Candidate genes for carotenoid coloration in vertebrates and their expression profiles in the carotenoid-containing plumage and bill of a wild bird

Abstract

Carotenoid-based coloration has attracted much attention in evolutionary biology owing to its role in honest, condition-dependent signalling. Knowledge of the genetic pathways that regulate carotenoid coloration is crucial for an understanding of any trade-offs involved. We identified genes with potential roles in carotenoid coloration in vertebrates via (i) carotenoid uptake (SR-BI, CD36 ), (ii) binding and deposition (StAR1, MLN64, StAR4, StAR5, APOD, PLIN, GSTA2), and (iii) breakdown (BCO2, BCMO1). We examined the expression of these candidate loci in carotenoid-coloured tissues and several control tissues of the red-billed quelea (Quelea quelea), a species that exhibits a male breeding plumage colour polymorphism and sexually dimorphic variation in bill colour. All of the candidate genes except StAR1 were expressed in both the plumage and bill of queleas, indicating a potential role in carotenoid coloration in the quelea. However, no differences in the relative expression of any of the genes were found among the quelea carotenoid phenotypes, suggesting that other genes control the polymorphic and sexually dimorphic variation in carotenoid coloration observed in this species. Our identification of a number of potential carotenoid genes in different functional categories provides a critical starting point for future work on carotenoid colour regulation in vertebrate taxa.

Male Red-backed Fairywrens appear to enhance a plumage-based signal via adventitious molt

“…Many studies report that bill color is typically brighter or more saturated in the sex with the more ornamented plumage (Alonso-Alvarez et al 2004, Kelly et al 2012, Walsh et al 2012, Cardoso et al 2014, Vergara et al 2015. In birds with sexually monochromatic plumage, males and females often have monochromatic bare parts (Eens et al 2000, Velando et al 2001, Massaro et al 2003, Jouventin et al 2005, Stirnemann et al 2009, Doutrelant et al 2013).…”

Correlations of Condition, Testosterone, and Age with Multiple Ornaments in Male House Sparrows: Patterns and Implications

“…The need for additional epidermal differentiation genes in order to achieve carotenoidcolored plumage might partially explain why carotenoid coloration is more commonly observed in bare parts. Carotenoids in bare skin, unlike in feathers, are protected from photodegradation by esterification (McGraw 2004, Walsh et al 2012, Pérez-Rodríguez et al 2016, which suggests they might be withdrawn for use at a later date; however, experimental evidence suggests that colorful skin …”

Ancient origins and multiple appearances of carotenoid-pigmented feathers in birds

“…This is perhaps not surprising considering that birds can extract carotenoids from food and circulate the pigments in blood using nutrient-uptake and -delivery mechanisms (e.g. lipoproteins) [8][9][10] that are conserved across vertebrates [11]. Hence, the dietary uptake of carotenoids is plesiomorphic to all birds, dinosaurs and reptiles (see [10] for further discussion).…”

“…lipoproteins) [8][9][10] that are conserved across vertebrates [11]. Hence, the dietary uptake of carotenoids is plesiomorphic to all birds, dinosaurs and reptiles (see [10] for further discussion). The carotenoids that circulate in the blood of many birds, snakes and lizards can accumulate in keratinous scales [12,13].…”