KOENE, J.M.; Vrije Universiteit: Tales of two snails: Sexual selection and sexual conflict in Lymnaea stagnalis and Helix aspersa

Sexual selection and sexual conflict have been shown to play key roles in the evolution of species with separate sexes. Experimental evidence is accumulating that this is also true for simultaneous hermaphrodites. For example, many species of land snails forcefully stab love darts into their mating partners. In the garden snail (Helix aspersa) this dart transfers an allohormone that inhibits sperm digestion, and thereby increases sperm storage and paternity. A recent inter-species comparison of dart-possessing snails revealed that this manipulation causes antagonistic co-evolution between darts and spermatophore receiving organs.

The pond snail (Lymnaea stagnalis) uses seminal products to manipulate its partner, and only mates in the male role when enough seminal fluid is available in the prostate gland. Receipt of semen initiates egg laying in virgin animals, but also feminizes the mating partner later in life. These increases in the female function have been shown to go at the expense of growth and seminal fluid production of the sperm recipient. Taken together, although the sperm donor benefits from the induced changes through increased fertilization success, the sperm recipient may experience injury, re-allocation of resources, and altered sperm storage. These findings support the existence of sexual conflict in simultaneously hermaphroditic snails and their importance for the evolution of mating behaviours and reproductive morphologies will be discussed.