The effect of colour-producing mechanisms on plumage sexual dichromatism in passerines and parrots

Sexual dichromatism (SD) often reflects intense sexual selection on males. It has been hypothesized that sexual selection should favour the elaboration of those male colours that honestly signal quality and that such colours should therefore show higher SD. Costliness of colours is expected to vary according to their production mechanism (pigment type, feather microstructure and combinations thereof). Carotenoid-based colours, due to their dietary origin and competing functions of carotenoid pigments, are the best documented costly colours, while endogenous pigments and structural colours are expected to be less costly. However, how SD varies with colour-producing mechanism has not been systematically addressed. Here, we test the link between SD and mechanisms of colour production across nearly all Australian passerines (n = 302) and parrots (n = 48), using reflectance spectrometry and visual models. We quantified SD [chromatic (hue and saturation) and achromatic (light to dark)] for i...性二色性（Sexual dichromatism, SD）通常反映了施加于雄性的强烈性选择压力。已有假说指出，性选择会青睐能够真实传递个体质量信号的雄性体色特征，因此这类体色往往表现出更为显著的性二色性。体色的生产成本会因其产生机制（色素类型、羽毛微观结构及其组合方式）而存在差异。其中，类胡萝卜素基色因源于饮食摄入且类胡萝卜素色素兼具多重竞争性功能，是目前研究最为充分的高成本体色；而内源性色素与结构色则被认为成本更低。然而，性二色性如何随体色产生机制发生变化，这一问题尚未得到系统性研究。 本研究借助反射光谱法（reflectance spectrometry）与视觉模型（visual models），针对澳大利亚几乎全部雀形目鸟类（n=302）与鹦鹉类（n=48），检验了性二色性与体色产生机制之间的关联。我们量化了各物种的性二色性指标，涵盖色彩维度（色调与饱和度）与消色差维度（明暗程度）……