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.

抚育回报假说（repayment hypothesis）预测，合作繁殖系统（cooperative breeding systems）中的繁殖雌性会过量产生协助抚育后代的性别。鉴于该理论预测的性比偏差已有充分记载的实例，抚育回报假说被认为是性分配模式变异的重要驱动因素。本研究依托28种合作繁殖鸟类的种群窝雏性比与条件性性分配（facultative sex allocation）数据，对该假说展开检验。研究结果与理论预测相悖：协助者的性比偏差与窝雏性比的生产偏差不存在相关性。我们同时检验了，当雌性面临抚育帮助不足（即拥有较少或无协助者）时，是否会条件性地产下协助抚育的性别。尽管在少数物种中观测到了这一现象，但整体上并非显著趋势，平均效应量接近零。令人意外的是，本研究得出结论：抚育回报假说似乎并非合作繁殖鸟类性比格局的普遍影响因素。本文探讨了本研究结果的可能解释，并呼吁学界进一步对抚育回报模型开展检验。