Nectar properties of the sunbird-pollinated plant Impatiens sakeriana: A comparison with six other co-flowering species

Adaptations of the nectar traits in bird-pollinated flowers are amongst the most discussed aspects of floral evolution. In the case of sunbird-pollinated plants, data on nectar traits originate almost exclusively from the South African region and are very scarce for tropical Africa, where paradoxically the highest sunbird diversity occurs. Here we present a study on the nectar properties of a sunbird-pollinated plant, Impatiens sakeriana, growing in the West African mountains, including the nectar production, diurnal changes in the nectar standing crop, the nectar concentrations, the nectar volumes, total sugar amounts and sugar composition. Moreover we compare the nectar traits of I. sakeriana with six other co-flowering insect-visited plant species.Our results showed that many nectar properties, including high volume (approx. 38 μL in flowers unvisited by sunbirds), low sugar concentration (approx. 30% w/w) and high sucrose content (95%), are specific to I. sakeriana, compared to the insect-visited plants. These are in accordance with the most recent theory that nectar properties of the sunbird-pollinated plants are similar to those pollinated by hummingbirds.

Research highlights
► Impatiens sakeriana produce a high volume of dilute, sucrose rich nectar.
► The nectar traits of the sunbird-pollinated I. sakeriana differ from the traits of the insect-visited species.
► The hypothesis on the nectar similarity of hummingbird- and sunbird-pollinated plants is supportable.