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）是生物应对挑战性与动态变化环境的核心途径。由于内分泌信号介导了绝大多数表型性状，因此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标。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水平的遗传力，但针对基础激素水平或是快速内分泌灵活性的演化潜力，目前人们仍了解甚少。本研究以野生幼年树燕（Tachycineta bicolor；样本量n=408）为研究对象，评估了自然选择作用于糖皮质激素反应规范的基础水平（循环激素水平）与急性束缚应激下的灵活性的潜力。通过多变量动物模型分析显示：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）均较低但显著，而急性应激响应下的糖皮质激素灵活性则具有中等程度的遗传力（h²=0.38）。进一步分析发现，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无遗传相关性。上述研究结果表明，基础糖皮质激素与急性应激响应属于可被自然选择独立塑造的不同性状。影响这些作为表型内分泌介导因子的表达或灵活性的微演化改变，或为种群适应变化环境与新型威胁的重要途径。