XTBG OpenIR  > 西双版纳热带植物园毕业生学位论文
中甸灯台报春(Primula chungensis)的繁殖生态学研究
Alternative TitleStudy of the Reproductive Ecology of Primula chungensis
蒋 显 锋
Subtype博士
Thesis Advisor李庆军
2017-11
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Discipline植 物 学
Keyword中甸灯台报春 二型花柱 同型花柱 不对称传粉假说 繁殖保障假说 传粉者介导的选择作用 自然选择
Abstract被子植物的繁殖器官有着极为多样的结构,全世界约有25万余种被子植物,不同类群的植物的花器官在颜色,大小,构造,气味等方面往往会有所不同。作为植物的繁殖器官,植物学家通常认为被子植物的花部构造与植物所处的传粉环境密切相关。
二型花柱是一种典型的花柱多态现象,存在于被子植物的约28个科中。二型花柱植物在一个居群内同时存在两种表型的个体,分别是花柱长花药短的长花柱型,以及花药长花柱短的短花柱型。大多数的二型花柱植物通常还伴随有自交/型内交配不亲和的特性,即只能通过不同表型的个体相互交配才能产生可育的后代。因此,二型花柱也是植物界中典型的促进异交的花部构造。但是,二型花柱在自然生境中并不总是稳定存在的,通过控制其二型花柱性状的超级基因发生重组,二型花柱有可能崩溃为自交亲和的同型花柱,这一转变也在多个类群中多次独立的发生。
中甸灯台报春,在多数情况下,同一个居群内有三种表型的个体,即长花柱型,短花柱型和等花柱型。前两种表型交互的放置彼此的雌雄生殖器官,而等花柱型的柱头与花药等高,并均位于花冠管的口部。因此,以中甸灯台报春作为研究材料,能够很好的了解是什么样的环境压力选择植物进化出二型花柱这一性状,又是何种选择压力选择二型花柱向同型花柱进化。
通过5年的野外观察和研究,本研究的主要研究问题及结论如下:
(1)二型花柱的生态学适应性意义是什么?
目前关于二型花柱的适应意义主要的假说是达尔文提出的不对称传粉假说,即二型花柱是为了更好的实现不同表型间的传粉。为了验证这一假说,我们在自然居群中寻找柱头高度位于等花柱型和短花柱型之间的变异个体。这些个体仅仅在柱头的高度上具有连续变异,在雄蕊位置,花冠展幅和花冠管长度上都相对比较稳定。由于中甸灯台报春在野外只有两种花药的高度,即高花药(等花柱型和短花柱型)和低花药(长花柱型),而不同高度的花药所产生的花粉在大小上也能够显著的区分,即高位花药产生大花粉,低花药产生小花粉。因此,本实验通过检验这一系列柱头高度连续变异的个体在花末期柱头上的花粉来源,来衡量是否当柱头的位置越接近花粉供体花药所在的位置时,就能够相应的获得更多的来自于该供体的花粉。研究结果表明,受体的柱头靠近低位花药所对应的位置时,它能明显的获得更多的小花粉,而当受体的柱头接近高花药的位置时,它能获得更多的大花粉。由此,验证了达尔文的不对称传粉假说,即二型花柱交互的在不同表型间放置彼此的雌雄器官能够更好的实现在表型间的不对称传粉。
(2) 二型花柱为什么会向同型花柱进化?
二型花柱向同型花柱的转变,核心的变化在于交配方式发生了转变。通过二型花柱的崩溃,进而过渡到自交的同型花柱,实质上是植物由异交向自交的转变过程。本实验通过比较同一个居群内的二型个体(包括长花柱型和短花柱型)和等花柱型个体的主动自交能力,繁殖成功和自交衰退程度,从而了解在缺少传粉者的生境下自交是否能够给中甸灯台报春的等花柱型个体提供繁殖保障作用。结果表明等花柱型个体在野外生境中明显具有更高的自然结实,即等花柱型的主动自交能力要显著的高于同一居群的二型个体,这表明自交给等花柱型个体提供了较强的繁殖保障作用。同时,研究并未发现等花柱型个体有很严重的自交衰退现象,这意味着,中甸灯台报春的等花柱型个体由于具有较强的繁殖保障能力而在缺少传粉者的生境下具有更高的繁殖成功,这也可能就是等花柱型个体能够广泛的分布于各个居群中的原因。
(3) 当异交的二型花柱型转变为自交的同型花柱型后,相同环境是否会对植物造成不同的选择压力?
自然界中某些植物在物种内部存在有许多性状的变异,如花的颜色,大小和数目,然而并非每一个性状的改变都会强烈的影响植物的适合度。二型花柱,作为一个关键的花部性状,深刻的影响着植物的交配方式,当二型花柱进化到同型花柱后,意味着植物的交配方式从异交进化到了自交。而交配方式的改变必然会对植物的繁殖适应性造成不同程度的选择压力。当二型花柱发生改变后,植物其他的相关性状,如花的数目,开花时间和花序结构,受到的选择压力是否会相应的发生改变?为了回答这个问题,本实验首先测量了中甸灯台报春花序内的资源分配模式,确定了花序基部所获得的资源最多;之后,测量了中甸灯台报春位于林芝县鲁朗地区和波密县嘎瓦隆山的两个居群所受到的选择压力,并挑选三个性状来进行表型选择分析,分别是第一轮花序的开花数,开花时间和总的开花数。通过比较异交个体和自交个体所受到的传粉者介导的选择压力。揭示了中甸灯台报春位于生态站的异交个体受到了传粉者介导的对开花时间和花数目的正向关联选择,以及对开花时间和第一轮花数目的负向关联选择。这表明异交个体在自然界中倾向于在早花期将较少的资源投入到第一轮,而在末花期投入较多的资源到第一轮。除此之外,在生态站居群的异交个体倾向于被传粉者选择而晚开花,而在波密的自交个体倾向于早开花。
综上所述,本论文通过一系列操控实验证明了二型花柱能够有效的促进不同表型间的对称传粉,然而,在缺少传粉者的生境下,二型花柱却不能够有效的保障植物的有性繁殖。自交的等花柱型如果在居群中出现,由于其主动自交能够给等花柱型个体提供繁殖保障,二型花柱将有可能会被选择逐渐向自交的同型花柱进化。当一个二型花柱植物完成向同型花柱的进化后,它所受到的选择压力也会相应的发生改变,这种改变更多的是因为交配方式发生了变化。由于二型花柱是完全异交,因此它对于所处生境的传粉限制将会更加敏感。两种交配方式的个体所被选择的强度和方向会有所不同,具体的选择压力改变表现为:一方面,异交的二型花柱个体倾向于晚开花,而自交的等花柱型个体更倾向于早开花;另一方面,异交的二型花柱会倾向于在早花期将较少的资源投入的第一轮,而自交的等花柱型则没有相应的选择压力。
 
 
关键词:中甸灯台报春,二型花柱,同型花柱,不对称传粉假说,繁殖保障假说,传粉者介导的选择作用,自然选择
 
Other AbstractThe reproductive organ of angiosperm has a variety of designs, for examples, more than 250 thousands species of plants are exhibited in the world. Most plants are similar in the leaf, root or stem shape. However, the flower, i.e., the reproductive organ of angiosperm, has an extremely diversity in the color, design, size and chemistry compound. For a long period, plant evolutionary scientists consider the flower being closely correlated with the pollination environment.
Distyly is a typical stylar polymorphism among the plants, it widely distributed in at least 28 families of angiosperm and characterized by a population simultaneously possessing two flower morphs, i.e., long-styled morph and short-styled morph, and these two floral morphs reciprocally place the anther and stigma. Most distylous species are accompanied with a self- and intra-morph incompatibility system, that is, only the mating between different morph of a distylous species can generate fertilized offsprings; otherwise, the mating within the same morph or same plants could not produce fertilized seeds. Distyly is one of the most typical flower traits that significantly promote cross-fertilization. However, distyly is not evolutionary stable, which may evolve to self-fertilized homostyly through the gene recombination occurring in the supergene that controls distylous syndrome.
Many studies focus on the evolution of distyly by molecular method within a genus. However, we could not understand clearly how a key flower traits of the plant was shaped if we do not know exactly the environmental condition that shaped distylous syndrome. The focusing species, Primula chungensis, is a tri-morph species that is simultaneously with distylous and homostylous individuals, which indicates that Primula chungensis is undergoing the evolutionary transition between distyly and homostyly. With the aid of this species, we can easily find out the ecology factors concerned with the transition from distyly to homostyly. Meanwhile, by measuring the selection pressure on the distylous and homostylous individuals in a population, more knowledge about the divergent selection on plants with different mating patterns would be found
 
  1. What is the evolutionary significance of disytly?
Until now, two hypothesis were proposed for the function of distyly, the most accepted hypothesis is the disassortative pollination hypothesis proposed by Charles Darwin, who claimed that the reciprocal herkogamy of distylous species is developed for better transferring pollen between morphs of a population. We aimed to examine this hypothesis with the aid of Primula chungensis. We found some variants that vary in the length of style in the field, those variants display the style length between homostylous and short-styled individuals. Therefore, the homostylous, shortstylous individuals and those variants were selected to construct a variation that sequentially varies in the length of style. The anthers differing in the height in a flower tube and differ in the pollen size. The high anthers located at the mouth of the flower tube and produce big pollen, the low anthers located at the middle of the flower tube and produce small pollen. This experiment provides evidence that the stigma has more pollen grain from the pollen donor as it matches the position of the anther of pollen donor, which would be a novel approach to examine the disassortative hypothesis.
  1. Why should distyly be selected to evolve to homostyly?
The core of the transition from disytly to homostyly is the evolutionary shift from cross-fertilization to self-fertilization. Two main hypothesis that were proposed for the evolution of self-fertilization. One is automatic selection hypothesis, and the other one is reproductive assurance hypothesis. Until now, the reproductive assurance hypothesis is more widely accepted. We aimed to reveal the question from the perspective of reproductive assurance. We compared the reproductive success, the capacity for the autonomous selfing, the degree of self-depression between the distylous and homostylous individuals in one population. The results indicate that the homostylous individuals have a better reproductive success than the distylous individuals within a population, and the capacity of autonomous self-fertilization of the homostylous individuals is stronger than the distylous individuals, meanwhile, the homostylous individuals did not show significant inbreeding depression. Consequently, we could reasonably reach the conclusion that self-fertilization provides reproductive assurance for the homostylous morph in the field, which is probably the reason why distyly is selected to evolve to homostyly.
  1. Will the selection pressure change if distyly, breaks into homostyly?
In order to answer this question, I measured the pollinator-mediated selection on the distylous and homostylous individuals located at ecology station, Chinese academy of science, and the Gawalong Mountain, Bomi County. Three traits were collected in each experimental set, i.e., the flowering time, the number of flower of each inflorescence and the flower production of the first whorl of an inflorescence. We compared the selection pressure between the morph in the same population, and compared the selection pressure between the self-fertilized morph in population ES and those in population BOMI. Our results showed that the flowering time of the cross-fertilized morph was under positive pollinator-mediated selection in population ES, which indicated that the cross-fertilized morph was favored to be later flowering in population ES. However, the flowering time was favored to be earlier flowering for the self-fertilized morph in population BOMI. Meanwhile, a negative correlational selection was found between the flowering time and first whorl flower production, which indicated that the less flower production was favored for the plants that flowering early, while more flower was favored for the plants that flowering late. Our result proved that the mating pattern greatly affected the strength and direction of the selection pressure on flowering time, flower number and first whorl flower production.
 
We proved that distyly can significantly promote the pollen transfer between the morphs of a population. However, distyly is unable to ensure the reproduction of plants in a pollination-limited habitat. Therefore, distyly is selected to evolve to homostyly mostly because homostyly could provide efficient reproductive assurance for the plants in a pollinator-limited environment. We demonstrated that the selection pressure on the flower traits would change if the distyly has already broken into homostyly. A large proportion of this change is accounted by the alteration of the mating pattern. Distylous species is obligate cross-fertilization, while homostylous species is predominantly self-fertilization. Thus, the cross-fertilized distylous morph are more sensitive to the pollination service in the field. Our results indicated that cross-fertilized distylous morph was selected to be later flowering, while the self-fertilized morph was selected to be earlier flowering.
 
 
Key words: distyly, homostyly, disassortative pollination hypothesis, reproductive assurance, phenotypic selection, pollinator-mediated selection
Language中文
Document Type学位论文
Identifierhttp://ir.xtbg.org.cn/handle/353005/10698
Collection西双版纳热带植物园毕业生学位论文
Recommended Citation
GB/T 7714
蒋 显 锋. 中甸灯台报春(Primula chungensis)的繁殖生态学研究[D]. 北京. 中国科学院研究生院,2017.
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