Data from: Transition in sexual system and sex chromosome evolution in the tadpole shrimp Triops cancriformis

Transitions in sexual system and reproductive mode may affect the course of sex chromosome evolution, for instance by altering the strength of sexually antagonistic selection. However, there have been few studies of sex chromosomes in systems where such transitions have been documented. The European tadpole shrimp, Triops cancriformis, has undergone a transition from dioecy to androdioecy (a sexual system where hermaphrodites and males coexist), offering an excellent opportunity to test the impact of this transition on the evolution of sex chromosomes. To identify sex-linked markers, to understand mechanisms of sex determination and to investigate differences between sexual systems, we carried out a genome-wide association study using restriction site-associated DNA sequencing (RAD-seq) of 47 males, females and hermaphrodites from one dioecious and one androdioecious population. We analysed 22.9 Gb of paired-end sequences and identified and scored >3000 high coverage novel genomic RAD markers. Presence–absence of markers, single-nucleotide polymorphism association and read depth identified 52 candidate sex-linked markers. We show that sex is genetically determined in T. cancriformis, with a ZW system conserved across dioecious and androdioecious populations and that hermaphrodites have likely evolved from females. We also show that the structure of the sex chromosomes differs strikingly, with a larger sex-linked region in the dioecious population compared with the androdioecious population.

性系统与生殖方式的转变可能会影响性染色体的演化进程，例如通过改变性拮抗选择的强度。然而，目前针对已记录存在此类转变的类群，其性染色体的相关研究仍较为匮乏。欧洲蝌蚪虾（Triops cancriformis）曾经历从雌雄异体到雄全同体（androdioecy，即同时存在雌雄同体与雄性的性系统）的演化转变，这为探究该类转变对性染色体演化的影响提供了极佳的研究契机。为鉴定性连锁标记、解析性别决定机制并探究不同性系统间的差异，本研究借助限制性酶切位点相关DNA测序（restriction site-associated DNA sequencing, RAD-seq）技术，对采自1个雌雄异株种群和1个雄全同体种群的47只雄性、雌性及雌雄同体个体开展了全基因组关联分析。本研究共获取22.9Gb的双端测序数据，鉴定并筛选得到超过3000个高覆盖度的新型基因组RAD标记。通过标记有无、单核苷酸多态性（single-nucleotide polymorphism, SNP）关联分析以及测序深度分析，最终识别出52个候选性连锁标记。研究结果显示，欧洲蝌蚪虾（Triops cancriformis）的性别由遗传因素决定，其ZW性别决定系统在雌雄异株与雄全同体种群中均保守存在，且雌雄同体个体大概率由雌性演化而来。此外，研究还发现性染色体结构存在显著差异：雌雄异株种群中的性连锁区域显著大于雄全同体种群。