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 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 > 6,000 F1-F3 progeny in pedigree designs that incorporated selective antibiotic treatments. F1 generations expressed a consistent bias across two years and populations that was driven by a ~5 % incidence of broods comprising {greater than or equal to} 80 % 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保持统一，但自私遗传元件（selfish genetic elements）——例如能够杀死雄性基因型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，该现象已得到证实。目前该研究范式仅局限于日本列岛南部的岛屿区域，在此区域中，雌性化表型的个体可产生可存活的全雌性后代群。本研究针对澳大利亚大陆的宽边黄粉蝶（E. hecabe）的性偏倚展开系统表征。研究以186只野外捕获的雌蝶为起始种群，通过整合选择性抗生素处理的谱系设计，繁育了超过6000只F1至F3代子代。F1代在两年采样周期及不同种群中均表现出稳定的性比偏倚，该偏倚由约5%的后代群驱动，这类后代群的雌性占比不低于80%。来自偏倚谱系的雌蝶，在与野生雄虫进行两代远交后，仍持续产生过量的雌性后代。不同强度的抗生素处理仅在偏倚谱系中产生影响，可诱导程度相当的不完全雄性后代过量产生。然而，后代群的性比在谱系内部及代际间均存在高度变异。值得关注的是，即便在无偏倚谱系的表型雌蝶中，雌性核型的细胞遗传学特征也完全缺失。分子生物学证据表明存在一种高流行率的单一沃尔巴克氏体菌株，但该菌株并未与后代群性比偏倚形成明确关联。综上，本研究证实了一种可遗传、经实验可逆转的不完全后代偏倚倾向。我们的研究结果与日本的雌性化范式存在显著差异，同时凸显了节肢动物中更为微妙的性别扭曲潜力。