposition began in late May, peaked in June, and fell to low levels by August. Hatching occurred in late June through August with young snails attaining a median length of 8 mm by the end of their first summer. Surviving individuals grew rapidly during the early part of their second summer but few individuals reached a size at which they could potentially oviposit (> 30 mm) by the end of the summer. In subsequent summers, snails grew more slowly but oviposited at rates of 5–19 eggs per snail per 48 h as long as they survived. Maximum recorded length was 59 mm in this population, a snail estimated to be entering its seventh summer. Egg production, partly a function of size (age) of mature snails, varied significantly between years with maximum rates in the field being only about half those recorded in a laboratory study where conditions were assumed to be optimal. Survival rates from year to year in the field appeared to be low but cause(s) of death remain essentially unknown.