Division of labour between dimorphic stamens in Melastoma candidum (Melastomataceae): role of stamen strength in the biomechanics of pollination

The left image shows a Melastoma candidum flower. The top-right image shows the primary pollinator, Xylocopa flavifrons, grasping the feeding stamens, while the bottom-right image shows Amegilla dulcifera vibrating a single pollinating anther.

 

By Hachiman et al.

Plants use various strategies to attract pollinators and ensure successful reproduction. One fascinating strategy involves the use of "dimorphic stamens," where a plant employs two different types of stamens, each serving a unique role. Some stamens provide pollen as food for pollinators, while others are specifically designed to aid in pollination.

In our study, we focused on Melastoma candidum, a plant species found on Okinawajima Island, Japan, that features two distinct types of stamens. We aimed to understand how flower structure and pollinator behavior work together to enhance pollination. By observing the behavior of several bee species visiting the flowers, we explored their stamen preferences and how often they contacted the stigma.

The main pollinator we identified was the carpenter bee, Xylocopa flavifrons. Interestingly, we discovered that this bee preferred the stamens that offered food (pollen), not only because their yellow anthers attracted the bee, but also because these stamens were strong enough to support the bee's weight, making it easier to collect pollen. The other stamens, which are primarily responsible for pollination, were structurally weaker and unable to bear the bee’s weight, limiting their role to pollen release. This flower structure and biomechanics helped keep the behavior of X. flavifrons consistent during flower visits, playing an important role in the division of labor between the dimorphic stamens.

Our findings reveal the important role that flower structure and biomechanics play in pollinator behavior and plant reproduction. This study highlights the intricate "division of labor" in the natural world, helping us better understand how plants and pollinators have evolved to work together.

Read the scientific publication in JPE here.