Data from: Eggshell spotting pattern is related to hatching asynchrony, hematocrit value and growth of nestling great tits (Parus major)

Eggshell pigmentation may signal the quality of the egg, that of the female and the environment, and thus nestling development may be related to this egg trait. However, so far, few studies have investigated the relationship between eggshell pigmentation and nestling development. Our aim was to study in a partial cross-fostering experiment whether the protoporphyrin-based eggshell pigmentation (spot intensity and spot distribution) showed any significant associations with several traits related to the development of nestling great tits (Parus major). We found that nestlings from clutches with darker spotted eggshells hatched more synchronously, had higher hematocrit value and shorter wings. Females under adverse environmental circumstances were previously shown to lay darker-spotted eggs, and these females probably delayed the start of incubation due to energetic constraints, resulting in a more synchronous hatching. The shorter wings of fledglings originating from clutches with darker-spotted eggs may be caused by the lower general quality of their mothers, mediated through either genetic factors or early maternal effects. Darker spotted eggs may contain different levels of some biomolecules than paler spotted eggs, which could have an effect on nestling metabolism and activity, resulting in an elevated hematocrit value. More aggregated eggshell spotting was related to faster bone growth and slightly longer fledging tarsus length. Eggs with aggregated spotting may have thinner eggshells that could lead to hatchlings with smaller bones due to the lower availability of calcium during development. Neslings may increase bone growth rate to compensate for their smaller initial size. Overall, our results indirectly suggest lower fitness for nestlings hatched from darker spotted eggs and for nestlings hatched from eggs with more aggregated spotting distribution due to the possible long-term costs of synchronous hatching, shorter wings, and accelerated tarsus growth rate.

蛋壳色素沉着可表征卵的品质、雌鸟的健康状况及其所处环境的优劣，故雏鸟发育或与该卵表性状相关联。然而迄今为止，鲜有研究探讨蛋壳色素沉着与雏鸟发育之间的关联。本研究通过部分交叉换巢实验，旨在探究基于原卟啉（protoporphyrin）的蛋壳色素沉着（即斑点强度与斑点分布）是否与大山雀（Parus major）雏鸟发育的多项性状存在显著关联。研究结果显示，来自斑点更深的卵簇的雏鸟孵化同步性更高，血细胞比容水平更高，翅长更短。此前已有研究表明，处于不利环境中的雌鸟会产下斑点更深的卵；这类雌鸟可能因能量限制而推迟孵化启动时间，进而使得雏鸟孵化同步性提升。来自斑点更深的卵簇的离巢幼鸟翅长更短，这或许是由其母鸟整体品质较低所致，该效应可通过遗传因素或早期母体效应介导。相较于斑点较浅的卵，斑点更深的卵所含部分生物分子水平存在差异，这可能会影响雏鸟的代谢与活动，进而导致血细胞比容水平升高。蛋壳斑点聚集程度更高的卵，其雏鸟骨骼生长速度更快，离巢时跗跖长度略长。斑点聚集程度更高的卵，其蛋壳可能更薄，这会因发育过程中钙的可获得性降低，导致孵出的雏鸟骨骼尺寸更小。雏鸟可能通过提高骨骼生长速率来弥补其初始体型较小的缺陷。综合来看，本研究结果间接表明：来自斑点更深的卵的雏鸟，以及来自斑点分布更聚集的卵的雏鸟，其进化适合度更低，这可能源于同步孵化、翅长更短以及跗跖生长速率加快所带来的潜在长期代价。