Mechanism of carotenoid coloration in the brightly colored plumages of broadbills (Eurylaimidae)
The plumage carotenoids of six species from five genera of broadbills (Eurylaimidae) have been examined. These plumages are crimson, violet, purple-maroon, or yellow. Two genera also have brilliant green plumages that are produced by a combination of structural coloration and unknown carotenoids. Six different carotenoids from nine different plumage patches were identified, including two previously unknown molecules, using high-performance liquid chromatography, mass spectrometry, and MS/MS fragment analysis. The yellow pigment in Eurylaimus javanicus and Eurylaimus ochromalus is identified as the novel carotenoid, 7,8-dihydro-3′-dehydro-lutein. The yellow and green plumages of Psarisomus dalhousiae contain the unmodified dietary carotenoids lutein and zeaxanthin. The brilliant green feathers of Calyptomena viridis contain a mixture of lutein and two other xanthophylls that have previously been found only in woodpeckers (Picinae). The crimson and violet colors of Cymbirhynchus, Sarcophanops, and Eurylaimus are produced by a novel pigment, which is identified as 2,3-didehydro-papilioerythrinone. The molecular structure of this carotenoid was confirmed using 1H nuclear magnetic resonance, correlated two-dimensional spectroscopy, and two-dimensional nuclear Overhauser effect spectroscopy. Resonance Raman (rR) spectroscopy carried out at room and low temperatures was used to probe the configuration and conformation of 2,3-didehydro-papilioerythrinone in situ within crimson C. macrorhynchos and purple-red E. javanicus feathers. The rR spectra reveal that the pigment is in an all-trans configuration and appears to be relatively planar in the feathers. The likely metabolic pathways for the production of broadbill carotenoids from dietary precursors are discussed.