Getting hooked? Testing the function of anther spurs in Vaccinium myrtillus

Flowers display remarkable diversity, much of which is shaped by interactions with pollinators. While various floral traits are considered adaptations to pollination, the function of many morphological features remains untested. In buzz-pollinated species, where bees use vibrations to extract pollen, anther morphology is diverse and can influence pollen removal and transfer. Poricidal anthers, common in these species, sometimes bear spur-like projections. These spurs are hypothesized to aid pollen release, but this has not been experimentally tested. Here, we investigated the function of anther spurs in Vaccinium myrtillus (Ericaceae). Using a laboratory setup, we conducted two complementary experiments: one where Bombus terrestris bumblebees foraged on flowers, and another applying 1 s artificial vibrations to mimic bee buzzes. We compared pollen release between flowers with intact anther spurs and those where spurs had been removed. Bumblebees produced vibrations during 90% of visits, irrespective of spur presence. Buzzing visits were shorter (21.70 ± 24 s; mean ± SD) and removed more pollen (60 ± 29%) than non-buzzing visits, which were three times longer (63.79 ± 70.45 s) but removed 23 ± 43% of pollen. Artificial 1 s buzzes removed an average of 23% of pollen. Spur removal increased pollen release in both the bee (54% to 60%) and the artificial buzzing experiment (18% to 28%). Our results suggest that anther spurs in V. myrtillus potentially act as a pollen-dispensing mechanism, but this effect depends on bee behaviour and visit duration. Further studies could explore other roles the spur has in interactions with non-buzzing visitors, such as regulating pollen release when visitors collect nectar.