寄主交换榕蜂系统中榕小蜂寄主选择与可塑性研究

The nursery pollination mutualism between Ficus species (Ficus, Moraceae) and their pollinators (Agaonidae, Hymenoptera) is considered an optimum model for examining interspecies interactions. The mutualism is long regarded as strictly specific-species, with each Ficus species being pollinated by an agaonid species which could only breed in its fig. Matches of reproductive structures between host species and fig wasps, and specific volatile organic compounds are key points to maintain the mutualistic stability. However, there are a few exceptions including more than one Ficus sharing the same pollinator species or different agaonid wasps associated with one fig species. Researches on the host selection and plasticity of pollinators in different Ficus favor to explore the occurrence of nonspecific fig-fig wasp mutualism, which provide new research aspects on coevolution of the mutualism..In Xishuangbanna, Ceratosolen emarginatus associated with F. auriculata and Ceratosolen sp. associated with F. hainanensis can exchange their host and successfully reproduce, which is the only host exchanged fig-pollinator system. The host-exchanged mutualism is an ideal material to study interactions in the nonspecific fig-fig wasp mutualism. .In this project, based on the host-exchanged mutualism, we will focus on volatile organic compounds attracting pollinators emitted by hosts, utilization patterns of chemical scents by pollinators, behavioral and physiological responses of offspring to natal and primal hosts, and changes in morphology and populations of offspring, by GC-MS, GC-EAD, control introductions, behavior responses, measurements and other ecological experiments. The objective of this project is to investigate the hosts' discrimination and plasticity in host-exchanged fig-fig wasp mutualism. Results will be very valuable to reveal causes of switching hosts and sharing pollinators in the mutualism, and then to explore the formation and stabilization mechanism of the nonspecific fig-fig wasp mutualism.

榕树与其传粉榕小蜂形成的专性育幼传粉互惠共生系统是研究种间互作关系的经典模型之一，榕小蜂与寄主匹配的繁殖特征及榕树特定阶段释放的特异性挥发物是保证该系统稳定共存的关键。但部分榕蜂关系并非专一，研究传粉者对不同寄主的识别和寄主对入侵者的可塑性有利于探讨非专一性榕蜂系统的存在和维持，并为研究榕蜂系统的协同进化提供新思路。本研究以西双版纳地区唯一存在的寄主交换榕蜂系统，即木瓜榕和海南榕及其传粉者为研究切入点，以寄主雌花期化学挥发物和对不同传粉者后代的可塑性为研究内容，应用化合物成分分析、电生理、行为反应、人工控制放蜂等化学生态学和行为生态学的方法，结合后代对寄主回溯性测试，解析两种榕小蜂及后代对不同寄主化学信息的利用方式和行为反应，明确寄主榕树对传粉者和入侵者后代的可塑性，进而揭示非专一性榕蜂系统的成因和稳定机制。

榕树与其传粉榕小蜂间存在着专性关系，雌花期榕果释放的化学挥发物是维持专性关系的关键，然而调查发现约有6%的榕-蜂组合并非严格的专一性，那么寄主是否会对非对应传粉榕小蜂产生可塑性？本研究以寄主交换榕蜂系统为研究材料，分析了寄主对榕小蜂的可塑性及行为选择影响。结果显示：1、将Ceratosolen emarginatus放入海南榕产生的后代个体变小，把Ceratosolen sp.放入木瓜榕产生的后代个体变大。寄主提供的营养能够影响后代个体大小。2、将C. emarginatus放入海南榕产生的后代数量比其在木瓜榕上的多，Ceratosolen sp.放入木瓜榕引发大量落果（88.30%），且榕小蜂后代数量较少。C. emarginatus产卵器较长，可在具有较短花柱的海南榕中顺利产卵，而短产卵器的Ceratosolen sp.无法在具长花柱木瓜榕中顺利产卵，故引发大量落果，且后代种群数量小。可见不同寄主对于传粉榕小蜂后代种群大小具有可塑性。3、木瓜榕雌花期收集53种挥发性化合物，其中烯萜类化合物40种，脂肪族12种，芳香族1种，(E)-β-Ocimene, Cis-β-Cedrene, Trans-β-Farnesene, ɑ-Farnesene, ɑ-Gurjunene, ɑ-Elemene, Khusimene, and Bicyclogermacrene 是主要化合物。海南榕雌花期收集挥发性化合物40种，其中烯萜化合物37种，脂肪族化合物3种。Isoledene，α- Cedrene，β- Cedrene，(+)-Aromadendrene，Caryophyllene为主要成分，两种榕树雌花期化学挥发物差异显著。4、C. emarginatus对木瓜榕有明显的偏好性，Ceratosolen sp.对海南榕有明显的偏好性，但木瓜榕和空气同时存在时，其对两者选择无差异。5、通过电生理测试，木瓜榕的有效活性成为为9种，海南榕吸引传粉者的有效活性成为为5种。6、C. emarginatus进入海南榕产生的后代对海南榕有明显的偏好性，说明寄生的寄主确实能够对榕小蜂的行为产生可塑性。本研究明确了寄主榕树对传粉者和入侵者后代的可塑性，进而揭示非专一性榕蜂系统的成因和稳定机制。