University of Vienna, Austria.
University of Colorado, Boulder, CO, USA.
Am J Bot. 2023 Jun;110(6):e16183. doi: 10.1002/ajb2.16183. Epub 2023 Jun 5.
Floral shape (relative arrangement and position of floral organs) is critical in mediating fit with pollinators and maximizing conspecific pollen transfer particularly in functionally specialized systems. To date, however, few studies have attempted to quantify flowers as the inherently three-dimensional (3D) structures they are and determine the effect of intraspecific shape variation on pollen transfer. We here addressed this research gap using a functionally specialized system, buzz pollination, in which bees extract pollen through vibrations, as a model. Our study species, Meriania hernandoi (Melastomataceae), undergoes a floral shape change from pseudocampanulate corollas with more actinomorphically arranged stamens (first day) to open corollas with a more zygomorphic androecium (second day) over anthesis, providing a natural experiment to test how variation in floral shape affects pollination performance.
In one population of M. hernandoi, we bagged 51 pre-anthetic flowers and exposed half of them to bee pollinators when they were in either stage of their shape transition. We then collected flowers, obtained 3D flower models through x-ray computed tomography for 3D geometric morphometric analyses, and counted the pollen grains remaining per stamen (male pollination performance) and stigmatic pollen loads (female pollination performance).
Male pollination performance was significantly higher in open flowers with zygomorphic androecia than in pseudo-campanulate flowers. Female pollination performance did not differ among floral shapes.
These results suggest that there is an "optimal" shape for male pollination performance, while the movement of bees around the flower when buzzing the spread-out stamens results in sufficient pollen deposition regardless of floral shape.
花的形状（花器官的相对排列和位置）对于与传粉者的适应和最大化同种花粉的传递至关重要，尤其是在功能特化的系统中。然而，迄今为止，很少有研究试图将花作为其固有的三维（3D）结构进行量化，并确定种内形状变异对花粉传递的影响。我们使用功能特化的传粉系统——蜜蜂通过振动来提取花粉的嗡嗡传粉作为模型来解决这一研究空白。我们的研究物种，Meliania hernandoi（Melastomataceae），在开花过程中经历了花形的变化，从具有更辐射对称排列的雄蕊的假钟形花冠（第一天）变为具有更两侧对称雄蕊的张开花冠（第二天），为测试花形变异如何影响传粉表现提供了一个自然实验。
在 M. hernandoi 的一个种群中，我们套袋了 51 朵预开花朵，并在它们处于花形转变的两个阶段之一时，将其中一半暴露给蜜蜂传粉者。然后，我们收集花朵，通过 X 射线计算机断层扫描获得 3D 花朵模型，进行 3D 几何形态测量分析，并计算每个雄蕊上残留的花粉粒（雄性传粉表现）和柱头花粉负荷（雌性传粉表现）。
具有两侧对称雄蕊的张开花朵的雄性传粉表现明显高于具有假钟形花冠的花朵。花形之间的雌性传粉表现没有差异。
这些结果表明，雄性传粉表现存在“最佳”形状，而当蜜蜂在展开的雄蕊周围嗡嗡作响时，它们在花朵周围的运动无论花形如何都会导致足够的花粉沉积。
