克隆生长对植物交配系统的影响

Clonal growth is widespread among angiosperm species, so many plants have a mixed reproductive strategy of both sexual and asexual reproduction. Clonality has been suggested to negatively impact aspects of sexual reproduction, especially mating patterns. Importantly, clonality could reduce female fitness, owing to among-ramet self-pollination (geitonogamy), especially in species with clumped ramets that display many flowers simultaneously. However, most previous studies compared the effects of variation in clone size, rather than between clonal and non-clonal individuals with the same resource investment in floral display. . Our recent paper suggested a novel mechanism for the evolution of clonality in clumped clonal plants. Pollinators often visit fewer flowers on plants with multiple ramets than on plants with a single inflorescence with the same total number of flowers. As a consequence, clonality can promote pollination quality without increasing geitonogamy when flowers simultaneously receive and donate pollen. Besides, there is growing evidence that the accumulation of somatic mutation may result in lower fitness of autogamous offspring than geitonogamous offspring; hence clonality may reduce the cost of selfing because of the dominance of geitonogamy in clonal plants. Therefore, it would be worthwhile and important to conduct experimental studies to test the above two hypotheses for the evolution of clonality.. Here, this project aims to test the new hypotheses and try to reveal the consequences of clonal growth on plant sexual reproduction, especially on mating system by addressing the following four questions. First, to compare the fitness between clonal and non-clonal growth forms, we will tie two or three ramets together to produce a single large inflorescence in a natural population of Aconitum kusnezoffii, and estimate the female and male reproductive success based on SSR multilocus genotypes of each chosen seed. Second, we will choose an isolated natural population of A. kusnezoffii, record the male and female phase duration of each flower, calculate the seed set of each collected fruit, and perform the paternity analysis to evaluate the potential effects of geitonogamy on male and female fitness. Third, we plan to choose two populations in shaded and two in sunny environments, observe the pollinators visiting behavior, measure the nectar volume, and estimate the selfing rate and inbreeding depression to reveal the ecology of geitonogamy in clonal plants. Finally, we will conduct literature research and empirical studies to evaluate the effects of accumulation of somatic mutation on fitness of clonal plants, particularly, on the comparisons of fitness between autogamous and geitonogamous pollination.. This project will provide hard evidence for the consequences of clonal growth on plant mating systems and inbreeding depression, and hence, will provide novel and valuable insights on the evolution of clonality in phalanx clonal plants.

克隆生长是被子植物最常见的无性繁殖方式，其生态和进化意义受到了广泛的关注，但对有性繁殖的影响尚缺乏系统的认识。先前的研究多认为克隆生长会增大同株异花自交并降低植物的适合度。但是，最新的理论进展表明克隆生长反而会降低同株异花授粉并提高传粉质量；体细胞突变累积理论也表明同株异花自交后代的适合度可能大于花内自交，因而克隆生长能降低近交衰退带来的适合度损失。因此，本项目拟针对克隆生长机制的最新理论进展，以密集型克隆植物草乌为研究对象开展实证研究。结合分子标记技术与野外实验，通过亲本分析的手段衡量同株异花授粉对雌性和雄性适合度的影响，比较克隆与非克隆生长方式的适合度差异，估计不同生境下自交率的变化；开展人工授粉试验评估体细胞突变累积对适合度的影响。从同株异花授粉和体细胞突变累积两个方面，全面解析植物克隆生长对交配系统的影响，进一步丰富和完善对克隆生长习性进化机制的认识。

克隆生长是被子植物最常见的无性繁殖方式，其生态和进化意义受到了广泛的关注，但对有性繁殖的影响尚缺乏系统的认识。本项目以密集型克隆植物草乌为研究对象，利用人工捆绑花序操作构建大花序，发现在花总量保持一致的情况下，克隆生长将等量花朵分散在若干分株上的花资源空间配置模式提高了对传粉者的吸引力，访花频率平均提高了50%，同时传粉者单次访花数量占克隆总花数的比例降低了13%；如果花朵同时接收和输出花粉，这种现象可以降低植株内同株异花授粉的发生几率。当每株植株每天产生超过40朵花时，草乌自交率显著提高，但提高花展示水平对花粉输出的影响不如增加开花分株数量明显，雄性阶段花朵比例的增加在提高自交率的同时降低了花粉输出。不同环境中克隆生长对同株异花授粉的影响研究表明，光照强度较弱的种群中草乌的花展示水平与传粉者数量显著降低，生活在郁闭环境中的草乌比生活在开放环境中的个体增加了超过50%的花蜜产量，通过提高传粉者回报的方式提高了传粉者访花比例及访花时长，并最终导致郁闭环境中草乌结籽率较开放环境提高了5%，种群水平和家系水平的自交率都显著增加。人工授粉实验评估体细胞突变累积对草乌交配系统的影响结果表明，长期的克隆生长可能由于累积了大量体细胞突变，降低了配子尤其是雄性配子的数量及活力，胚珠数量虽然没有表现出随克隆大小上升的下降趋势，但是作为母本时植株繁殖成功率却同作为父本时一样表现出了显著的下降。同时，克隆内部的体细胞突变累积通过严重的近交衰退降低了近距离同株异花自交的繁殖成功率，使得花序内同株异花自交结籽率比远距离花序间同株异花自交降低了20%。本论文为植物克隆生长习性进化的新机制提供了部分数据支持，揭示了随开花进程自交率先增加后降低的模式以及生态因子对克隆植物交配系统的影响；基于体细胞突变累积，提出分株间同株异花授粉导致的近交衰退程度低于花内自交或分株内同株异花自交；系统解析了克隆生长对植物有性繁殖的影响。