PARENT SESSION
Tuesday, August 8, 1:30-5:00 pm
COS 36 - Pollination ecology I
L-13, Lobby Level, Cook Convention Center
Presiders: S Travers and R Spigler
A functional explanation for dark, bitter nectar in a bird-pollinated plant.
Johnson, Steven1, Hargreaves, Anna*,2, Brown, Mark1, 1 University of KwaZulu-Natal, Pietermaritzburg, KwaZulu Natal, South Africa2 University of Calgary, Calgary, Alberta, Canada
ABSTRACT- Floral nectar is offered by plants to animals as a reward for pollination. While nectar is typically a clear, sweet liquid containing sugar and trace amounts of amino acids, coloured nectar has evolved in several plant families. Here we demonstrate a functional role for the phenolic compounds that impart a dark colour and bitter taste to the nectar of the South African succulent shrub Aloe vryheidensis. The short, open flowers of this aloe are visited for their nectar by a suite of short-billed birds that are occasional nectarivores, including bulbuls, white-eyes, rock thrushes and chats. Dark-capped bulbuls were more likely to probe model flowers containing dark nectar than those containing colourless nectar, suggesting a potential positive signaling function for dark nectar. However, the main effect of the phenolics appears to be to repel "unwanted" nectarivores that find their bitter taste unpalatable. Nectar-feeding sunbirds are morphologically mismatched for pollinating A. vryheidensis flowers, and strongly reject its nectar. However, frugivorous and insectivorous birds which effectively pollinate this aloe are seemingly unaffected by the nectar's bitter taste. Thus the dark phenolic component of the nectar appears to function as a floral filter by attracting some animals visually and deterring others by its taste.
Key words: pollination, angiosperm, plant reproductive ecology