模糊秀体溞（Diaphanosoma dubium）的中心与边缘种群的遗传差异与生态适应性

The Central-Peripheral Hypothesis (CPH) predicts that the genetic diversity of a species decreases significantly from center to edge of its distribution, and the ecological adaptability of populations becomes much weak at the edge. Cladocerans usually reproduce in cyclical parthenogenesis, but their exact reproductive strategy and dispersal capacity changes largely with environmental conditions. Therefore, the spatial distribution and genetic diversity of this group is species-specific. We strongly propose that, due to spatial differences in reproductive strategy and dispersal potential, spatial genetic structure of those Cladocerans with a wide species’ range can significantly deviate from the theoretical prediction of CPH, and the spatial distribution of genetic diversity becomes less steep; the leading peripheral populations and island or island-like populations at the edge differently maintain their genetic diversity and adapt to local conditions. Diaphanosoma dubium is a species endemic to Asia, and was distributed mainly in China. Contrast in the reproduction strategy northern and southern populations make this species be an ideal object for studying population spatial distribution. In this study, we will focus on Diaphanosoma dubium with Whole Genome Re-sequencing technology, and explore the genetic structure and diversity distribution of its populations along a south-north longitudinal transect over the species range in China. In view of the strong adaptability of the species to wide water temperature and eutrophication, we measure and compare the adaptability of the center populations and the peripheral populations to water temperature, food quality and their interaction in habitat crossing experiments. Our study will provide data to test CPH for Cladocera which was less touched, and improve our understanding of the potential mechanisms underlying the wide-range distribution of Cladocerans.

根据中心-边缘假说，从物种分布中心到边缘，种群遗传多样性显著下降，边缘种群的生态适应性较弱。枝角类营兼性孤雌生殖，其生殖方式与传播能力随环境条件变化，种群空间分布与遗传多样性分布具有自身的特点。我们推断，对空间分布广的枝角类，生殖方式上的空间差异导致其空间遗传结构有别于中心边缘假说的经典预测，遗传多样性分布曲线趋于平缓，边缘种群中的前边缘种群与类似岛屿的隔离种群具有不同的多样性形成机制和生态适应性。模糊秀体溞是亚洲特有的枝角类，我国为其主要分布区，是种群空间分布研究的理想物种。本项目以该种为对象，通过全基因组重测序，分析其在我国分布区南北纵向断面种群的遗传结构与多样性分布特征；针对该种对水温与富营养化的适应性强的特点，通过生境交叉实验，分析中心种群与两类边缘种群对水温、食物质量及两者相互作用的适应性差异。本研究有助于丰富中心-边缘假说，为认识枝角类在我国湖泊和水库分布的机制提供生态学依据。

根据中心-边缘假说，从物种分布中心到边缘，种群遗传多样性显著下降，边缘种群的生态适应性较弱。枝角类营兼性孤雌生殖，其生殖方式与传播能力随环境条件变化，种群空间分布与遗传多样性分布具有自身的特点。我们推断，对空间分布广的枝角类，生殖方式上的空间差异导致其空间遗传结构有别于中心边缘假说的经典预测，遗传多样性分布曲线趋于平缓，边缘种群中的前边缘种群与类似岛屿的隔离种群具有不同的多样性形成机制和生态适应性。本项目以东亚地区广泛分布的模糊秀体溞为对象，通过种群遗传学、组学和生活史试验，分析其在我国分布区种群的遗传结构多样性分布特征及其中心种群与边缘种群对温度的适应性差异。生境适合度分析结果表明，模糊秀体溞的迁移路径与我们之前预测的从南到北方向不一致，其迁移路线主要为东西向和南北向两条；岛屿种群（海南岛及邻近岛屿）具有较高的局部和区域遗传多样性以及古老的谱系，表明琼州海峡或邻近海域并未成为该物种扩散过程中的障碍。生活史试验结果表明，同一地区的年轻单倍型的温度生态位均比古老单倍型宽，反映了年轻单倍型对近期全球变暖的适应性；低纬度种群与高纬度种群具有不同的适应模式，高纬度的物种具有更宽的温度适应范围。通过比较转录组学分析，筛选到6个热休克蛋白，其中Hsp60A可能与单倍型的温度适应性有关。最后从基因组层面解读了模糊秀体溞广泛生态适应性的分子基础。组装了模糊秀体溞全基因组，其基因组大小为101.8Mb，其中98.92Mb (97.2%)可锚定到22条染色体上。通过比较基因组学分析，我们发现模糊秀体溞的anti-ROS、解毒功能、蛋白消化、生殖细胞调节和保护等相关基因都经历了扩张，可解释该物种广泛的地理分布和在富营养化水体中的优势度。本研究有助于丰富中心-边缘假说，为认识枝角类在我国湖泊和水库分布的机制提供生态学依据。