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. 在多数鸟类中，孵化异步性（hatching asynchrony）是一种常见现象，主要由孵卵行为模式所驱动。不过针对青山雀（Cyanistes caeruleus）的实验结果显示，较晚产出的卵所具备的内在特性可加速胚胎发育，从而降低孵化异步程度。
2. 早产卵与晚产卵之间的这类内在差异，可能源于雌性个体资源可获得性的变化，随后该变化被被动传递至卵内。另一种可能则是由预期性母体效应（anticipatory maternal effect）导致：雌性会主动向卵内投放某种信号或资源，这对同一产卵窝中较晚产出的卵更为有利。
3. 为区分这两种假说，我们设计了一项补充喂食实验：在雌性产卵阶段的特定时段为其提供食物。该实验未对胚胎发育速率或其他卵部特征产生可辨别的影响，这一结果与预期性母体效应的假说相符。
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波动（天气）是否会影响雌性对卵的资源投入。同样，研究发现卵部特征对这类环境波动相对不敏感，进一步支持了前述实验结果。