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 previous...

尽管历经数十年研究，脊椎动物是否能够且确实会适应性地调控子代性别比例这一科学问题，至今仍存在广泛争议。然而，这一争议或许源于此前的实证检验未能识别出雌性通过策略性调整子代性别比例所能获得的显著且可预测的适合度（fitness）收益。本研究以对严重且可预测的（由遗传决定的）适合度代价做出极端母性资源分配反应的色多态型七彩文鸟（Gouldian finch，*Erythrura gouldiae*）为研究对象，检验日粮质量与母体状态对其兼性性别比例调控的影响。当日粮质量较高时，雌性产下的子代性别比例相对均衡；而在日粮质量较差的情况下，雌性则会产下更多雄性后代。尽管该物种不存在雌雄体型二态性，但遭受营养胁迫的寄养雄性子代相较于雌性子代，健康状态更佳、生长速度更快且存活率更高。尽管上述研究结果与性别分配理论的预测相符，但此次观测到的调整幅度远低于此前的……