A comparison of the life cycles, reproductive ecologies, and size–weight relationships of Helisoma anceps, H. campanulatum, and H. trivolvis (Gastropoda, Planorbidae)

Abstract

Helisoma anceps, H. campanulatum, and H. trivolvis were studied separately in three ponds near Waterloo, Ontario, and were found to differ in the following parameters, respectively: life span, 2.1, and 2 years; mean growth rate during the first 2 months after hatching, 0.2, 1.0, and 0.06 mm/week; minimum size at which snails laid eggs, 8, 10, and 18 mm shell diameter; number of breeding periods during the life cycle, 2, 1, and 1: length of the spawning season, 18, 10, and 8 weeks; date by which 50% of the eggs had been laid, July 2, May 14, and May 15; mean number of eggs per egg capsule, 14, 14, and 24. Although mature H. trivolvis occurred throughout the pond during the spawning season, eggs were laid only along the margin. The average number of eggs laid during the life span of a snail was 300 for H. campanulatum and 590 for H. anceps. Linear regression equations relating size to live weight, shell weight, and shell-free dry weight were calculated for each species. Differences between the three species in geographic distribution, tolerance to environmental perturbations, and frequency of congeneric associations seem to be related to differences in their life histories.