Data from: Short- and long-term effects of egg size and feeding frequency on offspring quality in the collared flycatcher (Ficedula albicollis)

1) Despite the central importance for life-history theory, egg-size effects on offspring fitness are still considered ambiguous. Most previous studies were only observational and consequently might suffer from uncontrolled correlations between egg size and parental/territory quality. Even after cross-fostering is performed, direct genetic effects and parental adjustment of postnatal care might confound our estimates of egg-size effects per se. 2) I performed a full cross-fostering experiment in the collared flycatcher (Ficedula albicollis) exchanging the whole clutches between pairs of nests. I statistically controlled for direct genetic effects and parental feeding frequencies. I followed young until recruitment to estimate the long-term effects of egg size and parental provisioning. In addition, I compared the effects obtained in the cross-fostering experiment with those obtained from a set of unmanipulated nests. 3) Egg size per se affected offspring morphology in both the short- and long-term, while having no effect on offspring survival and immunity. Egg-size effects were not confounded by parental postnatal care and direct genetic effects. 4) The number of care-givers was an influential predictor of nestling performance. Apart from the variation caused by this factor, feeding frequencies had no consistent effect on offspring performance. 5) Fitness benefits of large eggs may be difficult to establish due to variation of egg-size effects between years and habitats. Feeding frequency may affect offspring state but offspring state may also affect feeding frequency. Varying causality between feeding rate and offspring state may preclude the detection of a positive effect of the former on the latter.1) 尽管卵大小对子代适合度的影响在生活史理论（life-history theory）中处于核心地位，但目前学界对其效应的认知仍存在歧义。既往多数相关研究仅为观察性研究，因此可能受限于卵大小与亲本/领地质量之间未受控制的相关性。即便开展了交叉抚育（cross-fostering）实验，直接遗传效应以及亲本对产后抚育的调整行为，仍可能干扰我们对卵大小本身效应的评估。2) 本研究以领姬鹟（Ficedula albicollis）为研究对象，开展了完整的交叉抚育实验：将成对巢箱中的全部窝卵进行互换。研究通过统计方法控制了直接遗传效应与亲本投喂频次，并对幼鸟进行跟踪直至其成功招募入种群，以评估卵大小与亲本育幼行为的长期效应。此外，本研究还将交叉抚育实验所得结果与一组未经过人工处理的自然巢箱所得结果进行了对比。3) 卵大小本身可在短期与长期层面影响子代形态特征，但对子代存活与免疫功能无显著作用。且本研究中，卵大小的效应并未受到亲本产后抚育与直接遗传效应的混淆。4) 育幼者数量是影响雏鸟表现的重要预测因子。在排除该因子带来的变异后，投喂频次对子代表现并无一致的显著影响。5) 由于不同年份与生境间卵大小效应存在变异，大型卵的适合度优势可能难以被准确证实。投喂频次既可能影响子代状态，子代状态反过来也可影响投喂频次。投喂速率与子代状态间存在双向因果关系，这可能使得我们无法检测到前者对后者的正向作用。