Mimicking orchids lure bees from afar with exaggerated ultraviolet signals

Abstract

AbstractFlowers have many sensory traits to appeal to pollinators, including ultraviolet (UV) absorbing markings, which are well known for attracting bees at close proximity (e.g. < 1 m). While striking UV signals have been thought to attract pollinators also at greater distances of meters, how the signals impact the plant pollination success over distance remains unknown. Here we report the case of the Australian orchid Diuris brumalis, a non-rewarding species, pollinated by bees via mimicry of rewarding pea plant Daviesia decurrens. When distant from the pea plant, Diuris brumalis was hypothesized to enhance pollinator attraction by exaggerately mimicking the floral ultraviolet (UV) reflecting patterns of its model.By experimentally modulating floral UV reflectance with a UV screening solution, we quantified the orchid pollination success at variable distance from the model plants.We demonstrate that the deceptive orchid Diuris brumalis attracts bee pollinators by emphasizing the visual stimuli, which mimic the floral UV signalling of the rewarding model D. decurrens. Moreover, the exaggerated UV reflectance of D. brumalis flowers impacted pollinators’ visitation at an optimal distance from D. decurrens, and the effect decreased when orchids were too close or too far away from the model.Our findings show that salient UV flower signalling plays a functional role in visual floral mimicry, likely exploiting perceptual gaps in bee neural coding, and mediates the plant pollination success at much greater spatial scales than previously expected.