The innate immune system provides important first-line defenses against invading pathogens and is considered especially important for developing organisms. However, we know little about how early-life conditions influence these defenses in wild animals. For oviparous species such as birds, embryonic development occurs in the egg, which can be subject to variation in thermal conditions. There is evidence from cavity-nesting species and species with precocial young that reduced incubation temperatures can result in reduced measures of innate immunity. Whether and how this thermal variation impacts innate immunity for open-cup-nesting species with altricial offspring has not been examined. In this study, we experimentally manipulated egg incubation temperature for American robins (Turdus migratorius) and compared the bacteria-killing ability (BKA) of the nestlings' blood plasma. We collected baseline and poststressor samples on day 7 and day 10 after hatch to gain additional insights into the ontogeny of this immune measure, as well as into whether any changes were linked to levels of the glucocorticoid hormone corticosterone (CORT). We found that nestlings incubated at the low treatment (36.1°C) had significantly reduced BKA compared with nestlings incubated at the high treatment (37.8°C) when controlling for the posthatch nest environment. We also documented a significant reduction in poststressor levels of BKA, as well as an increase in BKA from day 7 to day 10. We found a weak inverse association between CORT and BKA but no other indications that BKA was mediated via treatment-induced variation in CORT. Our results suggest that incubation temperature can affect development of innate immunity in open-cup-nesting passerines.

中文翻译：

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卵孵化温度影响美洲知更鸟（Turdus migratorius）固有免疫功能的发展。

天生的免疫系统为入侵的病原体提供了重要的一线防御，并且被认为对发育中的生物特别重要。但是，我们对生命早期条件如何影响野生动物的这些防御机制知之甚少。对于卵生物种，例如鸟类，卵中会发生胚胎发育，这可能会受热条件的影响。腔巢物种和早熟物种的证据表明，降低的孵化温度可以减少先天免疫的测量。尚未研究这种热变化是否以及如何影响具有后代的开杯巢物种的先天免疫力。在这个研究中，我们通过实验控制了美国知更鸟（Turdus migratorius）的卵孵化温度，并比较了雏鸟血浆的杀细菌能力（BKA）。孵化后第7天和第10天，我们收集了基线和应激源样本，以进一步了解这种免疫措施的个体发育，以及是否有任何变化与糖皮质激素激素皮质酮（CORT）的水平有关。我们发现，在控制孵化后的筑巢环境时，与在高温（37.8°C）下孵化的雏鸟相比，在低温（36.1°C）下孵化的雏鸟的BKA显着降低。我们还记录了从第7天到第10天BKA后应激源水平的显着降低以及BKA的升高。我们发现CORT与BKA之间存在弱的逆相关性，但没有其他迹象表明BKA是通过治疗引起的CORT变异介导的。我们的结果表明，温育温度可以影响杯状嵌套雀花碱中先天免疫的发育。