【作者】 田新民；

【导师】 刘建全；

【作者基本信息】 兰州大学 ， 生物地理学， 2011， 博士

【摘要】 翅果蓼属(Parapteropyrum)是青藏高原特有的单种属,该属与分布于中亚地区的木蓼属(Atraphaxis)、沙拐枣属(Calligonum)以及双翅蓼属(Pteropyrum)起组成蓼科(Polygonaceae)木蓼族(Atraphaxideae)。尽管翅果蓼属与该族其它三个属的地理分布区相隔很远,但是由于翅果蓼适应生存于干旱河谷地区的木质化灌木生存状态,以及在形态学上与木蓼族植物的若干相似性状,植物分类学家长期以来都一致地把它归入到木蓼族中,并认为与该族中的双翅蓼属有很近的亲缘关系。近期分子系统学的研究表明,翅果蓼与荞麦属有很近的亲缘关系,在分子系统树中与荞麦属聚为一支。然而翅果蓼确切的系统位置仍然模糊不清,其起源进化问题有待进一步深入的研究。本文通过细胞染色体、分子系统学等研究手段对翅果蓼的系统位置、起源进化等问题展开深入的研究和探讨。细胞染色体的研究证据表明,木蓼族各属的染色体总数和基数完全不一致,核型类型也存在明显差异：翅果蓼的染色体总数是2n=48=16m+16sm+16st,核型属于2B型,对称性很低；木蓼属两个种(东北木蓼,沙木蓼)的染色体总数都是2n=22=22m,核型属于1A型,对称性相当高；沙拐枣属的染色体总数为2n=18或者36。在已报道的分布于青藏高原及其周边地区的蓼科植物中,只有荞麦属的染色体基数X=8(2n=16或32),与翅果蓼相同。进一步通过核糖体DNA的内转录间隔区(ITS)和叶绿体片段rbcL、accD以及两套序列联合分别构建的系统发育树表明：木蓼族不是一个单系群；翅果蓼属与该族的其它三个属存在较大的遗传分化,而是深嵌于荞麦属(Fagopyrum)中,并以很高的支持率与荞麦属的一支形成姊妹群。形态学上,翅果蓼与荞麦属植物在几个主要的形态特征上也有非常大的相似性：总状花序,花被片5、深裂,8个雄蕊排成内外两轮(5个在外轮,3个在内轮),头状柱头3,三棱形的瘦果。综合形态学、细胞学以及分子系统学的证据,翅果蓼不能归入木蓼族中,应撤销其属级分类地位,并入到荞麦属中。通过分子进化速率标记的分化时间表明：翅果蓼与荞麦的分化时间大约发生在6.35-14.8百万年之间。这个时间段(尤其在15-13百万年和8-7百万年)正是青藏高原隆升的重要时期。我们推测第三纪中新世以来,由于青藏高原的强烈隆升,同时伴随着气候的剧烈变化,高原生境发生了严重的破碎化。在这种情况下,辐射式物种形成和趋同进化成为青藏高原物种形成和进化的主要方式。为了适应不断变化的环境和气候,提高自身的适合度,防止由于地理隔离而导致的近交衰退,翅果蓼从草本的荞麦属中分化出来,进化出了木质化的茎。因此,岛屿木质化这(insular woodiness)一岛屿特有的物种进化方式在青藏高原这个内陆大岛屿上也存在。另外,翅果蓼这样一种木本荞麦作为一种新资源将会在以后的种质资源开发应用中扮演重要的角色,这在解决日益严重的粮食危机方面可能有重要的应用意义。更多还原

【Abstract】 Parapteropyrum, a monotypic shrubby genus with the only endangered species endemic to the arid valleys of the central Qinghai-Tibetan Plateau (QTP), was universally placed in the Atraphaxideae because of their shared morphological traits although the other woody species of this tribe occurred mainly in the central Asia. It is suggested that Parapteropyrum is closely related to the small genus Pteropyrum based on morphological traits. However, recent molecular phylogenetic studies suggested that Parapteropyrum is closely related to Fagopyrum. The accurate position of Parapteropyrum is still uncertain and further research works are still needed to clarify the origination and evolution of this monotypic genus. In our studies, the karyological data show that the chromosome number and karyotype of P. tibeticum are formulated as 2n=48=16m+16sm+16st, belonging to 2B type. Both Atraphaxis manshurica and A. bracteata have the same chromosome number of 2n=22 and similar karyotypes (22m, belonging to 1A). The basic chromosome number of another genus (Calligonum) of the Atraphaxideae is x=9 (2n=18 or 36). Across the published karyological data of Polygonaceae that occurred in the QTP or adjacent areas, only Fagopyrum (2n=16 or 32) shares the same basic chromosomes with Parapteropyrum. We studied sequence variations of the nuclear internal transcribed spacer (ITS) and chloroplast DNA (cpDNA; rbcL and accD) for this genus and the other ten related genera of the Polygonaceae occurred in the QTP and adjacent areas. The constructed phylogenies based on ITS, cpDNA or a combination of both datasets suggested that currently recognized tribe Atraphaxideae is polyphyletic. The woody Parapteropyrum nested deeply within the herbal Fagopyrum and it showed no any relationships with the other genera of the Atraphaxideae. Morphologically, many common characters were also shared by Fagopyrum and Parapteropyrum:racemous inflorescence,5 deeply lobed perianth, stamens 8 (5 outer,3 inner), styles 3 with head-like stigmas, triangular achenes. Totally, the karyological, genetic and morphological evidences all suggested that shrubby P. tibeticum has derived from herbal Fagopyrum. Our results suggested that Parapteropyrum should be reduced and its only species should be incorporated under the genus Fagopyrum. Molecular datings revealed that this woody species probably originated between 6.35 and 14.8 million years ago (Mya). Meanwhile, during this stage, geological evidence suggested that the Qinghai-Tibetan Plateau had extensively uplifted, especially between 15-13 Mya and 8-7 Mya. The high species diversity in the QTP was suggested to result mainly from radiative diversification and convergent evolution of plants because of the rapid plateau uplifts and the dramatic climate change. These results together suggested that the large-scale QTP uplifts since the Miocene promoted not only extensive speciation in this region, but also the secondary acquirements of woodiness in a few herbal lineages under the strong counter-selection of inbreeding depression because of the geographical isolation. It is confirmed that insular woodiness has also happened in the QTP as occurred in most islands and its evolutionary significance is also discussed in detail. In addition, the confirmation of this woody species within Fagopyrum further implies its possible usage as an important buckwheat resource because of the rising food crisis.更多还原