Carotenoid Coloration Research Articles

Radiation Processing of Minimally Processed Carrot (Daucus carota) and Cucumber (Cucumis sativus) to Ensure Safety: Effect on Nutritional and Sensory Quality

ABSTRACT: In the present study, radiation processing of minimally processed carrot and cucumber at a dose of 2 kGy was carried out. The effect of this treatment on different quality parameters such as vitamin C content, total carotenoids content, sensory quality, texture, and color was determined over a storage period of 16 d at 8°C to 10° C. In the case of cucumber, treatment of irradiation as well as storage period showed no significant change in the total vitamin C content of either the control or the irradiated samples. In the case of carrots, a 2-kGy dose had no significant effect (P < 0.05) on total vitamin C content of the samples. However, during storage, both control as well as irradiated samples showed significant decrease (P < 0.05) in vitamin C content. Total carotenoids content in carrot remained almost unchanged after irradiation as well as during storage. Sensory evaluation results showed that irradiation had no significant (P < 0.05) effect on the ratings of any of the sensory attributes in carrot. Radiation processing of cucumber affected the flavor significantly. However, this change did not alter the overall acceptability of cucumber. Textural studies revealed that in both carrot and cucumber, there was no significant change (P < 0.05) in firmness of the central region after irradiation, whereas the peripheral region in carrot showed significant reduction in firmness. In the case of cucumber, there was no significant change (P < 0.05) in the texture of both peripheral regions. However, during storage, the peripheral regions of carrot and cucumber showed significant increase in firmness. Color measurement results indicated no drastic change in color coordinates of carrot samples. Thus, the nutritional as well as sensory quality of minimally processed foods did not alter significantly after gamma irradiation.

Effect of dietary zinc level on serum carotenoid levels, body and shank pigmentation of chickens after experimental infection with coccidia

Two experiments were conducted to test the effects of a dietary zinc amino acid complex (Zn-AA) and an anticoccidial drug on Eimeria acervulina or Eimeria tenella infections. In each experiment, 288 day-old Three-Yellow-Chickens were used in a 2 × 3 factorial experimental design. Six groups were arranged randomly to receive three levels of Zn-AA (0, 40, or 80 mg/kg) alone or with salinomycin (60 mg/kg). Additionally an uninfected group was set as negative control. At the age of 21 days birds in Exp. 1 were inoculated with 3 · 104 sporulated E. acervulina oocysts, while birds in Exp. 2 were inoculated with 1.5 · 104 sporulated E. tenella oocysts. In Exp. 1, E. acervulina did not suppress growth performance significantly, but in groups without salinomycin it significantly reduced serum carotenoid levels on day 7 after inoculation and body and shank pigmentation on day 42. Salinomycin medication maintained serum carotenoids and visual colour of inoculated birds, but Zn-AA did not influence these parameters. In Exp. 2, growth performances of infected and uninfected chickens were similar. Infection decreased to only serum carotenoid levels on day 14 after infection, and colour scores on day 42 in the inoculated group without salinomycin and Zn-AA supplementation. The birds that received Zn-AA had significantly higher serum carotenoid levels and colour scores than those that did not. Although supplementation of Zn-AA cannot avoid coccidial damage of caecum, it prevents the reduction of serum carotenoids and pigmentation of Three-Yellow-Chicken infected with E. tenella, but not after infection with E. avervulina. The interactive effects between Zn-AA and salinomycin on growth performance and pigmentation were not significant.

Parental effects on carotenoid-based plumage coloration in nestling great tits, Parus major

Carotenoid pigments have attracted much interest in behavioural and evolutionary ecology because of their dual function in immune physiology and as color signals. In vertebrates, carotenoids must ultimately be obtained from the diet, and the mechanisms and magnitude of this environmental dependence are central for understanding carotenoid signal functions and evolution. In the present cross-fostering experiment with great tits Parus major, we investigate pre- and postnatal parental effects (egg yolk carotenoids, parental coloration) on nestling size and carotenoid coloration, using HPLC analysis of egg yolk carotenoids, and a reflectance-based measure of ‘chroma’ that reflects the plumage pigment concentration. Both rearing environment and origin influenced offspring size and plumage chroma. Maternal allocation of carotenoids to eggs had a weak positive effect on nestling plumage chroma, whereas we found no prenatal maternal effects (egg size or yolk carotenoid concentration) on size. Nestling plumage chroma was also significantly predicted by the chroma of the rearing father, but not by the color of the rearing mother or either of the original (genetical) parents. Thus, both prenatal maternal effects and postnatal paternal effects influence the carotenoid-based plumage coloration of nestling great tits. Future studies will reveal if parental effects have long-term consequences for plumage development and associated fitness components.

Genetic Linkage and Color Polymorphism in the Southern Platyfish (Xiphophorus maculatus): A Model System for Studies of Color Pattern Evolution

Color pattern polymorphisms are widespread in animals, and are found within populations, among populations, and among species. The southern platyfish, Xiphophorus maculatus, represents one of the most extreme examples of color pattern polymorphism. Extensive research with this model system for melanoma formation has resulted in an understanding of the underlying genetic basis of over 40 sex-linked and autosomal color patterns, including alleles that code for melanin, pterin, and carotenoid coloration. Research has also found that genes that affect sex determination, timing of sexual maturation, and coloration are genetically linked on the sex chromosomes. In many animals, color patterns often show strong sexual dimorphism, with conspicuous coloration limited to males. Although some of the color pattern alleles are sex-limited in platyfish, many are expressed by both sexes. Despite the abundance of work on this model system, little is known about the evolutionary processes responsible for this diversity of color pattern alleles. This review discusses what is known about platyfish coloration, and the roles that genetic linkage and variation in environmental conditions within and among populations might play in the evolution and maintenance of the extreme color pattern polymorphism exhibited by this platyfish.

USING SPECTRAL DATA TO RECONSTRUCT EVOLUTIONARY CHANGES IN COLORATION: CAROTENOID COLOR EVOLUTION IN NEW WORLD ORIOLES

Carotenoid-based colors are thought to play an important signaling role in many animal taxa. However, little is known about evolutionary changes in carotenoid coloration, especially among closely related species. We used a phylogenetic perspective to examine carotenoid color changes within New World orioles (genus Icterus). Oriole color was quantitatively measured using reflectance spectrometry. We found continuous variation from short- to long-wavelength carotenoid colors in extant orioles—perceived by humans as ranging from yellow to scarlet—suggesting that these carotenoid-based colors have evolved as a continuous character. Ancestral state reconstruction suggests that short- and long-wavelength carotenoid colors have evolved independently multiple times, likely from a middle-wavelength ancestor. Although color showed considerable lability, we found a significant amount of phylogenetic signal across the entire genus. This implies that while labile, the colors of closely related taxa tended to resemble each other more than would be expected due to chance. To our knowledge, this is the first study to use quantitative character states derived from reflectance spectra in ancestral state reconstruction. Reflectance spectra provide an unbiased quantitative description of color that allowed us to detect subtle changes among closely related taxa. Using these quantitative methods to score and reconstruct color changes among closely related taxa provides a better understanding of how elaborate animal colors evolve.

Carotenoid coloration in great black‐backed gull Larus marinus reflects individual quality

Carotenoids are a large group of biochemicals, with similar properties, synthesised by bacteria, fungi, algae and plants. Vertebrates obtain these biologically active pigments through the diet, and they are a disproportionately common component of animal colour signals and play important roles in immune functions and as antioxidants. Carotenoids are believed to be a limited resource and because of the trade‐off between allocation of carotenoids to signals and to other functions, carotenoid based signals are often thought to be handicap signals. The purpose of this study was to investigate the signalling potential of carotenoid‐based tissue coloration in the great black‐backed gull Larus marinus. The intensity of carotenoid‐based coloration in bill, gape and eye‐ring coloration was investigated in relation to body condition, reproductive parameters, levels of immune activity, and sexual dimorphism. In males there was a positive relationship between colour intensity and body condition, but in females no such relationship was found. However, females with high colour intensity had larger eggs and clutches. Additionally, females with high red scores tended to have high density of circulating lymphocytes. There was no sexual dimorphism in coloration and there was a negative relationship between colour intensity and sampling time, which indicates that this coloration is most intensely expressed early in the breeding season. The results in this study suggest that carotenoid‐based coloration in great black‐backed gull are partly condition dependent and reveal information about individual quality in both males an females. Hence, it might have evolved as an important signal for assessing the quality of potential mates.

Carotenoid coloration in great black-backed gull Larus marinus reflects individual quality

Carotenoid coloration in great black-backed gull Larus marinus reflects individual quality

Kinetics of colour changes in dehydrated carrots

Carotenoid degradation and colour loss in dehydrated blanched and unblanched carrot slices during storage at 27, 37, 47 and 57 °C were investigated. The degradation of β-carotene and colour loss followed a first-order reaction. A significant relationship was found between the colour loss and β-carotene degradation in blanched ( r = 0.878–0.971, p < 0.05) and unblanched samples ( r = 0.903–0.998, p < 0.05). Degradation of β-carotene had an activation energy of 15.8 ± 0.81 kcal mol −1 and 9.3 ± 2.07 kcal mol −1 for blanched and unblanched carrots, respectively. For blanched samples, the activation energies of colour loss determined on the basis of a and b values were 15.7 ± 2.81 kcal mol −1 and 21.7 ± 4.13 kcal mol −1, while those for unblanched samples determined as 10.5 ± 0.62 kcal mol −1 and 14.7 ± 1.30 kcal mol −1, respectively. Nonenzymatic browning of dehydrated carrots was also investigated and this reaction fitted to zero-order kinetic model. Activation energies of nonenzymatic browning occurred in blanched (25.3 ± 2.30 kcal mol −1) and unblanched (25.9 ± 2.61 kcal mol −1) dehydrated carrots was found similar.

Reduction or delay of post‐harvest physiological deterioration in cassava roots with higher carotenoid content

AbstractPost‐harvest physiological deterioration (PPD) is one of the most important constraints in cassava production and commercialization. It has been hypothesized that the antioxidant properties of carotenoids in yellow cassava roots may help reduce or delay PPD. The industrial sector prefers cassava with a high dry matter content. The latter has also been reported to have a positive correlation with PPD. The objective of this study was to determine the correlation between both the dry matter and total carotenoid contents and PPD in the roots of 101 cassava clones. PPD was positively but weakly associated with dry matter content (R2= 0.100,P&lt; 0.01), and inversely associated with the total carotenoid content in roots (R2= 0.515,P&lt; 0.01). In addition, total carotenoid content and color intensity were strongly and positively associated (R2= 0.769,P&lt; 0.01), suggesting that the roots of cassava clones with a relatively high total carotenoid content can be selected through a simple visual inspection of the color intensity in the parenchyma. Copyright © 2005 Society of Chemical Industry

Interspecific variation in the use of carotenoid‐based coloration in birds: diet, life history and phylogeny

Birds show striking interspecific variation in their use of carotenoid-based coloration. Theory predicts that the use of carotenoids for coloration is closely associated with the availability of carotenoids in the diet but, although this prediction has been supported in single-species studies and those using small numbers of closely related species, there have been no broad-scale quantitative tests of the link between carotenoid coloration and diet. Here we test for such a link using modern comparative methods, a database on 140 families of birds and two alternative avian phylogenies. We show that carotenoid pigmentation is more common in the bare parts (legs, bill and skin) than in plumage, and that yellow coloration is more common than red. We also show that there is no simple, general association between the availability of carotenoids in the diet and the overall use of carotenoid-based coloration. However, when we look at plumage coloration separately from bare part coloration, we find there is a robust and significant association between diet and plumage coloration, but not between diet and bare part coloration. Similarly, when we look at yellow and red plumage colours separately, we find that the association between diet and coloration is typically stronger for red coloration than it is for yellow coloration. Finally, when we build multivariate models to explain variation in each type of carotenoid-based coloration we find that a variety of life history and ecological factors are associated with different aspects of coloration, with dietary carotenoids only being a consistent significant factor in the case of variation in plumage. All of these results remain qualitatively unchanged irrespective of the phylogeny used in the analyses, although in some cases the precise life history and ecological variables included in the multivariate models do vary. Taken together, these results indicate that the predicted link between carotenoid coloration and diet is idiosyncratic rather than general, being strongest with respect to plumage colours and weakest for bare part coloration. We therefore suggest that, although the carotenoid-based bird plumage may a good model for diet-mediated signalling, the use of carotenoids in bare part pigmentation may have a very different functional basis and may be more strongly influenced by genetic and physiological mechanisms, which currently remain relatively understudied.

A novel lipoprotein-mediated mechanism controlling sexual attractiveness in a colorful songbird

Sexually selected traits like complex vocalizations or vibrant colors communicate reliable information about mate quality when they are costly to display. Although several general condition-dependent mechanisms underlying the acquisition of mating advertisements have been identified, we rarely know the precise physiological and molecular challenges that animals must meet to develop their sexual ornaments. The flashy pigment-based colors commonly displayed by birds are ideal candidates for investigating the pathways and demands of sexual-signal expression, because we know the biochemical currency with which the trait is produced. Carotenoid colors in birds, for example, are derived from pigments that are acquired from the diet and assimilated into feathers and bare parts. In previous work, we showed that variation in the sexually attractive red carotenoid-colored beak of male zebra finches (Taeniopygia guttata) was predicted not by the amount of food or pigments ingested, but by the levels of carotenoids that birds circulated in blood. Here we elucidate a novel physiological mechanism by which birds are able to accumulate high levels of carotenoids in the body and develop a colorful bill. Carotenoids are transported through the bloodstream bound to lipoproteins. We assayed a critical component of lipoprotein particles–cholesterol–and found that males with higher cholesterol levels circulated more carotenoids and displayed redder beaks. Experimental supplementation of dietary cholesterol elevated carotenoid levels in the blood and beak hue. Experimental reductions in blood cholesterol, using the human lipid-lowering agent atorvastatin, diminished blood carotenoids and faded the beak; carotenoid and cholesterol levels were restored, however, by subsequent addition of dietary cholesterol. These results suggest that the production of circulating lipoproteins critically regulates the development of a colorful sexually selected trait in zebra finches.

Maternally derived carotenoid pigments affect offspring survival, sex ratio, and sexual attractiveness in a colorful songbird

In egg-laying animals, mothers can influence the development of their offspring via the suite of biochemicals they incorporate into the nourishing yolk (e.g. lipids, hormones). However, the long-lasting fitness consequences of this early nutritional environment have often proved elusive. Here, we show that the colorful carotenoid pigments that female zebra finches (Taeniopygia guttata) deposit into egg yolks influence embryonic and nestling survival, the sex ratio of fledged offspring, and the eventual ornamental coloration displayed by their offspring as adults. Mothers experimentally supplemented with dietary carotenoids prior to egg-laying incorporated more carotenoids into eggs, which, due to the antioxidant activity of carotenoids, rendered their embryos less susceptible to free-radical attack during development. These eggs were subsequently more likely to hatch, fledge offspring, produce more sons than daughters, and produce sons who exhibited more brightly colored carotenoid-based beak pigmentation. Provisioned mothers also acquired more colorful beaks, which directly predicted levels of carotenoids found in eggs, thus indicating that these pigments may function not only as physiological 'damage-protectants' in adults and offspring but also as morphological signals of maternal reproductive capabilities.

QUALITY ATTRIBUTES OF TOMATOES SUBMITTED TO DIFFERENT POSTHARVEST TREATMENTS

Shipping tomatoes to distant markets is always a great challenge for tomato growers in tropical countries. Delaying ripening can be a useful technique to maintain quality during transportation. This work investigated the ability of different postharvest treatments to extend the shelf life of tomatoes. 'Carmen' tomato (Lycopersicon esculentum) fruit, were harvested at the breaker stage in commercial fields in Goias, Brazil. After harvest, fruit with no external blemishes were graded for weight (250±5 g) and diameter (6±0.5 cm), and treated with coconut grease (applied to the stem end), 1 - methylcyclopropene (1000 nl.L -1 ), wrapped in plastic films (18 μm thickness), and control. Fruit were stored for 10 days under refrigerated conditions (10±0.5°C/90-95% RH) and were analyzed every 2 days for weight loss, firmness, color (L*a*b*), and total carotenoids. Weight loss increased during the storage period. Control fruit and fruit treated with 1-MCP lost around 4% of their initial weight, whereas fruit treated with coconut grease in the stem end lost around 2%. Fruit stored under modified atmosphere showed less weight loss compared with other treatments. Treatment with 1-MCP delayed fruit softening. At the end of the storage period fruit treated with the ethylene antagonist had a firmness that was 50% higher than control fruit. Application of 1-MCP significantly delayed chlorophyll degradation and concomitant synthesis of carotenoid pigments. After 10 days, 1-MCP-treated fruit had a predominant green color when compared with other treatments.

Plasma Glutathione and Carotenoid Coloration as Potential Biomarkers of Environmental Stress in Great Tits

Measures of oxidative stress in animals may be useful biomarkers of environmental stressors, such as anthropogenic pollution. In birds, studies of oxidative stress have focused on dietary antioxidants, primarily carotenoids, which are interesting due to their multiple physiological and pigmentary functions but therefore also unspecifically related to oxidative stress. A useful complementary biomarker may be the glutathione system, commonly used in human medicine, but rarely applied to wild, terrestrial vertebrates. In this study of urban versus rural adult and nestling great tits Parus major, we investigated both the carotenoid-based yellow plumage (by reflectance spectrometry) and the plasma levels of glutathione, the latter measured as total glutathione (tGSH) and as the ratio between oxidized and reduced glutathione (GSSG:GSH), respectively. We found that urban adults had higher current oxidative stress (GSSG:GSH) and paler yellow plumage compared to rural adults, suggesting elevated stress in the urban environment. Total glutathione levels (tGSH), however, which may indicate long-term up-regulation of the GSH reservoir, did not differ between the environments. Nestlings did not show any consistent pattern between environments in either tGSH or GSSG:GSH and, among individuals, glutathione levels were uncorrelated with carotenoid coloration. The results thus suggest some population-level correspondence between the two stress biomarkers in adult birds, but more work is obviously needed to understand how the two antioxidant systems interact in different individuals and in response to different environmental disturbances.

Development of an Atlantic salmon ( Salmo salar) genetic improvement program: Genetic parameters of harvest body weight and carcass quality traits estimated with animal models

The Atlantic Salmon Broodstock Development Program is a partnership of researchers and producers that aims to breed salmon with an optimal combination of fast growth rate, low incidence of early sexual maturation, and good carcass quality for commercial aquaculture in Atlantic Canada. Estimation of genetic parameters for these traits is an essential step in the development of this breeding program. Four year classes of Atlantic salmon were produced, each consisting of 48–93 full-sib families. Marked fish from each of these families were randomly distributed to several producers to be raised under commercial conditions. At harvest, gutted body weights and sexual maturation level were observed in 812–3471 individuals per year class at processing plants. Additionally, colour score, astaxanthin, canthaxanthin, fat and moisture contents were recorded on 472 immature individuals from one year class. Genetic parameters were estimated with single- and multiple-trait animal models. Body weight, astaxanthin, canthaxanthin, colour, fat and moisture all exhibited moderate heritabilities (0.1–0.2), indicating that these traits should respond to selection. Positive genetic correlations were found between body weight and the carotenoid pigments, colour, and fat. These results indicate that direct selection for weight may have favourable indirect responses of higher colour scores and pigmentation but also an undesirable increase in flesh fat content. A properly weighted selection index should therefore be used to select broodstock for increased harvest weight and flesh colouration, while controlling flesh fat content.

Bacterial protein grown on natural gas as protein source in diets for Atlantic salmon, Salmo salar, in saltwater

Bacterial protein meal (BPM) produced on natural gas was evaluated with respect to growth, nutrient digestibilities, feed conversion ratios, sensory quality, and histopathological indices in Atlantic salmon in saltwater. In the extruded diets, experimentally produced BPM accounted for 0, 10, or 20% of the ingredients or 0, 17.2, or 33.1% of dietary nitrogen, replacing high-quality fish meal. Each diet was fed to two groups of salmon with a mean initial weight of 1.4 kg for 5 months. The pens were organized in two randomized blocks. One block was located with one side of the pens exposed to the open sea. The other block was completely surrounded by other pens. During the experiment, the salmon increased to approximately 3.6–3.9 kg in weight. Analysis of variance revealed no significant ( P>0.05) differences in growth, but regression analysis showed that fish weights at 2 and 5 months and growth rates for the whole experiment were slightly reduced with increasing content of BPM. No significant effects of diet were seen on dressed-out carcass, liver, or intestine to body weight percentages. Carcass and visceral fat and dry matter contents decreased with increasing dietary BPM. There was a trend (0.10≤ P<0.05) that apparent digestibilities of nitrogen, fat, and energy were reduced when substituting fish meal with BPM, while the nitrogen retention was not significantly affected. Flesh carotenoid concentration and colour were not significantly affected by dietary composition, nor were any differences seen for sensory characteristics related to taste, smell or texture. Histological examination did not reveal abnormalities, or signs of allergic reaction against BPM components, and hematocrit values were within normal ranges. Significant block effects were seen for chemical composition of viscera, and digestibilities of nitrogen, fat, and energy.

The evolution of carotenoid coloration in estrildid finches: a biochemical analysis

The estrildid finches (Aves: Passeriformes: Estrildidae) of Africa, Asia, and Australia have been the focus of several recent tests of sexual selection theory. Many estrildids display bright red, orange, or yellow colors in the beak or plumage, which typically are generated by the presence of carotenoid pigments. In this study, we used high-performance liquid chromatography to investigate the carotenoid content of feathers and other colorful tissues in seven species of estrildids. Star finches ( Neochmia ruficauda) and diamond firetails ( Stagonopleura guttata) circulated two main dietary carotenoids (lutein and zeaxanthin) through the blood and liver and used both to acquire a yellow plumage color. However, five other estrildids (common waxbill, Estrilda astrild; black-rumped waxbill, Estrilda troglodytes; zebra waxbill, Amandava subflava; red avadavat, Amandava amandava; and zebra finch, Taeniopygia guttata) circulated these same dietary carotenoids along with two metabolites (dehydrolutein and anhydrolutein) through the blood and/or liver and used all four as yellow plumage colorants. We subsequently tracked the distribution of these pigments using a published phylogeny of estrildid finches to determine the evolutionary pattern of carotenoid metabolism in these birds. We found that finches from the most ancient tribe of estrildids (Estrildini) possessed the ability to metabolize dietary carotenoids. Although carotenoids from the most ancestral extant estrildid species have yet to be analyzed, we hypothesize (based on their relationships with other songbirds known to have such metabolic capabilities) that these finches inherited from their ancestors the capability to metabolize carotenoids. Interestingly, later in estrildid evolution, certain taxa lost the ability to metabolize dietary carotenoids (e.g., in the Poephilini), suggesting that the occurrence of carotenoid metabolism can be labile and is likely shaped by the relative costs and benefits of color signaling across different species.

Females prefer carotenoid colored males as mates in the pentamorphic livebearing fish, Poecilia parae.

The first results of female preference and chosen male mating success in a new model organism, the pentamorphic livebearing fish, Poecilia parae, are presented. Poecilia parae is a relative of the guppy, P. reticulata, and is assumed to have similar reproductive behavior. We tested the hypothesis that P. parae females, like female guppies, prefer carotenoid colored males as mates. Here we show that the time a female spent with males was significantly greater for carotenoid coloration in red and yellow melanzona, but time with these two morphs did not differ. The preferred red and yellow males mated significantly more often with their choosing females than did the non-preferred blue and parae males. The few blue melanzona and parae males that mated did so without performing courtship displays. Some females mated with all phenotypes including immaculata males during open group trials. Female P. parae clearly preferred males with carotenoid coloration, thereby corroborating the hypothesis. Alternative male mating tactics by blue melanzona, parae, and immaculata morphs and promiscuous mating by females also resembled features of reproductive behaviors exhibited by guppies.

Assortative mating by carotenoid-based plumage colour: a quality indicator in American goldfinches, Carduelis tristis.

We investigated the mating patterns in 22 breeding pairs of wild American goldfinches (Carduelis tristis) with respect to their body size, condition, and carotenoid-based, yellow plumage colour. Using reflectance spectrometry, we objectively quantified plumage colours across the bird-visible wavelengths, revealing a unexpected UV peak in the reflectance spectrum from yellow feathers. We summarized our colour measurements using a principal components analysis to create a single variable, carotenoid PC1, that represents the intensity of this carotenoid-based yellow colour, a measure of phenotypic quality in this species. We found no evidence of assortative mating with respect to measures of body size or condition but there was positive assortative mating by carotenoid PC1, such that the yellow plumage colours of males and females were significantly correlated within pairs. We argue that the yellow carotenoid coloration of goldfinches may be important in mutual mate choice and, thus, that sexual selection in this species may act upon female ornamentation, as well as the more obvious plumage signals of males. Because assortative mating results in an increase in genetic variance, we suggest that this might be a mechanism that maintains variance in ornamental traits in spite of the variance-eroding effects of sexual selection.

Lutein-based plumage coloration in songbirds is a consequence of selective pigment incorporation into feathers

Many birds obtain colorful carotenoid pigments from the diet and deposit them into growing tissues to develop extravagant red, orange or yellow sexual ornaments. In these instances, it is often unclear whether all dietary pigments are used as integumentary colorants or whether certain carotenoids are preferentially excluded or incorporated into tissues. We examined the carotenoid profiles of three New World passerines that display yellow plumage coloration—the yellow warbler ( Dendroica petechia), common yellowthroat ( Geothlypis trichas) and evening grosbeak ( Coccothraustes vespertinus). Using high-performance liquid chromatography, we found that all species used only one carotenoid—lutein—to color their plumage yellow. Analyses of blood carotenoids (which document those pigments taken up from the diet) in two of the species, however, revealed the presence of two dietary xanthophylls—lutein and zeaxanthin—that commonly co-occur in plants and animals. These findings demonstrate post-absorptive selectivity of carotenoid deposition in bird feathers. To learn more about the site of pigment discrimination, we also analyzed the carotenoid composition of lipid fractions from the follicles of immature yellow-pigmented feathers in G. trichas and D. petechia and again detected both lutein and zeaxanthin. This suggests that selective lutein incorporation in feathers is under local control at the maturing feather follicle.