Diel Variation in Flower Scent Reveals Poor Consistency of Diurnal and Nocturnal Pollination Syndromes in Sileneae.

The composition of flower scent and the timing of emission are crucial for chemical communication between plants and their pollinators; hence, they are key traits for the characterization of pollination syndromes. In many plants, however, plants are assigned to a syndrome based on inexpensive to measure flower traits, such as color, time of flower opening, and shape. We compared day and night scents from 31 Sileneae species and tested for quantitative and semi-quantitative differences in scent among species classified a priori as diurnal or nocturnal. As most Sileneae species are not only visited by either diurnal or nocturnal animals as predicted by their syndrome, we hypothesized that, even if flower scent were preferentially emitted during the day or at night, most species also would emit some scents during the opposing periods of the day. This phenomenon would contribute to the generalized assemblage of flower visitors usually observed in Sileneae species. We found that diel variations of scent often were not congruent with the syndrome definition, but could partially be explained by taxonomy and sampling times. Most species emitted compounds with attractive potential to insects during both the night and day. Our results highlight the current opinion that syndromes are not watertight compartments evolved to exclude some flower visitors. Thus, important information may be lost when scents are collected either during day- or night-time, depending on the a priori classification of the species as diurnal or nocturnal.