探究高山草甸群落中植物减免种间花粉干扰的适应策略

Whether mutualistic interactions between species facilitate diversification of interacting species remains a big problem in the area of evolutionary ecology. Reciprocal selection between plants and pollinators has been considered as one classical model of coevolution. However, recent studies on pollination ecology at community level had demonstrated that plant-pollinator interactions are usually generalized rather than specialized as previously thought, in that one pollinator can pollinate for various plant species and one plant species usually has different pollinators. Pollinator interspecific moves may deliver pollen between different species. It remains unclear how diverse flowering species coexist with shared pollinators and minimize the deleterious effects of reproductive interference caused by interspecific pollen transfer. Based on our previous investigations of plant-pollinator interactions in a biodiversity hotspot, in the project we plan to study potential negative relationships between pollinator interspecific visits and heterospecific pollen transfer, and between pre- and post-pollination process for a better understanding of plant-pollinator-plant interactions. To analyze the plant-plant interaction strength and its dynamic change in alpine meadows in Hengduan Mountains, southwest China, we plan to investigate the mechanical fit between flower and pollinator morphology, pollinator visits to conspecific and interspecific flowers, conspecific and heterospecific pollen deposition on stigmas of each species, conspecific- and heterospecific- pollen-pistil interactions. To a better understanding of how co-flowering species minimize interspecific pollen interference, we will examine the two mechanisms of avoidance and tolerance for deleterious effects of heterospecific pollen transfer. An exploration of interspecific pollination competition will provide new evidence for the evolution of floral traits. This project would not only shed insights into how floral phenotypes diverge in the widespread generalized interactions between plants and pollinators, but also be helpful for understanding the diverse pollination systems and biodiversity conservation.

群落水平的传粉生态学研究表明植物与传粉者之间关系常常是泛化的，一种传粉者可为多种植物传粉。共享传粉者引起的种间花粉传递干扰了植物的有性生殖，那么不同植物是如何减少和避免种间生殖干扰而维持共存的呢？项目计划在已有工作的基础上，以生物多样性的热点——横断山区的多花草甸为研究对象，深入研究植物—传粉者—植物之间的相互作用，调查花与传粉者之间的形态匹配程度及其对有效传粉的影响。研究传粉者种间访问与异种花粉传递之间为何出现负相关关系？柱头上接受较高比例的异种花粉的物种是否演化出传粉后的阻止机制？将分析植物与植物互作的强度及年际动态变化，深入认识共存的开花植物减免种间花粉干扰的适应策略，探讨影响植物形成避免或耐受异种花粉传递的原因，探寻种间的传粉竞争选择花部特征演化的新证据。该项目不仅有助于认识普遍存在的泛化的种间互作如何影响表型特征的演化，在认识植物与传粉者互作的属性及生物多样性保护上也有参考价值。

项目实施5年来，围绕群落水平上植物与传粉者互作的研究主旨，在植物避免种间花粉干扰的适应策略领域取得了如下主要成果。（1）在国际上率先证实了植物自然群落中存在减免种间花粉干扰的两种适应策略：即避免和耐受（Avoidance vs. Tolerance）异种花粉的生殖干扰；我们在多花草甸设置了75个永久样方，调查传粉者混访、同种与异种花粉传递、物种共存与开花丰富度的网络动态，分析6年的数据发现同时开花增加了传粉者种内和种间访问，但并没有增加柱头上的异种花粉；这些结果将为理解物种共存的适应机制从生殖策略的角度提出新见解。（2）对高山草甸25种禾本科植物的观察与实验表明，风媒植物避免种间花粉传递是通过花期或一天内的散粉时间错开，证伪了前人提出的柱头捕获同种花粉的假说。（3）揭示异种花粉的供体植物和受体植物不同花部性状，供体植物的花粉粒径往往较小、而耐受异种花粉的植物其柱头暴露、表面积大。（4）以熊蜂传粉的开花群落为对象，在国际上首次构建了植物与传粉者互作网络、熊蜂体表携带花粉的网络、异种花粉传递的有向网络；为揭示植物减免种间花粉干扰的适应机制奠定了基础。项目提出了花粉粒大小演化的新假说：花粉被传粉者采食的植物花粉粒小；植物保护花粉不被过度采食的化学防御策略；发现雄蕊的快速运动的生态功能是赶走访花者，缩短采食时间，保护了花粉同时促使花粉传递到多个受体。相关结果以项目主持人为通讯作者已在国际进化与生态学的主流刊物发表，如《Current Biology》、《eLife》、英国皇家协会会刊《Proceedings B》、《New Phytologist》（2篇）、《Oikos》、《Oecologia》、《American Journal of Botany》（4篇）、《Journal of Systematics & Evolution》（6篇）等SCI论文（IF>3）20余篇。2018年在《生物多样性》杂志，组织出版了“传粉网络的生态监测”专刊；2021年在《Trends in Ecology & Evolution》发表独著短评文章“可持续的传粉者多样性与传粉生态服务”。三项研究成果分别被选为《New Phytologist》封面文章、F1000推荐阅读（中国科学基金进展报道）、Current Biology专文评论。