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，绝大多数生物的性比应趋于均等，但自私遗传元件（selfish genetic elements）可引发性比偏倚，例如可杀死雄性基因型个体或使其雌性化的内共生体（endosymbionts）。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列岛的岛屿区域，在此处雌性化表型可产生可存活的全雌性产卵群。本研究针对澳大利亚大陆的宽边黄粉蝶（E. hecabe）的性比偏倚特征展开研究。我们以186头野生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繁育设计，饲养了超过6000头子一代至子三代（F1–F3）后代。F1代在两年间的不同种群中均表现出稳定的性比偏倚，该偏倚由约5%的产卵群引发——这些产卵群的雌性子代占比≥80%。来自偏倚谱系的雌蝶在与野生雄蝶异交两代后，仍持续产生过量的雌性子代。不同剂量的抗生素处理仅在偏倚谱系中产生影响，可诱导出程度一致的不完全雄性子代过剩表型。不过，各谱系内及不同世代间的产卵群性比仍存在高度变异。值得注意的是，即使在无偏倚谱系的表型雌蝶中，也均未检测到雌性核型的细胞遗传学特征。分子证据显示存在一种高感染率的单一沃尔巴克氏体菌株，但该菌株并未与产卵群性比偏倚明确关联。综上，我们证实了一种可遗传且可经实验逆转的不完全子代性比偏倚倾向。我们的研究结果在关键特征上与日本的雌性化范式显著不同，同时凸显了节肢动物中更为微妙的性比扭曲潜能。