An expression approach to the molecular basis of carotenoid signalling in birds

五颜六色的鸟类展示了自然界中一些最壮观的特征。许多这些表现依赖于羽毛和喙上亮红色或黄色类胡萝卜素的存在，这些特征在性选择研究中占有突出地位。特别是，类胡萝卜素的着色是诚实条件依赖着色的主要例子，它对潜在的配偶来说是吸引力和配偶质量的信号，对竞争对手来说是统治和战斗能力的信号。类胡萝卜素不是由鸟类（或任何其他脊椎动物）合成的，而是从它们的饮食中获得的，尽管它们可能经过化学修饰。除了着色，它们还具有抗氧化剂和免疫系统的重要功能，因此在使用它们时可能需要权衡。虽然影响类胡萝卜素着色的环境因素已经得到了很好的研究，但几乎没有关于遗传因素的信息，尽管这些因素在类胡萝卜素的转化和沉积中一定有几个重要的作用。该项目将首次分离出在鸟类类胡萝卜素着色中起重要作用的基因。研究对象是非洲寡妇鸟和奎利亚鸟，它们有很多优势：它们在类胡萝卜素的图案和展示中使用的类胡萝卜素类型上表现出极大的多样性；类胡萝卜素斑块的行为生态学已被深入研究；许多物种的类胡萝卜素含量和代谢已被研究；对这一群体进行了强有力的系统发育重建，这对检验比较进化假说很重要。该项目将分离出在寡妇鸟和奎利亚鸟的羽毛和喙中负责类胡萝卜素酶转化、运输和沉积的基因。从目标物种中分离出相关基因后，我们将继续确定它们在两性颜色中所起的相关作用，以及在暗红色和亮红色或黄色身体部位之间所起的作用。通过对魁利亚鸟和寡妇鸟的比较，我们可以确定，与羽毛毛囊相比，裸露身体部位的类胡萝卜素沉积是由相同还是不同的基因决定的。此外，通过检查基因在几个近亲和远亲物种中的作用，我们将致力于解决一些重要的进化问题，例如类胡萝卜素代谢和沉积的遗传机制保存得有多好，以及不同种类的类胡萝卜素的机制是否相同？这项研究将为鸟类类胡萝卜素着色的分子和进化基础提供独特的见解，这将引起行为生态学家和进化遗传学家的广泛兴趣。这项工作还将为未来研究类胡萝卜素着色的生理成本以及与其他类胡萝卜素功能（如抗氧化和免疫系统）的潜在权衡提供基础。

The colourful displays of birds represent some of the most spectacular features in the natural world. Many of these displays depend on the presence of bright red or yellow carotenoid pigments in feathers and bills, and these traits feature prominently in research on sexual selection. In particular, carotenoid-based coloration is the major example of honest condition-dependent coloration that functions either as a signal of attractiveness and mate quality to potential mates or dominance and fighting ability to competitive rivals. Carotenoids are not synthesized by birds (or any other vertebrates), but are obtained from their diet, although they may be chemically modified. In addition to coloration, they have important functions as antioxidants, and in the immune system, leading to the possibility of trade-offs in their usage. While environmental factors affecting carotenoid coloration have been well-studied, there is almost no information about the genetic factors involved, although these must have several important roles in carotenoid conversion and deposition. This project will for the first time isolate genes that are important in carotenoid-based coloration in birds. The study group are the African widowbirds and queleas, which have many advantages: they show great diversity in the carotenoid patterning and the type of carotenoid employed in displays; the behavioural ecology of carotenoid patches has been intensively studied; carotenoid content and metabolism have been studied in many species; and a robust phylogenetic reconstruction is available for this group, which is important for testing comparative evolutionary hypotheses. The project will isolate genes responsible for the enzymatic conversion, transport, and deposition of carotenoids in the feathers and bills of widowbirds and queleas. Having isolated the relevant genefrom target species, we will then go on to determine the relevant roles they play in the coloration of the two sexes, and between dull and bright red or yellow body parts. Comparison between the quelea and widow bird will allow us to determine if the same or different genes are responsible for carotenoid deposition in bare body parts compared to feather follicles. Also, by examining the role of the genes in several closely and more distantly related species, we will aim to address a number of important evolutionary questions, such as how well conserved are the genetic mechanisms of carotenoid metabolism and deposition, and are the mechanisms the same for different categories of carotenoids? This research will provide a unique insight into the molecular and evolutionary basis of carotenoid coloration in birds that will be of very broad interest to behavioural ecologists and evolutionary geneticists. The work will also provide the basis for future studies on physiological costs of carotenoid coloration and potential trade-offs with other carotenoid functions such as antioxidant and in the immune system.