同域分布桑寄生物候异步性的生态意义

In the seasonal tropics most plants flower in the rainy season, aggregated flowering of different species within plant communities is common; however, sympatric mistletoes in Xishuangbanna have flowering asynchrony which is rarely found in other plants. We hypotheses that phenological highly asynchrony is the results of adaptation to their specialist pollinators and seed dispersers of flowerpeckers. To test this hypothesis, we use 5 most common mistletoe plants (Loranthaceae) in Xishuangbanna, firstly the floral characteristics, pollination system, reproductive success, herbivory effect, seed dispersal, and the mutualism with birds during their flowering and fruiting periods will be comparative investigated. Reproductive ecology will be conducted among sympatric mistletoe species which flowering phenology overlapped to probe into the mechanisms of interspecies reproductive isolation at the same time. Secondly, we will reconstruct the phylogenetic trees of mistletoes, related birds and detect genetic differentiation among populations with molecular phylogeny and SSR methods to probe into the evolutionary history of sympatric mistletoes. Thirdly the related birds ecology, food structure and reproductive timing also will be studied to discuss the mutualism relationship between mistletoes and birds. Finally, we will analyze asynchronous phenology in relation to spatial variation in climatic seasonality combining with climatic data. The results will help us better understanding the ecological adaption and evolutionary trend of flowering phenology, and will provide a new study case for plants modulate their flowering and fruiting phenology to adapt their mutual animals.

在气候季节变化明显的热带地区，许多植物都在雨季开花，植物群落中同一类群的不同植物通常具有同步开花的物候，而西双版纳同域分布的桑寄生植物则表现出种间物候高度的不同步性，这可能是桑寄生植物为了适应专性传粉和种子散布者啄花鸟的结果。为验证这一假说，本研究以西双版纳分布的最常见的5种桑寄生植物为对象，通过对它们的花部特征、传粉系统、繁殖成功率、植食作用、种子散布等繁殖生物学特性研究，了解同域分布的桑寄生植物物候异步的生态适应性及其种间隔离机制；运用分子系统学和谱系地理学的分析方法，构建桑寄生同域分布物种的演化历史过程和种群遗传分化；研究相关鸟类生态习性、食物结构和繁殖物候，探讨鸟类与桑寄生互惠关系紧密程度；最后结合微环境气候因素分析气候季节性与繁殖物候的相关性，探究桑寄生物候异步性是否是对环境变化的适应。研究结果将为植物通过调整开花结果物候适应互惠动物一个新的案例。

寄生植物繁殖物候的研究对了解“寄主植物-桑寄生植物-传粉/种子散布者系统”中物种相互作用网络的维持机制、生态系统结构的稳定性具有重要意义。通过4年的研究，在以下方面取得进展：.（1）综述了桑寄生在景观、群落和种群尺度上繁殖物候的表现类型，发现桑寄生主要通过繁殖物候异步方式延长物候期，维持与传粉/种子散布者持久的互惠关系以保障自身种群的繁衍。.（2）通过详细的野外调查，弄清了西双版纳桑寄生与寄主植物多样性及分布特点，相比于上世纪八十年代，桑寄生-寄主网络在物种组成和网络结构上都发生了变化，桑寄生物种多样性下降，繁殖物候短的桑寄生消失风险更大。.（3）进一步采用13对SSR标记对四个种群76个亲本和829个子代个体进行异交率检测和传粉生物学研究，结果表明自交亲和且高度聚集的五蕊寄生种群保持高水平异交，这可能是由于无主动自交机制、雌雄异熟或其他限制自交的因素以及传粉及种子散布鸟类的行为所致。.（4）采用无线电追踪技术研究拜访鸟类行为，结果发现其活动范围较小，果色鲜艳的五蕊寄生吸引众多鸟类为其散布种子，而澜沧江寄生果色暗淡且果期与五蕊寄生花期重叠，导致大量果实无法散布，这可能是五蕊寄生更为泛性的原因之一。.（5）监测了勐仑、勐养及象明等三地8块样地中所有桑寄生及寄主植物2年的繁殖物候，结果表明五蕊寄生和鞘花都具集中大量开花模式，种内繁殖物候在群落和种群尺度都存在一定的异步性；种间繁殖物候在样地尺度有所错开；五蕊寄生的始花期受寄主种类、寄主胸径和寄生冠幅的影响；鞘花的花期受寄主高度的影响。在大尺度上寄主特异性的高低对桑寄生繁殖物候异步性的影响不大。.（6）利用叶绿体基因组重建桑寄生的系统发育树，结果表明鞘花、梨果寄生和槲寄生三个属的系统发育关系较以往研究一致，槲寄生属是最近发生的。.研究结果为认识同域分布桑寄生物候异步的生态适应性及其种间隔离机制，以及植物通过调整繁殖物候适应互惠动物提供可靠数据和新的案例。