亚雌雄异株植物柃木的繁殖特性及其进化意义研究

Plants show diverse and complex sexual expression, and mixture of individuals bearing various combinations of female, male, and hermaphrodite flowers are observed within a population. The majority of flowering plants are hermaphroditic and empirical evidence indicates that production of only perfect flowers is the ancestral condition in angiosperms. Dioecy is found in 5-6% of angiosperms across a broad range of plant families, and thus dioecy is thought to have evolved repeatedly. For the evolution of dioecy from hermaphroditism, many researchers have focused on ecological and genetic aspects of the evolutionary pathway towards dioecy via gynodioecy, however the complete picture of the gynodioecy–dioecy pathway (G-D pathway, as below) remains unclear due to insufficient research on the latter stage of the pathway. Subdioecy is a sexual system in which females, males and hermaphrodites coexist in a population, and is thought to occupy the latter position in the G-D pathway. Because reproductive success is thought to play an essential role in the evolution of individual’s sex expression, studies on reproductive success in subdioecious plants are needed to elucidate the G-D pathway. Another approach to explore the factors promoting the evolution to dioecy via gynodioecy is to examine the plasticity in sex allocation or sex expression (sex change) and to determine the conditions where females, males, or hermaphrodites are preferred. On the other hand, sex change may hinder subdioecious plants from moving to complete dioecy. The aims of this study were to determine the reproductive successes through male functions and to clarify the pattern of sex change in subdioecious Eurya japonic, in order to examine the G-D pathway. The female reproductive success was already compared between female individuals and hermaphrodite individuals sugguseted that females had advantages in female reproductive success: females had higher fruit set, and produced heavier fruit and more seeds with higher germination rates than hermaphrodites. Therefore, first, the siring success will be assessed in hand-pollination treatments with single pollen and mixed pollen from males and hermaphrodites. Secondely, the factors affecting the occurrence and the pattern of sex change will be explored. Finally, we will summarize expected results and discuss the evolutionary implication of subdioecious E. japonica in the context of pathway from hermaphroditism to dioecy via gynodioecy.

被子植物的性表现多样而复杂，是支配下一代繁殖成功的重要特征，繁殖成功也对性表现的进化起重要作用。种群中同时存在雌性个体、雄性个体和两性个体的亚雌雄异株种类约占3%，这种性型属于从雌雄同体到雌雄异株进化路径的后期阶段，其维持机制和进化意义尚不明确。目前对植物性表现的进化研究主要集中于这种进化路径的前期阶段。另外，性表现因各种因素影响会发生变化，这种性转换现象影响种群的性别比率，对性系统的进化发挥重要作用。以亚雌雄异株植物柃木为研究对象，通过野外调查、室内栽培和遗传实验对柃木的雄性繁殖特性进行研究，并通过研究种群的性转换模式和性别比率的波动，阐明性转换发生的起因及对种群的进化所产生的影响。通过以上的研究，结合柃木雌性繁殖特性，探讨柃木繁殖特性的维持机制及其在进化上的意义，从而进一步对亚雌雄异株植物由雌雄同体性到雌雄异株性的进化特性综合分析和推论。

植物的繁殖特性对于植物的进化起重要作用。被子植物的性别表现复杂多样，种群中同时存在雌性个体、雄性个体和两性个体的亚雌雄异株植物作为一个重要类群，目前此类种群的维持机制和进化意义尚不明确。同时，研究发现，性别表现受各种环境及自身因素影响会发生变化，这种性别转换现象影响种群的性别比率，对繁殖系统的进化发挥重要作用。.本项目以亚雌雄异株植物柃木（Eurya japonica Thunb.）为研究对象，通过野外实验（野外调查、人工授粉等）、室内观测、室内栽培（种子发芽率、幼苗成活率等）等实验手段，研究亚雌雄异株植物柃木的雄性繁殖特性及性转换机制。.在雄性繁殖特性研究中，我们采用人工授粉的方法，花粉分别来自雄性个体和两性个体，母本分别采用雌性个体和两性个体。分别测量了结实率、果实重、种子数、种子重，并比较了种子的发芽率及子代生长情况。结果发现，来自雄性个体的花粉授粉后产生的果实及种子的质和量及子代的生长情况都显著优于来自两性个体花粉授粉的个体。然而，这一特性只在以雌性个体为母本的实验中被发现，在以两性个体为母本的实验中没有显著性差异。.在性别转换机制研究中，我们采用野外调查及微环境观测的方法，对样地内个体性别转换情况进行了连续5年的观测。结果发现，性别转换呈现出单向或者双向转换模式。其中两性个体比雄性和雌性个体表现出更为活跃的转换频率。同时，虽然个体会发生较高频率的性别转换，但是柃木种群中雄性、雌雄及两性个体的比例相对稳定，始终维持在1:1:1。柃木的性别转换受到个体生理特性及周围微生态环境的联合介导。我们的结果表明，柃木是稳定的亚雌雄异株植物。.本研究结合前期雌性繁殖特性的研究成果，探讨亚雌雄异株植物繁殖特性的维持机制，形成较完善的研究模式并用于其他类似种类的研究，为植物进化研究提供新的思路和理论依据。