REDUCED REPRODUCTIVE COMPATIBILITY IN ARIANTA-ARBUSTORUM (GASTROPODA) FROM DISTANT POPULATIONS

Reproductive isolation was examined in the simultaneously hermaphroditic, self-incompatible land snail Arianta arbustorum. We tested individuals from two geographically isolated populations in Sweden and three populations in Switzerland. In mate-choice tests, within-population (homotypic) and between-population (heterotypic) meetings occurred among snails in frequencies expected by chance. We found no significant difference in courtship latency and courtship duration between homotypic and heterotypic pairs. However, snails from three populations preferred to mate with homotypic partners. Mating preferences could partly be explained by differences in mating propensity in two out of three populations, but not in matings between a Swedish and a Swiss population. Cross breeding demonstrated a high degree of reproductive compatibility between these two distant populations. In contrast, heterotypic pairs involving two Swiss populations had a reduced fertility. The experimental results indicate that partial premating and postmating isolation may exist between distant populations of A. arbustorum. However, the degree of isolation is not related to the geographical distance between populations.