Heritable variation in circulating glucocorticoids and endocrine flexibility in a free-living songbird

Phenotypic flexibility is a central way that organisms cope with challenging and changing environments. As endocrine signals mediate many phenotypic traits, heritable variation in hormone levels, or their context-dependent flexibility, could present an important target for selection. Several studies have estimated the heritability of circulating glucocorticoid levels under acute stress conditions, but little is known about the potential for either baseline hormone levels or rapid endocrine flexibility to evolve. Here we assessed the potential for selection to operate on the elevation (circulating hormone levels) and flexibility of glucocorticoid reaction norms to acute restraint stress. Multivariate animal models revealed low but significant heritability in baseline (h2=0.13-0.14) and stress-induced glucocorticoids (h2=0.18), and moderate heritability in glucocorticoid flexibility in response to acute stress (h2=0.38) in free-living juvenile tree swallows (Tachycineta bicolor; n=408). B...表型灵活性（phenotypic flexibility）是生物应对挑战性与动态变化环境的核心策略之一。鉴于内分泌信号可调控诸多表型性状，激素水平的可遗传变异，抑或是其情境依赖性的灵活性，或可成为自然选择的重要作用靶标。既往已有多项研究针对急性应激条件下循环糖皮质激素（glucocorticoid）水平的遗传力（heritability）展开估算，但目前对于基础激素水平或是快速内分泌灵活性的演化潜力，仍缺乏深入认知。本研究评估了自然选择作用于糖皮质激素反应规范（reaction norms）的水平（循环激素浓度）与灵活性的潜力，该反应规范针对急性束缚应激（restraint stress）。通过多变量动物模型（multivariate animal models）分析，我们在408只野生幼年树燕（Tachycineta bicolor；n=408）中发现：基础糖皮质激素（h²=0.13~0.14）与应激诱导型糖皮质激素（h²=0.18）的遗传力较低但显著，而针对急性应激的糖皮质激素灵活性则具有中等程度的遗传力（h²=0.38）。B...