Energy budgets in the simultaneously hermaphroditic pond snail, Lymnaea stagnalis : A trade-off between growth and reproduction during development

Maximum lifetime reproductive success is determined by the optimal partitioning of available resources between growth, maintenance and reproduction. The main question that is addressed here is how this resource allocation occurs in the simultaneously hermaphroditic pond snail, Lymnaea stagnalis. Snails were either reared in groups or in isolation and were fed a standard, restricted amount of lettuce; group-reared snails were isolated when egg laying started. Snails reared in isolation seldom produce eggs. Instead, they increase growth rate and the energy invested in this growth corresponds to that invested in eggs by group-reared animals. Additionally, animals reared in isolation have larger prostate glands. Hence, when no mating partners are available, snails mainly invest in growth as well as the male function. Allocation to female reproduction only starts once copulation has taken place. These findings reveal a trade-off between growth and female reproduction. Moreover, the difference in prostate glands indicates that there is also a trade-off between investment in the male and female function. The possible existence of a sexual conflict over the onset of female reproduction is discussed.