喜马拉雅-横断山冰缘带最具代表性的两种“温室植物”——蓼科大黄属的塔黄和苞叶大黄分别与两种蕈蚊形成“一对一”的种子寄生性传粉互利共生关系：蕈蚊为植物传粉，植物提供种子作为蕈蚊幼虫的食物，且一种蕈蚊只拜访一种植物，是研究冰缘带特殊生境下植物与昆虫协同进化的理想材料。在前期研究的基础上，本项目从进化生态学入手，综合多学科手段，从植物的营养质量、化学防御、物理形态性状、竞争与捕食以及非生物环境条件等几个方面来探讨塔黄和苞叶大黄与两种传粉蕈蚊“一对一”专性关系的形成与驱动机制。重点回答两个问题：①种子寄生性传粉互利共生关系为什么只出现在塔黄和苞叶大黄这两种“温室植物”上，而没有出现在同域分布的其它几种大黄属植物上？②同是“温室植物”，塔黄的传粉蕈蚊为什么不选择苞叶大黄作为寄主，苞叶大黄的传粉蕈蚊为什么不选择塔黄作为寄主？研究结果能丰富我们对专性互利共生关系的理解，并为其它相似系统的研究提供参考。

Rheum nobile and R. alexandrae (Polygonaceae), two species endemic to the subnival zone of Himalaya-Hengduan Mountains, have been chosen as the model species for studying ‘glasshouse’ plants in these areas. Pollination of the two plant species depends on their respective obligate mutualistic seed-consuming fly fungus gnats (Bradysia sp1. and Bradysia sp2.; Sciaridae), which represents a new obligate pollination mutualism and provide an idea system for studying coevolution between plant and insect in alpine areas. We will explore the drivers of host specificity of the two fly species using evolutionary-ecological theories and multidisciplinary methods by determining the following several factors, including plant food quality, plant chemical defense, physical morphological traits, competition and predation, and abiotic environmental conditions. The following two specific questions will be addressed: 1) why does the pollinating seed-consuming mutualism only occur on the two ‘glasshouse’ plants, but not on other sympatric Rheum plants in this area? 2) Within the two ‘glasshouse’ plant species, why did not the pollinators, Bradysia sp1., of R. nobile select R. alexandrae as their host plant, and why did not the pollinators, Bradysia sp2., of R. alexandrae select R. nobile as their host plant? This study can contribute to our understanding of the obligate pollination mutualism, and provides a model for studying the drivers of host specificity in other similar systems.