Assortative mating with respect to size in the simultaneously hermaphroditic land snail Bradybaena pellucida

There is ample evidence that body size is tightly linked with quality and fecundity of individuals in simultaneously hermaphroditic species. Especially in simultaneous hermaphrodites with reciprocal intromission, it has been thought that assortative mating with respect to body size occurs. Contrary to this expectation, studies on size-assortative mating in such simultaneous hermaphrodites have shown inconsistent mating patterns. It is important to gain an understanding of mating patterns with regard to body size in various hermaphroditic species as a first step for considering the causes for such species differences. In the present study, we examined the relationship between body size and fecundity in the simultaneously hermaphroditic land snail Bradybaena pellucida. We also tested size-assortative mating patterns in this species under a laboratory condition. The results of the experiments showed that life-span fecundity was positively correlated with body size and that the snails tended to choose mating partners of similar body size. As we had predicted, size also affected the mating pattern and assortative mating in simultaneous hermaphrodites with reciprocal intromission. This size-assortative mating pattern seems to result from sexual selection processes, not from mechanical constraints and habitat heterogeneity between large and small individuals.