Abstract Avian plumage colors and ornaments are excellent models to study the endocrine mechanisms linking sexually selected traits and individual parameters of quality and condition. Insulin-like growth factor 1 (IGF-1) is an evolutionarily highly conserved peptide hormone. Its regulatory role in cell proliferation and differentiation and its high sensitivity to the nutritional state of individuals suggest it as an interesting candidate, possibly providing a link between body condition and individual capacity to grow elaborated ornamental features. We investigated whether IGF-1 levels during molting correlate with the expression of multiple ornaments in a sexually dichromatic passerine species, the bearded reedling ( Panurus biarmicus ). We collected blood samples of males and females shortly before the molting completed and measured the size and colors of ornamental traits. Our results indicate that in males, structural plumage colors, the size of the melanin-based ornament (beard), and tail length are independent traits. IGF-1 levels are associated with the length of the tail and the expression of male structural plumage components (UV coloration), but not the melanin-based ornament. In females, plumage color and tail length were independent traits, which were not related to IGF-1 levels. To the best of our knowledge, this study provides the first evidence that IGF-1 could play a role in the development of secondary sexual characters in a bird species. Significance statement IGF-1 is an evolutionarily highly conserved peptide hormone, which recently entered the center stage of research enquiry in evolutionary biology. It is considered as one of the key factors shaping individual life histories, but little is known about its effects on sexually selected traits. We investigated whether IGF-1 levels during molting predict the elaboration of multiple ornamental plumage traits in male and female bearded reedlings ( Panurus biarmicus ). Our results indicate that higher IGF-1 levels had positive effects on male structural plumage colors and tail feather length. This is the first study, bringing indication for a potential role of IGF-1 in the expression of plumage ornaments in a bird species. Our findings suggest that IGF-1 might serve as an ideal candidate to study the mechanisms linking condition and the capacity to develop sexually selected ornaments.

中文翻译：

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胰岛素样生长因子 1 与雀斑类羽毛性状的表达有关

摘要 鸟类的羽毛颜色和饰物是研究将性选择特征与个体质量和状况参数联系起来的内分泌机制的极好模型。胰岛素样生长因子 1 (IGF-1) 是一种进化上高度保守的肽激素。它在细胞增殖和分化中的调节作用及其对个体营养状态的高度敏感性表明它是一个有趣的候选者，可能提供身体状况和个体生长复杂装饰特征的能力之间的联系。我们调查了蜕皮过程中 IGF-1 的水平是否与性二色雀形目雀科动物（Panurus biarmicus）中多种装饰物的表达相关。我们在蜕皮完成前不久收集了雄性和雌性的血液样本，并测量了观赏性状的大小和颜色。我们的结果表明，在雄性中，结构羽毛颜色、基于黑色素的装饰物（胡须）的大小和尾巴长度是独立的特征。IGF-1 水平与尾巴的长度和雄性结构羽毛成分（紫外线着色）的表达有关，但与基于黑色素的装饰无关。在雌性中，羽毛颜色和尾巴长度是独立的性状，与 IGF-1 水平无关。据我们所知，这项研究提供了第一个证据，表明 IGF-1 可以在鸟类第二性特征的发育中发挥作用。意义声明 IGF-1 是一种进化高度保守的肽类激素，最近进入了进化生物学研究的中心阶段。它被认为是塑造个人生活史的关键因素之一，但对其对性选择特征的影响知之甚少。我们调查了蜕皮过程中 IGF-1 的水平是否可以预测雄性和雌性有胡须的幼苗 ( Panurus biarmicus ) 的多种观赏羽毛特征的形成。我们的结果表明较高的 IGF-1 水平对雄性结构羽毛颜色和尾羽长度有积极影响。这是第一项研究，表明 IGF-1 在鸟类羽毛装饰表达中的潜在作用。我们的研究结果表明，IGF-1 可能是研究连接条件和发育性选择装饰品能力的机制的理想候选者。