冰期抑或间冰期避难所：山地植物鸡肫草谱系地理学研究

The chronology of lineage splitting is important for developing a testable hypothesis because it reveals causal mechanisms and forces behind diversification processes. To better understand the evolutionary history of the rich flora of China, phylogeography has been one major focus of evolutionary biology in China during recent years. However, being deeply influenced by the concept of Quaternary glacial refugia and postglacial recolonization, most phylogeographic studies in China often quote the Quaternary glaciation as the causal effect on shaping population divergence, but rarely considered the interglacial/postglacial refugia. More importantly, seldom is there time calibration to support this hypothesis of glacial refugia. In this study, we select a cold-adapted plant species, Parnassia wightiana with a disjunct distribution range in China-Himalaya floristic region to test the hypothesis that cold-adapted montane plants at low latitudes could have interglacial/postglacial refugia rather than glacial refugia. For the purpose, we plan to collect population samples across its distribution range. Then chloroplast markers and about ten nuclear loci will be employed to examine the phylogeographic pattern. In particular, population divergence time will be calculated by means of IMa. Through these efforts, we’d like to find robust evidence of interglacial/postglacial refugia for cold-adapted montane plants at low latitudes of China. The results of this project will provide a framework for the conservation cold-adapted montane plants of china in the context of global warming. In addition, the results will shed lights on the evolution and biogeography of Parnassia.

第四纪避难所是植物谱系地理学研究的主要内容之一。按时间尺度，第四纪避难所可分为冰期避难所和间冰期避难所。然而，我国现有大部分植物谱系地理学研究只考虑冰期避难所，很少有人考虑到间冰期避难所。更为重要的是，大多数此类研究没有群体分化时间的估算，冰期避难所的观点难以被证实。本研究选取中国—喜马拉雅特有种鸡肫草（梅花草属），该物种性喜冷凉气候且呈间断分布格局，这种格局极有可能是间冰期（冰后期）“避难”的结果。我们采用叶绿体和核基因多个基因位点，在研究其谱系地理格局的同时，采用IMa等方法计算群体分化时间，为推测该植物第四纪分布区变迁模式提供精确时间尺度。本研究结果可以确认中国山地喜冷（凉）植物间冰期避难所的存在，为全球气候变暖背景下此类植物的保护提供重要理论依据；另外，研究结果对于理解梅花草属的演化和地理分布也有重要的启示。

对我国许多山地喜冷植物来说，冰期扩张—间冰期收缩已被古孢粉资料所揭示，但是并没有给出较为详细的迁移模式。本研究选用中国—喜马拉雅地区山地喜冷植物鸡肫草为研究对象，解析山地喜冷植物冰期间冰期的种群迁移方式。本实验采用基于叶绿体和核基因序列，对38个居群458个鸡肫草个体进行谱系地理学分析。结果表明鸡肫草群体遗传多样性较高，主要原因可能是第四纪冰期间冰期鸡肫草分布区变化不是很大。鸡肫草遗传分化不明显，可能是鸡肫草祖先单倍型H1很早扩散至各个群体，后又经历了种群片段化。本研究可以推测鸡肫草种群经历了多次扩张收缩事件，因为数据分析中没有加入化石节点，此假说还需要进一步验证。通过对植物标本室标本(包括标本类型)和现存鸡肫草植物的研究，以及对原植物种类和分布的分析，我们发现，在印度北部、中国南部和泰国北部广泛分布的城口梅花草(Parnassia chengkouensis)和宽叶梅花草(P. dilatata)与鸡肫草(P. wightiana)是同一种植物。因此，这两种植物并入鸡肫草P. wightiana中。谱系地理学研究两种植物已经包含在内。

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