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

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.