How do floral changes affect the pollination ecology of Halenia deflexa

Abstract

Spurred gentian (Halenia deflexa) is named after the nectar spurs (i.e. nectar-storing appendages) that adorn its flowers. Nectar spurs generally affect the mechanical fit between plants and their pollinators because they restrict nectar access to animals with long-tongues or strong mouth parts. Nectar spurs are therefore an important floral trait that can shape species’ pollination ecology. Halenia deflexa’s pollination ecology, however, has not been documented and it is unclear whether the species has any insect pollinators at all. I aimed to determine the principal pollinators of H. deflexa. During summer 2019, I observed patches of H. deflexa for ~40 hours total to document visitation by pollinators. I found the species to be visited almost exclusively by bumblebees (Bombus sp.), including the endangered B. terricola (yellow banded bumblebee). The likelihood of visitation by Bombus sp. decreased every day before coming to a complete stop after August 7. I found that the total amount of time that a Bombus visitor spent foraging from a single plant, per patch, increased with the number of open flowers on a plant. Throughout the summer, I also noticed that spur length of H. deflexa decreased from the first and last flowers on a plant and I quantified this change in 16 marked individuals. Last, I found that reductions in spur length coincided with reductions in visitation by bumblebees. This work does not determine whether changes in pollinator behavior are influenced by spur length. It does, however, feature some novel observations of H. deflexa and demonstrate the importance of flower shape in a plant–pollinator system.