瘿椒树雄性繁殖适合度及雄全异株种群维持机制

Androdioecy is a rare breeding system in which populations consist of both of male and hermaphrodite individuals. Functional androdioecy was once thought to be nonexistent because of the stringent and unlikely condition required for its evolution and maintenance. Howvever, androdioecy has now been identified in more than 10 plant species. It has been proposed to be a possible evolutionary pathway from hermaphroditism to dioecy. Investigating on the evolution and maintenance of androdioecy will help us to understand the evolution dynamics and evolutionary direction of the angiosperm mating system. Tapiscia sinensis (Tapisciaceae) is an ancient rare plant endemic in China, the fruits of which take nearly 17 months to mature. Therefore, its flowers and fruits coexist in the same individual. Our preliminary survey indicates that some Tapiscia population is purely androdioecy. We speculate that the evolution and maintenance of androdioecy in Tapiscia are due to synchronous developing of both flowers and fruits as well as habitat fragmentation. In this project, more than 10 populations of T. sinensis are chosen in natural habitat to assess their breeding system by investigating their gender expression and reproductive capability. Then, the pollen limitation and inbreeding depression will be estimated in the field by hand-pollinated and other pollination treatment, and the effect on male function by flower and fruit coexistence in the same plant will be assessed. Furthermore, we will apply paternity analysis to natural populations, using SSR markers to analyze the mating structure within the population, estimating the male reproductive success of males and hermaphrodites to understand how androdioecy is maintained in T. sinensis. Finally, we will try to inquire the role of androdioecy in the evolution of plant breeding system and the reason why the Tapiscia are endangered.

雄全异株是种群中雄性和两性个体共存，虽在自然界中罕见，但它可能是雌雄同花向雌雄异株演化的重要中间类型。雄全异株种群的演化和维持要求雄株具有明显的适合度优势，通过该繁育系统演化和维持机制的研究，对探明被子植物繁育系统进化动力和演化方向具有重要意义。我国特有的古老珍稀植物瘿椒树两性花与雄花异株，部分种群为功能性雄全异株。花与果实发育期重叠及生境斑块化，可能是该物种雄全异株演化与维持的主要因素， 本项目拟在瘿椒树分布区选择10个种群（或斑块），分析其性别表达特征和时空动态，评估其繁育系统类型及其与种群大小和性别比例相关性。在此基础上，研究种群内花粉限制、自交衰退，以及花果同期发育对雄性功能的影响，结合人工控制授粉和SSR分子标记的父本分析, 评估种群中雄性和两性雄性功能的适合度，检验我们的假说，阐明瘿椒树雄全异株种群的维持机制，揭示其濒危的原因，探讨雄全异株在繁育系统进化中所起作用。

瘿椒树（Tapiscia sinensis，瘿椒树科Tapisciaceae）为我国特有的第三纪古热带孑遗植物。种群中雄性和两性个体共存；两性株中果实越年成熟，呈现出4-7月间花果同期发育现象。本项目通过对瘿椒树开花生物学、性别表达特征的研究及亲本分析，发现两性株和雄株开花物候期一致，两性花雌蕊先熟、能产生可育的花粉、自交亲和，为风媒和虫媒混合传粉类型。雄株在花序长度、小花数目、花粉活力、适应风媒传粉等特征均表现出显著的雄性适合度优势。野生种群的父本分析也证明来自雄性父本的子代是来自两性株父本的1.6倍以上，为功能性雄全异株。同一生理整合单元的取果实验与花药糖代谢相关基因的表达分析表明，两性株花果同期发育引起了花与果实对繁殖资源竞争，导致两性花中分配给雄性的资源减少，雄性功能低下，同时为雄株的入侵和在两性种群中的维持创造了条件。不仅如此，瘿椒树花果同期发育而导致的两性株严重偏雌的性别分配，促成了瘿椒树由两性花的祖先向雄全异株的演化。