Data from: Local adaptation of sex-induction in a facultative sexual crustacean: insights from QTL mapping and natural population of Daphnia magna

Dormancy is a common adaptation in invertebrates to survive harsh conditions. Triggered by environmental cues, populations produce resting eggs that allow them to survive temporally unsuitable conditions. Daphnia magna is a crustacean that reproduces by cyclical parthenogenesis, alternating between the production of asexual offspring and the sexual reproduction of diapausing eggs (ephippia). Prior to ephippia production, males (necessary to ensure ephippia fertilization) are produced parthenogenetically. Both the production of ephippia and the parthenogenetic production of males are induced by environmental factors. Here, we test the hypothesis that the induction of Daphnia magna resting egg production shows a signature of local adaptation. We postulated that Daphnia from permanent ponds would produce fewer ephippia and males than Daphnia from intermittent ponds, and that the frequency and season of habitat deterioration would correlate with the timing and amount of male and ephippia production. To test this, we quantified the production of males and ephippia in clonal D. magna populations in several different controlled environments. We found that the production of both ephippia and males varies strongly among populations in a way that suggests local adaptation. By performing QTL mapping with parent clones from contrasting pond environments, we identified non-overlapping genomic regions associated with male and ephippia production. Since the traits are influenced by two different genomic regions and both are necessary for successful resting egg production, we suggest that the genes for their induction co-evolve.滞育（Dormancy）是无脊椎动物抵御恶劣环境的常见适应策略。当接收环境信号触发后，种群会产生休眠卵，借此在暂时不适宜的环境中存续。大型溞（Daphnia magna）是一类采用周期性孤雌生殖（cyclical parthenogenesis）的甲壳动物，其繁殖模式交替产出无性繁殖后代，以及用于产生滞育卵（卵鞍，ephippia）的有性生殖过程。在卵鞍生成前，种群会通过孤雌生殖产生雄性个体——这是保障卵鞍完成受精的必要前提。卵鞍的生成与雄性的孤雌生殖均由环境因素诱导产生。本研究旨在验证“大型溞休眠卵的诱导过程呈现本地适应特征”这一假说。我们提出如下推测：相较于来自间歇池塘的种群，永久栖息于永久池塘的大型溞会产出更少的卵鞍与雄性个体；且生境恶化的发生频率与季节，会与雄性及卵鞍的产出时机和产量存在关联。为验证上述假说，我们在多种可控环境中，对克隆化大型溞种群的雄性个体与卵鞍产量进行了量化分析。结果显示，不同种群的卵鞍与雄性产量存在显著差异，这一现象提示本地适应的存在。通过对来自不同池塘生境的亲本克隆开展QTL定位（QTL mapping），我们鉴定出了与雄性及卵鞍生成相关的非重叠基因组区域。鉴于这两类性状分别受不同基因组区域调控，且二者均为成功产生休眠卵的必要条件，我们认为其诱导基因存在协同进化关系。