Does pollination syndrome reflect pollinator efficiency in Silene nutans?

Abstract

Despite the specialization of floral traits towards particular floral visitors (pollination syndrome), insect-pollinated plants can display generalist rather than specialist interactions with their pollinators. This is the case of several Silene species that were viewed as nocturnally pollinated but are factually visited, and then potentially pollinated, by both nocturnal and diurnal insects. This opens the question of the consistency of pollination syndromes and the impact of different pollinator assemblages on plant reproductive success. In this work, we measured diurnal and nocturnal pollinators’ contributions to pollination success (fruit and seed production) and offspring quality (seed mass and germination rate) of hermaphrodite plants in an artificial population of Silene nutans, by experimentally restricting pollinator access and controlling for floral and resource traits. We found that fruit and seed production was higher for nocturnal pollination, and that only very few seeds were produced by diurnal visitors. In our experimental system, plants did not benefit from being open during daytime, as they showed no fruit or seed production advantage in the open pollination treatment compared to the nocturnal one. Seeds generated from diurnal pollination were heavier but did not germinate better, so that the plant fitness proxy remained higher for nocturnal pollination than diurnal one, without any obvious evidence of a pollination mixed strategy. These data are in accordance with the nocturnal pollination syndrome of S. nutans, contrasting with several other studies carried out on other Silene species.