EGG-LAYING AND ASSOCIATED BEHAVIORAL-RESPONSES OF LYMNAEA-PEREGRA (MULLER) AND LYMNAEA-STAGNALIS (L) TO CALCIUM IN THEIR ENVIRONMENT

In laboratory trials, specimens of the freshwater pulmonate snail Lymn aea peregra from Ullswater, a soft-water lake in the English Lake Dist rict (6.5 mg/l [Ca2+], pH 7.1), showed a significant preference for la ying eggs on clean, dead conspecific snail shells (chi(2) = 38.91, P < 0.001 n = 20), thereby confirming anecdotal field observations of thi s behaviour. A choice chamber was used to investigate to test the hypo thesis that lymnaeid snails might be able to use calcium as a cue for orientation, for example as a stimulus to find target shells for ovipo sition. Lymnaea stagnalis showed a more positive response to calcium t han did L. peregra (t = 4.2, P < 0.05, n = 137). When snails from soft -water environments were reared in soft water in the laboratory, speci mens of L. peregra showed a strong preference for calcium (chi(2) = 19 .6, P < 0.001, n = 202), but specimens reared in hard water (84 mg/l [ Ca2+], n = 44)) showed no such preference. The hypothesis that snails could use a calcium cue to select a shell as an oviposition site was s upported, and, in addition, the breadth of the chemical niche of L. pe regra appears to be wider than that of L. stagnalis.