Can an introduced predator select for adaptive sex allocation?

Most species produce equal numbers of sons and daughters, and sex differences in survival after parental care do not usually affect this pattern. Temporary overproduction of the scarcer sex can be adaptive when generations overlap, the sexes differ in life history expectations, and parents can anticipate future mating opportunities. However an alternative strategy of maximising the competitiveness of the more abundant sex in these circumstances remains unexplored. We develop theory showing how mothers can maximise reproductive value when future mate competition will be high by producing more sons in the advantageous early hatching positions within their broods. Our model for optimal birth order was supported by long term data of offspring sex in a parrot facing catastrophic female mortality caused by introduced predators. Swift parrots (Lathamus discolor) suffer high female mortality due to introduced sugar gliders (Petaurus breviceps) creating fluctuating male biased adult sex ratios. ...多数物种的子代雌雄个体数量均等，且双亲抚育后的存活性别差异通常不会改变这一比例格局。当种群存在世代重叠、两性生活史预期存在差异，且双亲能够预判未来交配机会时，暂时性过量生产稀有性别个体可具备适应性优势。然而，在上述情境下提升数量更充裕的性别竞争力的替代性策略，迄今尚未得到探索。我们构建理论模型，揭示了当未来交配竞争加剧时，亲代雌性可通过让更多雄性占据一窝子代中有利的早期孵化位置，以最大化自身繁殖价值。我们提出的最优孵化顺序模型，得到了某鹦鹉种群长期子代性别数据的支持——该种群正遭受外来捕食者引发的雌性灾难性死亡。雨燕鹦鹉（Lathamus discolor）因入侵物种蜜袋鼯（Petaurus breviceps）的捕食而面临极高的雌性死亡率，进而导致种群成年性比呈现波动的雄性偏倚状态……