Laboratoire Évolution et Diversité Biologique, UMR5174 (CNRS, Université Paul Sabatier), 118 route de Narbonne, 31062 Toulouse, France
Cambridge Infectious Diseases Consortium, Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB30ES, UK.
J Exp Biol. 2019 Nov 11;222(Pt 21):jeb210237. doi: 10.1242/jeb.210237.
Carotenoid-based ornaments are common signaling features in animals. Although the mechanisms that link color-based signals to individual condition is key to understanding the evolution and function of these ornaments, they are most often poorly known. Several hypotheses have been posited. They include: (i) the role of foraging abilities on carotenoid acquisition and thereby carotenoid-based ornaments, and (ii) the role of internal processes linked to individual quality on the allocation and conversion of carotenoids in integuments. Here, we tested the influence of dietary carotenoid access versus internal process on gape coloration in black-legged kittiwakes (). This seabird displays a vibrant red gape, whose coloration varies with individual quality in males and is due to the deposition of red ketocarotenoids, such as astaxanthin. We decreased hydroxycarotenoid and ketocarotenoid levels in plasma, but increased efficiency in internal processes linked to nutritional condition, by supplementing breeding males with capelin, a natural energy-rich fish prey. We found that, despite having lower carotenoid levels in plasma, supplemented birds developed redder coloration than control birds, but only in the year when dietary levels of astaxanthin in the natural diet were low. In contrast, in the astaxanthin-rich year, supplemented males had a less-red gape than unsupplemented birds. These results suggest that inter-individual differences in internal processes may be sufficient to maintain the honesty of gape coloration under conditions of low dietary astaxanthin levels. Nonetheless, when inter-individual variations in dietary astaxanthin levels are elevated (such as in the crustacean-rich year), carotenoid access seems a more limiting factor to the expression of gape coloration than internal processes. Therefore, our study revealed a complex mechanism of gape color production in kittiwakes, and suggests that the main factor maintaining the condition dependency of this ornaments may vary with environmental conditions and diet composition.
基于类胡萝卜素的装饰是动物中常见的信号特征。尽管将基于颜色的信号与个体状况联系起来的机制是理解这些装饰物的进化和功能的关键，但这些机制通常知之甚少。已经提出了几种假设。它们包括：（i）觅食能力对类胡萝卜素获取的影响，从而影响基于类胡萝卜素的装饰物，以及（ii）与个体质量相关的内部过程对表皮中类胡萝卜素的分配和转化的影响。在这里，我们测试了饮食类胡萝卜素获取与内部过程对黑腿海鸥（）口角颜色的影响。这种海鸟显示出鲜艳的红色口角，其颜色因个体质量而异，这是由于红色酮类胡萝卜素（如虾青素）的沉积所致。我们通过给繁殖雄性补充毛鳞鱼（一种天然富含能量的鱼类猎物）来降低血浆中的羟基类胡萝卜素和酮类胡萝卜素水平，但提高了与营养状况相关的内部过程的效率。我们发现，尽管血浆中的类胡萝卜素水平较低，但补充组的鸟类比对照组的鸟类发育出更红色的颜色，但仅在天然饮食中虾青素水平较低的那一年。相比之下，在富含虾青素的那一年，补充组的雄性比未补充组的鸟类口角颜色较浅。这些结果表明，个体间内部过程的差异可能足以在低饮食虾青素水平的条件下维持口角颜色的诚实性。然而，当饮食中虾青素水平的个体间差异升高时（例如在富含甲壳类动物的年份），类胡萝卜素获取似乎比内部过程更能限制口角颜色的表达。因此，我们的研究揭示了海鸥口角颜色产生的复杂机制，并表明维持这种装饰物状况依赖性的主要因素可能因环境条件和饮食组成而异。
