兼性自交植物角蒿的花粉限制、近交衰退和大花展示的进化机制

Understanding the adaptive significance and evolutionary mechanism of mixed mating (in which hermaphrodite plant species reproduce by both self- and cross-fertilization) is a challenging problem in plant evolutionary ecology. Obligate outcrossing species usually produce large, showy flowers to enhance pollinator attraction, whereas obligate self-fertilizing species often bear small, inconspicuous flowers because it is not necessary to invest much in attractive structures when selfing occurs autonomously. However, many species with a mixed mating system, even at high selfing rates, devote considerable resources to attraction structures. Evidence from both case study and meta-analysis have showed that attractive traits were the target of natural selection in many outcrossing species. But we know a little about evolutionary mechanism of flower size in facultatively selfing (mixed mating system but predominantly selfing) plants that produce large flowers. In this project, we will estimate pollen limitation, inbreeding depression and natural selection on attractive traits in a facultative selfing annual plant, Incarvillea sinensis var. sinensis, in two populations (Ordos and Beijing) that are different in soil type. Incarvillea mairei, a perennial with outcrossing mating system, will also be chosen to be compared to I. sinensis. Pollen limitation will be estimated by contrasting total seed production by plants with determinate versus indeterminate flowering. Plants in the determinate treatment will be limited to mean number of flowers by excision of excess flower buds, whereas flower production by the indeterminate treatment will not be experimentally constrained. All flowers on plants in both treatments will be subject to unmanipulated (controls), pollen addition, and pollen reduction and flower and total seed production will be measured. Effect of flowering time on pollen limitation will be investigated by contrasting total seed production by plants flowering in early, before and after peak flowering stages. All flowers on plants in three treatments will be subject to unmanipulated (controls) and pollen addition. Inbreeding depression will be estimated by contrasting fitness of progenies (i.e. total seed production, seed germination rate and plant size of progenies) by plants with small versus large inflorescences, and flowering in three stages (early, before and after peak flowering). All flowers on plants in these treatments will be subject to selfing and outcrossing hand-pollination. Selection on attractive traits (i.e. flowering time, corolla tube length and floral shape) will be estimated in four pollination environments (pollinator exclusion, supplemental hand-pollination, open pollination and open pollination after emasculating). Plants will be caged to establish pollinator exclusion treatment. Selection target and selective pressures (selection media) will be identified. Pollen limitation, inbreeding depression and selection on attractive traits will also be compared between populations, years and species (facutatively selfing versus outcrossing). We will discuss the adaptive significance and evolutionary mechanism of a facultatively selfing plant with large floral display by integrating studies of ecology, genetics and evolution. This project will not only provide insights into adaptive significance and evolutionary mechanisms of mixed mating system, but also provide new evidence for our understanding of diversification of the angiosperm flower and its formation and evolutionary mechanisms.

混交植物的适应意义和进化机制是进化生态学研究中富有挑战的主题。专性异交植物为了吸引传粉者通常产生大而鲜艳的花，而专性自交植物因不需要吸引传粉者而常常开很小、不显眼的花。然而，很多具有混交系统甚至自交率较高的植物对吸引性状投入相当多的资源、开很大的花，对这类植物的进化机制和适应意义我们知之甚少。本项目以一年生兼性自交但具大花展示的角蒿为主要研究对象、以同属多年生异交植物鸡肉参为对照，通过因素控制实验，分析角蒿吸引性状对花粉限制和近交衰退的影响及其在群体间、年际间的变化及与异交种的异同；通过人工操控传粉环境(传粉者排除、人工补充授粉、自然受粉和去雄自然受粉)，估测角蒿吸引性状所受自然选择的强度和方向，分析自然选择的目标和媒介及其群体间、年际间的变化及与异交种的异同，从生态、遗传和进化的角度探讨混交但具大花展示植物的适应意义和进化机制，为进一步理解植物多样性的形成和进化机制提供新的证据。

自花受粉综合征认为自交植物因不需要吸引传粉者而常常开很小、不显眼的花，但很多自交率很高的植物对吸引性状投入相当多的资源、开很大的花，对这类植物的进化机制和适应意义我们知之甚少。本项目以一年生兼性自交但具大花展示的角蒿为研究对象，通过控制实验建立不同开花数目和开花时间的植物群，检测吸引性状对花粉限制的影响。通过建立不同密度的样方和控制实验，检测微环境对表型可塑性的影响及其与传粉环境交互作用对自然选择的影响。..尽管角蒿是兼性自交植物，但依然存在显著的花粉限制，且花粉限制的程度随着每株花数的增加而降低。开花时间、花数、植株高、花冠长、花冠宽和花冠口高在样方之间和年际间均存在显著差异。在降水多的年份，开花时间普遍比干旱年份晚，植株也更高。每株平均花数目在降水多的年份也要更多（多55%），自然受粉的个体花数目随着不能结实的花数目的增加而增加。花冠长、花冠宽和花冠口高在降水多的年份均比干旱年要长或大。植物表型在样方间的差异主要是由于微环境条件下土壤资源（水分和营养）的差异造成的。.由花冠脱落后柱头闭合的花的比例在开花早的个体比开花稍晚的个体低，而且花冠脱落后柱头是否闭合影响果实发育的可能性。在所有花中，柱头闭合的花结果的比例比预期的高。开花时间所受到的选择是负向的，且在降水多的年份比干旱的年份要强，开花越早的个体结籽数越多。花冠长和花冠宽经历的是正向选择，花冠越长、越宽的个体结籽数越多。花冠口高所经受的正向选择只有在人工授粉个体中检测到。这种相关在传粉处理间和年际间无显著差异。对于自花受粉的个体，开花时间和植株高所受到选择的强度和方向与自然混交受粉的个体没有显著区别，这一结果不支持自交率高的兼性自交植物不受选择的假说。..这些结果表明兼性自交但具大花展示的植物其生态适应机制不同于完全自交和异交植物，在半荒漠地区具有独特的适应意义，为我们进一步理解植物尤其是花的多样性的形成和进化机制提供新的证据。