Data from: Incomplete offspring sex bias in Australian populations of the butterfly Eurema hecabe

Theory predicts unified sex ratios for most organisms, yet biases may be engendered by selfish genetic elements such as endosymbionts that kill or feminize individuals with male genotypes. Although rare, feminization is established for Wolbachia-infected Eurema butterflies. This paradigm is presently confined to islands in the southern Japanese archipelago, where feminized phenotypes produce viable all-daughter broods. Here, we characterize sex bias for E. hecabe in continental Australia. Starting with 186 wild-caught females, we reared >6000 F1–F3 progeny in pedigree designs that incorporated selective antibiotic treatments. F1 generations expressed a consistent bias across 2 years and populations that was driven by an ~5% incidence of broods comprising greater than or equal to80% daughters. Females from biased lineages continued to overproduce daughters over two generations of outcrossing to wild males. Treatment with antibiotics of differential strength influenced sex ratio only in biased lineages by inducing an equivalent incomplete degree of son overproduction. Brood sex ratios were nevertheless highly variable within lineages and across generations. Intriguingly, the cytogenetic signature of female karyotype was uniformly absent, even among phenotypic females in unbiased lineages. Molecular evidence supported the existence of a single Wolbachia strain at high prevalence, yet this was not clearly linked to brood sex bias. In sum, we establish an inherited, experimentally reversible tendency for incomplete offspring bias. Key features of our findings clearly depart from the Japanese feminization paradigm and highlight the potential for more subtle degrees of sex distortion in arthropods.

理论预测多数生物的性比应趋于统一，但自私遗传元件（如可杀伤雄性基因型个体或使其雌性化的内共生体（endosymbionts））可能引发性比偏倚。尽管雌性化现象较为罕见，但在感染沃尔巴克氏体（Wolbachia）的黄粉蝶属（Eurema）蝴蝶中已被证实。目前该雌性化范式仅局限于日本南部群岛区域，在此环境中雌性化表型可产生可存活的全雌子代群。本研究针对澳大利亚大陆的E. hecabe的性偏倚特征展开研究。我们以186头野外捕获的雌蝶为起始材料，通过整合选择性抗生素处理的谱系设计，繁育得到6000余头F1至F3代子代。F1代在两年间的多个种群中均表现出稳定的性比偏倚，这一偏倚由约5%的子代群引发，这类子代群的雌性占比≥80%。来自偏倚谱系的雌蝶，在与野生雄蝶进行两代异交后，仍持续产生过量雌性子代。不同强度的抗生素处理仅在偏倚谱系中发挥作用，通过诱导程度相当的不完全雄性子代过量产生来调整性比。尽管如此，子代群的性比在谱系内部及代际间仍存在高度变异。有趣的是，即便在无偏倚谱系的表型雌蝶中，雌性核型（karyotype）的细胞遗传学特征也完全缺失。分子证据表明存在一种高流行率的单一沃尔巴克氏体菌株，但该菌株并未与子代群性比偏倚形成明确关联。综上，我们证实了一种可遗传、经实验可逆转的不完全子代性偏倚倾向。本研究结果的关键特征与日本的雌性化范式存在显著差异，凸显了节肢动物中更为微妙的性别畸变程度的潜在可能性。