Nectar Sugar Composition in Relation to Pollination Syndromes in Sinningieae (Gesneriaceae)

A putative correlation between nectar sugar composition and pollination syndrome was evaluated in the tribe Sinningieae (Neotropical Gesneriaceae). Sucrose, fructose and glucose were quantified in the nectar of 45 species using high performance anion-exchange chromatography. Representative species of the hummingbird, bee, bat and moth pollination syndromes were sampled in relation to their numeric importance in the tribe. In hummingbird and bee flowers, which represent 95% of the species in Sinningieae, nectar was sucrose-dominant (ratio [sucrose]/[hexose] > 1). Sugar ratios below one were only found in the nectar of three species with moth and bat syndromes. Sugar concentration averaged 23.9 ± 10.6% (wt/total wt) in hummingbird flowers and 28.7 ± 10.6% in bee flowers, whereas diluted nectar (7.1 ± 3.4%) was restricted to bat flowers. Similarities in the nectar of hummingbird and bee flowers contrast with the presence of specific morphological traits associated with these two syndromes, indicating that plant-pollinator relationships rely on flower display rather than on nectar characteristics. By contrast, distinct nectar chemistry is correlated with the bat syndrome in which a particularly low sucrose production is responsible for hexose dominance.