干旱荒漠区三种蜥蜴的比较谱系地理学研究

The arid desert region is a particular geographical unit in China, and it is also a key area of biodiversity of the arid areas in the world. It is very important to unravel the effects of its formation and evolution on genetic divergence and historical population dynamics of arid-adpated species endemic to this region. A model of range expansions during glacial maxima (GM) for cold-adapted species is generally accepted for the Northern Hemisphere. Given that GM in the arid desert region resulted in the expansion of desert rather than glaciations, it could be expected that arid-adapted species might have had expanded ranges at GM and contracted ranges at interglaciation, as cold-adapted species did in the Northern Hemisphere. On the basis of previous studies, three co-distributed and typical arid-tolerant lizards, i.e., Phrynocephalus axillaris, Eremias vermiculata and Teratoscincus przewalskii, are chosen to study the shared historical demographies across the arid desert region, and to explore the ways in which historical geological and climatic events have influenced local adaptation and diversification of populations. We will trace the evolutionary history of populations by combining genetic (mitochondrial and multiple nuclear DNA loci and microsatellite markers) with environmental data, and using integrative phylogeographical analyses such as ecological niche modeling and approximate Bayesian computation. Our objectives are (i) to test alternative GM expansion model; (ii) to explore the relative contribution of environmental isolation (caused by mountains and oases) versus geographical distance to the observed genetic divergences occurring among populations within a species; and (iii) to assess the concordant or nonconcordant phylogeographical patterns by testing hypotheses of shared evolutionary history among the co-distributed lizard groups. The results of this study will add new information to a more comprehensive understanding of how climatic oscillations in the Quaternary and the aridification of Arid Central Asia affected shifts in species’ distribution, and can also provide new clues to explore the evidence of shared biogeographical processes at the community level.

干旱荒漠区是我国特殊的自然地理单元，也是世界干旱区生物多样性的关键区域。揭示其形成与演化对旱适应物种的遗传分化和群体动态的影响具有重要意义。冷适应物种分布区在冰盛期扩张而在间冰期收缩的模型通常被接受。鉴于干旱荒漠区在冰盛期沙漠面积扩张，推测耐干旱物种的分布区符合冰盛期扩张模型。本项目拟选择该区域广泛分布的三种典型的耐干旱蜥蜴（叶城沙蜥、虫纹麻蜥和西域沙虎）为对象，利用野外调查取样，联合遗传（线粒体、核DNA序列和微卫星标记）和环境数据，运用整合的谱系地理学和生态位模型的理论和方法来重建基因谱系的时空格局、追溯种群的进化历史。既检验冰盛期扩张模型，又解析生境隔离（山脉、绿洲）和地理距离对遗传分歧的贡献，还评估三者谱系地理格局的一致性和特殊性。研究结果将为更全面认识第四纪冷暖交替和亚洲中部干旱区的干旱化过程对生物分布的影响提供新的信息，也将为探讨群落水平共享的生物地理学过程提供新的线索。

干旱荒漠区是我国特殊的自然地理单元，也是世界干旱区生物多样性的关键区域，有关该区域动物种群分化的模式、过程和机制的研究非常薄弱。本项目选择叶城沙蜥、虫纹麻蜥和西域沙虎为对象，联合遗传和环境数据，利用谱系地理学和生态位模型的理论和方法对三种蜥蜴的谱系地理格局和种群进化历史进行了比较研究。. 基于mtDNA，叶城沙蜥和虫纹麻蜥表现出与地形地貌相对应的遗传分化，且它们的最近共祖时间 (TMRCA)也较接近。叶城沙蜥包括两个大的分支：Clade I (A支:敦煌盆地；B支: 吐-哈盆地; C: 吐鲁番盆地)，而Clade II (塔里木盆地:又分为8个地理上几乎不重叠的亚支)。虫纹麻蜥包括4个分支：Phylogroup A (准噶尔盆地和阿拉善高原等)与Phylogroup B (吐鲁番-哈密盆地)，Phylogroup C (敦煌盆地)与Phylogroup D (塔里木盆地和焉耆盆地)。叶城沙蜥TMRCA为0.98 Ma，虫纹麻蜥TMRCA为1.47 Ma。西域沙虎TMRCA为 0.28 Ma。这三种蜥蜴的母系进化历史一致地支持了天山、北山等地理屏障对基因流有阻隔效应，对遗传分化的贡献大于地理距离的贡献。对于西域沙虎，因分化时间较短，表现出不完全谱系分选现象，并未形成3个独立的谱系分支。三种蜥蜴的群体历史分析和生态位模型均一致地支持了GM扩张模模型，但各个地理谱系对冰期的响应又具有谱系特异性。而基于核DNA，这三种蜥蜴均表现出与mtDNA不一致的谱系地理格局。对于叶城沙蜥，微卫星分析分为2个主要族群，地理距离对遗传分化贡献较小，而生境异质性可能是引起遗传分化的主导因素，但多数居群间遗传分化很小，各个地理居群间有广泛的基因流，暗示了偏雄扩散对基因流的影响。对于虫纹麻蜥，nuDNA由于不完全谱系分选表现出遗传分化较浅。对于西域沙虎，nuDNA表现出较mtDNA更明显的不完全谱系分选现象。. 这些发现表明运用多基因位点的遗传标记比单一的线料体遗传标记能更全面地反映种群的遗传格局和演化历史，对同一地区多个物种进行比较谱系地理学研究，可以了解共同的历史事件对它们种群进化的影响，从而探讨地区间的历史关系。本项目为更全面认识第四纪冷暖交替和亚洲中部干旱区的干旱化过程对生物分布的影响提供了新的案例，也为探讨群落水平共享的生物地理学过程提供了线索。