Retention of colour-changed flowers increases pollinator attraction to Lantana undulata inflorescences

Abstract

Many flowers change colour as they age or after pollination, which can have direct effects on pollinator behaviour affecting both pollination (on the plant side) and foraging efficiency (on the insect side). The retention of colour-changed flowers might increase plant attractiveness to pollinators over long distances, while directing pollinators at short range towards flowers that still present rewards and are sexually receptive. In this study, we used Lantana undulata Schrank (Verbenaceae), which presents yellow-centered and white flowers within an inflorescence, as a model plant species to study the influence of floral colour change on pollinator visitation. We first show that colour change from yellow to white occurs over a 24 h period regardless of pollination, and is associated with reduced stigma receptivity and nectar reward availability. We then used pollinator visitor observations and experimental manipulations of inflorescence display patterns to investigate the effects of floral colour change on pollinator attraction, behavior and choices. Pollinators exhibited strong preference for visiting yellow-centered flowers, suggesting the colour change to white in older flowers is an honest signal directing pollinators to rewarding and receptive flowers within the inflorescence. In addition, the absence of white flowers on manipulated inflorescences significantly reduced their attractiveness to pollinators. Our results suggest that the retention of colour-changed white flowers is important to attract pollinators at long distances, while the yellow colour of young flowers guides pollinators to the sexually viable, rewarding flowers on inflorescences at short distances, maximizing both pollination and foraging efficiency.