From a bee's eye: Effects of UV bullseye size on reproductive success in a dioecious vine Herpetospermum pedunculosum (Cucurbitaceae).

Abstract

Descriptions of floral traits based on the visual capabilities of pollinators would advance our understanding of flower evolution and plant-pollinator relationships. One such trait is the contrasting UV bullseye color pattern, which is invisible to human eyes but can be perceived by bee pollinators. However, it remains largely unknown how UV bullseye size affects male and female reproductive fitness. We examined UV bullseye patterns in the dioecious Herpetospermum pedunculosum, and quantified the effects of UV bullseye size on male and female fitness. Both UV bullseye size and flower size were larger in male flowers than in female flowers. The dominant pollinators of H. pedunculosum were bees, which could perceive the UV bullseye pattern. Bee pollinators exhibited a preference for male flowers with nectar rewards, and visited a greater number of male flowers on plants with a larger UV bullseye. Male reproductive fitness was found to decrease in plants with larger UV bullseyes, likely due to the high rate of intra-plant pollen transfer. Rewardless female flowers were less attractive to bee pollinators, resulting in pollen limitation of seed production. Female flowers with moderate UV bullseye size produced more seeds. Our results suggest that UV bullseye is subject to different selection via male and female fitness of H. pedunculosum with deceptive pollination, and large UV bullseye is generally not favored. This research is the first to examine the relationship between UV bullseye size and plant reproductive success, highlighting that floral evolution should be investigated from the pollinator's eye in future research.