1. Elucidating factors that limit the number of offspring produced is fundamental to understanding life‐history evolution. Here, we examine the hypothesis that parental ability to maintain an optimal physical developmental environment for all offspring constrains clutch size via effects on offspring quality.
2. Experimental laboratory studies of birds have shown that a <1°C difference in average incubation temperature has diverse effects on fitness‐related post‐hatching offspring phenotypes. Thus, the inability of parents to maintain optimal incubation temperatures could constrain clutch sizes.
3. A fundamental question that has not been sufficiently addressed is whether larger clutch sizes lead to within nest variation in egg temperature that is large enough to produce offspring with different phenotypes within a brood. This could lead to differential survival among offspring, and could create a trade‐off between offspring number and quality.
4. We manipulated clutch size in nests of free‐living wood ducks and measured incubation temperature among and within clutches using multiple temperature loggers.
5. As clutch size increased, average incubation temperatures were lower and more variable, and eggs took longer to hatch. Notably, the range in average incubation temperature among eggs within nests increased with clutch size and exceeded 1°C in large clutches. Clutch size did not affect hatch success.
6. In conjunction with our companion laboratory studies that used artificial incubation to document the effects of temperature variation on fitness‐related traits in this species, our work suggests that suboptimal incubation temperatures could be a factor that limits clutch size through diminishing returns on post‐hatch offspring quality.

中文翻译：

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孵化温度是离合器尺寸发展的制约因素

1. 阐明限制后代数量的因素是了解生命历史演变的基础。在这里，我们检验了一个假设，即父母对所有后代保持最佳身体发育环境的能力会通过对后代质量的影响来限制离合器的大小。
2. 对鸟类的实验室实验研究表明，平均孵化温度的差异小于1°C对与适应性相关的孵化后代表型有多种影响。因此，父母无法保持最佳的孵化温度可能会限制离合器的尺寸。
3. 一个尚未得到充分解决的基本问题是，较大的离合杆是否会导致蛋温在巢内发生变化，而该变化又大到足以在育雏中产生具有不同表型的后代。这可能导致后代之间的生存差异，并可能在后代数量和质量之间做出权衡。
4. 我们操纵了自由活动的野鸭巢中的离合器大小，并使用多个温度记录仪测量了离合器之间和内部的孵化温度。
5. 随着离合器尺寸的增加，平均孵化温度会降低并且变化更大，并且孵化所需的时间也会更长。值得注意的是，巢中卵的平均孵化温度范围随着离合器尺寸的增加而增加，在大型离合器中超过1°C。离合器尺寸不会影响孵化成功。
6. 结合我们的伴随实验室研究，该研究使用人工孵化记录温度变化对该物种适应性相关性状的影响，我们的研究表明，最佳孵化温度可能是通过减少孵化后代回报而限制离合器大小的因素。质量。