Hidden floral adaptation to nocturnal moths in an apparently bee-pollinated flower, Adenophora triphylla var. japonica (Campanulaceae).

Abstract

The discrepancy between observed flower visitors and those predicted based on floral phenotype has often cast doubt on the pollination syndrome concept. Here we show that this paradox may be alleviated by gaining better knowledge of the contributions of different flower visitors to pollination and the effects of floral traits that cannot be readily perceived by humans in Adenophora triphylla var. japonica. The blue, bell-shaped and pendant flowers of A.triphylla appear to fit a bee pollination syndrome. In contrast to this expectation, recent studies show that these flowers are frequented by nocturnal moths. We compared the flower visitor fauna, their visitation frequency and their relative contributions to seed set between day and night in two field populations of A.triphylla in Japan. We also determined the floral traits associated with temporal changes in the visitor assemblage, i.e. the timing of anthesis, the timing of changes in the sexual phase and the diel pattern of nectar production. While A.triphylla flowers were visited by both diurnal and nocturnal insects, the results from pollination experiments demonstrate that their primary pollinators are nocturnal settling-moths. Moreover, the flowers opened just after sunset, changed from staminate to pistillate phase in successive evenings and produced nectar only during the night, which all conform to the activity of nocturnal/crepuscular moths. Our study illustrates that the tradition of stereotyping the pollinators of a flower based on its appearance can be misleading and that it should be improved with empirical evidence of pollination performance and sufficient trait matching.