Variation of distal genitalia in the simultaneously hermaphroditic land snail Arianta arbustorum (Pulmonata, Stylommatophora) caused by sexual selection

The most likely explanation for genitalic extravagance may be sexual select ion acting either before, during, or after copulation. In promiscuous speci es, the intensity of postmating sexual selection may be a function of popul ation density. In this study we examined the variability of the distal geni talia involved in spermatophore production, reception and manipulation of 1 13 adult individuals of the simultaneously hermaphroditic land snail Ariant a arbustorum (L.) from six natural populations in the Eastern Alps (Gesause ; Austria). We investigated the hypothesis that these genitalia increase in relation to shell size with increasing population density (range: 0.9 to 3 9.8 individuals/m(2)) and expected a higher variance of the genitalia compa red to shell dimensions due to sexual selection. Genitalic size was unexpec tedly inversely related to population density, probably due to increased in hibitory effects of snail mucus. Patterns of variation of female and male c haracters did not differ. Coefficients of variation of the genitalia were s ignificantly higher than those of the shell dimensions as predicted. This w as due to a higher dispersion around the regression lines rather than highe r allometric values. However, the influence of sexual, selection on genital ic size and variance cannot be unambiguously determined. We discuss differe nt scenarios emphasizing the importance of sexual selection to differing de grees and conclude that sexual selection has probably played only a minor r ole. (C) 2000 The Linnean Society of London.