The gene crtI mediates the conversion of phytoene into colored carotenoids in Rhodopseudomonas capsulata

Carotenoids are membrane pigments present in all photosynthetic organisms, providing essential photoprotective functions. The first carotenoid formed in the pathway is phytoene, a colorless compound which is then converted into colored carotenoids by a series of dehydrogenation reactions. In the photosynthetic bacterium Rhodopseudomonas capsulata mutations that affect carotenoid biosynthesis before colored carotenoids are formed have a "blue-green" phenotype as opposed to the "red" of wild type cells. We have extracted carotenoids from several blue-green mutants and found that two strains (BPY69 and BPY102) accumulate phytoene and no colored carotenoids. These mutants failed to dehydrogenate phytoene in an in vitro assay. However, dehydrogenation of this compound can be achieved in vitro by adding a cell-free extract from another blue-green mutant blocked earlier in the pathway. Genetic complementation and deletion mapping indicate that the gene crtI is responsible for the conversion of phytoene into colored carotenoids in these mutants.     

Botryococcus as an alternative source of carotenoids and its possible applications – an overview

The enhanced interest in carotenoid research arises partly because of their application in the food and health industries and partly because of the necessity to find a commercially viable natural source for their mass production. The bottlenecks in finding a natural source of carotenoids which can compete with the synthetic products is the mass production of the organism that produces carotenoids, cell harvesting and extraction methods of carotenoids. The microalga Botryococcus braunii is an interesting organism for its commercial value as a rich source of carotenoids. It contains lutein as major carotenoid which is considered to be one of the beneficial carotenoids in human health applications. The current paper reviews the status of B. braunii as an alternative source of carotenoid production on the commercial scale addressing aspects like cultures of algae, factors that enhance the production and accumulation of carotenoids, cell harvesting methods, and carotenoid extraction. The paper also presents an overview of identification, characterization and structural elucidation of carotenoids from B. braunii and their bioactivity.     

Asymmetrically acting lycopene β-cyclases (CrtLm) from non-photosynthetic bacteria

Carotenoids have important functions in photosynthesis, nutrition, and protection against oxidative damage. Some natural carotenoids are asymmetrical molecules that are difficult to produce chemically. Biological production of carotenoids using specific enzymes is a potential alternative to extraction from natural sources. Here we report the isolation of lycopene -cyclases that selectively cyclize only one end of lycopene or neurosporene. The crtLm genes encoding the asymmetrically acting lycopene -cyclases were isolated from non-photosynthetic bacteria that produced monocyclic carotenoids. Co-expression of these crtLm genes with the crtEIB genes from Pantoea stewartii (responsible for lycopene synthesis) resulted in the production of monocyclic -carotene in Escherichia coli. The asymmetric cyclization activity of CrtLm could be inhibited by the lycopene -cyclase inhibitor 2-(4-chlorophenylthio)-triethylamine (CPTA). Phylogenetic analysis suggested that bacterial CrtL-type lycopene -cyclases might represent an evolutionary link between the common bacterial CrtY-type of lycopene -cyclases and plant lycopene - and -cyclases. These lycopene -cyclases may be used for efficient production of high-value asymmetrically cyclized carotenoids.Communicated by E. Cerdá-Olmedo     

Carotenoids: separation methods applicable to biological samples

Epidemiologic and clinical studies have shown that a high intake of vegetables and fruit, with consequently high intakes and circulating concentrations of carotenoids, is associated with reduced risk of cardiovascular and other chronic diseases. The antioxidant properties of carotenoids are thought to contribute to these effects. The analysis of carotenoids in plasma, foods and tissues has thus become of interest in studies examining the role of diet in chronic disease prevention and management. High-performance liquid chromatography with ultra-violet or photodiode array detection is most often employed in routine use. We review these and other current methods for carotenoid analysis and information on sample stability relevant to epidemiological studies. The carotenoids remain an important and intriguing subject of study, with relevance to prevention of several important "lifestyle-related" diseases. Research into their physiological functions and their use as dietary markers requires sensitive, accurate and precise measurement. Further advances in these methodological areas will contribute to basic, clinical and public health research into the significance of carotenoid compounds in disease prevention.     

Biosynthesis and regulation of carotenoids in Dunaliella: progresses and prospects

Natural carotenoids are high in demand in global market owing to their widespread applications in nutrition, medicine, food coloring agent and cosmetic, as well as to the natural and healthy preference of consumers today. Some strains of Dunaliella are well known for their talent of massive beta-carotene accumulation. Content of the high bioavailability stereoisomer of beta-carotene, the 9-cis stereoisomer, is highest in Dunaliella among all the natural carotenoids sources. These valuable algae have been exploited commercially for beta-carotene-rich Dunaliella powder and natural beta-carotene in many countries since 1980s. However, drawbacks of traditional production methods have hampered the worldwide promotion of carotenoids production with Dunaliella. To shake off the dilemma, complete understanding of carotenogenic mechanism is urgent. Carotenogenic mechanism in Dunaliella is described in present paper, including carotenogenic pathway and its regulation. Generally, it seems that carotenogenic pathway in Dunaliella is close to the one of higher plants. It is known that reactive oxygen species (ROS) were involved in signal transduction for gene activation. Induction of ROS is in parallel with the enhanced beta-carotene accumulation in Dunaliella. It is suggested that ROS trigger massive carotenoids accumulation in Dunaliella. It also revealed that relation may exist between enhanced beta-carotene accumulation and lipid metabolism. For the talent of beta-carotene synthesis, it is possible that Dunaliella massively accumulates beta-carotene and other high-value carotenoids by genetic technologies.     

Age-Related Relationships between Innate Immunity and Plasma Carotenoids in an Obligate Avian Scavenger

Variation in immunity is influenced by allocation trade-offs that are expected to change between age-classes as a result of the different environmental and physiological conditions that individuals encounter over their lifetime. One such trade-off occurs with carotenoids, which must be acquired with food and are involved in a variety of physiological functions. Nonetheless, relationships between immunity and carotenoids in species where these micronutrients are scarce due to diet are poorly studied. Among birds, vultures show the lowest concentrations of plasma carotenoids due to a diet based on carrion. Here, we investigated variations in the relationships between innate immunity (hemagglutination by natural antibodies and hemolysis by complement proteins), pathogen infection and plasma carotenoids in nestling and adult griffon vultures (Gyps fulvus) in the wild. Nestlings showed lower hemolysis, higher total carotenoid concentration and higher pathogen infection than adults. Hemolysis was negatively related to carotenoid concentration only in nestlings. A differential carotenoid allocation to immunity due to the incomplete development of the immune system of nestlings compared with adults is suggested linked to, or regardless of, potential differences in parasite infection, which requires experimental testing. We also found that individuals with more severe pathogen infections showed lower hemagglutination than those with a lower intensity infection irrespective of their age and carotenoid level. These results are consistent with the idea that intraspecific relationships between innate immunity and carotenoids may change across ontogeny, even in species lacking carotenoid-based coloration. Thus, even low concentrations of plasma carotenoids due to a scavenger diet can be essential to the development and activation of the immune system in growing birds.     

The Evolution of Oxygen As a Biosynthetic Reagent

The biosynthesis of certain cell constituents: monounsaturated fatty acids, tyrosine, and nicotinic acid, is oxygen-dependent in many higher organisms. The same compounds can be synthesized by different, oxygen-independent pathways in lower organisms. The general outlines of these pathways are described and the importance of the compounds synthesized is discussed. An examination of the distribution of these pathways among living organisms reveals that oxygen-dependent pathways replaced the "anaerobic" pathways at different branch points on the evolutionary tree. Other groups of compounds are discussed, which are not distributed as widely among living organisms, but are found in all higher organisms. These compounds have specialized functions and their biosynthesis requires molecular oxygen. The oxygen-dependent portions of the biosynthetic pathways leading to porphyrins, quinone coenzymes, carotenoids, sterols, and polyunsaturated fatty acids are summarized. The distribution and functions of these compounds are also considered and an attempt is made to place them in the framework of evolution. While sterols and polyunsaturated fatty acids are found exclusively in the higher Protista and multicellular organisms, carotenoids, porphyrins, and quinones are also found in bacteria. The possibility of oxygen-independent mechanisms for their biosynthesis is discussed.     

The role of carotenoids and their derivatives in mediating interactions between insects and their environment

Carotenoids are long conjugated isoprenoid molecules derived mainly from plants and microbial organisms. They are highly diverse, with over 700 identified structures, and are widespread in nature. In addition to their fundamental roles as light-harvesting molecules in photosynthesis, carotenoids serve a variety of functions including visual and colouring pigments, antioxidants and hormone precursors. Although the functions of carotenoids are relatively well studied in plants and vertebrates, studies are severely lacking in insect systems. There is a particular dearth of knowledge on how carotenoids move among trophic levels, influence insect multitrophic interactions and affect evolutionary outcomes. This review explores the known and potential roles that carotenoids and their derivatives have in mediating the ecological interaction of insects with their environment. Throughout the review, we highlight how the fundamental roles of carotenoids in insect physiology might be linked to ecological and evolutionary processes.     

Flesh Color Diversity of Sweet Potato: An Overview of the Composition,Functions, Biosynthesis,and Gene Regulation of the Major Pigments

Sweet potato is a multifunctional root crop and a source of food with many essential nutrients and bioactive compounds. Variations in the flesh color of the diverse sweet potato varieties are attributed to the different phytochemicals and natural pigments they produce. Among them, carotenoids and anthocyanins are the main pigments known for their antioxidant properties which provide a host of health benefits, hence, regarded as a major component of the human diet. In this review, we provide an overview of the major pigments in sweet potato with much emphasis on their biosynthesis, functions, and regulatory control. Moreover, current findings on the molecular mechanisms underlying the biosynthesis and accumulation of carotenoids and anthocyanins in sweet potato are discussed. Insights into the composition, biosynthesis, and regulatory control of these major pigments will further advance the biofortification of sweet potato and provide a reference for breeding carotenoid- and anthocyanin-rich varieties.     

Biological functions of carotenoids--diversity and evolution

Carotenoids first emerged in archaebacteria as lipids reinforcing cell membranes. To serve this function their long molecules have extremely rigid backbone due to the linear chain of usually 10 to 11 conjugated C=C bonds in transconfiguration--the length corresponding the thickness of hydrophobic zone of membrane which they penetrate as "molecular rivets". Carotenoids retain their membrane-reinforcing function in some fungi and animals. The general structure of carotenoid molecule, originally having evolved for mechanical functions in membranes, possess a number of other properties that were later used for independent functions. The most striking fact is that these properties proved to fit some new functions to perfection. The polyene chain of 9-11 double bonds absorbs light precisely in the gap of chlorophyll absorption--function as accessory light-harvesting pigments in all plants; Unique arrangement of electronic levels owing to the by polyene chain structure makes carotenoids the only natural compounds capable of excitation energy transfer both (i) from carotenoid excited state to chlorophyll in the light-harvesting complex and (ii) from triplet chlorophyll or singlet oxygen to carotenoid in photosynthetic reaction centers--protection of RC from photodamage. The linear system of conjugated C=C bonds provides high reducing potential of carotenoid molecules making them potent antioxidants in lipid formations. Still, there is a lack of evidence of the chemical antioxidant function of carotenoids, especially in higher organisms; most data demonstrate an antioxidant ability rather than a function. Carotenoids have many other independent biological functions, including: specific coloration patterns in plants and animals, screening from excessive light and spectral filtering, defense of egg proteins from proteases in some invertebrates; the direct carotenoid derivative--retinal--acts as visual pigment in all animals and as chromophore in bacteriorhodopsin photosynthesis, retinoic acid in animals and abscisic acid in plants serve as hormones. All these functions utilize various properties (mechanical, electronic, stereospecific) of a single structure evolved in bacteria for a single membrane-reinforcing function, thus demonstrating an example of pure evolutionary preadaptation. One of the practical conclusions that can be reached by reviewing uniquely diverse properties and functions of carotenoids is that, when considering possible mechanisms of their effects in organisms (e.g., anticarcinogenic action), all their functional traits should be taken into account.     

茶类胡萝卜素研究进展

类胡萝卜素是茶(Camellia sinensis (L.) O. Ktze.)中一类重要的光合色素,具有光保护、抗氧化等众多生理功能,同时也是脱落酸、独脚金内酯和胡萝卜内脂等植物激素的合成前体,在茶生长发育过程中起极其重要的作用。类胡萝卜素还是构成茶叶外形、叶底色泽的重要成分,也是茶叶重要致香物质的前体物,其种类、含量对茶叶品质起着至关重要的作用。本文对茶中类胡萝卜素种类、代谢途径及其对制茶品质的影响等方面的研究进展进行了综述,同时对茶类胡萝卜素下一步的研究方向进行了展望。     

Carotenoids in fish. XX. Carotenoids in Salmo gairdneri rich. And Salmo trutta morpha fario L.

The author investigated the presence of various carotenoids in Salmo gairdneri Rich. and Salmo trutta morpha fario L. from the trout fish farm (artificial food) and from the river as the natural conditions (natural food).The findings of these investigations indicate that the trout bred in natural conditions are richer in carotenoids, provitamins of vitamin A, than are trout from the trout fish farm. In all probability the variety of food available in natural conditions provides better facilities for the accumulation of carotenoids in the body of trout in their natural habitat.     

Outdoor cultivation of microalgae for carotenoid production: current state and perspectives

Microalgae are a major natural source for a vast array of valuable compounds, including a diversity of pigments, for which these photosynthetic microorganisms represent an almost exclusive biological resource. Yellow, orange, and red carotenoids have an industrial use in food products and cosmetics as vitamin supplements and health food products and as feed additives for poultry, livestock, fish, and crustaceans. The growing worldwide market value of carotenoids is projected to reach over US$1,000 million by the end of the decade. The nutraceutical boom has also integrated carotenoids mainly on the claim of their proven antioxidant properties. Recently established benefits in human health open new uses for some carotenoids, especially lutein, an effective agent for the prevention and treatment of a variety of degenerative diseases. Consumers’ demand for natural products favors development of pigments from biological sources, thus increasing opportunities for microalgae. The biotechnology of microalgae has gained considerable progress and relevance in recent decades, with carotenoid production representing one of its most successful domains. In this paper, we review the most relevant features of microalgal biotechnology related to the production of different carotenoids outdoors, with a main focus on β-carotene from Dunaliella, astaxanthin from Haematococcus, and lutein from chlorophycean strains. We compare the current state of the corresponding production technologies, based on either open-pond systems or closed photobioreactors. The potential of scientific and technological advances for improvements in yield and reduction in production costs for carotenoids from microalgae is also discussed.     

Diversifying carotenoid biosynthetic pathways by directed evolution.

Microorganisms and plants synthesize a diverse array of natural products, many of which have proven indispensable to human health and well-being. Although many thousands of these have been characterized, the space of possible natural products--those that could be made biosynthetically--remains largely unexplored. For decades, this space has largely been the domain of chemists, who have synthesized scores of natural product analogs and have found many with improved or novel functions. New natural products have also been made in recombinant organisms, via engineered biosynthetic pathways. Recently, methods inspired by natural evolution have begun to be applied to the search for new natural products. These methods force pathways to evolve in convenient laboratory organisms, where the products of new pathways can be identified and characterized in high-throughput screening programs. Carotenoid biosynthetic pathways have served as a convenient experimental system with which to demonstrate these ideas. Researchers have mixed, matched, and mutated carotenoid biosynthetic enzymes and screened libraries of these "evolved" pathways for the emergence of new carotenoid products. This has led to dozens of new pathway products not previously known to be made by the assembled enzymes. These new products include whole families of carotenoids built from backbones not found in nature. This review details the strategies and specific methods that have been employed to generate new carotenoid biosynthetic pathways in the laboratory. The potential application of laboratory evolution to other biosynthetic pathways is also discussed.     

Inhibitory Effect of Carotenoids on the Degranulation of Mast Cells via Suppression of Antigen-induced Aggregation of High Affinity IgE Receptors

Carotenoids have been demonstrated to possess antioxidative and anti-inflammatory effects. However, there is no report that the effects of carotenoids on degranulation of mast cell is critical for type I allergy. In this study, we focused on the effect of carotenoids on antigen-induced degranulation of mast cells. Fucoxanthin, astaxanthin, zeaxanthin, and β-carotene significantly inhibited the antigen-induced release of β-hexosaminidase in rat basophilic leukemia 2H3 cells and mouse bone marrow-derived mast cells. Those carotenoids also inhibited antigen-induced aggregation of the high affinity IgE receptor (FcϵRI), which is the most upstream of the degranulating signals of mast cells. Furthermore, carotenoids inhibited FcϵRI-mediated intracellular signaling, such as phosphorylation of Lyn kinase and Fyn kinase. It suggests that the inhibitory effect of carotenoids on the degranulation of mast cells were mainly due to suppressing the aggregation of FcϵRI followed by intracellular signaling. In addition, those carotenoids inhibited antigen-induced translocation of FcϵRI to lipid rafts, which are known as platforms of the aggregation of FcϵRI. We assume that carotenoids may modulate the function of lipid rafts and inhibit the translocation of FcϵRI to lipid rafts. This is the first report that focused on the aggregation of FcϵRI to investigate the mechanism of the inhibitory effects on the degranulation of mast cells and evaluated the functional activity of carotenoids associated with lipid rafts.Mast cells play pivotal roles in inflammation and immediate-type allergic reactions by secreting biologically active substances including histamine, eicosanoids, proteolytic enzymes, cytokines, and chemokines. The antigen-induced aggregation of the high affinity IgE receptor (FcϵRI)² expressed on the cell surface triggers the degranulation of mast cells. FcϵRI has a tetrameric structure comprised of an IgE binding α-chain, a β-chain, and a disulfide-linked γ-chain dimer (1). The aggregation of FcϵRI by means of multivalent antigen-IgE complexes activates cytosolic Src protein-tyrosine kinases, such as Fyn and Lyn, which then regulate the activation of mast cells (2). Fyn kinase plays a key role in mast cell degranulation and in cytokine production by regulating Gab2 and phosphatidylinositol 3-kinase (3). Phosphorylated Lyn activates immunoreceptor tyrosine-based activation motifs of the β- and γ-chains, and the phosphorylated immunoreceptor tyrosine-based activation motifs of the γ-chain phosphorylate Syk kinase. Thereafter, a number of other signaling and adaptor molecules, such as phospholipase Cγ and protein kinase C (PKC), are phosphorylated (4). Phospholipase Cγ catalyzes the generation both of inositol 1,4,5-trisphosphate and diacylglycerol. Inositol 1,4,5-trisphosphate is an inducer of intracellular Ca²⁺ mobilization, which is critical for degranulation, and diacylglycerol is an activator of PKC (5). Activated PKC is translocated from the cytosol to the plasma membrane fraction. PKC regulates many functions of mast cells, including leukotriene generation, cytokine synthesis, and degranulation (6, 7).Many studies have provided evidence that lipid rafts are involved in the activation of intracellular signaling molecules mediated by FcϵRI, the T cell receptor, the B cell receptor, and other cell surface receptors (8, 9). Lipid rafts are originally defined as microdomains in terms of their resistance to solubilization by non-ionic detergents such as Triton X-100, and are enriched in sphingolipids and cholesterol (10). Because numerous cell surface receptors and palmitoyl-anchored signaling molecules, including Src family tyrosine kinases, are associated with lipid rafts, it has been suggested that lipid rafts function as platforms regulating the induction of signaling pathways. Aggregated, but not non-aggregated, FcϵRIs are localized in lipid rafts fractionated by sucrose density gradient ultracentrifugation of detergent-treated cells (11, 12). The translocation of FcϵRI to lipid rafts is the key event that initiates the degranulation.Carotenoids are a class of widespread natural pigments that have multiple functions (13). Dietary carotenoids have been associated with a decreased risk for certain types of immune diseases, such as asthma and atopic dermatitis. Consumption of β-carotene suppresses the production of specific IgE and IgG₁ and decreases antigen-induced anaphylactic responses due to an improvement of the T_h1-T_h2 balance (14). Furthermore, β-carotene blocks nuclear translocation of the NF-κB p65 subunit, which correlates with the prevention of IκBα phosphorylation and degradation (15). It has been reported that fucoxanthin, a major carotenoid of edible brown algae, shows an anti-inflammatory effect on endotoxin-induced uveitis by decreasing the production of prostaglandin E₂ and tumor necrosis factor-α (16). Astaxanthin, found in the red pigment of crustacean shells and salmon, also has anti-inflammatory effects due to its suppression of NF-κB activation (17, 18). It has been assumed that these anti-inflammatory activities of carotenoids are due to their antioxidant activity. However, there is no information to date about the direct effect of carotenoids on the degranulation of mast cells.In the present study, we investigated the effects of carotenoids on antigen-induced degranulation of RBL-2H3 cells and mouse bone marrow-derived mast cells. In addition, to elucidate the mechanism of the modulation of degranulation by carotenoids, we focused on FcϵRI-mediated signaling in mast cells.     

Effects of carotenoid sequestration on a caterpillar's cryptic coloration and susceptibility to predation

Carotenoids are used for many functions by animals, including combining with other pigments to produce aposematic and cryptic coloration. Carotenoids in combination with blue pigments are responsible for green coloration in many caterpillars, and thus carotenoid sequestration may reduce their contrast against a green foliage background. We tested the hypothesis that carotenoid sequestration reduces contrast and enhances survival by rearing Trichoplusia ni Hübner (Lepidoptera: Noctuidae) on Brassica oleracea L. var. Acephala (Brassicaceae) leaves and exposing them to predators. We found that carotenoids derived from the host plant are partially excreted, along with chlorophyll, but also sequestered in hemolymph. Larvae that were given plants that provided carotenoids showed less contrast against their host plants within 1 day compared to larvae that were not provided with carotenoids. Last, both short‐term field observations and laboratory trials of larvae caged with predatory Podisus maculiventris Say (Hemiptera: Pentatomidae) nymphs showed that survival of carotenoid‐sequestering larvae was higher compared to larvae that did not sequester. These results suggest that carotenoid sequestration may be an important adaptive strategy that reduces susceptibility to natural enemies that hunt by sight. Further research that examines the mechanisms by which carotenoids are absorbed and modified will lend insights into the evolution of carotenoids functioning as passive defensive compounds.     

Dissection of the pathway required for generation of vitamin A and for Drosophila phototransduction

Dietary carotenoids are precursors for the production of retinoids, which participate in many essential processes, including the formation of the photopigment rhodopsin. Despite the importance of conversion of carotenoids to vitamin A (all-trans-retinol), many questions remain concerning the mechanisms that promote this process, including the uptake of carotenoids. We use the Drosophila visual system as a genetic model to study retinoid formation from beta-carotene. In a screen for mutations that affect the biosynthesis of rhodopsin, we identified a class B scavenger receptor, SANTA MARIA. We demonstrate that SANTA MARIA functions upstream of vitamin A formation in neurons and glia, which are outside of the retina. The protein is coexpressed and functionally coupled with the beta, beta-carotene-15, 15'-monooxygenase, NINAB, which converts beta-carotene to all-trans-retinal. Another class B scavenger receptor, NINAD, functions upstream of SANTA MARIA in the uptake of carotenoids, enabling us to propose a pathway involving multiple extraretinal cell types and proteins essential for the formation of rhodopsin.     

Carotenoids in evolutionary ecology: re‐evaluating the antioxidant role

The antioxidant role of carotenoids in the living organism was proposed as a possible basis for the honesty of carotenoid‐based signals. However, recent studies have questioned the relevance of carotenoids as powerful antioxidants in vivo. Current evidence does not seem to support the “antioxidant role” hypothesis, but it does not allow us to reject it either. This paper proposes some steps to solve this controversy, such as taking a dynamic approach to antioxidant responses, designing protocols that expose individuals to oxidative challenges, analyzing tissues other than blood, and obtaining measures of antioxidant capacity and oxidative damage simultaneously. However, it should be considered that, irrespective of their antioxidant potential, carotenoids might still give information on oxidative stress levels if they are particularly sensitive to free radicals. Finally, lumping together the immunostimulatory and antioxidant roles of carotenoids should be avoided as these functions are not necessarily associated.     

Carotenoid coloration in greenfinches is individually consistent irrespective of foraging ability

Carotenoid-based plumage coloration of birds has been hypothesized to honestly reflect individual quality, either because carotenoids are difficult to acquire via food or because of a trade-off in allocation of carotenoids between maintenance and signaling functions. We tested whether differential foraging ability is a necessary precondition for maintaining individual differences in carotenoid-based plumage coloration in male greenfinches (Carduelis chloris). Wild-caught birds were brought into captivity, where half of them were supplemented with carotenoids while the other half was maintained on a carotenoid-poor diet. Color of the yellow parts of tail feathers, grown under natural conditions, was compared with that of the replacement feathers, grown in captivity. Carotenoid supplementation increased feather chroma (saturation). Color of wild-grown feathers significantly correlated with the color of lab-grown feathers. This result demonstrates the existence of a significant component of variation in carotenoid coloration, which reflects physiological qualities or genetic differences among individuals independent of foraging ability. Among both experimental groups, plasma carotenoid concentration during feather growth strongly correlated with chroma of the feathers grown in captivity. This indicates that carotenoid-based plumage coloration can reveal circulating carotenoid levels over a very wide range of concentrations, suggesting the ample signaling potential of such a mechanism.