Carotenoid content and reflectance of yellow and red nuptial plumages in widowbirds (Euplectes spp.)

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Abstract
Summary: Ornamental carotenoid coloration is commonly based on several different pigments with different nutritional and metabolic constraints. The identification and quantification of carotenoid pigments is therefore crucial to the understanding of signal content and signal evolution. In male widowbirds (Euplectes spp.), the striking yellow and red carotenoid colours have been measured by reflectance spectrometry and studied with respect to sexual selection through male contest competition, but their biochemical mechanisms have not been analysed. Here we use reflectance analysis and high performance liquid chromatography (HPLC) to describe the species‐specific colours and plumage carotenoids in three widowbird species: yellow‐mantled widowbird (YMW) Euplectes macrourus, red‐shouldered widowbird (RSW) E. axillaris and red‐collared widowbird (RCW) E. ardens. YMW yellow (‘hue’ colorimetric λR50 = 522 nm) derives from the two ‘dietary yellow’ xanthophylls lutein and zeaxanthin, together with small amounts of ‘derived yellow’ pigments (3′‐dehydrolutein and canary xanthophylls). RCW red (λR50 = 574 nm) is achieved by the addition of low concentrations of ‘derived red’ 4‐keto‐carotenoids, notably α‐ and β‐doradexanthin and canthaxanthin. RSW red (λR50 = 589 nm) is, in contrast, created by high concentrations of ‘dietary yellow’ pigments (lutein, zeaxanthin) and ‘derived yellow’ anhydrolutein, the latter only recently described in birds. The two different mechanisms of producing red plumage are compared with other bird species and discussed with regard to costs and signal ‘honesty’.