Unusual carotenoid use by the Western Tanager (Piranga ludoviciana) and its evolutionary implications

Abstract

I used spectrophotometric, chromatographic, and chemical means to establish that rhodoxanthin, a 3-keto-retrodehydro carotenoid, was the only red pigment in the head feathers of the Western Tanager (Piranga ludoviciana). In contrast, the red head and body feathers of a close relative, the Scarlet Tanager (P. olivacea), exhibited several 4-keto-carotenoids. Other tanagers and emberizids also displayed 4-keto-carotenoids. The deposition of presumed canary xanthophylls and phaeomelanins differed quantitatively between the Western Tanager and other tanagers belonging to the genus Piranga. Uniquely among the Piranga spp. examined, the head feathers of the Western Tanager had flattened bards without barbules. Partly because the head colors of the Western and Scarlet tanagers were indistinguishable either in the hand or when examined by reflectance spectrophotometry, I excluded selection for a variant color as the basis for the observed chemical and morphological differences. Biochemical costs, including putative costs associated with the endogenous production of 4-keto-carotenoids, could have led to the conversion in the Western Tanager to an available dietary pigment. This tanager, unlike the other species studied, has access to an abundant source of rhodoxanthin in the coniferous forests of western North America. The pigment changes in the Western Tanager could have taken place with minimal effect on head color.

Individual colour patches as multicomponent signals

“…Red keto-carotenoids tend to be less abundant than yellow carotenes and xanthophylls in the diet of most vertebrates (Hill, 1996). Costs of metabolic conversion may make red carotenoids more costly, and thus more reliable as indicators of phenotypic quality, than yellow carotenoids (Hudon, 1991 ;Hill, 1996). This hypothesis appears to be supported by Hill's (1996) comparative study of cardueline finches (the degree of sexual dichromatism and the redness of male plumage correlate positively across species in this clade), and also by a food limitation study (controlling for carotenoid intake, better fed house finches Carpodacus mexicanus were redder; Hill, 2000).…”

Variation in carotenoid–protein interaction in bird feathers produces novel plumage coloration

“…In the present study, we employed rR spectroscopy to investigate carotenoidprotein interactions responsible for the coloration of brilliant red and purple plumages of the scarlet ibis Eudocimus ruber (Threskiornithidae), summer tanager Piranga rubra (Cardinalidae) and white-browed purpletuft Iodopleura isabellae (Tityridae). All these plumage patches contain canthaxanthin (b,b-carotene-4,4 0 -dione) as the primary carotenoid [33][34][35] (figure 1).…”

Absence of Reproductive Consequences of Hybridization in the Northern Flicker (Colaptes auratus) Hybrid Zone

“…The retro-carotenoid of deep red hue is not typically produced by birds from dietary carotenoids, but rather acquired exogenously from the diet (Hudon andBrush 1989, Hudon 1991; but see Hudon et al 2007). The carotenoid has been documented in at least 2 species of songbirds with aberrant red colors in eastern North America (Hudon andBrush 1989, Hudon et al 2013), and suspected in several additional species that have turned up with atypical red feathers in eastern North America and the American Midwest (Mulvihill et al 1992, Brooks 1994, Craves 1999, Flinn et al 2007, Hudon et al 2013.…”

“…In Cedar Waxwings (Bombycilla cedrorum) and Baltimore Orioles (Icterus galbula), the aberrant color results from the incorporation of a carotenoid of deep red hue, rhodoxanthin, acquired exogenously (Hudon and Brush 1989, Brush 1990, Mulvihill et al 1992, Witmer 1996, Hudon et al 2013. Known sources of rhodoxanthin are few in nature, especially in forms that birds can ingest (see Hudon 1991). One recognized source is the berries of Tatarian (Lonicera tatarica) and Morrow's (L. morrowii) honeysuckles and their hybrid, Bell's honeysuckle (L. 3 bella), bush honeysuckles native to southern Russia, western and central Asia (L. tatarica), and Japan (L. morrowii), introduced as early as the 1700s and now naturalized and widely distributed in eastern North America and the American Midwest (Edminster 1950, Jackson 1974, Witmer 1996.…”