兰花-果蝇传粉系统中花部气味信号与传粉者嗅觉系统作用机制及适应性进化式样的研究

Co-evolution of flowering plants and pollinators has been a core issue in evolution biology research. Numerous cases of the pollinating behavior characteristics evoked by floral volatile signals have been extensively studied. However, how the nervous systems of pollinators receive and transduce the floral volatile signals in pollination process is poorly understood. This situation hinders our deeply understanding of the evolution patterns between pollinator behaviors and floral volatile signals. Previous study reported that some orchids are pollinated by Drosophila species in reward or rewardless pollination systems, including Cypripedium bardolphianum, C. micranthum, Bulbophyllum penicillium, Specklinia endotrachys and related species. Our previous study found out a putative new floral volatile compounds attractive mechanism in C. bardolphianum. In this pollination system, the Drosophila pollinators are attracted by the floral volatile compounds as both sexual and food cues. The aims of this project are: 1) to analyze and bio-assess the effects of the main volatile compounds emitted by those orchid flowers; 2) to find out the specific glomerulus in the antennal lobe responding to the orchid floral volatile signals, and to address the primary neural mechanism processing the orchid floral volatile compounds in Drosophila melanogaster; 3) to identify the neural circuits activated by the floral volatile signals of those orchids in Drosophila pollinators, referring to their neural circuits counterpart in D. melanogaster. And our study will particularly focus on the floral volatile signals valued as sexual and food cues. Based on these neural circuits, we will explore the potential evolutionary adaptation mechanisms of floral volatile compounds and olfactory receptor neural circuits of Drosophila pollinators, especially the interaction between floral volatile compounds and pollinating behavior. The study of this interaction will deliver new insights into the pollinating behavior characteristics and neural mechanisms of pollinators in Orchid- Drosophila pollination system. Taken together the improvement of these basic theory and knowledge of pollination biology from our study can be considered as a new strategy to increase the pollinator efficiency, and eventually helps to buffer the global insufficiency of pollination services in ecosystems and agricultural systems.

有花植物与传粉动物之间的协同进化关系一直是进化生物学研究的核心问题。花部信号被传粉者接收后产生相应的传粉行为特征等方面已有丰富的理论和实证研究。但有关传粉者神经系统接收和处理花部信号的机制研究却很少，严重妨碍了对花部信号与传粉者之间协同进化关系的深入探讨。本项目拟以3种兰科植物的果蝇传粉系统，特别是无苞杓兰聚集性激素/性激素和食源性化合物混合花气味吸引传粉者的新机制为平台，借助模式生物黑腹果蝇的优势，率先开展导致果蝇传粉者行为的花气味化合物在果蝇大脑神经系统中被接收和处理的途径和机制等方面研究，探讨花气味信号与传粉昆虫初级嗅觉感受神经回路之间的进化适应关系，深入阐明花气味化合物成分与传粉者行为之间的关系。同时，利用模式生物黑腹果蝇解析传粉者在传粉活动中的行为特性和神经系统运行式样和机制的结果将为提高传粉者传粉效率贡献基础性理论和知识，为解决全球性的生态系统与农业系统传粉者不足‘添砖加瓦’。

有花植物与传粉动物之间的协同进化关系一直是进化生物学研究的核心问题。传粉者神经系统接收与传导花部信号的相互作用可以为协同进化提供基础性证据。通过野外实验和实验室各种手段，开展了无苞杓兰、小花杓兰和毛唇石豆兰等 3种兰科植物花气味化合物成分及成分组合对黑腹果蝇和无苞杓兰传粉果蝇，即伊米果蝇的行为响应式样，确定无苞杓兰花气味中介导传粉伊米果蝇吸引响应的关键化合物惕各酸乙酯Ethyl tiglate，以及该化合物吸引伊米果蝇的浓度范围。确定了惕各酸乙酯在黑腹果蝇初级嗅觉感受神经回路的接收途径、信号传递模式及机制。根据传粉伊米果蝇与黑腹果蝇在触角小叶神经系统形态结构特征方面的相似性和特化性，提出惕各酸乙酯嗅觉信号在伊米果蝇初级嗅觉感受神经回路的可能接收途径。此外，伊米果蝇V嗅小球体积较黑腹果蝇显著增大，可能是一个相对特化的神经回路，是无苞杓兰吸引伊米果蝇为其传粉的神经基础。此外，这种特化的V嗅小球也存在其它传粉果蝇中，包括南美州几种兰花的传粉果蝇中。因此我们认为，这种特化的V嗅小球神经回路可能是一种进化上适应花气味有效化合物的特化现象。.另一方面，我们发现在无苞杓兰花黄龙生境内中没有找到传粉伊米果蝇的食源和产卵地基质，也没有发现可发出含ET气味的食源和产卵地基质。所以，我们在传粉伊米果蝇的潜在可能起源区域，包括云南勐海、四川黄龙、广西雅长和湖南新宁等地开展不同海拔和不同季节的种群密度、食源以及产卵地调查。伊米果蝇的产卵地选择表现出泛化的特点，没有表现出对某一类植物的偏好。同时，伊米果蝇存在不同海拔迁徙的现象，并且在不同季节和不同海拔其食物来源的宽窄和产卵地基质等都存在明显的变化。.综上所述，我们认为无苞杓兰在欺骗机制中利用了传粉者伊米果蝇神经回路中预先存在的选择偏好，是一种预适应。该欺骗性传粉系统中的花部关键信号惕各酸乙酯可能在传粉者生活史中具有社会信号和食源产卵信号等多重功能。