小叶榕传粉榕小蜂和欺骗性小蜂共存的生态行为机制

The fig-fig pollinator mutualism is one of the classical cases of interspecific cooperation. Figs (Ficus spp.) depend on wasps for transmission of their pollen and, therefore, viable seed production, whereas fig wasps (Agaonidae) rely on fig inflorescences for the completion of their life cycle. It is known that the prevention of cheating evolution in the partners is required to achieve the mutualism stabilization. However, a Ficus species could be pollinated by more than one wasp species, the colonization events involving wasp multiple symbionts provide a likely scenario for the transition from mutualism to antagonism. Up to now, only three cases of pollinating wasp species having evolved into cheaters are known among around 400 species of pollinating fig wasps. Recently, we found the third case of cheater agaonids associated with Ficus microcarpa, but the coexistence and evolution mechanism between cheater and pollinator have not been thoroughly studied. In this project, the trees of F. microcarpa grown in natural habitats and planted in urban areas and their fig wasps will be selected. Long-term phenology observation and quantity-controlled experiments will be performed and the methods of Headspace-SPME, GC-MS and Y-tube olfactometer will be employed as well. We will compare the ecological and behavioral differences of pollinator and cheater on F. microcarpa, which involve the coexistence pattern, occurrence regularity, and reproductive difference. Furthermore, we will also identify the chemical signals released by receptive figs in different seasons and habitats, and compare the behavioral responses between pollinator and cheater to active compounds. The quantitative pollinator and cheater will be introduced into the fig wall to observe the intraspecific and interspecific recognition behavior during the receptive phase. Finally, we will explain the ecological and behavioral mechanism of pollinator and cheater on Ficus microcarpa, which we hope will shed some light on how to better understand the cheating evolution in the mutualistic system.

榕树依赖专一的榕小蜂传粉，同时也为榕小蜂提供繁殖场所，两者互惠共存，是动植物间协同进化的典范。已知互惠系统的维持需要防止互作双方出现欺骗性，然而多种传粉者共存于一种榕树为传粉者演化为欺骗者创造了契机，目前约400种传粉榕小蜂中仅有3种演化为欺骗者。近期我们在小叶榕上发现了第3种欺骗性小蜂，它与传粉榕小蜂共存、演化的机制尚未开展研究。本项目将针对该系统，在西双版纳小叶榕分布区，选择自然分布和绿化种植的树，在不同时间、季节内采用野外系统调查与精准控制试验相结合的方法，借助顶空固相微萃取技术、气相色谱质谱联用仪、Y型嗅觉仪等，从生态学和行为学角度对比研究小叶榕上传粉榕小蜂和欺骗性小蜂的共存模式、发生规律、繁殖差异、以及对雌花期引诱活性化合物的行为反应，进入榕果时种内、种间识别行为的差异，最终揭示传粉榕小蜂和欺骗者小蜂在小叶榕上共存的生态行为机制，为理解互惠共生系统中欺骗性的演化机制提供案例。

榕树与传粉榕小蜂之间的关系为协同进化、互惠共生关系的典型案例。然而已发现有3种传粉者演化为欺骗者。项目组通过对小叶榕上传粉者演化为欺骗者的案例进行了深入研究。. 本研究聚焦分布于西双版纳热带地区的榕树(Ficus microcarpa)，进行了17个月定期、定树的结果物候观察，对共存其隐头花序内的传粉者(Eupristina verticillata)及欺骗者(Eupristina sp.)的种群动态进行了系统研究。结果表明：榕树结果物候雌花期和雄花期衔接紧密，但种子及榕小蜂的繁殖呈现极端的季节变异；传粉者主要发生于雨季，同时繁殖更多的种子；而欺骗者则主要发生于干热季；两者发生季节不重叠有利于共存。这种季节性周期变化，反映在传粉者表现不佳的季节，竞争减弱促进了欺骗者的演化和共存。鉴于榕小蜂中传粉欺骗性演化比较罕见，且有两种出现在西双版纳热带地区，表明地处热带北缘极端的季节气候变化为欺骗者的演化创造了条件。 . 为揭示榕树(Ficus microcarpa)及其传粉榕小蜂Eupristina verticillata之间的化学通讯机制，该研究采用固相微萃取法提取榕树隐头花序不同发育期(花前期、雌花期传粉前后、间花期、雄花期和花后期)释放的挥发物，并用气相色谱-质谱联用仪鉴定挥发物成分，分析其变化动态，再通过Y型嗅觉仪检测榕树传粉榕小蜂对各发育期隐头花序的行为反应。结果表明：榕树隐头花序释放的挥发性化合物共鉴定出21种。行为检测的结果表明：雌花期隐头花序对传粉榕小蜂的吸引作用最强，而雄花期的隐头花序释放的挥发物对传粉榕小蜂有趋避作用，形成了对传粉榕小蜂“推拉”的互作模式。有多种化合物在榕树传粉榕小蜂的寄主识别过程中发挥作用，表明榕树及其传粉榕小蜂的互惠共生关系是通过多种化合物的“泛化”策略来维系的。. 项目开展中发现，传粉者和欺骗者都存在线虫寄生现象，而非传粉者没有，说明传粉者和欺骗者可能释放相似的化学信号，以至于线虫不能准确区分定位。. 目前已发表标注本项目资助的文章4篇（Q1、Q2各1篇，CSCD 2篇）。培养研究生2人。