榕-传粉小蜂共生体系关键生态适应的进化机制

Ecological adaptation is one of the critical issues in speciation and diversity conservation. At present, studies concerning the evolutionary mechanisms of ecological adaptation mainly focused on abiotic environments, but rarely on the interspecific interactions. These interactions not only play an essential role in stabilizing local ecosystems but also lead to niche differentiation and speciation. The obligate mutualism between figs and their pollinating wasps is highly specific, and with only a few exceptions, a fig species is pollinated by one pollinating wasp species whose larvae can only develop in the ovaries of the plant. Such tight relationship is thought to have driven the diversification and eventually form two highly diverse taxa. In this project, we will study the evolutionary mechanisms concerning the key factor linking the two taxa, i.e. volatile organic compounds (VOCs). After choosing typical fig species and their pollinating wasps, we will detect the spatio-temporal pattern of VOCs released by the fig trees and test the preferential selection of the pollinating wasps. The critical components of VOCs that attract the pollinators will be determined by comparing the components of VOCs from pre-receptive and receptive figs. Further, based on the analyses of transcriptomes and proteomes of figs at different stages and of naive and VOCs-stimulated pollinating wasps, we will reveal the regulation modes of VOCs releases in figs and the identification and response modes to the VOCs in pollinating wasps, and will locate the critical genes regulating these pathways. Then, we will sample all fig species in the same subsections of the typical fig species and their pollinating wasps. Using the critical genes, the phylogenetic patterns of all sampled figs and their pollinators will be delineated and compared to test if the critical components of VOCs significantly contribute to the coevolution of the two taxa. Finally, we will measure the relative roles of co-diversification and host shift in speciation via analyzing the transcriptome-based phylogenetic trees of the two taxa, and will examine whether positive selection occurs in the critical genes. Our study will shed light on the evolutionary mechanisms of ecological adaptation in adaptive radiation.

生态适应是物种形成与生物多样性保护研究的核心议题之一，目前有关生态适应进化机制的研究多集中于对非生物环境的适应，很少关注相互作用物种间的相互适应，而这种作用不仅是涉及生态系统调节，也可导致生态位分化与物种形成。榕与其传粉小蜂构成了高度专一、相互依存的强制性共生共生体系，两者相互适应被认为是这两个类群适应性分化、物种形成的重要驱动因素。本项目拟以代表性榕属植物及其传粉小蜂为对象，围绕联系两个类群的关键----挥发性有机物(VOCs)的释放与响应，研究榕果释放VOCs的时空格局及对传粉小蜂的吸引规律，确定吸引专一性传粉小蜂的关键组分；通过转录组和蛋白质组分析探讨榕属植物关键VOCs合成的调控模式及传粉小蜂相关感知基因的调控，分析相关基因的分子进化格局，比较两类群的系统进化关系，厘清生态适应特征的进化机制，为理解生态适应在辐射成种中的作用提供实证。

种间互作关系是驱动协同进化与物种形成的重要因素。榕属植物仅能由专性传粉榕小蜂为其传粉，两者构成高度专一的强制性共生关系。长期的相互适应与协同进化被认为是导致两者多样性化的重要原因。然而，目前仍不明确这一共生关系形成和维持的机制。已有研究表明这一强制性共生体系的维持依赖于两个关键因素：(1) 植物释放的吸引专性传粉榕小蜂的挥发性有机物(VOCs)；(2) 传粉榕小蜂幼虫适应宿主榕属植物子房内化学防御。本项目以薜荔(Ficus pumila var. pumila)及其传粉榕小蜂(Wiebesia pumilae)为主，采用多组学方法开展研究，目前已取得突破性进展，揭示了薜荔释放挥发性有机物质的时空格局和体内生物合成调控机制，以及传粉榕小蜂感受VOCs的分子机制。基于这一发现，采用信息论模型验证了榕属植物与传粉榕小蜂间的化学交流是驱动两者关系特化的重要因素。尽管薜荔传粉榕小蜂对植物防御性次生代谢物质的解毒能力较弱，但是幼虫所在的虫瘿通过拟态种子有效避免了植物宿主的惩罚，为传粉榕小蜂幼虫生长发育提供了稳定的化学环境。除上述分子机制外，以舟山群岛为研究体系，发现该区域的薜荔传粉榕小蜂隐存种通过源-汇种群动态得以长期维持。此外，薜荔与其近缘种珍珠莲(Ficus sarmentosa)存在着种质渐渗现象，表明传粉者宿主转移导致杂交成种可能是榕属植物进化的潜在驱动因素。将研究拓展至绵毛榕亚组，进一步研究榕属植物释放VOCs与传粉榕小蜂响应的分子机制，发现了植物VOCs组成存在明显系统发育信号，且气候变化也是驱动两者适应性进化的重要因素。综上所述，项目研究成果有助于理解协同进化和物种多样性形成的机制。已发表和录用26篇学术论文，其中SCI收录源24篇，含Nature Ecology & Evolution、Moecular Ecology、Journal of Ecology、Journal of Animal Ecology等生态与进化重要刊物。