Data from: Sex allocation patterns across cooperatively breeding birds do not support predictions of the repayment hypothesis

The repayment hypothesis predicts that reproductive females in cooperative breeding systems overproduce the helping sex. Thanks to well-documented examples of this predicted sex ratio bias, repayment has been considered an important driver of variation in sex allocation patterns. Here we test this hypothesis using data on population brood sex ratios and facultative sex allocation from 28 cooperatively breeding bird species. We find that biased sex ratios of helpers do not correlate with production biases in brood sex ratios, contrary to predictions. We also test whether females facultatively produce the helping sex in response to a deficiency of help (i.e., when they have fewer or no helpers). Although this is observed in a few species, it is not a significant trend overall, with a mean effect size close to zero. We conclude that, surprisingly, repayment does not appear to be a widespread influence on sex ratios in cooperatively breeding birds. We discuss possible explanations for our results and encourage further examination of the repayment model.

抚育偿还假说（Repayment Hypothesis）预测，合作繁殖系统（cooperative breeding systems）中的繁殖雌性会过度繁育具有协助抚育行为的后代性别。鉴于该理论预测的性别比例偏差已有大量详实的实证案例支撑，抚育偿还假说被视为性分配模式变异的重要驱动因素之一。本研究依托28种合作繁殖鸟类的种群窝卵性别比例与兼性性分配（facultative sex allocation）数据，对该假说开展检验。研究结果显示，协助者的性别比例偏差与窝卵性别比例的生产偏差并无相关性，这与理论预测相悖。我们同时检验了雌性是否会在协助者不足（即拥有的协助者数量较少或无协助者）时，兼性地调整后代性别比例，生产更多协助抚育的个体。尽管在少数物种中观察到了这一现象，但整体上未呈现显著趋势，平均效应量接近零。令人意外的是，本研究得出结论：抚育偿还假说似乎并非合作繁殖鸟类性别比例的普遍影响因素。本文讨论了本研究结果的可能解释，并呼吁学界对抚育偿还模型开展进一步的检验与探讨。