THE EVOLUTION OF FLORAL COLOR CHANGE: POLLINATOR ATTRACTION VERSUS PHYSIOLOGICAL CONSTRAINTS IN FUCHSIA EXCORTICATA

Field experiments showed that the green-to-red color change in the flowers of Fuchsia excorticata is age-dependent, rather than pollination-induced. Nectar is produced only in green and, to a lesser extent, intermediate-phase flowers; red flowers are postreproductive and are avoided by pollinators (bellbirds). Additional experiments suggested that the red flowers are retained because pollen tubes require at least three days to reach the ovaries, and abscission of the floral tube and accompanying style requires at least another 1.5 days. The change in color directs pollinators away from the postreproductive flowers while these physiological processes are occurring, thereby increasing foraging efficiency and visitation to flowers that are still capable of receiving and donating pollen. No evidence was found to suggest that red-phase flowers function to attract pollinators. Finally, we suggest that the color change evolved through neotenous retention of the green coloration of buds and is a derived trait reflecting an interaction between natural selection and physiological constraints.