Asymmetric reproductive isolation during simultaneous reciprocal mating in pulmonates

Abstract

The generality of asymmetric reproductive isolation between reciprocal crosses suggests that the evolution of isolation mechanisms often proceeds in reciprocal asymmetry. In hermaphroditic snails that copulate simultaneously and reciprocally, asymmetry in premating isolation may not be readily detectable because the failure of the symmetric performance of courtship would prevent copulation from occurring. On the other hand, through their prolonged copulation, snails discriminate among mates when exchanging spermatophores for their benefit and thus may exhibit asymmetric reproductive isolation during interspecific mating. However, no clear case of reciprocal asymmetry has been found in reproductive isolation between snail species. Here we show a discrete difference in hybridization success between simultaneous reciprocal copulations between two species of pulmonate snails. Premating isolation of Bradybaena pellucida (BP) and Bradybaena similaris (BS) is incomplete in captivity. In interspecific copulation, BP removes its penis without transferring a spermatophore, while BS sires hybrids by inseminating BP. Thus, 'male' BP or 'female' BS rejects the other individual, while female BP and male BS accept each other, so that the two sexes of either BP or BS oppose each other in mate discrimination. Our results are a clear example of asymmetry in reproductive isolation during simultaneous reciprocal mating between hermaphroditic animals.

Divergence before and after the isolation of islands: Phylogeography of the Bradybaena land snails on the Ryukyu Islands of Japan

“…When interspecific copulation occurs, B. pellucida removes its penis without transferring a spermatophore, while B. similaris sires hybrids by inseminating B. pellucida (i.e. reproductive interference; Wiwegweaw, Seki, Mori, & Asami, ; Wiwegweaw, Seki, Utsuno, & Asami, ). Therefore, the difference in the micro‐sculpture patterns on the penial wall of these species might be associated with a function in physical mate recognition during copulation among Bradybaena , including the species in the Ryukyu Islands.…”

Hybridization relics complicate barcode‐based identification of species in earthworms

“…Such asymmetric reproductive isolation during simultaneous reciprocal mating was also described between sibling species of land snails by Wiwegweaw et al . () by conducting mate choice experiments and examining spermatophore transfer. They showed that one species would reject the other species in the ‘male’ or ‘female’ role despite accepting that species in the opposite sexual role.…”

<i>Deroceras panormitanum</i> and congeners from Malta and Sicily, with a redescription of the widespread pest slug as <i>Deroceras invadens</i> n. sp.

“…We wonder whether these traits evolved as adaptations for forced fertilisation of same-species partners that are not yet ready to donate their own sperm; we did observe two unilateral copulations within pairs of D. panormitanum. WIWEGWEAW et al (2009) provided another example of interspecific sperm transfer in a terrestrial pulmonate and again this was predominantly unilateral with the donor being the faster species.…”