Abstract
Some floral visitors collect nectar by piercing flower external whorls, acting as nectar robbers. They leave robbery vestiges, which can cause changes in floral characteristics, including physical and chemical signals that may influence flower recognition by pollinators. If pollinating bees associate these changes with absence or reduction in nectar volume, they can avoid these flowers, negatively affecting pollination. We aimed to investigate the effect of robbery on primary and secondary attractants. Additionally, we experimentally investigated if the visual signs present in robbed flowers affect the bee pollination of this plant species by discouraging pollinator visits. This study was performed in a very common pollinator-plant-cheaters system comprised by a bee-pollinated Bignoniaceae species and a nectar-robber bee that lands on the corolla tube and makes slits at its base during the nectar robbery. We experimentally isolated the effect of nectar consumption by this nectar-robber and investigated if the slits caused by the nectar-robbers affected the floral scent emission. In addition, we experimentally evaluated the effect of visual signs (slits) associated to the nectar robbery and the effect of nectar depletion on the pollination of Jacaranda caroba (Bignoniaceae). The robbers visited around 75% of the flowers throughout the day and removed significant amounts of nectar from them. However, the damages the robbers cause did not affect floral scent emission and we did not verify significant differences on pollen deposition neither when comparing flowers with slits and control nor when comparing flowers with and without nectar. We showed that even though nectar-robbers visually honestly signal the robbery and deplete high amounts of nectar, they did not affect pollinator visitation. These results showed that presumably antagonistic interactions might in fact not be so.
Highlights
Some groups of floral visitors feed on nectar without pollinating the flowers, and when they cause holes or slits on external whorls, they are named robbers [1]
Many studies investigate the effects of floral nectar robbery on pollination, but they focus mainly on changes in pollinator behaviour due to the reduction in nectar volume [2, 3, 4], which may indirectly affect plant fitness [5]
Visual signs of nectar-robbery do not discourage bee pollination which allowed it to access the nectar accumulated in the nectariferous chamber
Summary
Some groups of floral visitors feed on nectar without pollinating the flowers, and when they cause holes or slits on external whorls, they are named robbers [1]. Flowers rely on chemical and visual sensory signals to advertise their resources [6]. Bees, throughout their lives, learn to use floral cues as predictors of resource and, focus their visits on more profitable flowers [7]. Contrasting patterns within a flower are important cues for flower short-distance recognition by bees [9]. Among all these floral traits, olfactory cues are considered the basis of pollinators’ choice of flowers, especially for bees, that learn faster and remember easier these cues, as compared to their ability to learn visual cues [10]. The floral scent can work as an honest signal, advertising the presence of this trophic resource [10]
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