Whole genome resequencing of males and females of three Daphnia magna genotypes

Mechanisms of sex determination (SD) differ widely across the tree of life. In genotypic sex determination (GSD), genetic elements determine whether individuals are male or female, while in environmental sex determination (ESD), external cues control the sex of the offspring. In cyclical parthenogens, females produce mostly asexual daughters, but environmental stimuli such as crowding, temperature or photoperiod may cause them to produce sons. In aphids, sons are induced by ESD, even though GSD is present, with females carrying two X chromosomes and males only one (X0 SD system). In contrast, although ESD exists in Daphnia, the two sexes were suggested to be genetically identical, based on a 1972 study on Daphnia magna (2n=20) that used three allozyme markers. This study cannot, however, rule out an X0 system, as all three markers may be located on autosomes. Motivated by the life cycle similarities of Daphnia and aphids, and the absence of karyotype information for Daphnia males, we te...生物界的性别决定（sex determination, SD）机制在生命之树的各个类群中差异显著。在基因型性别决定（genotypic sex determination, GSD）体系中，遗传元件决定个体的性别；而在环境型性别决定（environmental sex determination, ESD）体系中，外部环境信号调控子代的性别。周期性孤雌生殖类群的雌性个体大多产出无性繁殖的雌性后代，但拥挤、温度、光周期等环境刺激可诱导其产生雄性后代。以蚜虫为例，尽管其本身存在基因型性别决定系统——雌性携带两条X染色体，雄性仅携带一条（即X0型性别决定系统），但雄性个体的产生仍由环境型性别决定途径诱导。与之形成对比的是，尽管水蚤（Daphnia）同样存在环境型性别决定现象，但1972年一项以大型溞（Daphnia magna，染色体数目2n=20）为研究对象、采用3种同工酶标记的研究提出，水蚤雌雄个体的遗传组成完全一致。然而，由于这3个标记位点均可能位于常染色体上，该研究无法排除X0型性别决定系统存在的可能性。鉴于水蚤与蚜虫的生活史具有相似性，且目前尚无水蚤雄性个体的核型（karyotype）信息，本研究旨在……