Partial precopulatory isolation between two geographically distant populations of the land snail Arianta arbustorum (L.)

Abstract

Different mechanisms of reproductive isolation were examined in the simultaneously hermaphroditic land snail Arianta arbustorum. Snails from two geographically isolated populations in the Swiss Alps were allowed to copulate with both a homotypic (individual from the same population) and a heterotypic (individual from the other population) partner (in half of the pairs in reversed order). Control snails mated twice with a homotypic partner. In the first mating, successful copulations occurred in a lower frequency in heterotypic pairs (55.6%) than in homotypic pairs (82.9%). Heterotypic pairs that eventually copulated showed more breaks during courtship than homotypic pairs. However, neither the number of eggs produced nor their hatching success was influenced by the type of mating partner. In the second mating, the sequence of different partners had an effect on the proportion of successful copulations in snails from one geographical population. Snails that copulated first with a homotypic partner remated more frequently with a homotypic partner than snails that copulated first with a heterotypic partner. Paternity analyses of progeny of snails that mated twice indicate no influence of the origin of the mating partner. The proportion of hatchlings sired by the second mate (P2) averaged 0.39, indicating a slight first-mate advantage. However, highly skewed paternity patterns were found in the progeny of 44.4% of the double-mated snails. Genetic analyses also revealed a low frequency of self-fertilization (3.7%). These findings indicate the presence of partial precopulatory isolation between two distant snail populations, although reproductive compatibility is still maintained.