Behavior, Ecology, Evolution and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, USA.
Behavior, Ecology, Evolution and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, USA.
Gen Comp Endocrinol. 2022 Apr 1;319:113964. doi: 10.1016/j.ygcen.2021.113964. Epub 2021 Dec 16.
Variation in nestling growth and survival is often influenced by hatching order, with first-hatched offspring having an advantage over later-hatched younger siblings. In house wrens (Troglodytes aedon), this effect of hatching order is especially evident in asynchronously hatched broods and can lead to sex-specific differences in the size and condition of nestlings. Females appear to allocate the sex of their offspring across the laying order to capitalize on these differences. We hypothesized that levels of circulating corticosterone, the primary metabolic hormone in birds, mediates these sex-specific effects in nestlings. We predicted that: i) baseline levels of corticosterone in nestlings should vary along the hatching order, ii) effects of hatching order on baseline corticosterone should be sex specific, and iii) any sex-specificity of hatching order on baseline corticosterone could be contingent on the degree of hatching synchrony. We tested these predictions in a study in which we measured baseline corticosterone in first- and last-hatched nestlings in synchronously and asynchronously hatching broods. To assess whether any differences in nestling baseline corticosterone levels could be attributed to pre-natal maternal effects, the post-natal environment, or both, we conducted two additional studies in which we measured i) yolk corticosterone in first- and last-laid eggs and ii) baseline corticosterone in nestlings that were cross-fostered to create simulated 'asynchronously' hatched broods. There was a significant interaction between sex and relative hatching order in their effects on nestling baseline corticosterone, but no effect of hatching synchrony. Corticosterone levels remained relatively constant across the hatching order in males but decreased in females. There was a significant effect of laying order on yolk corticosterone, with first-laid eggs containing significantly higher levels of yolk corticosterone than last-laid eggs. Cross-fostering of nestlings at different points of development had no significant effect on nestling corticosterone levels. These results indicate that sex-dependent differences in corticosterone levels across the hatching order may arise, at least in part, from embryonic exposure to maternally derived corticosterone, whereas the post-natal rearing environment plays, at best, a minimal role in determining nestling baseline corticosterone levels.
雏鸟的生长和生存变化通常受到孵化顺序的影响，先孵化的后代比后孵化的年幼兄弟姐妹具有优势。在房主鸫（Troglodytes aedon）中，这种孵化顺序的影响在异步孵化的雏鸟中尤为明显，并且会导致雏鸟的大小和状况出现性别特异性差异。雌性似乎会根据产卵顺序分配后代的性别，以利用这些差异。我们假设，循环皮质酮的水平，鸟类的主要代谢激素，调节这些雏鸟的性别特异性效应。我们预测：i）雏鸟的基础皮质酮水平应沿孵化顺序变化，ii）孵化顺序对基础皮质酮的影响应具有性别特异性，iii）孵化顺序对基础皮质酮的任何性别特异性都可能取决于孵化同步的程度。我们在一项研究中检验了这些预测，我们在同步和异步孵化的雏鸟中测量了第一只和最后一只孵化的雏鸟的基础皮质酮。为了评估雏鸟基础皮质酮水平的任何差异是否可以归因于产前母体效应、产后环境或两者兼而有之，我们进行了另外两项研究，在这些研究中，我们测量了 i）第一只和最后一只产下的卵中的蛋黄皮质酮，以及 ii）被交叉寄养以创建模拟“异步”孵化的雏鸟的雏鸟的基础皮质酮。在对雏鸟基础皮质酮的影响方面，性别和相对孵化顺序之间存在显著的相互作用，但孵化同步性没有影响。皮质酮水平在雄性中相对稳定，但在雌性中随孵化顺序下降。产卵顺序对蛋黄皮质酮有显著影响，第一只产卵的卵中含有明显更高水平的蛋黄皮质酮。在不同发育阶段对雏鸟进行交叉寄养对雏鸟皮质酮水平没有显著影响。这些结果表明，孵化顺序中性别依赖性的皮质酮水平差异可能至少部分源于胚胎暴露于母体衍生的皮质酮，而产后饲养环境在决定雏鸟基础皮质酮水平方面的作用最小。
