Data from: 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). Baseline glucocorticoids were not genetically correlated with either stress-induced glucocorticoids or glucocorticoid flexibility. These findings indicate that baseline glucocorticoids and the acute stress response are distinct traits that can be independently shaped by selection. Microevolutionary changes that influence the expression or flexibility of these endocrine mediators of phenotype may be an important way that populations adapt to changing environments and novel threats.

表型灵活性（phenotypic flexibility）是生物体应对挑战性与动态变化环境的核心策略之一。由于内分泌信号介导诸多表型性状，激素水平的可遗传变异，或是其情境依赖的灵活性，或可成为自然选择的重要作用靶点。既往已有多项研究评估了急性应激条件下循环糖皮质激素（glucocorticoid）水平的遗传力（heritability），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，学界仍所知甚少。本研究针对野生幼年树燕（Tachycineta bicolor；样本量n=408），评估了自然选择作用于糖皮质激素反应规范（reaction norms）应对急性束缚应激（acute restraint stress）时的水平（即循环激素浓度）与灵活性的潜力。多变量动物模型（multivariate animal models）分析结果显示，在该种群中，基础糖皮质激素的遗传力（h²=0.13~0.14）与应激诱导型糖皮质激素的遗传力（h²=0.18）虽较低但具有统计学显著性，而应对急性应激的糖皮质激素灵活性的遗传力则处于中等水平（h²=0.38）。基础糖皮质激素与应激诱导型糖皮质激素、糖皮质激素灵活性均未检测到遗传相关性。上述研究结果表明，基础糖皮质激素与急性应激响应属于独立的性状，可被自然选择独立塑造。影响这类表型内分泌介导因子的表达或灵活性的微进化改变，或为种群适应变化环境与新型威胁的重要途径之一。