Consistent Buzz‐Pollination Posture Suggests Division of Labour Between Dimorphic Stamens in Bredia hirsuta (Melastomataceae) on Okinawa‐Jima Island, Japan

ABSTRACT

Pollen flowers face a trade‐off (pollen dilemma) between rewarding pollinators with pollen and retaining sufficient pollen content. The division of labour between feeding and pollinating stamens mitigates this dilemma; however, whether it occurs in small flowers with closely positioned stamens remains unclear. We investigated the pollination ecology of Bredia hirsuta (Melastomataceae) through behavioral observations, fluorescent powder experiments, and emasculation experiments. Of the two buzz‐pollinating bees observed, Amegilla dulcifera showed a consistent visitation posture and stable stigma contact, whereas Lasioglossum sp. mainly acted as a pollen thief and stigma‐pollen remover. The Amegilla bee gripped the short stamens ventrally, whereas the long‐stamen anther tips and the stigma were positioned dorsally on the abdomen. Fluorescent powder experiments confirmed the spatial separation between stigma‐contact and gripping sites on the bee's body, suggesting that short stamens function as feeding stamens and long stamens as pollinating stamens. The emasculation experiments revealed that dimorphic stamens also provide mechanical support that stabilizes pollinator posture. These results suggest that dimorphic stamen differentiation can occur in small flowers through consistent pollinator behavior and physical stamen support.