传粉者不同的三种杓兰的群体遗传结构和基因流

Genetic diversity and population structure of flowering plants are not only indicators of potential adaptability to changing environments in the future, but also genetic consequences for adaptation to historical environments. Studies on genetic structure of plant populations and its influence factors such as gene flow have been the central themes of plant evolutionary biology and conservation genetics in the past decades. However, few attempts have been made to explore spatial patterns of genetic variation at different scales and estimate historical and ongoing gene flow using both direct and indirect methods. In this project, genetic structure and gene flow of three single-flowered species of Orchidaceae (Cypripedium bardolphianum, C. tibeticum and C. flavum) characteritzed with sympatrical distribution in Hengduan Mountains, overlapping blooming periods and pollination by different types of insects in Huanglong National Nature Reserve, are investigated using 20 SSR markers. At least 20 natural populations of each species were chosen for investigation of geographical distribution of genetic variation and historical gene flow, and a natural population in Huanglong was chosen for investigation of fine-scale spatial genetic structure (SGS) and both historical and on-going gene flow. SGS at different age stages of Huanglong population was investigated by mapping and genotyping adults (reproductive individuals) and seedlings of each species. Pattern of historical gene flow among populations of each species was indirectly estimated by the mathematical model of Wright's FST, while pattern of historical gene flow within Huanglong population was indirectly estimated using an approach that is based on the slope of the regression of pairwise kinship coefficients on spatial distance and estimates of the effective population density. Pattern of on-going gene flow within Huanglong population was directly estimated using methods of parentage analysis after excluding the impossible fathers using stained pollen and variations of dates of flowering, pollen removal and pollination between the mather and the impossible fathers. We compared genetic structure at different scales and patterns of historical and on-going gene flow among three orchid species.This project will not only enrich our understangding of population genetic consequences of different species of Orchidaceae adapted to different types of pollinators in the same community and the geographical scale, but also contribute to help to develop strategies for the conservation and sustainable utilization of these orchids in China.

植物群体的遗传变异水平和遗传结构不仅是对未来变化的环境适应潜力的特征，也是适应过去（历史）环境的遗传后果。研究群体遗传结构及其影响因素（基因流）是国际上植物进化生态学和保护遗传学的热点问题之一。然而，从不同空间尺度探讨不同植物群体遗传变异的分布式样、运用不同方法估测基因流及其对遗传结构的影响的研究很少。本项目以我国横断山区三种兰科植物（无苞杓兰、西藏杓兰和黄花杓兰）为研究对象，利用微卫星标记，从地理尺度和群体内小尺度研究三种植物的群体遗传变异水平和分布式样，应用间接（FST法和SGS法）和直接方法（花粉染色法和父本分析），对比分析三种杓兰群体间和群体内的基因流格局，探讨传粉者对花粉基因流以及基因流对群体遗传结构的影响，为进一步揭示兰科植物多样的适应机制尤其是不同植物适应于不同传粉者的遗传后果以及在不同空间尺度上适应的遗传后果提供重要信息，并为兰科植物的有效保护和合理利用提供有益的资料。

探讨植物的多样性及其遗传和生态适应后果是植物进化生态学的核心主题。单花性（每个个体只开一朵花）是被子植物中的一个普遍现象。然而，很少有研究来探讨单花植物尤其是由不同传粉者传粉的单花植物的遗传和生态适应意义。本项目以我国横断山区三种单花兰科植物（无苞杓兰、西藏杓兰和黄花杓兰）为研究对象，利用分子标记从不同空间尺度研究三种植物的群体遗传变异水平和分布式样，应用不同方法对比分析三种单花兰科植物群体内和群体间的基因流格局，探讨三种单花兰科植物的遗传后果；通过野外调查和文献调查相结合、种间比较和种内分析，探讨三种单花兰科植物的生态适应后果。..单花兰科植物遗传适应后果的研究结果显示，无苞杓兰呈现明显的小尺度空间遗传结构，而西藏杓兰和黄花杓兰的小尺度空间遗传结构不明显，这可能与传粉者的飞行能力和花粉散播距离有关。无苞杓兰的传粉者是果蝇，个体小、飞行能力弱，染色的花粉散播距离较近，由此会导致明显的空间遗传结构。与之相反的是，西藏杓兰和黄花杓兰的传粉熊蜂，其个体大、飞行能力强，染色的花粉散播距离较长，加之二者个体相对较高，种子散播范围广，因此不容易形成明显的空间遗传结构。这一研究结果为我们深入认识同域同属植物的遗传适应后果提供了新的证据。..单花兰科植物的生态适应研究结果显示，单花种植物（三种杓兰）的花粉限制显著高于同域生长的花序种。单花种的花粉移走率显著高于花序种兰科植物。然而，单花种植物的结实率和每株结籽数显著低于花序种，这说明单花种植物在雌性生殖成功方面明显不如花序种植物。另外，从文献中搜集28种单花种和花序种兰科植物的生殖成功数据并进行系统独立比较（PICs）显示，花粉移走率与花数目无关，而结实率随着花数目的增多而显著增加（R = 0.516, P = 0.0058）。由此可见，与花序种比较，单花的杓兰的雌性生殖成功明显不如花序种植物，这一研究结果为认识植物尤其是单花植物的生态适应后果和花的多样性及其适应机制提供了新的证据。