单花兰科植物的生殖代价和交配格局

Understanding the diversification mechanisms of flower and its ecological and evolutionary consequences is a central theme in plant evolutionary ecology. Singleness, characterizing by producing a single flower or leaf, is common found in many taxa of angiosperm. However, the reproductive consequences of phenotype producing a single flower are poorly understood. Our recent study on many species over many years indicated that single-flowered species had significant lower proportion of fruit set and seed number per plant than multiple-flowered species. In order to investigate the potential compensatory mechanisms for such reproductive disadvantages in single-flowered species, a full factorial experiment manipulating microsite and floral density will be conducted in two populations of two species pairs producing either a single flower or multiple flowers per plant (Changnienia amoena vs Phaius delavayi, Cypripedium tibeticum vs Cypripedium henryi). Reproductive allotment will be estimated in two species pairs by comparing the relative dry weight of reproductive tissue in relation to total plant weight. Costs of natural investment in reproduction will be assessed by experimentally preventing fruit set by pollinator exclusions, whereas costs of increased reproductive investment are examined by the use of supplemental hand-pollination, maximizing fruit set under contrasting microsites and floral densities. Pollen flow within and between plants will be monitored by following the movement of the coloured pollen. Outcrossing rate in two species pairs will be estimated using a multilocus mixed model and selfing rate is compared the same species under contrasting microsites and floral densities. We discuss the possible compensatory mechanisms for reproductive disadvantages in single-flowered species by comparing cost of reproduction and mating pattern with multiple-flowered species. This project will not only enrich our understanding of life historical characteristics and mating pattern in different phenotypes producing a single flower or multiple flowers per plant, but also contribute to develop strategies for the conservation and sustainable utilization of these orchids in China.

探讨花的多样性及其生态和进化后果是植物进化生物学的核心主题。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性的生态和进化意义。近期我们利用多年积累的数据研究发现，单花种植物在结实率和每株结籽率上显著低于花序种。本项目以两对单花种和花序种兰科植物为主要研究对象，在前期研究基础上，通过全因素试验设计和实验操纵法，对比分析单花种和花序种在不同微生境和开花密度条件下生殖分配和生殖代价；应用花粉染色法和分子标记法比较单花种和花序种植物的交配格局及其对微生境和密度的响应，从生活史适应策略和遗传后果方面探讨在数量上具有生殖劣势的单花种的可能补偿机制，为进一步理解花多样的适应和进化机制提供重要信息，并为作为植物保护中的“旗舰”类群的兰科植物的有效保护和合理利用提供有益的资料。

探讨花的多样性及其生态和进化后果是植物进化生物学的核心主题。单花性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性的生态和进化意义。本项目以两对单花种和花序种兰科植物为主要研究对象，通过实验操纵法和花粉染色法和分子标记法，对比分析单花种和花序种的生殖分配、生殖代价和交配格局，从生活史适应策略和遗传后果方面探讨在数量上具有生殖劣势的单花种的可能补偿机制，为进一步理解花多样的适应和进化机制提供重要信息。..生殖代价的研究结果显示，四种植物中有三个种的次年抽芽率均很高，但次年抽芽率在三种受粉处理之间均无显著区别。三种传粉处理对次年开花率的影响，两个非克隆植物增加结实的开花率代价显著高于克隆植物，花序种自然结实的开花代价高于单花种。对于两种克隆植物（黄花杓兰和少花鹤顶兰），受粉处理对次年开花率的影响取决于克隆大小。去花处理显著增加了两种植物最大克隆（或单分株）次年的开花率，这使得开花代价高于中等大小的克隆，而人工授粉并未显著降低任何大小克隆的次年开花率。受粉处理显著影响次年总叶面积，多花非克隆的广布小蝶兰增加结实的生长代价在四个种中最大。对于两种克隆植物而言，受粉处理对次年总叶面积的影响取决于克隆大小。对于单花种黄花杓兰而言， 增加结实的生长代价比单分株和小克隆的高。对于多花种少花鹤顶兰而言，传粉处理不影响总叶面积代价。这些结果显示生殖代价的表达差异与共存物种的生活史差异密切相关。..交配格局的研究结果显示，花序种自花受粉的比率并不比单花种的高，这可能与这四个种都是欺骗传粉系统有关，且存在同株异花受粉避免机制如广布小蝶兰花粉块柄弯曲。采集结实个体的果实（子代）和母本个体的叶片材料、利用AFLP分子标记估测异交率的结果显示，单花种和花序种的异交率均很高，在不同年份存在一定差异，这可能与传粉者丰度的年度变化有关。这些结果显示植物交配格局与花数目的多少关系不如预料的高，这可能与传粉机制有关。