Data from: Asynchronous hatching provides females with a means for increasing male care but incurs a cost by reducing offspring fitness

In species with biparental care, sexual conflict occurs because the benefit of care depends on the total amount of care provided by the two parents while the cost of care depends on each parent’s own contribution. Asynchronous hatching may play a role in mediating the resolution of this conflict over parental care. The sexual conflict hypothesis for the evolution of asynchronous hatching suggests that females adjust hatching patterns in order to increase male parental effort relative to female effort. We tested this hypothesis in the burying beetle Nicrophorus vespilloides by setting up experimental broods with three different hatching patterns: synchronous, asynchronous and highly asynchronous broods. As predicted, we found that males provided care for longer in asynchronous broods whereas the opposite was true of females. However, we did not find any benefit to females of reducing their duration of care in terms of increased lifespan or reduced mass loss during breeding. We found substantial negative effects of hatching asynchrony on offspring fitness as larval mass was lower and fewer larvae survived to dispersal in highly asynchronous broods compared to synchronous or asynchronous broods. Our results suggest that, even though females can increase male parental effort by hatching their broods more asynchronously, females pay a substantial cost from doing so in terms of reducing offspring growth and survival. Thus, females should be under selection to produce a hatching pattern that provides the best possible trade-off between the benefits of increased male parental effort and the costs due to reduced offspring fitness.

在双亲抚育（biparental care）的物种中，会出现性冲突（sexual conflict）：亲本抚育（parental care）的收益取决于双亲共同提供的总抚育量，而抚育的成本则取决于每个亲本自身的投入。异步孵化（asynchronous hatching）或可介导亲本抚育相关冲突的解决过程。针对异步孵化演化的性冲突假说提出：雌性会调整孵化模式，以提升雄性相对于雌性的亲本抚育投入水平。我们以埋葬甲（Nicrophorus vespilloides）为实验对象，设置同步孵化、异步孵化与高度异步孵化三种不同孵化模式的实验育幼群，对该假说进行验证。正如预期，我们发现异步孵化育幼群中的雄性抚育时长更长，而雌性则呈现相反趋势。不过，我们未发现雌性缩短抚育时长可在繁殖期获得寿命延长或体重损失减少的收益。我们还发现，孵化异步性对子代适合度（offspring fitness）存在显著负面影响：相较于同步孵化或异步孵化育幼群，高度异步孵化育幼群中的幼虫体重更低，且存活至扩散阶段的幼虫数量更少。我们的研究结果表明，尽管雌性可通过提升孵化的异步性来增加雄性的亲本抚育投入，但此举会对子代的生长与存活造成显著代价。因此，雌性将面临选择压力，需要演化出能在增加雄性抚育投入的收益与子代适合度降低带来的代价之间实现最优权衡的孵化模式。