Data from: Prenatal maternal effects appear to be insensitive to experimental or natural environmental variation

1. In many birds, hatching asynchrony is a common phenomenon, primarily driven by patterns of incubation behaviour. However, experimental results in blue tits (Cyanistes caeruleus) have shown that asynchrony is reduced by intrinsic properties of later eggs that accelerate pre-natal development. 2. These intrinsic differences between early and late eggs could be driven by changes in resource availability to females, which are then passively passed onto the egg. Alternatively, it may be due to an anticipatory maternal effect, wherein some signal or resource is actively placed within the egg, which is beneficial to those eggs laid late within the clutch. 3. In order to distinguish between these hypotheses we designed a supplementary feeding experiment, wherein females were provided with food at certain times during the laying phase. This had no discernible effect on development rate, or other egg characteristics, consistent with anticipatory maternal effects. 4. Using a larger data set we also tested whether natural environmental variation (weather) during egg formation affected maternal investment in eggs. Similarly, egg characteristics were found to be relatively insensitive to the environmental variation, supporting the experimental results.1. 在众多鸟类中，孵化异步性（hatching asynchrony）是一种常见现象，其主要由孵化行为模式所驱动。不过，针对青山雀（Cyanistes caeruleus）开展的实验结果表明，后期产出的卵所具备的内在特性可加速胚胎产前发育，从而降低孵化异步程度。 2. 早产卵与晚产卵之间的这种内在差异，可能源于雌性亲鸟可获得的资源量变化——这类变化会被动传递至卵内。另一种可能则是由预期性母体效应（anticipatory maternal effect）所导致：亲鸟会主动向卵内投放某种信号或资源，以惠及该窝中后期产出的卵。 3. 为区分这两种假说，我们设计了一项补充投喂实验：在产卵期的特定时段为雌性亲鸟提供食物。实验结果显示，该处理对胚胎发育速率及其他卵相关特征均无显著影响，这一结果与预期性母体效应假说相符。 4. 我们还利用更大规模的数据集，检验了卵形成期间的自然环境变化（即天气状况）是否会影响亲鸟对卵的资源投入。同样地，研究发现卵相关特征对这类环境变化相对不敏感，这一结果进一步佐证了前述实验结论。