Plumage Pigment Differences in Manakins of the Pipra Erythrocephala Superspecies

Abstract

-We investigated the carotenoids found in the head feathers of three members of the Pipra erythrocephala superspecies by chromatographic, spectrophotometric, and chemical means. The Golden-headed Manakin (P. erythrocephala) primarily deposited yellow hydroxycarotenoids in its head feathers, predominately lutein. Red keto-carotenoids were also deposited locally. Canthaxanthin, for instance, was identified in the tips of nape feathers. In contrast, the Red-headed Manakin (P. rubrocapilla) deposited mostly orange and red ketocarotenoids. An orange pigment identified as a-doradexanthin was the most abundant. The common red pigments astaxanthin and canthaxanthin were also present. Finally, feathers of the red-headed Round-tailed Manakin (P. chloromeros) yielded a complement of carotenoids very similar to the Red-headed Manakin's. In addition, the Round-tailed Manakin deposited moderate amounts of rhodoxanthin, a plant keto-carotenoid of pronounced red hue. Within individual Red-headed Manakins, we observed differences in total carotenoid content and composition among head regions that differed slightly in color. The distal and proximal portions of individual feathers also differed markedly. We discuss possible physiological and biochemical mechanisms for these conditions, and suggest their relationship to the mechanisms responsible for the species-specific differences in manakin coloration. We reveal the probable origin of the Latin misnomer for the Golden-headed Manakin. Received 2 August 1988, accepted 2 August 1988. THE four species of Neotropical manakins that compose the Pipra erythrocephala superspecies (Snow 1979) differ conspicuously in the combination of their head, thigh, and underwing colors (Table 1). The difference in head color is particularly striking between the Golden-headed Manakin (Pipra erythrocephala) and its close relatives. The golden top and sides of the head of P. erythrocephala, belying its scientific name, contrast sharply with the bright red head of the other three allospecies. The colors involved are generally bright, and presumably implicate carotenoid pigments (Brush 1981). However, the biochemical and genetic basis of the color differences remains unexplored. P. erythrocephala is closely related to the Redheaded Manakin (P. rubrocapilla), with which it has been grouped in a single species (P. e. erythrocephala and P. e. rubrocapilla of Hellmayr 1929). The distribution of P. erythrocephala and P. rubrocapilla at their area of closest contact is delimited largely by the Amazon River. The 3To whom all reprint requests should be sent. occurrence of morphological differentiation associated with rivers is often found among understory Amazonian forest birds, a pattern largely unique to Amazonia (e.g. Hellmayr 1910, Snethlage 1913). One interpretation is that rivers act as barriers to gene flow and serve as geographical isolating mechanisms (Sick 1967). Capparella (1987, in press) reported large genetic distances between the two manakins, in excess of the mean for avian species [Nei's (1978) D = 0.101; avian mean 0.0440 ? 0.0221 SD, Barrowclough 1980] based on allozyme studies. Moreover, fixed differences were detected at three loci, a condition often lacking between undisputed avian species. Carotenoid pigments, responsible for most of the bright colors in birds, are relatively wellknown chemically. Furthermore, considerable work has been concerned with their biochemical modification and processing in birds (reviewed in Brush 1981). Differences in feather carotenoids are determined by both the processes responsible for their absorption and transport, and the metabolic capacities of the 34 The Auk 106: 34-41. January 1989 This content downloaded from 157.55.39.135 on Sun, 03 Jul 2016 06:06:41 UTC All use subject to http://about.jstor.org/terms January 1989] Pigment Differences in Pipra 35 birds to modify the pigments. Hence, carotenoid analysis can be used to infer physiological, and the underlying genetic, differences. In addition to providing specific plumage color and patterns (Fox and Hopkins 1966, Fox et al. 1967, Brush 1970, Brush and Johnson 1976, Troy and Brush 1983), carotenoid differences account for color polymorphisms (Volker 1964, Brush and Seifried 1968, Johnson and Brush 1972), subspecific plumage variation (Test 1942, Ford and Simpson 1987), and plumage variants (Volker 1964, Brush 1970, Hudon and Brush in press). To elucidate the nature of the physiological differences that confer species specificity of coloration in the manakins, we determined the pigment constitutions responsible for the difference in head color between P. erythrocephala and P. rubrocapilla. The Round-tailed Manakin (P. chloromeros), another member of the P. erythrocephala superspecies, was also ex-