Data from: Context-dependent effects of yolk androgens on nestling growth and immune function in a multibrooded passerine

Female birds may adjust their offspring phenotype to the specific requirements of the environment by differential allocation of physiologically active substances into yolks, such as androgens. Yolk androgens have been shown to accelerate embryonic development, growth rate and competitive ability of nestlings, but they can also entail immunological costs. The balance between costs and benefits of androgen allocation is expected to depend on nestling environment. We tested this hypothesis in a multibrooded passerine, the spotless starling, Sturnus unicolor. We experimentally manipulated yolk androgen levels using a between-brood design and evaluated its effects on nestling development, survival and immune function. Both in first and replacement broods, the embryonic development period was shorter for androgen-treated chicks than controls, but there were no differences in second broods. In replacement broods, androgen-treated chicks were heavier and larger than those hatched from control eggs, but this effect was not observed in the other breeding attempts. Androgen exposure reduced survival with respect to controls only in second broods. Regarding immune function, we detected nonsignificant trends for androgen treatment to activate two important components of innate and adaptive immunity (IL-6 and Ig-A levels, respectively). Similarly, androgen-treated chicks showed greater lymphocyte proliferation than controls in the first brood and an opposite trend in the second brood. Our results indicate that yolk androgen effects on nestling development and immunity depend on the environmental conditions of each breeding attempt. Variation in maternal androgen allocation to eggs could be explained as the result of context-dependent optimal strategies to maximize offspring fitness.雌性鸟类可通过将生理活性物质差异化分配至卵黄，例如雄激素（androgens），从而调整子代的表型以适配环境的特定需求。已有研究表明，卵黄雄激素（yolk androgens）可加速雏鸟的胚胎发育、生长速率与竞争能力，但同时也会带来免疫相关的代价。雄激素分配的成本与收益之间的平衡，被认为取决于雏鸟所处的环境。我们在多窝繁殖的雀形目鸟类——纯色椋鸟（Sturnus unicolor）中验证了这一假说。我们采用窝间设计对卵黄雄激素水平进行实验操控，并评估其对雏鸟发育、存活与免疫功能的影响。在首窝繁殖与替补繁殖窝中，经雄激素处理的雏鸟胚胎发育期均短于对照组，但在第二繁殖窝中未观察到此差异。在替补繁殖窝中，经雄激素处理的雏鸟体重与体型均大于对照卵孵化出的雏鸟，但在其他繁殖尝试中未观察到此效应。仅在第二繁殖窝中，雄激素暴露组雏鸟的存活率较对照组有所降低。关于免疫功能，我们发现雄激素处理对先天免疫与适应性免疫的两个重要组分——分别为白细胞介素6（IL-6）与免疫球蛋白A（Ig-A）水平——的激活作用未达到统计学显著性。同样，经雄激素处理的雏鸟在首窝繁殖中表现出比对照组更强的淋巴细胞增殖能力，但在第二繁殖窝中则呈现相反的趋势。我们的研究结果表明，卵黄雄激素对雏鸟发育与免疫功能的影响取决于每次繁殖尝试所处的环境条件。母体向卵中分配雄激素的差异，可被解释为依赖于环境背景的最优策略的结果，以最大化子代的适合度。