Vitousek Maren N, Jenkins Brittany R, Hubbard Joanna K, Kaiser Sara A, Safran Rebecca J
Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA; Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA; Cornell Lab of Ornithology, Ithaca, NY 14850, USA.
Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA.
Gen Comp Endocrinol. 2017 Jun 1;247:97-106. doi: 10.1016/j.ygcen.2017.01.021. Epub 2017 Jan 28.
Because elevated glucocorticoid levels can impair reproduction, populations or species that engage in particularly valuable reproductive attempts may down-regulate the glucocorticoid stress response during reproduction (the brood value hypothesis). It is not clear, however, whether individuals rapidly modulate glucocorticoid responses based on shifting cues about the likelihood of reproductive success. By manipulating brood size to create broods that differed in potential value, we tested whether female barn swallows (Hirundo rustica) rapidly modulated the glucocorticoid stress response to promote investment in high-value broods, and whether nestling phenotype was influenced by treatment. Within-individual changes in female corticosterone, body mass, and measures of oxidative stress were unrelated to brood size treatment. Standard offspring provisioning rate did not differ across treatments; however, in the presence of a model predator, females raising enlarged broods maintained higher offspring feeding rates relative to control broods. Brood size did influence nestling phenotype. Nestlings from enlarged broods had lower body mass and higher baseline corticosterone than those from reduced broods. Finally, in adult females both baseline and stress-induced corticosterone were individually repeatable. Thus, while under moderately challenging environmental conditions brood size manipulations had context-dependent effects on parental investment, and influenced nestling phenotype, maternal glucocorticoid levels were not modulated based on brood value but were individually consistent features of phenotype during breeding.
由于糖皮质激素水平升高会损害繁殖能力，因此参与特别有价值繁殖尝试的种群或物种可能会在繁殖期间下调糖皮质激素应激反应（育雏价值假说）。然而，目前尚不清楚个体是否会根据繁殖成功可能性的变化线索迅速调节糖皮质激素反应。通过操纵窝卵数来创造具有不同潜在价值的窝，我们测试了雌性家燕（Hirundo rustica）是否会迅速调节糖皮质激素应激反应以促进对高价值窝的投入，以及雏鸟表型是否受处理影响。雌性皮质酮、体重和氧化应激指标的个体内变化与窝卵数处理无关。不同处理间标准的后代喂养率没有差异；然而，在有模型捕食者存在的情况下，饲养扩大窝的雌性相对于对照窝维持了更高的后代喂养率。窝卵数确实影响雏鸟表型。来自扩大窝的雏鸟比来自减少窝的雏鸟体重更低，基线皮质酮水平更高。最后，成年雌性的基线和应激诱导的皮质酮水平在个体间是可重复的。因此，虽然在中等挑战性的环境条件下窝卵数操纵对亲代投入有情境依赖效应，并影响雏鸟表型，但母体糖皮质激素水平并非基于窝卵价值进行调节，而是繁殖期间表型个体一致的特征。
