Data from: Context-dependent sex allocation: constraints on the expression and evolution of maternal effects

Despite decades of research, whether vertebrates can and do adaptively adjust the sex ratio of their offspring is still highly debated. However, this may have resulted from the failure of empirical tests to identify large and predictable fitness returns to females from strategic adjustment. Here we test the effect of diet quality and maternal condition on facultative sex ratio adjustment in the color polymorphic Gouldian finch (Erythrura gouldiae), a species that exhibits extreme maternal allocation in response to severe and predictable (genetically-determined) fitness costs. On high quality diets, females produced a relatively equal sex ratio, but over-produced sons in poor dietary conditions. Despite the lack of sexual size dimorphism, nutritionally-stressed foster sons were healthier, grew faster, and were more likely to survive than daughters. Although these findings are in line with predictions from sex allocation theory, the extent of adjustment is considerably lower than previously reported for this species. Females therefore have strong facultative control over sex allocation, but the extent of adjustment is likely determined by the relative magnitude of fitness gains and the ability to reliably predict sex-specific benefits from environmental (versus genetic) variables. These findings may help explain the often inconsistent, weak or inconclusive empirical evidence for adaptive sex ratio adjustment in vertebrates.尽管已有数十年研究积累，但脊椎动物（vertebrates）是否能够且确实会适应性地调整子代性比（sex ratio），这一议题至今仍存在广泛争议。然而，这一争议或许源于现有实证检验未能识别出雌性通过策略性调整所获得的显著且可预测的适合度（fitness）收益。本研究以具有色多态性的七彩文鸟（Erythrura gouldiae）为研究对象——该物种会针对严重且可预测的（由遗传决定的）适合度代价实施极端的母体分配（maternal allocation）——检验日粮质量与母体状态对其兼性性比调整（facultative sex ratio adjustment）的影响。当日粮质量较高时，雌性所产子代的性比相对均衡；但在日粮匮乏的条件下，它们会过量产出雄性后代。尽管该物种不存在雌雄体型二态性（sexual size dimorphism），但经历营养胁迫的雄性幼鸟比雌性幼鸟更为健康、生长速度更快，且存活率更高。尽管上述发现与性分配理论（sex allocation theory）的预测相符，但性比调整的幅度远低于此前针对该物种的报道。因此，雌性对子代性分配具备较强的兼性调控能力，但性比调整的幅度大概率取决于适合度收益的相对大小，以及能否可靠地从环境变量（而非遗传变量）中预测出性特异性收益。上述发现或有助于解释脊椎动物适应性性比调整相关实证证据往往不一致、效力薄弱或无法得出明确结论的现象。