Post-pollination barriers contribute to coexistence of partially pollinator-sharing species (Araceae).

Reproductive isolation plays an important role in maintaining the species integrity of sympatric close relatives. For sympatric species, interspecific gene flow is expected to be effectively prevented by pre-pollination barriers, particularly strong pollinator isolation mediated by fungus gnats. However, due to the lack of quantitative studies combining multiple pre- and post-pollination barriers, it is not known whether pre-pollination isolation is complete, and whether post-pollination barriers also contribute to reproductive isolation among some species. In this study, we quantified the individual strengths and absolute contributions of four pre- and post-pollination barriers (phenological isolation, pollinator isolation, hybrid fruit formation, and hybrid seed formation) among three sympatric species (, , and ). Although phenological isolation and pollinator isolation reduced the frequencies of interspecific pollen transfer among these species, the partial overlap of flowering times and pollinator assemblages resulted in incomplete pre-pollination isolation. Post-pollination barriers also contributed to reproductive isolation at the hybrid fruit and seed formation stages. We propose that, although pre-pollination barriers are expected to contribute more to total isolation than post-pollination barriers in , pre-pollination barriers may not completely prevent interspecific pollen transfer among some species. Post-pollination barriers, which are generally ignored, may also have contributed significantly to reproductive isolation in .