榕树及其传粉榕小蜂互惠种对非专一性演化的机制

The interaction between fig wasps and their host fig trees (Ficus spp.) is a striking example of an obligate pollination mutualism that has great ecological significance, producing fruits that are fed on by more birds and mammals than any other plants in the tropics. Species-specificity in fig pollination appears to be extreme compared with most other insect pollination mutualisms. Most fig species are pollinated by only one wasp species and about fifty fig species are now known to have multiple pollinator species and as many as four different wasp species are known to pollinate a single fig species. However, the breakdown mechanism of one to one species specificity in fig–fig wasp mutualism are rarely studied. In this project, two dioecious Ficus squamosa and Ficus heterostyla who are distributed in Asian tropical continent will be selected, which the two Ficus species share the same species of pollinating fig wasp (Ceratosolen sp.) in Xishuangbanna tropical region and they also have other 2–3 species of pollinating fig wasps in different regions. Therefore, the two Ficus species and their mutualistic pollinating wasps provide a unique model to study the evolutionary mechanism of breakdown in one to one species specificity. The methods of ecology, chemical ecology and molecular ecology will be synthetically used in this project. Firstly, we will systematically compare the reproductive phenology of fig trees and fig wasps in different distribution areas, and widely collect fig wasps to know the wasp species, population sizes, fig wasp community, and study physiological tolerance and interspecific hybridization in the controlled experiments. Secondly, it is known that successful pollination of fig trees depends on a specific species of fig wasp managing to find receptive figs of the correct host plant, and the receptive figs can emit species-specific volatile chemicals to attract their pollinators. So we will focus on the volatile compounds produced by female flowers in receptive phase. The volatiles emitted by the figs of F. squamosa and F. heterostyla at pre-receptive, receptive, post-pollination will be collected by dynamic headspace sampling and analyzed by gas chromatography–mass spectrometry (GC–MS). The traits of interspecific chemical mimicry and intraspecific chemical divergence of two Ficus species will be studied. Thirdly, using DNA sequencing technology and microsatellite markers, we will research genetic polymorphism and gene flow of the two Ficus species and their pollinating fig wasps so that we can discover the population genetic structure and the factors driving the evolution of population genetic structure. Through co-phylogeographic studies of interacting fig and fig wasp pairs and DNA association study, haplotypes will be constructed phylogenetic relationships, combining with geological and climatic data, we can trace the evolutionary history, migratory route, geographical distribution pattern, possible glacial refugium, as well as the factors influencing them. Finally, we will show the evolutionary mechanism of breakdown in one to one species specificity through three-dimensional perspectives including ecology, chemical ecology and molecular ecology. The results will provide scientific basis for interspecific interaction theory and conservation of species diversity.

榕树及其传粉榕小蜂互惠共生体是动植物界协同进化的典范，两者高度专一、互不可缺。大多数情况下，一种榕树依赖一种专一榕小蜂传粉，随着研究的深入一种榕树有多种传粉榕小蜂，以及一种榕小蜂为多种榕树传粉的现象逐渐增多，然而，这种打破一对一关系、非专一性演化的机制研究很少。本研究选择两种既能共享一种传粉榕小蜂又各自有多种不同传粉榕小蜂的系统。综合运用生态学、化学生态学及分子生物学研究方法，系统比较研究不同分布区榕–蜂繁殖物候、榕小蜂种类、生理耐受性、种群、群落结构，以及种间杂交情况；再聚焦研究雌花期引诱传粉榕小蜂的挥发物，弄清榕–蜂之间化学联系信号的模拟及分化特征；进一步通过DNA测序技术和微卫星分子标记，研究榕–蜂种群遗传结构、多样性分化、进化历程、迁移路线及地理分布格局成因。从生态学、化学生态学及分子生态学三维角度揭示互惠榕–蜂种对非专一性演化的机制，为物种间互作理论及生物多样性保护提供科学依据。

榕树及其传粉榕小蜂互惠共生体是动植物界协同进化的典范，两者高度专一、互不可缺。大多数情况下，一种榕树依赖一种专一榕小蜂传粉，随着研究的深入一种榕树有多种传粉榕小蜂，以及一种榕小蜂为多种榕树传粉的现象逐渐增多，然而，这种打破一对一关系、非专一性演化的机制研究很少。本研究选择有代表性的肉托榕和异形化榕传粉系统。研究不同分布区传粉榕小蜂种类、共享传粉者导致的杂交、比较榕–蜂之间化学联系信号、研究榕-蜂的亲缘地理学及进化关系。结果如下：形态和分子鉴定显示肉托榕、异形花榕和对叶榕传粉榕小蜂形成一个包含9种传粉榕小蜂的复合体，其中有6新种。控制性引蜂试验，肉托榕和异形花榕之间相互可以产生杂交种子，但杂交程度在果和种子水平上均不对称。肉托榕和异形花榕雌花接收期释放相同化合物可能有利于吸引同种传粉榕小蜂，而在不同分布区释放的主要化合物有差异，可能促进了传粉榕小蜂的分化。cpDNA分析有24个异形花榕叶绿体单倍型和12个肉托榕叶绿体单倍型，其中4个单倍型为两个种所共有。AMOVA分析显示异形花榕和肉托榕的遗传变异均主要位于种群间，表明两个物种的种子流均较弱。对异形花榕和肉托榕开发、选取其中13对多态性较高的位点对样本进行了扩增分析；AMOVA分析结果表明异形花榕和肉托榕的遗传变异主要位于种群内，表明两个物种都具有比较高的花粉流。种群遗传结构分析显示异形花榕分化为明显的东西两个地理组，肉托榕没则有表现出明显的地理分化格局。分子证据也显示：异形花榕和肉托榕之间存在种间基因流，且种间基因流水平随着两个物种种群间距离的增加而减弱；两者种间基因流并非对称，主要由异形花榕向肉托榕方向，而反向的基因流很弱。执行该项目已发表研究论文10篇，其中3篇发在SCI期刊上，还将继续产出相关文章2-3篇。培养博士研究生2人、硕士研究生4人。最终揭示互惠榕–蜂种对非专一性演化的机制，为物种间互作理论及生物多样性保护提供科学依据。