The origins of asexual brine shrimps

Determining how and how often asexual lineages emerge within sexual species is central to our understanding of sex-asex transitions and the long-term maintenance of sex. Asexuality can arise “by transmission” from an existing asexual lineage to a new one, through different types of crosses. The occurrence of these crosses, cryptic sex, variation in ploidy and recombination within asexuals greatly complicates the study of sex-asex transitions, as they preclude the use of standard phylogenetic methods and genetic distance metrics. In this study we show how to overcome these challenges by developing new approaches to investigate the origin of the various asexual lineages of the brine shrimp Artemia parthenogenetica. We use a large sample of asexuals, including all known polyploids, and their sexual relatives. We combine flow cytometry with mitochondrial and nuclear DNA data. We develop new genetic distance measures and methods to compare various scenarios describing the origin of the diffe...明确有性物种内无性谱系的产生路径与发生频率，是解析性-无性转换机制以及性的长期维持原理的核心研究内容。无性性状可通过不同杂交类型，以“传递”模式从已存在的无性谱系向新的无性谱系扩散。此类杂交事件的发生、隐蔽性有性生殖（cryptic sex）、倍性变异以及无性类群内的重组现象，极大地提升了性-无性转换研究的复杂度——上述因素导致标准系统发育方法与遗传距离度量手段无法直接适用。本研究以孤雌生殖卤虫（Artemia parthenogenetica）为研究对象，通过开发全新分析方法探究其各类无性谱系的起源，以此阐明如何攻克上述研究瓶颈。本研究采集了涵盖所有已知多倍体无性类群及其有性近缘类群的大样本数据集，整合了流式细胞术（flow cytometry）、线粒体DNA与核DNA的测序数据，并开发了全新的遗传距离度量方法与分析工具，用于对比阐释各类描述不同无性谱系起源的假说（原文末尾内容截断为“diffe...”）。