传粉者身体上多区域花粉落置对传粉精确性的影响

The evolution of floral traits has been thought to be driven by pollinator selection, but it is difficult to evaluate the selection strength. Pollination accuracy (coincidence of the area of pollen placed on and stigma contact on pollinator body) has been proposed to examine pollinator-mediated selection on floral evolution, i.e., successful pollen transfer depending on flowers “mechanical fit” with their pollinators. Most orchids place their pollinia on one particular area on the pollinator body, whereas some species from Orchidaceae place pollinia on the six legs of the insect pollinators, resulting in a multi-area of pollen placement. Such a large variation in pollinia placement seems inconsistent with the hypothesis of pollination accuracy. In our previous study in the orchid Habenaria aitchisonii, we observed its pollinia placed on multiple legs of moth pollinators. In this proposal, we plan to trace location of pollinia placed on and stigma contact on the pollinator body using dye to examine their match degree. To investigate the effect of leg placement on pollinia removal and receipt, we will quantitatively measure pollen limitation, pollen geitonogamy and pollen transfer efficiency in H. aitchisonii with a comparison of a congener orchid H. glaucifolia whose pollinia are placed on the tongue of moth pollinators. With phenotypic selection analysis and flower manipulation experiment, we could confirm the key floral traits be attributable to this kind of pollination pattern. We will examine the location of pollen placement and stigma contact on the pollinator body in different field populations, and measure the floral traits and pollinator body size to investigate the mechanical fit degree between key floral traits and pollinators. Our proposal aims to investigate the effects of multi-area pollen placement on pollination accuracy, to a better understanding the evolution of mechanical fit between pollinator and flower morphology, and provide new evidence for selection on evolution of floral traits.

传粉者介导的选择被认为是花部特征进化最重要的动力，分析选择的强度及变异是理解花部特征进化的有效途径。如果传粉者身体上携带花粉与接触柱头的位置不重合，将大大降低传粉的精确性，导致植物花粉传递和生殖成功的下降，那么选择趋使花部特征与传粉者之间的机械配合，将最大化传粉精确性。以往的观察表明，兰科植物往往有较高的传粉精确性，兰花的花粉块常常落置在传粉者身体的特定部位。我们在前期研究中注意到玉凤花属落地金钱的花粉块可被蛾类传粉者的六个足携带，这种花粉块多点落置是否降低了传粉精确性？据此，本项目拟以落地金钱为对象，调查花药和柱头与传粉者接触部位的重合程度，定量花粉块的移出率与落置率等指标，分析多个足携带花粉块对花粉传递的影响；通过表型选择分析、花部特征改变实验和多居群调查分析花部特征与传粉者之间的机械匹配程度。本项目旨在解释传粉者身体上多区域花粉落置的适应性意义，期望为花部特征的选择动力提供新证据。

传粉者介导的选择被认为是花部特征进化最重要的动力，分析选择的强度及变异是理解花部特征进化的有效途径。如果传粉者身体上携带花粉与接触柱头的位置不重合，将大大降低传粉的精确性，导致植物花粉传递和生殖成功的下降，那么选择趋使花部特征与传粉者之间的机械配合，将最大化传粉精确性。以往的观察表明，兰科植物往往有较高的传粉精确性，兰花的花粉块常常落置在传粉者身体的一个特定部位，但是本项目所研究的兰科玉凤花属植物落地金钱，其花粉块被蛾类传粉者的六个足携带和转运，这种花粉块多点落置与以往兰科植物精确的花粉块落置模式截然不同。本项目选择落地金钱和本地同属吻部传粉的粉叶玉凤花为研究材料，调查了兰花花部特征与传粉者口器长度的机械匹配程度、兰花花粉移动和繁殖成功水平，确认了落地金钱中稳定而高效的足部传粉模式，而这种特殊的传粉模式可能是落地金钱与当地长口器蛾类传粉者机械匹配的结果；另外，本项目通过落地金钱和本地同属粉叶玉凤花的表型选择分析、花部特征改变实验，验证了足部传粉模式和吻部传粉模式对花部特征截然不同的选择方向和强度，落地金钱的花数目受到了显著的正向选择，而粉叶玉凤花被选择则是花距长度。本项目旨在解释传粉者身体上多区域花粉落置的适应性意义，期望为花部特征的选择动力提供新证据。