Article

Carotenoid Pigments in Male House Finch Plumage in Relation to Age, Subspecies, and Ornamental Coloration

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Abstract

Like males of many bird species, male House Finches (Carpodacus mexicanus) have patches of feathers with ornamental coloration that are due to carotenoid pigments. Within populations, male House Finches vary in expression of ornamental coloration from pale yellow to bright red, which previous research suggested was the result of variation in types and amounts of carotenoid pigments deposited in feathers. Here we used improved analytical techniques to describe types and amounts of carotenoid pigments present in that plumage. We then used those data to make comparisons of carotenoid composition of feathers of male House Finches at three levels: among individual males with different plumage hue and saturation, between age groups of males from the same population, and between males from two subspecies that differ in extent of ventral carotenoid pigmentation (patch size): large-patched C. m. frontalis from coastal California and small-patched C. m. griscomi from Guerrero, Mexico. In all age groups and populations, the ornamental plumage coloration of male House Finches resulted from the same 13 carotenoid pigments, with 3-hydroxy echinenone and lutein being the most abundant carotenoid pigments. The composition of carotenoids in feathers suggested that House Finches are capable of metabolic transformation of dietary forms of carotenoids. The hue of male plumage depended on component carotenoids, their relative concentrations, and total concentration of all carotenoids. Most 4-keto (red) carotenoids were positively correlated with plumage redness, and most yellow carotenoid pigments were negatively associated with plumage redness, although the strength of the relationship for specific carotenoid pigments varied among age groups and subspecies. Using age and subspecies as factors and concentration of each component carotenoid as dependent variables in a MANOVA, we found a distinctive pigment profile for each age group within each subspecies. Among frontalis males, hatch-year birds did not differ from adults in mean plumage hue, but they had a significantly lower proportion of red pigments in their plumage, and significantly lower levels of the red piments adonirubin and astaxanthin, but significantly higher levels of the yellow pigment zeaxanthin, than adult males. Among griscomi males, hatch-year birds differed from adults in plumage hue but not significantly in pigment composition, though in general their feathers had lower concentrations of red pigments and higher concentrations of yellow pigments than adult males. Both adult and hatch-year frontalis males differed from griscomi males in having significantly higher levels of most yellow carotenoid pigments and significantly lower levels of most red carotenoid pigments. Variation in pigment profiles of subspecies and age classes may reflect differences among the groups in carotenoid metabolism, in dietary access to carotenoids, or in exposure to environmental factors, such as parasites, that may affect pigmentation.

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... The third tier of ornamentation, involving the most complex mechanisms of production, is the oxidation of yellow dietary carotenoids into red keto-carotenoid pigments. This mechanism accounts for the red plumage of rosefinches, bullfinches, redpolls, crossbills, and some grosbeaks and siskins (genera Carpodacus, Uragus, Pyrrhula, Rhodopechys, Loxia, Carduelis, Haematospiza, and Pinocola;Stradi et al. 1996Stradi et al. , 1997Inouye et al. 2001). ...
... In every cardueline finch with red feather coloration for which the pigment composition of feathers has been quantified, the predominant red keto-carotenoid is 3-hydroxyechinenone (Stradi et al. 1996(Stradi et al. , 1997Stradi 1998;Inouye et al. 2001; see fig. 2 for the structure of 3-hydroxy-echinenone and other carotenoids). The 3-hydroxy-echinenone is formed from dietary b-cryptoxanthin through the ketolation of one of the two b-ionone rings. ...
... These pigments follow one of two pathways ( fig. 3). b-cryptoxanthin is oxidized into the red pigment 3hydroxy-echinenone (approximately 85%) or adonirubin (3-hydroxy-b,b-carotene-4,4 -dione; approximately 15%; Inouye et al. 2001) by a b-carotene ketolase as follows: ...
... Still other songbirds ketolate dietary pigments by introducing ketone groups to produce red ketocarotenoids. Ketolation of yellow dietary pigments is the primary source of red coloration in songbirds (Stradi et al. 1996(Stradi et al. , 1997Inouye et al. 2001; fig. 1). ...
... Male house finches have extensive carotenoid plumage coloration that varies from red to yellow and that is developed in a relatively short window of time in the late summer during prebasic molt (Hill 2002). On the basis of likely precursor-product relationships, it has been argued that house finches derive their red coloration by oxidizing primarily dietary b-cryptoxanthin into primarily the red ketocarotenoid 3-hydroxy-echinenone (Inouye et al. 2001;McGraw et al. 2006). We collected wild molting male house finches and analyzed the carotenoid content of cellular fractions of homogenized liver to test a key assumption of the hypothesis that carotenoid pigments used for ornamental feather coloration are oxidized in hepatic mitochondria. ...
... Our observations of high concentrations of carotenoids within or in intimate association with the mitochondria of the hepatic cells of molting hatching-year male house finches have important implications for the cellular mechanisms that regulate the production of ornamental plumage coloration. Ornament elaboration is a function of the redness of plumage display in the house finch and other birds (Hill 1996), and plumage redness is a function of the ratio of ketocarotenoids versus xanthophylls deposited in feathers (Inouye et al. 2001;McGraw et al. 2006). If carotenoid ketolation occurs within or on the outer surface of mitochondria, then carotenoid oxidation will likely be linked to core electron transporting events, including cytochrome b5 and vitamin C reduction on the outer mitochondrial membrane and oxidative phosphorylation on the inner mitochondria membrane. ...
Article
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Vertebrates cannot synthesize carotenoid pigments de novo, so to produce carotenoid-based coloration they must ingest carotenoids. Most songbirds that deposit red carotenoids in feathers, bills, eyes, or skin ingest only yellow or orange dietary pigments, which they oxidize to red pigments via a ketolation reaction. It has been hypothesized that carotenoid ketolation occurs in the liver of vertebrates, but this hypothesis remains to be confirmed. To better understand the role of hepatocytes in the production of ketolated carotenoids in songbirds, we measured the carotenoid content of subcellular components of hepatocytes from wild male house finches (Haemorhous mexicanus) that were molting red, ketocarotenoid-containing feathers (e.g., 3-hydroxy-echinenone). We homogenized freshly collected livers of house finches and isolated subcellular fractions, including mitochondria. We found the highest concentration of ketocarotenoids in the mitochondrial fraction. These observations are consistent with the hypothesis that carotenoid pigments are oxidized on or within hepatic mitochondria, esterified, and then transported to the Golgi apparatus for secretory processing.
... We focused on these two tissue types for the following reasons: (1) molting males uniquely circulate ketocarotenoid pigments (e.g. 3-hydroxy-echinenone) through blood at this time of year, which they metabolize from dietary sources for developing red plumage coloration [34,35]; hence at this time of year we can investigate the widest pool of available carotenoids, as they relate to the key process of male pigmentation, when MG incidence is at its annual peak [36]; and (2) retinal carotenoids are understudied compared to other tissue pools of carotenoids [37], and disease-related shifts in retinal carotenoid allocation would have consequences not just for health state or color signaling, but also color vision, given the role of oil-droplet carotenoids in tuning avian spectral sensitivity [23]. Few links have been made previously in the literature between pathogenic infections and vision in non-human animals [38] and, despite evidence for relatively stable pools of carotenoids in retina (as above), an eye-specific disease might be among the most likely modulators of eye carotenoid status. ...
... Here we monitored carotenoid circulation during molt in house finches and revealed an association between disease status and levels of a pigment specific to developing sexually attractive red plumage coloration. House finches acquire red plumage by depositing red ketocarotenoids like 3-hydroxy-echinenone (3HE) into feathers, which they metabolize from dietary precursors [34,35]. Compared to birds showing no MG symptoms, we detected a severe decrease -by 61% in males and by 70% in females, on average -in 3HE circulation for birds infected with MG. ...
... ketolases). Models of carotenoid signal evolution predict high differential costs of developing elaborate plumage when animals metabolize dietary pigments [66,67], compared to when birds deposit dietary forms directly into feathers (e.g. as occurs with dietary xanthophylls and the production of sexually disfavored yellow plumage in male H. mexicanus; [34]). It is suspected that these enzymes are highly sensitive to stress (e.g. ...
... Male finches express carotenoid-based pigmentation that can range from yellow to red (Hill 1993). Pigment concentration and corresponding extent and hue of colorful plumage varies widely across populations (Hill 1993;Inouye et al. 2001). While some individual-and population-level variation is explained by diet composition (Hill 1992;Inouye et al. 2001;Hill et al. 2002) suggested an additional role for physiological and/or genetic mechanisms of control (Hill 1993(Hill , 2002. ...
... Pigment concentration and corresponding extent and hue of colorful plumage varies widely across populations (Hill 1993;Inouye et al. 2001). While some individual-and population-level variation is explained by diet composition (Hill 1992;Inouye et al. 2001;Hill et al. 2002) suggested an additional role for physiological and/or genetic mechanisms of control (Hill 1993(Hill , 2002. Multiple studies have demonstrated an association between male plumage coloration and reproductive success (Hill et al. 1999, Badyaev et al. 2001. ...
... Unlike melanin-based pigments, birds are unable to synthesize carotenoid pigments from basic biological precursors (Fox, 1976;Goodwin, 1984). Therefore expression of carotenoid-based coloration is linked to the ability of an individual to acquire carotenoid pigments from their diet (Brush, 1978;Brush and Power, 1976;Slagsvold and Lifjeld, 1985), as well as the physiological processes that determine their absorption, transport, and deposition (Brush, 1990;Hill, 1999;2000a;2002;Inouye et al., 2001;Olson and Owens, 1998). Thus, the production of carotenoid-based coloration, provides a mechanism which allows the signal to honestly reflect phenotypic quality (Gray, 1996). ...
... Limited access to food, independent of access to carotenoid pigments, has also been found to negatively influence expression of carotenoid-based plumage (Hill, 2000a); individuals in better nutritional condition have been found to grow brighter carotenoid-based plumage . In addition, Inouye et al. (2001) found that carotenoid pigments are deposited variably, at both the individual and population level, due to differences in absorption, metabolism, and transportation. Other studies have confirmed that species, as well as individuals, differ in absorption rates of ingested carotenoids (Scheidt, 1989), their ability to convert absorbed carotenoids into usable pigments (Goodwin, 1984;McGraw et al., 2003c), and the rate at which they deposit these pigments (Brush and Power, 1976;Hudon, 1991). ...
Thesis
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Many birds display brilliant and colorful patches of ornamental plumage. Melanin and carotenoid pigments are responsible for some of the important colors of ornamental plumage, yet the proximate mechanisms controlling the production and expression (e.g. size and color characteristics) of these pigment-based colors are different. Therefore, ornamental melanin and carotenoid pigmented plumage may represent unique ornamental characters that may be used differently by females when selecting social and extra-pair mates. I studied the mating and reproductive success of American redstart (Setophaga ruticilla) males to determine if the expression of melanin and carotenoid based plumage influenced their ability to attract social mates or their reproductive success. I found that the expression of ornamental patches of melanin- and carotenoid-based pigmentation was unrelated within an individual. Melanin pigmentation was an important predictor of pairing success; males that successfully attracted a social mate had significantly smaller melanin-based bibs. A component of the appearance of this ornament was also positively related to male provisioning rates. Contrary to previous studies carotenoid-based coloration was negatively related to within-pair and total reproductive success. Males that successfully sired extra-pair young had significantly darker orange carotenoid-based ornamental flank plumage than males that they cuckolded. The expression of carotenoid-based colors was also negatively correlated with male provisioning rates. These results confirm the growing recognition that different types of colored plumage may be used to assess potential social mates and extra-pair partners. In American redstarts, females appear to rely on the expression of melanin-based plumage to assess male parental care abilities and on the expression of carotenoid-based plumage to assess male genetic qualities.
... Similarly, some metabolic neighborhoods can underlie greater color diversity than others. Second, metabolic pathways commonly differ in their efficiency (e.g., [40]); relative concentration of compounds produced by different pathways within species' network and mixtures of different carotenoids and distribution of flux [41] further alter correspondence between metabolic and plumage color space. Third, plumage color is affected by integration of carotenoid compounds and feather keratin proteins and species differences in this integration [42,43] changes correspondence between metabolic and color diversification space across species. ...
... To form a color-producing pathway, birds can either link dietary, intermediate, and expressed compounds present in each species in a linear, step-wise fashion [24,87,88], utilize the diversity of redundant pathways that link them [29,40], or use a mixture of these strategies. Thus, to make an unbiased assessment of the effect of network structure on avian carotenoid diversification, we built two kinds of networks for each speciesa "minimum" and "maximum" networks. ...
Article
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Background Resolution of the link between micro- and macroevolution calls for comparing both processes on the same deterministic landscape, such as genomic, metabolic or fitness networks. We apply this perspective to the evolution of carotenoid pigmentation that produces spectacular diversity in avian colors and show that basic structural properties of the underlying carotenoid metabolic network are reflected in global patterns of elaboration and diversification in color displays. Birds color themselves by consuming and metabolizing several dietary carotenoids from the environment. Such fundamental dependency on the most upstream external compounds should intrinsically constrain sustained evolutionary elongation of multi-step metabolic pathways needed for color elaboration unless the metabolic network gains robustness – the ability to synthesize the same carotenoid from an additional dietary starting point. Results We found that gains and losses of metabolic robustness were associated with evolutionary cycles of elaboration and stasis in expressed carotenoids in birds. Lack of metabolic robustness constrained lineage’s metabolic explorations to the immediate biochemical vicinity of their ecologically distinct dietary carotenoids, whereas gains of robustness repeatedly resulted in sustained elongation of metabolic pathways on evolutionary time scales and corresponding color elaboration. Conclusions The structural link between length and robustness in metabolic pathways may explain periodic convergence of phylogenetically distant and ecologically distinct species in expressed carotenoid pigmentation; account for stasis in carotenoid colors in some ecological lineages; and show how the connectivity of the underlying metabolic network provides a mechanistic link between microevolutionary elaboration and macroevolutionary diversification.
... We chose a slightly lower dosage of paraquat than in the first experiment knowing that house finches in this study would receive the treatment for 3 months, compared to 4 weeks in experiment 1. In addition, we decided to supplement birds with canthaxanthin during molt instead of zeaxanthin because canthaxanthin is a component of the sexually attractive red coloration of house finch plumage (Inouye et al. 2001; by comparison, zeaxanthin is a yellow plumage colorant). We measured body mass and drew blood from captive finches as above every month, starting on the first day of the experiment. ...
... P=0.004) than desert birds. Desert males had a higher concentration of plasma 3-hydroxyechinenone (the main red plumage carotenoid in house finches; Inouye et al. 2001) than urban males (Z=3.17, P= 0.02), but similar levels of lutein (P>0.5). ...
Article
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Worldwide urbanization continues to present new selection pressures on organisms. Carotenoid pigmentation of animals provides an ideal study system for identifying the source and significance of urban impacts because it is an environmentally derived trait and carotenoid molecules have widespread physiological, phenotypic, and fitness functions. Prior work indicates that in some bird species, urban individuals display less colorful carotenoid ornaments than rural birds. However, few studies have experimentally identified the causal factors that drive such a pattern of reduced “sexiness in the city”. We performed two common-garden experiments with house finches, in which we manipulated carotenoid access and exposure to oxidative stress to understand how urban and desert birds respond to these drivers of carotenoid utilization. Urban finches were less colorful than desert birds at capture, but we found no differences between urban and desert finches in how carotenoid provisioning or oxidative stress affected plumage coloration. The only notable site differences in our experiments were that (a) the oxidative challenge caused a larger mass loss in urban compared to desert birds (experiment 1), (b) urban birds circulated higher levels of carotenoids than desert birds after receiving the same diet for 4 months (experiment 2), suggesting that, compared to desert birds, urban finches can better assimilate carotenoids from food or do not deplete as many carotenoids for use in free-radical scavenging. Overall, our results fail to reveal key carotenoid-specific physiological differences in urban and desert finches, and instead implicate other ecophysiological factors that drive urban/desert differences in carotenoid ornamentation.
... The HSB system was adopted as it has a biologically relevant interpretation of its components. In finches, hue (with higher values in more yellowish coloration) is indicative of the type of carotenoids present in the feathers (Inouye et al. 2001); saturation reflects the quantity of carotenoid present (Saks et al. 2003a) and lightness appears to be determined by the structure of the feather's microsurface with higher values in degraded feathers (Shawkey et al. 2007). Birds are capable of recognizing reflectance in the UV part of the light spectrum (320e400 nm) and this aspect cannot be evaluated from the digital images. ...
... In species related to the scarlet rosefinch (such as the house finch, Carpodacus mexicanus) males with more elaborate ornaments cope better with infectious pathogen diseases (Hill & Farmer 2005). Carotenoid-based ornamental coloration is composed of three independent variables: hue (indicating mostly the type of pigments deposited), saturation (indicating amount of carotenoids deposited with higher values in healthier males) and lightness (referring to surface structure with higher values indicative of feather damage; Inouye et al. 2001;Hill 2002;Saks et al. 2003a;Shawkey et al. 2007). Our results seem to contradict most of the current evidence on the association between immunity or health and ornamentation as they show a negative linkage of the magnitude of the PHA-triggered immune response to plumage saturation and a positive one to feather lightness. ...
Article
The phytohaemagglutinin (PHA) skin-swelling test is one of the most widely used methods for cell-mediated immunity measurement in immunoecology. Although several studies have investigated the condition-dependent traits associated with the magnitude of cutaneous inflammatory response to PHA, the results concerning signalling of the responsiveness through ornamental traits are still controversial. This is especially true for carotenoid-based feather ornamentation in birds. We therefore examined the linkage between several condition-dependent traits, including the red ornamental coloration of the plumage, and the magnitude of the PHA-induced immune response in scarlet rosefinch, Carpodacus erythrinus, males. Our results show two important aspects of the PHA-induced inflammation in this species. First, histological analysis showed that the swelling response was dependent on basophil activity. Second, the magnitude of the response (increase in patagium thickness) was associated with individual size, carotenoid-based ornamental coloration and a ptilochronological marker of feather growth at the time of moulting (mean growth bar width), thus mirroring the long-term quality of the individual. The positive linkage between the individual size or mean growth bar width and the PHA response suggests an association between the magnitude of the response and individual metabolic rate. However, as the magnitude of the response was also related negatively to ornament saturation and positively to ornament lightness, our results indicate stronger responsiveness in inferior males. Highly ornamented, healthier individuals recruited fewer basophils into the inflamed tissue causing less intense swelling. To our knowledge, this study is the first to show a negative association between carotenoid-based plumage coloration and the magnitude of the PHA-induced immune response.
... The interesting ketocarotenoids astaxanthin, adonixanthin and adonirubin have been detected, either in diester, monoester and free forms, in the coral trout Plectropomus leopardus , in the gonads of sea cucumbers (Maoka et al., 2015) and in the Mediterranean marine sponge Phorbas topsenti (Nguyen et al., 2012). Finally, carotenoids such as adonirubin, canthaxanthin, adonixanthin, astaxanthin, β-carotene, zeaxanthin, lutein b-cryptoxanthin and α-doradexanthin have been detected in bird plumage (Hudon et al., 2015;Inouye et al., 2001;LaFountain et al., 2013;Prager et al., 2009;Prum et al., 2012;Stradi et al., 2001) and bird ocular tissues (Bhosale et al., 2007). ...
Article
Given their multifaceted roles, carotenoids have garnered significant scientific interest, resulting in a comprehensive and intricate body of literature that occasionally presents conflicting findings concerning the proper characterization, quantification, and bioavailability of these compounds. Nevertheless, it is undeniable that the pursuit of novel carotenoids remains a crucial endeavor, as their diverse properties, functionalities and potential health benefits make them invaluable natural resources in agri-food and health promotion through the diet. In this framework, particular attention is given to ketocarotenoids, viz., astaxanthin (one of them) stands out for its possible multifunctional role as an antioxidant, anticancer, and antimicrobial agent. It has been widely explored in the market and utilized in different applications such as nutraceuticals, food additives, among others. Adonirubin and adonixanthin can be naturally found in plants and microorganisms. Due to the increasing significance of natural-based products and the remarkable opportunity to introduce these ketocarotenoids to the market, this review aims to provide an expert overview of the pros and cons associated with adonirubin and adonixanthin.
... The carotenoid contents, including myxoxanthophyll, zeaxanthin, 3 -hydroxy echinenone, echinenone, and β-carotene, were calculated using the following equations from [23]: C car = C chl × [(ε chl × A car )/(ε car × A chl )], where C chl = the chlorophyll concentration in the pigments extracts was determined by the extinction coefficient of chlorophyll a using 820, and the absorbance of the pigment extract at 663 nm. ε chl and ε car = the specific extinction coefficients of the chlorophyll a and the carotenoids at 440 nm, respectively, were taken from [56,57]. A chl and A car = the chlorophyll a and the carotenoid peak areas on the chromatogram, respectively, were detected at 440 nm. ...
Article
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In the antioxidant system in cyanobacteria, non-enzymatic antioxidants, such as carotenoids, are considered good candidates for coping with oxidative stress, particularly light stress, and pharmaceutical therapeutic applications. A significant amount of carotenoid accumulation has been recently improved by genetic engineering. In this study, to achieve higher carotenoid production with higher antioxidant activity, we successfully constructed five Synechocystis sp. PCC 6803 strains overexpressing (OX) native genes related to the carotenoids biosynthetic pathway, including OX_CrtB, OX_CrtP, OX_CrtQ, OX_CrtO, and OX_CrtR. All of the engineered strains maintained a significant quantity of myxoxanthophyll, while increasing zeaxanthin and echinenone accumulation. In addition, higher components of zeaxanthin and echinenone were noted in all OX strains, ranging from 14 to 19% and from 17 to 22%, respectively. It is worth noting that the enhanced echinenone component responded to low light conditions, while the increased β-carotene component contributed to a high light stress response. According to the higher antioxidant activity of all OX strains, the carotenoid extracts presented lower IC50 in lung cancer cell lines H460 and A549, with values less than 157 and 139 µg/mL, respectively, when compared with those of WTc, particularly OX_CrtR and OX_CrtQ. A higher proportion of zeaxanthin and β-carotene in OX_CrtR and OX_CrtQ, respectively, may considerably contribute to the ability to treat lung cancer cells with antiproliferative and cytotoxic effects.
... Obtaining information on the distribution of different avian subspecies is often challenging due to subtle differences in morphology, plumage colour or songs (Clayton, 1990;Inouye et al., 2001;Wojczulanis-Jakubas et al., 2011). This can be even more complicated for migratory animals that occur at multiple sites throughout the year. ...
Article
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Until recently, Limosa limosa melanuroides was thought to be the only subspecies of Black-tailed Godwit in the East Asian–Australasian Flyway. For this reason, all previous occurrences and counts of Black-tailed Godwits in the flyway have been assigned to melanuroides. However, a larger-bodied subspecies, bohaii, has recently been discovered in the flyway. As a result, the occurrence of Black-tailed Godwits in the flyway needs to be reconsid- ered such that the specific distribution of each subspecies becomes known. To this end, we developed a simple discriminant function to assign individuals to subspecies based on their bill and wing length. Cross-validation with individuals known to be bohaii or melanuroides, based on molecular analysis, showed the developed function to be 97.7% accurate. When applied to measurements of godwits captured at 22 sites across 9 countries in East–Southeast Asia and Australia, we found that bohaii and melanuroides occurred at most sites and overlapped in their distribution from Kamchatka to Australia. We examined photos from all along the flyway to verify this surprising result, confirming that both subspecies co-occur in most locations. Based on these results, we hypothe- sise that bohaii and melanuroides from the west of their breeding ranges mostly migrate over mainland China. Birds of both subspecies from the east of their ranges are expected to migrate along the Pacific Ocean. We encour- age ringing groups in East–Southeast Asia and Australia to use this simple method to keep adding knowledge about Black-tailed Godwits in the East Asian–Australasian Flyway.
... It is particularly unlikely, however, that the present case reflects differential physiological ability because such variations are gradual and observed in substantially higher proportion in a population 14,19 . Since 1995, 141 Pin-tailed Manakins have been mist-netted in the study area, of which 49 were males in definitive plumage. ...
... In house finches, females select mates on the basis of carotenoid pigment plumage coloration, which is hypothesized to reveal information about the quality of a potential mate (Hill, 2002). The color of carotenoid pigment plumage is largely determined by the concentration of pigment in the feather (Butler et al., 2011;Inouye et al., 2001;Saks et al., 2003;Shawkey et al., 2006). Therefore, we wondered whether and how changes in the spectral filtering of the cone oil droplets might impact the assessment of feather carotenoid content during mate choice. ...
Article
Carotenoids color many of the red, orange and yellow ornaments of birds and also shape avian vision. The carotenoid-pigmented oil droplets in cone photoreceptors filter incoming light and are predicted to aid in color discrimination. Carotenoid use in both avian coloration and color vision raises an intriguing question: is the evolution of visual signals and signal perception linked through these pigments? Here, we explore the genetic, physiological and functional connections between these traits. Carotenoid color and droplet pigmentation share common mechanisms of metabolic conversion and are both affected by diet and immune system challenges. Yet, the time scale and magnitude of these effects differ greatly between plumage and the visual system. Recent observations suggest a link between retinal carotenoid levels and color discrimination performance, but the mechanisms underlying these associations remain unclear. Therefore, we performed a modeling exercise to ask whether and how changes in droplet carotenoid content could alter the perception of carotenoid-based plumage. This exercise revealed that changing oil droplet carotenoid concentration does not substantially affect the discrimination of carotenoid-based colors, but might change how reliably a receiver can predict the carotenoid content of an ornament. These findings suggest that, if present, a carotenoid link between signal and perception is subtle. Deconstructing this relationship will require a deeper understanding of avian visual perception and the mechanisms of color production. We highlight several areas where we see opportunities to gain new insights, including comparative genomic studies of shared mechanisms of carotenoid processing and alternative approaches to investigating color vision.
... However, food quantity is not equal to food quality and in urban areas the available food can lack needed nutrients, such as carotenoids when compared with rural food sources (Isaksson and Andersson 2007;Narango et al. 2017). Potentially, rural areas have food richer in carotenoids, which is associated with redder plumage (Inouye et al. 2001), as observed in our rural birds with a higher red dominance than the urban birds. Similarly, rural great tit (Parus major) chicks had higher yellow carotenoid-based pigments compared with their urban counterparts (Biard et al. 2017). ...
Article
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Urbanization is one of the most extreme forms of land transformation and results in changes to ecosystems and species compositions. As a result, there are strong directional selection pressures compared to nearby rural areas. Despite a surge in research on the different selection pressures on acoustic communication in urban and rural areas, there has been comparatively little investigation into traits involved with visual communication. We measured the plumage of museum specimens of white-crowned sparrows (Zonotrichia leucophrys) from urban and adjacent rural habitats in San Francisco, CA, to assess the effects of divergent habitats on plumage. We found significant differences in dorsal plumage, but not crown plumage, between urban and rural populations that have been diverging over the past 100 years. Urban birds have increasingly darker and duller dorsal plumage, whereas rural birds in adjacent areas have plumage with richer hues and more color complexity. Our findings suggest a newly observed adaptation to urban environments by native species and suggest that many traits, in addition to acoustic signals, may be changing in response to urban selection pressures. Additional collections in urban areas are needed to explore likely divergences in plumage coloration between urban and rural environments.
... The near absence of 3 ′ -hydroxy-echinenone and accumulation of 3hydroxy-echinenone in most hybrid flickers is of interest because 3-hydroxy-echinenone is the main carotenoid in many red cardueline finches (Stradi et al., 1996;Inouye et al., 2001;McGraw et al., 2006). It is still unclear why or how male cardueline finches preferentially accumulate this pigment and not other possible products of ketolation of dietary carotenoids, like 3 ′ -hydroxy-echinenone, adonirubin, and di-ketocarotenoids generally, and specifically 3-hydroxy-echinenone from β-cryptoxanthin (Fig. 1). ...
Article
Hybridization can bring in single individuals alleles that were never designed to work together, which can result in unexpected or transgressive phenotypes. The Yellow-shafted (auratus group) and Red-shafted (cafer group) subspecies groups of the Northern Flicker (Colaptes auratus) differ conspicuously in the coloration of their flight feathers, but hybridize freely where their ranges overlap in western North America. The difference in color is largely the result of the Red-shafted form harboring ketolated products at C4(4 ′) of the carotenoids found in the Yellow-shafted form. Characterizing the carotenoid pigments in a series of birds of intermediate color (presumed hybrids) revealed that most accumulated a product of β-cryptoxanthin with a keto group on its hydroxylated ring (3-hydroxy-echinenone), while a few accumulated the product with a keto group on the unhydroxylated ring (3 ′-hydroxy-echinenone). Surprisingly, the latter group also had feather barbs that were noticeably yellower than the associated rachis, corresponding to a lower level of ketolation at C4(4 ′). We assessed possible biochemical explanations for the differences by probing the relative carotenoid concentration data in individuals of varying color. The difference between the hybrids could not be explained by the general level of ketolation of carotenoids or a particular selectivity of the 4-ketolase involved. We present a testable genetic explanation that invokes incompatibilities between divergent alleles of the two parental forms at interacting loci. Because the idiosyncrasies affect oxidation, they may be the product of mitonuclear incompatibilities.
... In general, animals with a more developed carotenoidbased colouration have a better immune system (McGraw and Ardia, 2003;Baeta et al., 2008) and antioxidant function (Henschen et al., 2016), because of immunostimulant and antioxidant properties of carotenoids and pteridines (Svensson and Wong, 2011;Simons et al., 2012;McGraw, 2005). Saturation and hue metrics of carotenoid-based colouration are good proxies of carotenoid concentration in some birds (Butler et al., 2011;Inouye et al., 2001). Consequently, it is expected that a female would preferentially opt for males exhibiting a greater overall colour change as well as greater hue and saturation changes, as it may reflect a better immune system and antioxidant function. ...
Article
Colour change is involved in various functions ranging from thermo- and hydroregulation to camouflage and communication. The role of colour change in communication has received increased attention over the past few decades, yet has been studied predominantly in the context of intrasexual competition. Here, we investigate the role of colour change in mate choice in an animal that can change its colour, the panther chameleon ( Furcifer pardalis ). We conducted behavioural experiments and colour analysis to investigate whether colour changes, including in the UV range, are involved in mate choice. This study presents evidence of female mate choice for specific aspects of colour change in courting males, both in the visible and the UV range. Females chose males exhibiting more saturation changes regardless of the body region and spectral range. In addition, females chose males showing fewer brightness changes at the level of the lateral line and males showing lower hue changes at the level of the bands and the interbands, in the visible range. In the UV, selected males showed more brightness changes and higher maximum brightness. These results suggest that male colour change is important in female mate choice in the panther chameleon.
... This theoretical framework was generated from studies in house finches (Haemorhous mexicanus). In that species, males exhibit yellow to red plumages produced by xanthophylls (such as β-cryptoxanthin) or ketocarotenoids (mostly 3hydroxyechinenone; "3HOE"), respectively (Inouye et al. 2001;Hill et al. 2002;Johnson and Hill 2013), and females clearly display significant preferences for the most colorful males (Hill 1990). The question was, nonetheless, first addressed by Otto Völker in 1957. ...
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The mechanisms involved in the production of red carotenoid‐based ornaments of vertebrates are still poorly understood. These colorations often depend on enzymatic transformations (ketolation) of dietary yellow carotenoids, which could occur in the inner mitochondrial membrane (IMM). Thus, carotenoid ketolation and cell respiration could share biochemical pathways, favoring the evolution of ketocarotenoid‐based ornaments as reliable indices of individual quality under sexual selection. Captive male red crossbills (Loxia curvirostra Linnaeus) were exposed to redox‐active compounds designed to penetrate and act in the IMM: an ubiquinone (mitoQ) or a superoxide dismutase mimetic (mitoTEMPO). MitoQ can act as an antioxidant but also distort the IMM structure, increasing mitochondrial free radical production. MitoQ decreased yellow carotenoids and tocopherol levels in blood, perhaps by being consumed as antioxidants. Contrarily, mitoTEMPO‐treated birds rose circulating levels of the second most abundant ketocarotenoid in crossbills (i.e. canthaxanthin). It also increased feather total red ketocarotenoid concentration and redness, but only among those birds exhibiting a redder plumage at the start of the study, that is, supposedly high‐quality individuals. The fact that mitoTEMPO effects depended on original plumage color suggests that the red‐ketocarotenoid‐based ornaments indicate individual quality as mitochondrial function efficiency. The findings would thus support the shared pathway hypothesis. This article is protected by copyright. All rights reserved
... Seasonal variation in carotenoidbased pigmentation has been observed in House Finches (Haemorhous mexicanus) and Great Tits (Parus major) (McGraw andHill 2004, Figuerola andSenar 2005), likely due to feather or pigment degradation. In House Finches, adults express more carotenoids than hatch-year birds (Hill 1992, Inouye et al. 2001. In Golden-winged Warblers, first winter birds often have some yellow on their underparts but adults have white underparts (Parkes 1951). ...
Article
Hybrids with different combinations of traits can be used to identify genomic regions that underlie phenotypic characters important to species identity and recognition. Here, we explore links between genomic and plumage variation in Blue-winged Warbler x Golden-winged Warbler (Vermivora cyanoptera x V. chrysoptera) hybrids, which have traditionally been categorized into 2 discrete types. “Lawrence’s” hybrids are yellow overall, similar to Blue-winged Warblers, but exhibit the black throat patch and face mask of Golden-winged Warblers. “Brewster’s” hybrids are similar to Golden-winged Warblers, but lack the black throat patch and face mask, and sometimes have yellow on their underparts. Previous studies hypothesized that (1) first generation hybrids are of the Brewster’s type and can be distinguished by the amount of yellow on their underparts, and that (2) the throat patch/mask phenotype is consistent with Mendelian inheritance and controlled by variation in a locus near the Agouti-signaling protein (ASIP) gene. We addressed these hypotheses using whole genome re-sequencing of parental and hybrid individuals. We found that Brewster’s hybrids had genomic hybrid index scores indicating this phenotype can arise by majority ancestry from either parental species, that their plumage varied in levels of carotenoid pigmentation, and individuals captured in multiple years grew consistently less yellow over time. Variation in carotenoid pigmentation showed little relationship with genomic hybrid index score and is thus inconsistent with previous hypotheses that first generation hybrids can be distinguished by the amount of yellow in their plumage. Our results also confirm that variation near ASIP underlies the throat patch phenotype, which we refined to an ~10–15 Kb region upstream of the coding sequence. Overall, our results support the notion that traditional categorization of hybrids as either Lawrence’s or Brewster’s oversimplifies continuous variation in carotenoid pigmentation, and its inferred underlying genetic basis, and is based primarily on one discrete trait, which is the throat patch/mask phenotype.
... Here, we test these scenarios using the recent colonization of western North America by house finches (Haemorhous mexicanus), which has produced replicated, hierarchical sequences of known-age populations across one of the widest ecological ranges of any extant bird species 31 (Fig. 3). From their native range in southwestern North America to their newly established range, house finches are exposed to diverse plant communities that provide widely distinct sources of carotenoid precurors 32 , use different subsets of a carotenoid-producing metabolic network, and show an array of feather modifications in response to carotenoids 22,33 . These modifications, illustrated in Fig. 1, vary from a near complete loss of barbules in ancestral and older populations to full barbule development in new populations, with a variety of intermediate stages. ...
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Robustness against environmental fluctuations within an adaptive state should preclude exploration of new adaptive states when the environment changes. Here, we study transitions between adaptive associations of feather structure and carotenoid uptake to understand how robustness and evolvability can be reconciled. We show that feather modifications induced by unfamiliar carotenoids during a range expansion are repeatedly converted into precise coadaptations of feather development and carotenoid accommodation as populations persist in a region. We find that this conversion is underlain by a uniform and coordinated increase in the sensitivity of feather development to local carotenoid uptake, indicative of cooption and modification of the homeostatic mechanism that buffers feather growth in the evolution of new adaptations. Stress-buffering mechanisms are well placed to alternate between robustness and evolvability and we suggest that this is particularly evident in adaptations that require close integration between widely fluctuating external inputs and intricate internal structures.
... in Table 1), with TCC accounting for 76% of the variation in yolk H (model 1 in Table 1, Figure 1a), a strong correlation (r = 0.87) that has also been reported for the plumage of the House Finch Haemorhous mexicanus (Inouye et al. 2001). Previous studies of egg yolk also used hue to measure yolk colour (McGraw 2006, Szigeti et al. 2007, Hipfner et al. 2010. ...
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Carotenoids are essential antioxidant micronutrients. Oviparous species acquire carotenoids from their food and deposit them in the egg yolk, where they support embryonic development. The total carotenoid concentration in the egg yolk is typically measured analytically, which requires time, equipment and expertise and can limit the sample available for other measurements, at least in species laying small eggs. Here we evaluate whether yolk colour can be used as a reliable, alternative measure for the total yolk carotenoid concentration. We compare two non‐analytical methods, digital photography and visual colour scoring, using eggs from a wild population of Blue Tits Cyanistes caeruleus. Yolk hue estimated from digital photographs correlated more strongly with total yolk carotenoid concentration measured by High Performance Liquid Chromatography (HPLC) than did the visually assessed colour score based on a Yolk Colour Fan. Previous results based on HPLC measurements of the total carotenoid concentration could be reproduced using yolk hue measurements. The results suggest that measuring yolk hue is a suitable proxy for assessing natural variation in the total yolk carotenoid concentration in eggs of free‐living birds.
... To do so, we compared the relationships between carotenoid coloration and mitochondrial performance in male house finches (Haemorhous mexicanus) that were actively producing ornamental feather coloration (figure 1). To produce red feather coloration used to attract females, house finches oxidize the yellow dietary carotenoid cryptoxanthin to the red pigment 3-hydroxyechinenone (3HE) in a process requiring the gene encoding the cytochrome P450 monooxygenase CYP2J19 [21,24]. Our central hypothesis is that the efficiency of the oxidation of yellow dietary pigments, and hence the coloration of feathers, is controlled either directly or indirectly by mitochondrial function (figure 2) [19,25]. ...
Article
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Carotenoid coloration is widely recognized as a signal of individual condition in various animals, but despite decades of study, the mechanisms that link carotenoid coloration to condition remain unresolved. Most birds with red feathers convert yellow dietary carotenoids to red carotenoids in an oxidation process requiring the gene encoding the putative cytochrome P450 enzyme CYP2J19. Here, we tested the hypothesis that the process of carotenoid oxidation and feather pigmentation is functionally linked to mitochondrial performance. Consistent with this hypothesis, we observed high levels of red ketolated carotenoids associated with the hepatic mitochondria of moulting wild house finches (Haemorhous mexicanus), and upon fractionation, we found the highest concentration of ketolated carotenoids in the inner mitochondrial membrane. We further found that the redness of growing feathers was positively related to the performance of liver mitochondria. Structural modelling of CYP2J19 supports a direct role of this protein in carotenoid ketolation that may be functionally linked to cellular respiration. These observations suggest that feather coloration serves as a signal of core functionality through inexorable links to cellular respiration in the mitochondria.
... Melanins may occur at such high concentrations in Zebra Finch feathers due to the large amounts needed to confer rich ornamental colors. Carotenoids that color bird feathers, for example, have extremely high extinction coefficients (a measure of the light-reflecting properties of molecules; Bauernfeind 1981) and occur in the sexually selected plumage of male American Goldfinches and House Finches (Carpodacus mexicanus) at concentrations of no more than 2 mg per g (Inouye et al. 2001, McGraw, Hill et al. 2002). In contrast, the extinction coefficients for phaeomelanins and eumelanins are more than an order of magnitude lower than carotenoids (Sarna and Swartz 1988), which means that more pigment is required to generate an equally rich color. ...
Article
The carotenoid-pigmented bill of Zebra Finches (Taeniopygia guttata) has received much recent attention as a sexually selected signal of quality, but these birds also display several sexually dichromatic plumage traits, including rust-colored cheek patches, a black breast band, and brown flanks. Black, brown, and earth-toned features in animals are thought to be produced by melanin pigments, but few studies have identified the melanin content of such colors in bird feathers. We used a series of biochemical techniques to investigate the pigmentary basis of these plumage colors in male Zebra Finches. All three feather traits contained melanin pigments, but varied in the amounts of the two basic forms of melanin (eumelanin and phaeomelanin). Black breast feathers contained predominantly eumelanin, whereas cheek and flank feathers contained extraordinarily high concentrations of phaeomelanin. Conventional methods of carotenoid analysis detected no carotenoids in either the cheek or flank feathers. Coloración Basada en Melaninas en las Plumas Ornamentales de los Machos de Taeniopygia guttata Resumen. El pico pigmentado con carotenoides de Taeniopygia guttata ha sido destacado recientemente como una señal de calidad seleccionada sexualmente, pero estas aves también presentan varios caracteres de plumaje sexualmente dicromáticos, incluyendo parches en las mejillas de color óxido, una faja pectoral negra y flancos de color café. Se cree que las tonalidades negras, cafés y color tierra son producidas por melaninas en los animales, pero existen pocos estudios que hayan identificado el contenido de melanina de dichos colores en las plumas de las aves. En este estudio empleamos una serie de técnicas bioquímicas para investigar la base pigmentaria de estos colores del plumaje en machos de T. guttata. Los tres caracteres de las plumas contaron con pigmentos melánicos, pero variaron en las cantidades de las dos formas básicas de melanina (eumelanina y feomelanina). Las plumas negras del pecho presentaron principalmente eumelanina, mientras que las de las mejillas y los flancos presentaron concentraciones extraordinariamente altas de feomelanina. Los métodos tradicionales de análisis de carotenoides no detectaron este tipo de pigmentos en las plumas de las mejillas y los flancos.
... Interestingly, three other carotenoids (3Ј-dehydrolutein and canary-xanthophylls A and B) were also present in the yellow plumage of this mutant cardinal. 3Ј-dehydrolutein is an uncommon yellow carotenoid in bird feathers (e.g., thus far found only in the Red-billed Leiothrix [Leiothrix lutea], Stradi et al. 1996;Pine Grosbeak [Pinicola enucleator], Stradi 1998;House Finch [Carpodacus mexicanus], Inouye et al. 2001), whereas the canary-xanthophylls are some of the more common yellow carotenoids in bird plumage, found in the tail feathers of waxwings (Bombycilla spp.; Brush 1989, Stradi 1998) and the body plumage of Carduelis finches, for example , McGraw et al. 2001, 2002. As dehydrolutein and the canary-xanthophylls have never been reported in avian diets, we presume they are of metabolic origin, putatively derived from both lutein and zeaxanthin . ...
Article
Birds that use carotenoids to color their feathers must ultimately obtain these pigments from the diet, but they are also capable of metabolically transforming dietary carotenoids into alternate forms that they use as plumage colorants. The genetic and enzymatic control mechanisms underlying carotenoid metabolism are poorly understood. We investigated carotenoid pigments present in the feathers of an aberrantly colored yellow Northern Cardinal (Cardinalis cardinalis) to determine how metabolic pathways may have been altered. Normal red cardinals display four primary keto-carotenoids in plumage that are endogenously derived from a series of common food carotenoids. We found that the yellow feathers of this mutant lacked all four of the typical red pigments, and instead contained a yellow dietary carotenoid (lutein) and three yellow metabolic derivatives (3′-dehydrolutein and canary-xanthophylls A and B). Because yellow metabolites appear to be manufactured via a different metabolic process (dehydrogenation) than the usual red forms (oxidation at the C-4 or -4′ positions), it seems that this genetic mutation did not broadly disrupt all metabolic activity, but specifically impaired only one class of metabolic reactions and its associated enzymes. Pigmentos Carotenoides en un Cardenal Mutante: Implicaciones para los Mecanismos Genéticos y Enzimáticos de Control del Metabolismo de Carotenoides en las Aves Resumen. Las aves que utilizan pigmentos carotenoides para dar color a sus plumas deben obtenerlos de la dieta, pero también son capaces de transformar metabólicamente los carotenoides dietarios en formas alternativas que utilizan para colorear las plumas. Los mecanismos genéticos y enzimáticos de control involucrados en el metabolismo de los carotenoides no han sido bien establecidos. En este estudio investigamos los pigmentos carotenoides presentes en las plumas de un cardenal Cardinalis cardinalis con coloración amarilla aberrante para determinar cómo se podrían haber alterado las rutas metabólicas. Los cardenales normales de color rojo despliegan cuatro keto-carotenoides primarios en el plumaje, los cuales son derivados endógenamente a partir de una serie de carotenoides comunes en la dieta. Encontramos que las plumas amarillas del mutante carecían de los cuatro pigmentos rojos típicos, y contenían en cambio un carotenoide dietario amarillo (luteína) y tres derivados metabólicos amarillos (3′-dehidro luteína y xantofilas de canario A y B). Debido a que los metabolitos amarillos parecen ser fabricados mediante un proceso metabólico diferente al de las formas rojas usuales (deshidrogenación y oxidación en las posiciones C-4 o -4′, respectivamente), parece que esta mutación genética no alteró ampliamente toda la actividad metabólica. En cambio, parece haber inhabilitado sólo una clase de reacciones metabólicas y sus enzimas asociadas.
... In relation to signalisation of health, considerable attention has recently focused on carotenoids, which unlike the abovementioned pigments originate in plant food and animals cannot produce them on their own. Availability of carotenoids has a direct impact on the quality of yellow, orange, or red colouration and signalisation of carotenoids levels by colourful patches could be an instance of honest signalling [32]; [18]; [56]; [79]. ...
Chapter
In this chapter, we use the example of colouration of animal surfaces to show how processes based on interactions of the individual parts enter, as units, into processes on other levels and how this processual scaffolding leads to the emergence of ‘meaning’ on the level of communication between individuals. We review recent understanding of colour production and pattern formation in animals. We describe self-organization and dynamical nature of these processes. To highlight the inseparability of seeing and appearing, we discuss shared evolutionary origins of sight and colouration. Common evolutionary explanations of colouration are then discussed. Due to the complementarity of appearance and perception, the exposed surfaces of organisms ultimately become semi-autonomous entities subjected to their own evolution.
... Three studies (Inouye et al., 2001;McGraw et al. 2004;McGraw and Hardy, 2006) reported the occurrence of ATX in the plumage of ornamental birds. No relationship to oral intake was described. ...
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Astaxanthin is a pigmenting carotenoid occurring naturally in plankton, crustaceans and fish. The astaxanthin under assessment is of synthetic origin. The FEEDAP Panel considers synthetic astaxanthin safe for salmonids up to 100 mg/kg complete diet. The conclusion on the safety of astaxanthin for salmonids can be extrapolated to other fish and ornamental fish at the same dose. Dietary concentrations of up to 100 mg astaxanthin/kg feed are safe for crustaceans. The FEEDAP Panel could not conclude on the safety of astaxanthin for ornamental birds. Based on a BMDL10 of 3.4 mg/kg bw per day (calculated for liver hypertrophy in female rat in a carcinogenicity study) and applying an uncertainty factor of 100, it is possible to set an ADI of 0.034 mg ATX/kg bw (equivalent to 2.0 mg ATX per 60 kg person per day). The use of astaxanthin up to the maximum permitted dietary level for salmon and trout is of no concern for the safety of the consumer. As some formulations of astaxanthin may be dusty, and in the absence of data on inhalation toxicity, it is prudent to regard astaxanthin-containing additives as being potentially hazardous by inhalation. In the absence of any information on irritancy to skin or eyes or on skin sensitisation, astaxanthin-containing additives should be regarded as hazardous by exposure to skin or eyes. The FEEDAP Panel considers that the use of synthetic astaxanthin (100 mg astaxanthin/kg fish feed) does not pose a significant additional risk to the environment compared with natural astaxanthin. Astaxanthin is efficacious in colouring the flesh of salmonids and the epidermis of crustaceans. Astaxanthin is efficacious in pigmenting the flesh of food-producing fish other than salmonids and the skin of ornamental fish. No conclusion can be made on the efficacy of oral astaxanthin in pigmenting the plumage of ornamental birds.
... Parallel conversion pathways likely explain our finding that in canary plumage, carotenoid concentration predicts saturation but not hue of feathers. Hue has been found to reflect the ratio of red to yellow carotenoid pigments in feathers of House Finches, which do not use parallel conversion pathways (Inouye et al. 2001); the lack of a relationship between carotenoid pigment concentration and hue in the canary indicates that the feathers contain a generally uniform ratio of red and yellow pigments, indicative of parallel conversion pathways. Saturation, on the other hand, tends to reflect the absolute concentrations of carotenoid pigments in feathers (Hill and McGraw 2006). ...
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Atlantic Canaries (Serinus canaria) are the most commonly kept caged bird with extensive carotenoid-based plumage coloration. Domestic strains of canaries have been bred for a variety of colors and patterns, making them a valuable model for studies of the genetic bases for feather pigmentation. However, no detailed account has been published on feather pigments of the various strains of this species, particularly in relation to dietary pigments available during molt. Moreover, in the twentieth century, aviculturists created a red canary by crossing Atlantic Canaries with Red Siskins (Carduelis cucullata). This "red-factor" canary is reputed to metabolically transform yellow dietary pigments into red ketocarotenoids, but such metabolic capacity has yet to be documented in controlled experiments. We fed molting yellow and red-factor canaries seed diets supplemented with either β-carotene, lutein/zeaxanthin, or β-cryptoxanthin/β-carotene and measured the coloration and carotenoid content of newly grown feathers. On all diets, yellow canaries grew yellow feathers and red canaries grew orange or red feathers. Yellow canaries deposited dietary pigments and metabolically derived canary xanthophylls into feathers. Red-factor canaries deposited the same plumage carotenoids as yellow canaries, but also deposited red ketocarotenoids. Red-factor canaries deposited higher total amounts of carotenoids than yellow canaries, but otherwise there was little effect of dietary supplementation on feather carotenoid content, hue, or chroma. These observations indicate that canaries can use a variety of dietary precursors to produce plumage coloration and that red canaries can metabolically convert yellow dietary carotenoids into red ketocarotenoids.
... For each male, we sampled three to five feathers from each ornamental area (breast, crown and rump) within 30 days of moult completion, and then again three to six months after the moult. The mean time between feather samples (mean + s.e.: 154 + 6 days) approximately corresponds to the time between the species' single post-breeding moult (August-September) and breeding season (January-February) for this population [46]. See the electronic supplementary material, Methods for details of carotenoid extraction and identification. ...
Article
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The evolutionarily persistent and widespread use of carotenoid pigments in animal coloration contrasts with their biochemical instability. Consequently, evolution of carotenoid-based displays should include mechanisms to accommodate or limit pigment degradation. In birds, this could involve two strategies: (i) evolution of a moult immediately prior to the mating season, enabling the use of particularly fast-degrading carotenoids and (ii) evolution of the ability to stabilize dietary carotenoids through metabolic modification or association with feather keratins. Here, we examine evolutionary lability and transitions between the two strategies across 126 species of birds. We report that species that express mostly unmodified, fast-degrading, carotenoids have pre-breeding moults, and a particularly short time between carotenoid deposition and the subsequent breeding season. Species that expressed mostly slow-degrading carotenoids in their plumage accomplished this through increased metabolic modification of dietary carotenoids, and the selective expression of these slow-degrading compounds. In these species, the timing of moult was not associated with carotenoid composition of plumage displays. Using repeated samples from individuals of one species, we found that metabolic modification of dietary carotenoids significantly slowed their degradation between moult and breeding season. Thus, the most complex and colourful ornamentation is likely the most biochemically stable in birds, and depends less on ecological factors, such as moult timing and migration tendency. We suggest that coevolution of metabolic modification, selective expression and biochemical stability of plumage carotenoids enables the use of unstable pigments in long-term evolutionary trends in plumage coloration. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
... For each male, we sampled three to five feathers from each ornamental area (breast, crown and rump) within 30 days of moult completion, and then again three to six months after the moult. The mean time between feather samples (mean + s.e.: 154 + 6 days) approximately corresponds to the time between the species' single post-breeding moult (August-September) and breeding season (January-February) for this population [46]. See the electronic supplementary material, Methods for details of carotenoid extraction and identification. ...
... Each of these axes of color tends to relate to different properties of the colored ornament itself. For example, chroma may be a good generalization of pigment density, while hue may be more representative of the proportion of red to yellow pigments in a carotenoid-colored ornament (Inouye et al. 2001;Hill and McGraw 2006). The choice of color parameter used in a particular study is therefore important to include in our analysis because it may affect study conclusions by representing different properties of the ornament measured. ...
Article
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Carotenoid coloration is the one of the most frequently studied ornamental traits in animals. Many studies of carotenoid coloration test the associations between carotenoid coloration and measures of performance, such as immunocompetence and oxidative state, proceeding from the premise that carotenoids are limited resources. Such studies commonly involve supplementing the diets of captive birds with carotenoids. In many cases, however, the amount of carotenoid administered is poorly justified, and even supposedly carotenoid-limited diets may saturate birds' systems. To quantify the relationships among the amount of carotenoids administered in experiments, levels of circulating carotenoids, and quantities of carotenoids deposited into colored ornaments, we performed a meta-analysis of 15 published studies that supplemented carotenoids to one of seven songbird species. We used allometric scaling equations to estimate the per-gram carotenoid consumption of each study's subjects, and we used meta-regression to evaluate the effects of this carotenoid dose on differences in coloration and plasma carotenoid levels between supplemented and control groups of birds. After accounting for supplementation duration and species, we observed a significant positive correlation between carotenoid intake and response of plasma carotenoid level to supplementation. The presence of supplemental carotenoids also tended to increase the expression of ornamental coloration, but the magnitude of the carotenoid dose did not significantly affect how strongly coloration changed with supplementation. Further, coloration effect sizes had no significant relationship with plasma carotenoid effect sizes. We also found significant heterogeneity in responses among studies and species, and the parameters used to measure color significantly affected response to supplementation. Our results emphasize the importance of performing dosage trials to determine what supplementation levels provide limited versus surplus carotenoids and of measuring the natural level of carotenoid intake by the study species to validate the appropriateness of supplementation levels for a particular study species and experimental design.
... In the case that carotenoid-based plumage is an honest signal of quality, one may expect that age and condition would affect colouration (Andersson 1994, Inouye et al. 2001. This is, indeed, what we found, with older males having higher values of plumage SWS ratio (more saturated colouration), meaning that older males are capable of mobilizing higher concentrations of carotenoids in their plumage. ...
Article
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A fundamental assumption of theories on the evolution of sexual signals is that they should be costly to produce in order to honestly signal the quality of the sender. The expression of carotenoid-based plumage signals is considered to be condition-dependent, due to the role of carotenoids functioning as pigments and as health modulators. We assessed carotenoid-based plumage colouration in relation to male condition in a free living population of male European serins Serinus serinus during the breeding season. Male serins were trapped for morphometric and colouration measurements, during a four-year field study, in order to evaluate the signalling value of colouration in relation to body condition and parasites level. We compared two different forms of colour quantification based on spectral data - the most commonly used tristimulus colour variables and physiological models of avian colour vision - and found that they were highly correlated for this species. We investigated the signalling value of male plumage colouration and it was found to be related to age and ectoparasite load. Plumage double cone and patch size were negatively related to parasites level, whereas SWS ratio was positively related to parasites and age. Colouration was also related with the time since moult. Our results indicate that the colour expression of serin's plumage is age dependent and is related, in complex ways, with the ability to cope with parasitic infection.
... Animals do not synthesize these organic terpenoids themselves: they are received only in plant nutrition. Access to carotenoids then directly influences the quality (hue, brightness) of yellow, orange, and red color of animal tissues, which are further subjected to sexual selection (Inouye et al. 2001;Faivre et al. 2003;Saks et al. 2003). Pterins have similar optical properties as carotenoids (Martínez and Barbosa 2010) and in female Scleropus virgatus, one can observe during their reproductive period the appearance of pterin-based orange spots which serve as a signal towards males. ...
Article
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Turtles are among the most intriguing amniotes but their communication and signaling have rarely been studied. Traditionally, they have been seen as basically just silent armored ‘walking stones’ with complex physiology but no altruism, maternal care, or aesthetic perception. Recently, however, we have witnessed a radical change in the perception of turtle behavioral and cognitive skills. In our study, we start by reviewing some recent findings pertaining to various highly developed behavioral and cognitive patterns with special emphasis on turtles. Then we focus on freshwater turtles and use data about their sexual behavior and size sexual dimorphism (SSD) to test whether conspicuous coloration of the head is in these animals related to sexual processes. We found that absence of aggressive mating behavior is statistically associated with the presence of conspicuous coloration on turtles’ heads. It also seems that while species with female-biased SSD are characterised by conspicuously colored head ornaments, in species with male-biased SSD conspicuous coloration is absent. Unlike large females, males thus seem to be under pressure to develop conspicuous coloration and engage in non-aggressive behavior using signaling to succeed in courtship. And finally, we discuss possible roles of head color patterns in turtle communication during mating.
... The loss of red coloration in captive House Finches, which was first noted in the literature more than a century ago (Keeler 1893), is apparently a consequence of the lack of suitable carotenoid precursors for the production of red plumage pigments. The primary red pigment in the feathers of male House Finches is 3-hydroxy-echinenone (Inouye et al. 2001), which is hypothesized to be the metabolic derivative of β-cryptoxanthin (Stradi 1998). The seeds that are typically used to maintain House Finches in captivity contain primarily zeaxanthin and lutein, with small amounts of β-cryptoxanthin and β-carotene . ...
Chapter
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... Specifically, MP was expected to be higher in clutches of larger or older females than in clutches of smaller or younger individuals. Over the 4 years of genetic study, MP was positively associated with female age, but not body size, suggesting that male painted turtles rely on phenotypic traits other than body size to assess female age-specific qualities (e.g., the intensity and contrasts of red and yellow colors, Inouye et al. 2001). In contrast to increased mating attempts by males directed at higher quality females that result in higher MP, the longer reproductive intervals of lower quality females may result in increasing their opportunities to mate and store sperm between reproductive events and that may also increase the incidence of MP. ...
Article
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Male reproductive success (RS) in polygamous species with minimal social systems is often determined by the number of mates. However, because male RS is translated through females, the number of offspring sired can also be influenced by female qualities. Empirically sufficient data to document how tradeoffs between mate number and quality influence male RS are seldom available for long-lived, iteroparous species. We combined long-term life history data (1983–2006) on the E. S. George Reserve (ESGR, MI, USA) with parentage data from 155 clutches of 59 female painted turtles (Chrysemys picta marginata) of varying reproductive frequencies (2003–2006) to determine the relative contribution of female numbers and qualities on male RS. One previously documented trait of female painted turtles that can have substantial influences on male RS is repeat paternity through the use of stored sperm to fertilize over 95 % of within-year clutches. In addition, our study found that second-clutch producing female painted turtles on the ESGR have higher among-year reproductive frequencies than do first-clutch only females. Multiple paternity was detected in 14.1 % of clutches (min-max = 6.1–30.0 % annually), and the number of mates of both sexes was low annually (males 1.0; females 1.2) and over 4 years (males 1.1; females 1.7). Among successful males, RS varied substantially (1–32 offspring) and was strongly influenced by the combination of female reproductive frequency and repeat paternity (>38 % among years), but not mate number. Low mate number for both sexes was unexpected in a species without complex mating behaviors or parental care.
... Young, second year males have a smaller alula than older males: this pattern may be expected as second year males can be visually distinguished from older males by other plumage features (Rae and Marquiss 1989). Second year snow buntings may have had less time or resources to allocate to growing a large alula during feather production, which occurred when they were nestlings (Inouye et al. 2001). ...
Article
While studies of achromatic plumage signaling are scarce relative to chromatic ornaments, achromatic ornaments have the potential to act as an efficient form of visual communication due to the highly conspicuous contrast between black and white body regions. Recently, achromatic plumage reflectance has been shown to indicate condition, yet the condition‐dependence of achromatic patch size remains unstudied. Here we show the first evidence that alula size, an achromatic plumage patch, has the potential to signal a male’s condition and predict reproductive performance. In Arctic‐breeding snow buntings Plectrophenax nivalis, the size of the alula simultaneously predicted pre‐breeding physiological health and the number of offspring produced, through an intermediate variable (lay date). Snow buntings appear to pair assortatively; males and females arriving earlier pair together, and changes in body condition over the breeding season are positively related within pairs. We suggest that simple achromatic plumage patches, like alula size, have the potential to act as condition‐dependent signals. Consequently, females may benefit from assessing these signals to reliably evaluate a male’s condition and reproductive potential as a means of maximizing their reproductive success.
... Knowledge of the mechanisms that control the amount and type of carotenoids deposited in integument is prerequisite to understanding the proximate causes of carotenoid color variation. Studies in birds have shown that variation in carotenoid-based coloration can simply reflect presence or absence of carotenoids in the tissue (Eriksson et al., 2008;Walsh et al., 2012), or be caused by differences in carotenoid types (Brush and Seifried, 1968), concentrations (Brush, 1970;Inouye et al., 2001) or both (Crozier, 1967;Hudon et al., 1989). For example, T. moorii populations (Fig. 3) differ not only in total carotenoid content but also in the types of integumentary carotenoids, the latter inferred from the shapes of carotenoid absorption spectra and patterns of HPLC chromatograms (Mattersdorfer et al., 2012;K. ...
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Animal colors play important roles in communication, ecological interactions and speciation. Carotenoid pigments are responsible for many yellow, orange and red hues in animals. Whereas extensive knowledge on the proximate mechanisms underlying carotenoid coloration in birds has led to testable hypotheses on avian color evolution and signaling, much less is known about the expression of carotenoid coloration in fishes. Here, we promote cichlid fishes (Perciformes: Cichlidae) as a system in which to study the physiological and evolutionary significance of carotenoids. Cichlids include some of the best examples of adaptive radiation and color pattern diversification in vertebrates. In this paper, we examine fitness correlates of carotenoid pigmentation in cichlids and review hypotheses regarding the signal content of carotenoid-based ornaments. Carotenoid-based coloration is influenced by diet and body condition and is positively related to mating success and social dominance. Gaps in our knowledge are discussed in the last part of this review, particularly in the understanding of carotenoid metabolism pathways and the genetics of carotenoid coloration. We suggest that carotenoid metabolism and transport are important proximate mechanisms responsible for individual and population-differences in cichlid coloration that may ultimately contribute to diversification and speciation.
... Para profundizar más sobre la medición del color y sobre las diferencias entre distintos métodos puede consultarse (Endler, 1990;Zuk & Decruyenaere, 1994;Repentigny et al., 1997;Tella et al., 1998;Villafuerte & Negro, 1998;Hill, 1998a;Figuerola et al., 1999a;Cuthill et al., 1999b;Grill & Rush, 2000;Osorio & Ham, 2002). Algunos trabajos recientes estan intentando relacionar el color de las plumas con su contenido en pigmentos, especialmente carotenos (Inouye et al., 2001;Saks et al., 2003a), pero el tema es más complejo de lo que pueda parecer y esta todavía en sus inicios (ver también Hill, 2002). ...
... The loss of red coloration in captive House Finches, which was first noted in the literature more than a century ago (Keeler 1893), is apparently a consequence of the lack of suitable carotenoid precursors for the production of red plumage pigments. The primary red pigment in the feathers of male House Finches is 3-hydroxy-echinenone (Inouye et al. 2001), which is hypothesized to be the metabolic derivative of β-cryptoxanthin (Stradi 1998). The seeds that are typically used to maintain House Finches in captivity contain primarily zeaxanthin and lutein, with small amounts of β-cryptoxanthin and β-carotene . ...
... Another explanation for our results might be that red is a carotenoid pigment (Finger and Burkhardt 1994), and there-fore has special signal value (Inouye et al . 2001). Carotenoid pigments can be acquired only by direct ingestion and, conceivably, birds might be more sensitive to this colour because it would attract them to food sources or would have special signal value. This, in turn, could influence bird responses to a researcher approaching in a red shirt. If this was the case, it could explain th ...
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The species-confidence hypothesis states that birds are attracted to colours found on their own body and are repelled by colours not found on their body. Previous studies have examined this hypothesis by measuring the distance at which birds took flight in response to humans approaching them while wearing different-coloured clothes. One study found that birds without red or orange on their bodies had longer flight-initiation distances when an orange vest was worn, while birds with those colours on their bodies were not affected. We evaluated the species- confidence hypothesis by approaching Spiny-cheeked Honeyeaters ( Acanthagenys rufogularis ) while wearing four different-coloured T-shirts and noted their flight-initiation distance. We predicted that birds would allow us to approach closer if we were wearing a colour found on their body. Unlike previous studies, we accounted for the fact that different colours are differentially detectable in the field because detectability alone may influence flight- initiation distance (i.e. bright colours are more detectable simply because they are bright). Two shirts were highly detectable (red and yellow) and two were relatively cryptic (tan and olive). Specifically, Spiny-cheeked Honeyeaters were found to have the longest flight-initiation distances when approached by a person wearing a yellow T-shirt (a colour not found on the bird), and the shortest flight-initiation distances when approached by a person wearing a red T-shirt (a colour found on the bird). The species-confidence hypothesis may account for variable flight-initiation distances.
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The carotenoid-based colors of birds are a celebrated example of biological diversity and an important system for the study of evolution. Recently, a two-step mechanism, with the enzymes cytochrome P450 2J19 (CYP2J19) and 3-hydroxybutyrate dehydrogenase 1-like (BDH1L), was described for the biosynthesis of red ketocarotenoids from yellow dietary carotenoids in the retina and plumage of birds. A common assumption has been that all birds with ketocarotenoid-based plumage coloration used this CYP2J19/BDH1L mechanism to produce red feathers. We tested this assumption in house finches ( Haemorhous mexicanus ) by examining the catalytic function of the house finch homologs of these enzymes and tracking their expression in molting birds. We found that CYP2J19 and BDH1L did not catalyze the production of 3-hydroxy-echinenone (3-OH-echinenone), the primary red plumage pigment of house finches, when provided with common dietary carotenoid substrates. Moreover, gene expression analyses revealed little to no expression of CYP2J19 in liver tissue or growing feather follicles, the putative sites of pigment metabolism in molting house finches. Finally, although the hepatic mitochondria of house finches have high concentrations of 3-OH-echinenone, observations using fluorescent markers suggest that both CYP2J19 and BDH1L localize to the endomembrane system rather than the mitochondria. We propose that house finches and other birds that deposit 3-OH-echinenone as their primary red plumage pigment use an alternative enzymatic pathway to produce their characteristic red ketocarotenoid-based coloration.
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In many species of animals, red carotenoid-based coloration is produced by metabolizing yellow dietary pigments, and this red ornamentation can be an honest signal of individual quality. However, the physiological basis for associations between organism function and the metabolism of red ornamental carotenoids from yellow dietary carotenoids remains uncertain. A recent hypothesis posits that carotenoid metabolism depends on mitochondrial performance, with diminished red coloration resulting from altered mitochondrial aerobic respiration. To test for an association between mitochondrial respiration and red carotenoids, we held wild-caught, molting male house finches in either small bird cages or large flight cages to create environmental challenges during the period when red ornamental coloration is produced. We predicted that small cages would present a less favorable environment than large flight cages and that captivity itself would decrease both mitochondrial performance and the abundance of red carotenoids compared to free-living birds. We found that captive-held birds circulated fewer red carotenoids, showed increased mitochondrial respiratory rates, and had lower complex II respiratory control ratios—a metric associated with mitochondrial efficiency—compared to free-living birds, though we did not detect a difference in the effects of small cages versus large cages. Among captive individuals, the birds that circulated the highest concentrations of red carotenoids had the highest mitochondrial respiratory control ratio for complex II substrate. These data support the hypothesis that the metabolism of red carotenoid pigments is linked to mitochondrial aerobic respiration in the house finch, but the mechanisms for this association remain to be established.
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Because studies of plumage coloration often focus on highly elaborate and conspicuous males, little is known about the factors driving the evolution of drab plumage in females of dichromatic species. We explored variation in the color properties of drab female plumage across subspecies of the Variable Seedeater (Sporophila corvina), and found a correlation between plumage brightness of male and female plumage patches. This correlation is consistent with the hypothesis that differences in plumage brightness among females result, at least partially, from a genetic correlation or shared developmental pathway with the more conspicuous male plumage traits that are shaped by sexual selection. Further, we modeled the perception of female plumage using the avian visual system and found that most of the variation in color among females is mostly undetectable by birds; therefore, it is unlikely for such variation to have evolved via direct sexual selection as a signal for recognition or assortative mating. Together, these results suggest that variation in S. corvina female color result from non-adaptive processes. However, we found a reduced variation on color of dorsal patches compared with that of ventral patches among females, which could be explained by natural selection operation on crypsis, reducing the variation on dorsal patches. Finally, we found little differences in plumage color between adult females and juveniles, which suggest selection for juveniles to resemble adult females possibly to reduce aggression from adult males. Additional within-population studies and behavioral experiments are needed to discern the evolutionary factors driving variation on S. corvina female color and its function.
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We investigated potential information content in red carotenoid-based undertail coverts of 28 pairs of breeding Great Spotted Woodpeckers by comparing plumage reflectance to measures of body condition and reproductive success. Plumage coloration was not significantly associated with sex or age, and did not correlate with body condition or the number of offspring fledged. Further, we found no evidence of assortative mating related to plumage colour. Our research provides an example of an exception from the commonly held hypothesis that carotenoid-based plumage coloration signals individual condition. Future surveys incorporating other plumage traits and physiological measures of condition in Great Spotted Woodpeckers are needed to verify our findings.
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Reproductive success can improve with experience, which increases with age in many long-lived species. Signals that provide reliable information about age are therefore of importance for mate choice and consequently are under sexual selection. In birds, these are often vocal signals as well as visual signals in the form of plumage coloration. King penguins, Aptenodytes patagonicus, are sexually monomorphically ornamented seabirds that perform a complex visual and acoustic courtship display. Coloured beak spots and ear patches contain information about the condition and physiological status of adult males and females, but their role as a signal of age has previously only been studied in young birds. Vocalizations have mainly been studied as signals of individuality and not in the context of courtship. We investigated two multicomponent signals in the context of mate choice by analysing beak spot, ear patch and call parameters of wild king penguins. We explored the relation between these signals and age as well as age classes (chicks, juveniles, adults). Ornament parameters were weakly correlated with in males, but not in females, while acoustic parameters were highly correlated with age in both sexes. The calls' fundamental frequency and energy parameters and all the beak spot parameters reliably classified individuals into their age class. Since age class was redundantly encoded in both acoustic and colour parameters, we hypothesize that calls and ornaments function as back-up signals that increase the chance of accurately conveying the age class of the sender to receivers. King penguins might sequentially analyse age class signals during courtship, where acoustic signals serve as long-range communication when sender and receiver are out of sight, and ornamentation signals become important at close range. We show the importance of considering bimodal, multicomponent signals when studying complex behaviour and discuss how signalling environment, the species’ life history and mating system influence the evolution of communication signals.
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There is widespread contemporary interest in causes and consequences of blood glucose status in humans (e.g., links to diabetes and cardiovascular disease), but we know comparatively less about what underlies variation in glucose levels of wild animals. Several environmental factors, including diet, disease status, and habitat quality, may regulate glucose circulation, and we are in need of work that assesses many organismal traits simultaneously to understand the plasticity and predictability of glucose levels in ecological and evolutionary contexts. Here, we measured circulating glucose levels in a species of passerine bird (the house finch, Haemorhous mexicanus) that has served as a valuable model for research on sexual selection, disease, and urban behavioral ecology, as these animals display sexually dichromatic ornamental coloration, harbor many infectious diseases (e.g., poxvirus, coccidiosis, mycoplasmal conjunctivitis), and reside in both natural habitats and cities. We tested the effects of sex, habitat type, body condition, coccidiosis and poxvirus infections, and expression of carotenoid plumage coloration on blood glucose concentrations and found that the body condition and poxvirus infection significantly predicted circulating glucose levels. Specifically, birds with higher blood glucose levels had higher body condition scores and were infected with poxvirus. This result is consistent with biomedical, domesticated-animal, and wildlife-rehabilitation findings, and the premise that glucose elevation is a physiological response to or indicator of infection and relative body weight. The fact that we failed to find links between glucose and our other measurements suggests that blood glucose levels can reveal some but not all aspects of organismal or environmental quality.
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Mimicry is an adaptation where one species evolves color similarity to another species to avoid predation. Often, a single species evolves resemblance to multiple species, leading to color variation in the mimic species. How these shared colors evolve among distant relatives and how a single species is capable of evolving a suite of colors to matching multiple species is not well understood. We studied the mechanisms underlying color mimicry in the Peruvian poison dart frog species Ranitomeya imitator, and found that color variation and mimicry is largely controlled by the thickness of nanocrystals in the skin. These crystals are responsible for the structural color of the skin, which results in highly reflective coloration that may be important for producting effective warning coloration to avoid predation. Other species of poison dart frogs, including the species mimicked by Ranitomeya imitator as well as other poison dart frogs not involved in mimicry, also regulate color through structural mechanisms. These results demonstrate that much of the color diversity seen across poison frogs, including mimetic colors, is controlled by a single trait: the thickness of reflective nanocrystals in the skin. Mimicry appears to have evolved from a common set of color mechanisms found across poison dart frogs, rather than from novel color mechanisms having evolved ‘from scratch’ in the mimetic species. These results add further weight to the idea that convergent evolution often occurs through parallel evolution within a shared set of developmental pathways rather than the evolution of completely novel structures.
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Urban environments create a unique suite of conditions, leading to changes in animal behavior, morphology, phenology, and physiology. Condition-dependent traits such as the carotenoid-based coloration offer a unique opportunity to assess the impacts of urbanization on organisms because they reflect the nutrition, health, or other resource-based attributes of their bearers and they play an essential role in intra and intersex interactions. To determine if and how the carotenoid-based coloration of male house finches (Haemorhous mexicanus) varies along a gradient of urbanization, we quantified the plumage coloration of more than 1000 individuals in urban, suburban , rural, and desert habitats over the course of 17 months. We also examined for the first time the preference of females for male plumage coloration across the urban-rural gradient, to test if and how female preferences varied relative to the plumage coloration displayed by males in their local population. We found that carotenoid-based coloration decreased along the gradient of urbanization, suggesting that the enzyme-driven metabolic conversion of dietary carotenoids into red carotenoids used to color plumage is sensitive to urban stressors. The stronger negative effect of urbanization on carotenoid-based plumage coloration during breeding than during molt and winter suggests that urbanization affects color fading rate, maybe through modifications of feather-degrading bacterial load. Finally, we have shown that urbanization influences female mate-choice behavior, suggesting that female color preferences may track the variation in male coloration across the gradient of urbanization.
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The yellow and red feather pigmentation of many bird species [1] plays pivotal roles in social signaling and mate choice [2, 3]. To produce red pigments, birds ingest yellow carotenoids and endogenously convert them into red ketocarotenoids via an oxidation reaction catalyzed by a previously unknown ketolase [4-6]. We investigated the genetic basis for red coloration in birds using whole-genome sequencing of red siskins (Spinus cucullata), common canaries (Serinus canaria), and "red factor" canaries, which are the hybrid product of crossing red siskins with common canaries [7]. We identified two genomic regions introgressed from red siskins into red factor canaries that are required for red coloration. One of these regions contains a gene encoding a cytochrome P450 enzyme, CYP2J19. Transcriptome analysis demonstrates that CYP2J19 is significantly upregulated in the skin and liver of red factor canaries, strongly implicating CYP2J19 as the ketolase that mediates red coloration in birds. Interestingly, a second introgressed region required for red feathers resides within the epidermal differentiation complex, a cluster of genes involved in development of the integument. Lastly, we present evidence that CYP2J19 is involved in ketocarotenoid formation in the retina. The discovery of the carotenoid ketolase has important implications for understanding sensory function and signaling mediated by carotenoid pigmentation.
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Parasites are widely assumed to cause reduced expression of ornamental plumage coloration, but few experimental studies have tested this hypothesis. We captured young male house finches Carpodacus mexicanus in Alabama before fall molt and randomly divided them into two groups. One group was infected with the bacterial pathogen Mycoplasma gallicepticum (MG) and the other group was maintained free of MG infection. All birds were maintained through molt on a diet of seeds with tangerine juice added to their water as a source of β-cryptoxanthin, the natural precursor to the primary red carotenoid pigment in house finch plumage. All males grew drab plumage, but males with MG infection grew feathers that were significantly less red (more yellow), less saturated, and less bright than males that were not infected. MG targets upper respiratory and ocular tissue. Our observations show that a pathogen that does not directly disrupt carotenoid absorption or transportation can still have a significant effect on carotenoid utilization.
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Carotenoid pigments produce the ornamental red, orange, and yellow integumentary coloration of many species of animals. Among individuals of a population, the hue and saturation of carotenoid-based ornaments can be extremely variable, and studies of fish and birds have shown that females generally prefer males that display the most saturated and reddest coloration. Consequently, there has been a great deal of interest in determining the proximate factors that affect individual expression of carotenoid-based pigmentation. Parasites might affect production of ornamental coloration, and the Hamilton-Zuk hypothesis proposes that parasitized males will show decreased expression of the secondary sexual traits preferred by females. We found that captive male House Finches (Carpodacus mexicanus) experimentally infected with Isospora spp. (coccidians) and/or Mycoplasma gallisepticum produced carotenoid-based plumage coloration that was significantly less red and less saturated than that of noninfected males. These observations validate a necessary condition of the Hamilton-Zuk hypothesis, but heritable resistance to the pathogens we examined remains to be demonstrated.
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The Colortron (Light Source, San Rafael, California) is an inexpensive, compact, Macintosh-compatible reflectance spectrophotometer that can be used to quantify the coloration of the plumage and soft parts of birds. The Colortron provides a reflectance spectrum (390-700 nm) of the object being measured as well as tristimulus color scores that can be compared to scores from the Methuen or Munsell color references. Because the Colortron fails to measure ultraviolet light (wavelength <390 nm), which is visible to some species of birds, Colortron output must be interpreted cautiously when it is used to describe plumage that may reflect UV, especially if the focus of the study is understanding the function of coloration. The Colortron is especially useful for quantifying carotenoid-based plumage coloration, which reflects primarily in the visible spectrum. I compared visual scores of carotenoid-based ornamental plumage of House Finches (Carpodacus mexicanus) made by comparison to The Methuen Handbook of Colour to tristimulus color scores generated by the Colortron. Hue and saturation scores from visual assessment were significantly positively correlated with hue and saturation scores from the Colortron. I recommend the use of the Colortron as a means to quantify plumage and soft-part coloration.
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In many passerine species males do not attain definitive breeding plumage until after their first potential breeding season. Such delayed plumage maturation has been the subject of numerous studies, most of which have focused on the adaptive value of female-like plumage for young males in single populations. Thus, although studies of delayed plumage maturation have been presented as tests of evolutionary hypotheses, most have lacked an appropriate comparative perspective. Moreover, most studies of subadult plumage in passerines have been conducted without information on the general function of ornamental plumage in the species being studied. A study of delayed plumage maturation in the House Finch (Carpodacus mexicanus) provided an opportunity to overcome these problems. The function and proximate control of ornamental plumage coloration in House Finches have been studied extensively. In addition, House Finches occupy a wide range across North America with approximately 15 subspecies recognized, and populations vary in expression of delayed plumage maturation. In most populations, including the most familiar subspecies, C. m. frontalis, males acquire definitive basic plumage in their first prebasic molt. In at least three populations, C. m. griscomi of southern Mexico, C. m. amplus of Guadalupe Island, and Great Basin populations of C. m. frontalis, however, males do not acquire definitive plumage until the completion of their second prebasic molt, spending their first potential breeding season in a female-like plumage. Using a composite phylogeny and parsimony analysis, I show that delayed plumage maturation likely was lost in the ancestral House Finch population and was regained independently by the three taxa in which it is now observed. Thus, delayed plumage maturation in the House Finch is a derived trait. In addition, I show that the acquisition of delayed plumage maturation is associated with a reduction in the extent of ornamental plumage (i.e. a reduction in patch size). These observations support the idea that delayed plumage maturation in the House Finch is an adaptation to increased production costs of red ornamental display plumage in some populations.
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I compared the mate preferences of female house finches (Carpodacus mexicanus) from populations in which males differ in both plumage coloration and the extent of ventral pigmentation (patch size). Phylogenetic analysis indicated that the small patch of ventral coloration displayed by males in some populations is derived from a larger-patched ancestral state. Regardless of the appearance of males in their own populations, however, females from all populations showed a preference for the most brightly colored males and males with the largest patches. A reduction in patch size independent of a change in female mate preference is not consistent with sensory-bias or reproductive isolation models of sexual selection or with general predictions of runaway models of sexual selection. In contrast, a lack of congruence between female mate preference and male trait expression is predicted by the honest advertisement model, with house finches responding to variation in regional and local access to carotenoid plumage pigments.
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Independent of age or geographic variation, males of many species of birds exhibit dramatic variation in the expression of elaborate secondary sexual characters. ''Good genes'' models of sexual selection propose that males with relatively low resistance to parasites suffer high parasite loads that inhibit their ability to express these characters fully. In turn, variation in such characters may reliably indicate male quality and may be used by females to choose males. This is the first study to monitor (via mark-recapture) the long-term effects of parasites on color and growth of plumage in individual birds. Specifically, we used house finches, Carpodacus mexicanus, a sexually dimorphic species in which females are known to prefer more brightly plumaged males for mating, to test the hypothesis that high parasite load in males is correlated with poor physiological condition and reduced development of male secondary sex characters. Our results clearly demonstrate that both ectoparasitic feather mite (Proctophyllodes sp.) infestations and endoparasitic avian pox viral infections during molt are correlated with poor physiological condition and reduced development of bright male plumage during the same molt period, thus supporting good genes models.
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The majority of studies examining the role of hormones in the proximate mechanisms of plumage coloration in birds have focused on intersexual differences (plumage dichromatism) and on structural- or melanin-based plumage coloration. The relationship between hormones and carotenoid-based plumage color, and in particular intrasexual plumage color variation, has received little attention. We manipulated testosterone levels of both captive and wild male House Finches to determine whether testosterone influences the expression of male plumage color in this species. We found that in captive male House Finches elevated testosterone delayed molt and resulted in drabber, less red plumage, even when birds were supplemented with dietary carotenoids. Elevated testosterone also resulted in drab plumage color in wild males, and appeared to delay molt in wild birds as well. Wild males implanted with testosterone showed wide variation in expression of plumage coloration. Those implanted early in the year molted plumage similar in color to their pre-treatment plumage, but those implanted later molted substantially duller plumage, possibly because delayed molt resulting from elevated testosterone caused these males to molt when carotenoid pigments were not available in sufficient amounts. These observations have the potential to explain previously reported relationships between plumage color and behavior in male House Finches, and highlight the importance of considering the proximate mechanisms of plumage coloration in avian sexual selection.
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In the wild, male House Finches (Carpodacus mexicanus) vary in plumage color from pale yellow to bright red. I investigated the proximate basis of this variation in plumage brightness, as well as the basis for variation in the extent of ventral carotenoid pigmentation. Regardless of their age or coloration in the wild, captive males converged on a similar appearance after completing prebasic molt on a standardized diet, with significantly less variance in coloration than is found among wild males. Captive males that were fed a diet deficient in carotenoid pigments grew pale yellow feathers; males fed a diet supplemented with β-carotene grew pale orange feathers; and males fed a diet supplemented with canthaxanthin grew bright red feathers. Stored carotenoids did not appear to be an important source of feather pigments. Red males captured from the wild just prior to fall molt and fed a carotenoid-deficient diet did not grow more colorful feathers than males that had been held in captivity on a carotenoid-deficient diet for six to nine months prior to fall molt. In a wild House Finch population in southeastern Michigan, the mean plumage coloration of yearling males was significantly drabber than the mean coloration of older males, although both groups displayed approximately the same range of coloration. Wild males tended to become brighter between their first and second springs, but thereafter, males tended to display a similar plumage coloration between years. The extent of ventral carotenoid pigmentation (color-patch size) also was partly dependent on carotenoid intake. Captive males whose diet was supplemented with canthaxanthin produced significantly larger patches after captive molt than before captive molt, and canthaxanthin-supplemented males also expressed significantly larger patches than males in the carotenoid-deficient or β-carotene-supplemented groups. Among wild males, there was a significant positive correlation between patch size and plumage brightness.
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Understanding the relative costs of different forms of ornamental displays is fundamental to research on the evolution of such traits. For traits such as elongated tails, assessing the degree of exaggeration is straight-forward: bigger is more exaggerated and more costly. In contrast, assignment of such a hierarchical ranking of costliness and exaggeration to color displays has not been possible. In this paper, I consider whether red carotenoid displays represent a more energetically costly form of ornamentation than yellow or orange carotenoid displays. Several lines of evidence support the idea that red carotenoid pigmentation is particularly costly. Red carotenoid pigments are less abundant than yellow pigments in the diet of virtually all vertebrates. Although many vertebrates can convert some yellow carotenes and xanthophylls to red pigments, all species appear to be restricted in the types of metabolic conversions of which they are capable as well as by the costs of such conversions. In virtually all avian taxa with carotenoid-based coloration, when females and juvenile males show plumage hue that is different than that of adult males, their plumage is less red (more orange or yellow). Finally, in a comparative study of cardueline finches, there was a significant positive relationship between the degree of sexual dichromatism and the redness of male plumage, suggesting that red is a particularly costly color display. The finding that red is a more costly color display than yellow or orange has important implications for comparative studies of the evolution of ornamental plumage.
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Nesospiza buntings have speciated at the Tristan da Cunha archipelago in the central South Atlantic Ocean. Two species, the Tristan Bunting (N. acunhae) and Wilkins' Bunting (N. wilkinsi), differ markedly in size and co-occur without interbreeding on Night- ingale Island. Nearby Inaccessible Island supports two altitudinally segregated color morphs of N. acunhae, as well as a hybrid complex involving acunhae and wilkinsi. Plumage variation was evaluated for 581 buntings, most of which were caught on Inaccessible Island. Nesospiza plumages vary with age and sex; immature plumage is retained for at least two years. Despite age and sex differences, there is no overlap in coloration between the upland and lowland morphs of N. acunhae on Inaccessible Island. The two morphs are distinct from the time of hatching; chicks of lowland acunhae are pinkish, whereas upland acunhae are yellow. Color differences between acunhae morphs were quantitative rather than qualitative; their feathers contain the same suite of carotenoid pigments, but at three times greater concentration in upland birds. Dispersion of different bunting populations on Inaccessible Island is closely related to vegetation types. Individually marked individuals were largely sedentary; only immature birds moved more than 400 m. The parapatric dispersion of acunhae morphs prob- ably results from habitat-specific dietary differences. Nertera fruits are likely sources of ca- rotenoid pigments in the diets of buntings, but feeding experiments on captive birds are needed to elucidate fully the basis of color variation between morphs. Whatever the proximate cause, plumage-color variation may allow population differentiation if birds mate assortatively on the basis of color. A review of previous visits to the islands suggests that the diversity of forms on Inaccessible Island could have been overlooked. Received 3 August 1992, accepted 22
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Many animal species have bright, carotenoid-based integumentary coloration that is an important criterion in female choice. It has generally been assumed that carotenoid-based colour displays act as signals of quality because they reflect the foraging ability of the bearer, but this hypothesis has not been tested. In birds, carotenoid pigmentation of feathers is deposited at the time of moult. During moult, feathers grow in regular daily cycles resulting in `growth bars' that provide a record of the rate of feather growth. To test the idea that the brightness of carotenoid coloration reflects nutritional condition during moult, we compared the brightness of carotenoid-based plumage coloration with both feather growth rate and timing of moult in male house finches (Carpodacus mexicanus). Among four populations with substantial differences in mean male plumage brightness, there was no significant variation in mean feather growth rate. Thus, the reduced brightness of some populations is not the result of reduced access to food per se. Within populations, we found a significant positive relation between the growth rate of a male's tail feathers and the brightness of his plumage, suggesting that males growing brighter feathers are in better nutritional condition. The growth rate of tail feathers of captive males provided with ad libitum food was also significantly greater than the growth rate of males in any wild populations. Within populations, we also found a significant negative relation between the onset of moult and plumage colour, with males growing brighter feathers starting moulting earlier. These observations provide support for the hypothesis that carotenoid-based plumage coloration is an indicator of nutritional condition during moult. Variation in nutritional condition may arise from differences among individuals in either their foraging ability or their health.
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Thesis
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This review will present not only our own recent results, but also the achievements in the biochemistry of animal carotenoids during the past three years in general.
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