CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, InBIO Laboratório Associado, Biodiversity and Land Planning, CIBIO, Campus de Vairão, Vairão 4485-661, Portugal.
BIOPOLIS Program in Genomics, Biodiversity and Land Planning, CIBIO, Campus de Vairão, Vairão 4485-661, Portugal.
Proc Biol Sci. 2022 Oct 12;289(1984):20221677. doi: 10.1098/rspb.2022.1677.
Carotenoid-based colour signals can be costly to produce and maintain, and trade-offs between signalling and other fitness traits are expected. In mutually ornamented species, trade-offs with reproduction may be stronger for females than males, because females often dedicate more resources to offspring production, which may lead to plastic investment in colour signals and plastic sexual dichromatism. Oestradiol is a candidate mediator of this trade-off because it regulates reproductive physiology and may also influence the expression of coloration. We tested this hypothesis by giving female common waxbills () either oestradiol (17β-oestradiol) or empty implants during the early breeding season and measured spectral reflectance of carotenoid-based bill coloration weekly for two months. Using a model of avian vision, we found that bill colour in oestradiol-implanted females became less saturated, less red in hue and brighter, compared with control females and with unimplanted males. This resulted in a change in bill sexual dichromatism from imperceptible to perceptible. Results support the hypothesis that female reproductive physiology influences investment in coloration through changes in oestradiol and show a form of female-driven plastic sexual dichromatism. Greater sensitivity of female colour to physiological and/or environmental conditions helps explain why differences in sexual dichromatism among species differing in ecology often evolve owing to changes in female rather than male phenotype.
类胡萝卜素为基础的颜色信号的产生和维持可能是昂贵的，并且预计信号和其他适合度特征之间存在权衡。在相互装饰的物种中，与繁殖的权衡对女性来说可能比男性更强，因为女性通常会投入更多的资源来生产后代，这可能导致颜色信号的可塑性投资和可塑性性二态性。雌激素是这种权衡的一个候选中介，因为它调节生殖生理，也可能影响颜色的表达。我们通过在早期繁殖季节给雌性普通蜡嘴雀（）注射雌激素（17β-雌二醇）或空植入物来测试这个假设，并在两个月内每周测量一次基于类胡萝卜素的喙颜色的光谱反射率。使用鸟类视觉模型，我们发现与对照雌性和未植入雄性相比，雌激素植入的雌性的喙颜色变得不那么饱和，色调上的红色更少，更亮。这导致喙性二态性从不可察觉变为可察觉。结果支持这样的假设，即雌性生殖生理通过雌激素的变化影响颜色的投资，并显示出一种雌性驱动的可塑性性二态性。女性颜色对生理和/或环境条件的敏感性增加有助于解释为什么在生态上不同的物种中，性二态性的差异通常是由于女性而不是男性表型的变化而进化的。
