BEESE, K.*; BAUR, B.; Univ. of Basel, Switzerland: Coevolution of reproductive traits in a hermaphroditic land snail

Postcopulatory sexual selection arising from interactions between the sexes can lead to a rapid evolution of reproductive traits and may contribute an important part to the speciation process. A correlated evolution between sperm traits and certain dimensions of the female reproductive tract has been identified in several gonochoristic species. However, similar data on hermaphrodites, in which the �male� and �female� reproductive functions are closely linked, are so far lacking. We examined the variation of �male� and �female� reproductive traits in six geographically separated populations of the simultaneously hermaphroditic land snail Arianta arbustorum. Virgin snails were allowed to mate once and afterwards the spermatophores transferred were obtained for sperm counts and sperm length measurements. Histological examination of dissected sperm storage organs (spermathecae) included the recording of their length and volume. Except for spermatheca length, evidence of significant evolutionary divergence among the populations could be found in all traits studied. The correlated evolution of the sex-specific traits was examined by regressing mean population values for the �male� traits on mean population values for the �female� traits. Sperm length did not correlate with spermatheca size. However, the number of sperm transferred was significantly correlated with the volume of the sperm storage organ of the receiver. The divergence of �male� and �female� traits in A. arbustorum can be explained by an antagonistic coevolution and could result in a reproductive isolation among the populations studied. Possibly sexual conflict over fertilization decisions is driving the �arms race� of the genital traits in the struggle for control over reproduction.