Beyond robbery: the role of upside-down behaviour performed by small oil-collecting bees in Malpighiaceae

Abstract

In plant–pollination interactions, the antagonists collect the same set of resources offered to legitimate visitors, but their morphologies and behavioural approaches possibly make their effect on plant fitness negative rather than positive. Depending on the morphology of Malpighiaceae flowers, these small-bodied bees can adopt an upside-down position, biting and damaging the floral pedicel. Therefore, we hypothesized that small-bodied bees may reduce female reproductive fitness, due to increased floral abscission. We observed small Tetrapedia bees approaching bagged and unbagged flowers of Peixotoa tomentosa, and compared abscission rates associated with the upside-down behavior performance. When Tetrapedia bees exhibited the upside-down behaviour the floral abscission was about 1.7 times more frequent than without this behaviour. We observed that abscission frequency increased to 80% if upside-down behavior is performed at least three times per flower. Additionally, the frequency of upside-down behaviours were positively related to the number of flowers visited per plant. Overall, the upside-down behaviour of Tetrapedia compromised most flowers that were viable for fruit formation, potentially decreasing the female reproductive fitness of plant population. We emphasize that different roles of floral visitors, including the robbers, are associated with visitors’ body size and behaviour. Such features of interactions determine whether floral visitors are pollinators, thieves or robbers and shape a continuum from mutualistic to antagonistic interactions.