极小种群野生植物滇桐在破碎化居群中的交配系统及更新能力研究

Of the relict genus Craigia, widespread in the Tertiary, only two species survived to modern times in South-east Asia: Craigia yunnanensis and C. kwangsiensis. The last one is now possibly extinct and the other one, C. yunnanensis (national second-class protected plant), was found to be severely endangered due to environment destruction. Extensive surveys have located only six small populations of C. yunnanensis in Yunnan province, south China.. Spatial isolation within the population, induced by habitat fragmentation, can cause serials reproductive barriers, which will adversely impact on the regeneration and adaption of a species, including: pollen limitation, decrease of seed production resulted from self-incompatibility and inbreeding depression resulted from increase of selfing, et al. Previous investigation and research of C. yunnanensis have indicated that the reproductive efficiency varied in populations which suffered different degrees of fragmentation and individual isolation, and that pollination is a weak link for C. yunnanensis in the reaction of habitat destruction. The SSR (Simple Sequence Repeats) will be employed to study the variation of mating system in three populations of C. yunnanensis, which are under different levels of fragmentation, in order to analyze the impact of human disturbance on the process and the pattern of pollen dispersion, and also the impact on genetic structures between generations. Together with the investigation of reproductive viabilities, the regeneration of three populations will be evaluated. Through the reproductive depression that was caused by reduction or isolation of fertile individuals, the endangering mechanism of C. yunnanensis will be also discussed. This research could give scientific implications for in-situ conservation and renewal of C. yunnanensis.

滇桐属曾在第三纪广泛分布，现代仅在亚洲东南部残存两个分布狭窄的种：滇桐与桂滇桐，是一孑遗属。其中桂滇桐可能已野外灭绝。因生境破坏，滇桐（国家二级保护植物）目前仅在云南省残存六个小居群，被列入国家极小种群野生植物。. 生境破碎导致的居群内空间隔离增加，会引发一系列不利于物种更新及适应环境变化的繁殖障碍，如：花粉流限制、自交不亲和导致种子产量下降、自交率提高导致近交衰退等。根据前期调查和研究，破碎化及成株隔离程度不同的滇桐居群在繁殖效率上存在差异；传粉过程是滇桐应对生境破坏的薄弱环节。本项目利用SSR分子标记，研究破碎化程度不同的三个滇桐居群内交配系统的变化，比较分析人为干扰对花粉流过程与式样的影响，及其造成的代继遗传结构差异；结合繁殖活力的测试，评估居群的更新能力；通过可育个体减少或隔离引发的繁殖衰退，探索滇桐的致濒机制。研究结果将为滇桐的就地保护和居群重建提供科学指导。

滇桐是国家二级重点保护野生植物，也被列为国家极小种群野生植物。其现存个体数量低于200株。大部分居群受人为干扰严重，居群内生境呈现破碎化和斑块化。项目通过检测三个滇桐代表居群的花粉流、居群的代继遗传结构和交配系统，探讨了生境破坏对居群更新产生的遗传影响，为种群回归提供理论依据。结果表明，滇桐的花粉流主要限制在200米以下，居群内自交率较高，符合其主要传粉昆虫的传粉特征。长距离传粉成为居群内隔离个体间的重要传粉补充。村舍、道路和开垦地对滇桐居群内个体间的传粉交流的影响并不显著，个体较少的居群虽然遗传多样性低，但子代遗传多样性并没有丧失。但是自交后代在幼苗后期生长量显著低于异交后代，杂种优势的发现可能预示了滇桐在生长环节仍不可避免的受到了交配系统的限制。项目结论是：滇桐居群被破坏后，如果居群个体数量下降，会导致自交率提高和居群遗传多样性下降。虽然这种小居群中的子代在一代的时间内没有观察到明显的遗传多样性下降，但是在传粉环节的高自交率会导致后代在幼苗建成期生长优势下降。一定程度的居群内斑块化隔离对传粉影响并不明显。揭示了人为干扰对滇桐居群更新能力的短期限制主要体现在个体数量减少通过交配系统对幼苗成长环节产生了负面影响。