密点麻蜥复合体物种形成及其与青藏高原隆起的关系

Speciation is a fundamental issue in biology,and has been a major focus of evolutionary biology research in recent years,with many important advances.However, the patterns, processes and mechanisms of speciation are still uncelar. Lizards have been model organisms for linking phylogeographic and speciaiton studies. The racerunner lizard, Eremias multiocellata species complex occurs in highly heterogenous habitats. There is overlap in distriubiotn among some species, such as E. multiocellata and E. przewalskii. The species boundaries among some species or subspeices are still unclear. In a previous study based on mtDNA 16S rRNA, we found that Eremias przewalskii is nested within Eremias multiocellata, likely owing to introgressive hybridization or incomplete lineage sorting. Specifically, the divergence time of E. multiocellata species complex was dated to about 5.2 million years ago (with the 95% confidence interval ranging from 2.5 to 7.9 Ma), which suggests that the diversification of this complex might be correlated with the evolution of an East Asian monsoon climate triggered by the rapid uplift of the Tibetan Plateau approximately 8 Ma. In the present study, we will integrate genetic (both mitochondrial DNA and multiple nuclear DNA markers),phenotypic and environmental data into investigating the evolutionary history of the E. multiocellata species complex and the possible driving forces for their speciation. Samples will be collected from across the entire range of the complex. We will combine the phylogenetic-based phylogeographical analyses and coalescent-based population genetic models as well as GIS-based ecological niche moedeling technique to infer the divergence for each lineage pair within the species complex. Coalescent-based population genetic models that account for both stochastic lineage sorting and changes in demography, such as the isolation-with-migration (IM) model, can better approximate population-level divergence processes than phylogenetic-based phylogeographical methods. Our objectives are (i) to reconstruct the evolutionary relationships of species in the E.multiocellata complex and to reveal its speciaiton modes and patterns;(ii) to explore the influence of uplift of the Qinghai-Tibetan Plateau and its consequential Late Cenozoic dramatic environmental changes on the E. multiocellata species complex and gain insights into the relative roles played by vicariance and ecological selection in speciation; and (iii) to test the macroevolutionary null hypothesis of no gene flow between species, and if gene flow is found, to explore its influence on speciation. The results of this study will provide a basis for further investigation that will help to gain insights into the evolutionary forces, ecological circumstances and genetic mechanisms of speciation. This will promote discussion on the common themes that underlie disparate speciation processes.

物种形成是生物学的一个基本问题，已成为进化生物学研究的热点，然而其模式、过程和机制仍不清楚。蜥蜴是联结谱系地理学和物种形成研究的理想类群。密点麻蜥复合体栖息环境异质性很高，部分物种分布区域有重叠，物种（亚种）界限不清。申请者在前期研究中发现此复合体中密点麻蜥和荒漠麻蜥可能有渐渗杂交或不完全的谱系筛选，物种分化可能与8 Ma以来青藏高原的快速隆升所引起的东亚季风气候的演化密切相关。本项目在此基础上，拟广泛采样，整合形态数据、线粒体基因和多个核基因以及环境数据，联合基于系统发育的谱系地理分析和基于溯祖模型的种群遗传学方法重建此复合体的演化历史，检验其物种形成模式，探讨基因流对物种形成的影响；结合生态位模拟来阐明生态位分化对物种分化过程的影响；进而揭示青藏高原隆升及气候环境变化对密点麻蜥复合体的物种形成与分化的影响机制；以期为深入研究物种形成的进化动力、生态环境和遗传机制奠定基础。

物种形成是生物学的一个基本问题，也是进化生物学研究的热点之一。影响生物成种的因素很多，例如地质事件引起的地理隔离导致种群遗传分化，而生态位分化则进一步加强并维持了这种分化，进而促进新种形成；相反，杂交带来的基因流则促进种群之间的相互融合。密点麻蜥复合体，是典型的干旱荒漠区物种类群，其栖息环境异质性很高，一些居群从沙漠延伸到黄土高原和松辽平原。已有研究表明此复合体不同居群间形态变异大、部分物种分布区有重叠，物种（亚种）界限不清，通过研究该复合体的分化过程，有助于我们深入理解物种形成的过程和机制。我们采集了170个样点、2100余号标本，覆盖了其分布区(中国、蒙古、哈萨克斯坦和吉尔吉斯坦)的代表居群。通过分析117个居群、734号个体的线粒体和核基因序列，同时结合GIS数据进行的生态位分析重建了密点麻蜥复合体物种分化过程。结果支持麻蜥属胎生类群（即此复合体）为一次起源，有显著的地理结构，包含20个主要的异域分布支系，这提示异域物种形成起主导作用。结合形态特征和地理分布，识别了当前界定的一些种的系统发育位置，比如E. szczerbaki与天山麻蜥(E. stummeri)构成姐妹种，在整个复合体的进化树上位于最基础的地位；莎车麻蜥与喀什麻蜥构成姐妹种；科克沙尔麻蜥与采自且末的新种关系最近。密点麻蜥并没有构成单系，其中包括了10个隐存支系。荒漠麻蜥没有形成单系，有二个隐存支系；荒漠麻蜥图瓦亚种与密点麻蜥南山亚种关系更近，建议将图瓦亚种和南山亚种分别提升至种级地位。荒漠麻蜥阿拉善居群存在渐渗杂交现象，线粒体完全被来自密点麻蜥指名亚种的线粒体所替代。多数支系间有地理隔离和明显的生态位分化且与青藏高原和天山隆起造成的气候变化相关，结合分歧时间估算（密点麻蜥复合体MRCA约为4.31 Ma）揭示了青藏高原和天山晚中新世以来的强烈隆升以及之后亚洲中部干旱区的气候环境变化对于该复合体物种分化有重要影响。这些结果提示密点麻蜥复合体的演化历史比以往想象的更加复杂，对其进一步深入的研究将对全面认识亚洲中部干旱区（Arid Central Asia）特殊环境下麻蜥属蜥蜴响应环境改变的生物地理学和物种形成机制具有重大意义。依托此项目，我们还对分布区有重叠的虫纹麻蜥和叶城沙蜥等开展了相关的比较谱系地理学研究，以期评估干旱荒漠区共享的谱系地理格局和群体历史动态。