Seasonal but not sex-biased gene expression of the carotenoid ketolase, CYP2J19, in the sexually dichromatic southern red bishop (Euplectes orix)

Intense red colours in birds are often owing to ketocarotenoids (KCs). In many land birds, KCs are oxidized from dietary yellow precursors, presumably by the avian carotenoid ketolase CYP2J19, the regulation and constraints of which have important implications for condition-dependence and honest signalling of carotenoid colour displays. We investigated hepatic CYP2J19 gene expression in the seasonally and sexually dichromatic southern red bishop (Euplectes orix) in relation to season, sex, progression of the prenuptial moult, testis size, body condition, redness and circulating sex steroids. A coloration function of CYP2J19 is supported by a seasonal upregulation prior to and during the carotenoid-depositing stage of the male prenuptial moult. However, CYP2J19 expression was similarly high in females (which do not moult prenuptially), and remained high in males after moult, suggesting additional or alternative roles of hepatic CYP2J19 or its products, such as detoxification or antioxidant functions. In males, the CYP2J19 upregulation preceded and was unrelated to the rise in plasma testosterone, but was correlated with androstenedione, probably of adrenal origin and compatible with luteinizing hormone-induced and (in females) oestrogen-suppressed moult. Finally, contrary to ideas that carotenoid ketolation rate mediates honest signalling of male quality, CYP2J19 expression was not related to plumage redness or male body condition.

Seasonal but not sex-biased gene expression of the carotenoid ketolase, CYP2J19, in the sexually dichromatic southern red bishop (Euplectes orix)

Intense red colours in birds are often owing to ketocarotenoids (KCs). In many land birds, KCs are oxidized from dietary yellow precursors, presumably by the avian carotenoid ketolase CYP2J19, the regulation and constraints of which have important implications for condition-dependence and honest signalling of carotenoid colour displays. We investigated hepatic CYP2J19 gene expression in the seasonally and sexually dichromatic southern red bishop (Euplectes orix) in relation to season, sex, progression of the prenuptial moult, testis size, body condition, redness and circulating sex steroids. A coloration function of CYP2J19 is supported by a seasonal upregulation prior to and during the carotenoid-depositing stage of the male prenuptial moult. However, CYP2J19 expression was similarly high in females (which do not moult prenuptially), and remained high in males after moult, suggesting additional or alternative roles of hepatic CYP2J19 or its products, such as detoxification or antioxidant functions. In males, the CYP2J19 upregulation preceded and was unrelated to the rise in plasma testosterone, but was correlated with androstenedione, probably of adrenal origin and compatible with luteinizing hormone-induced and (in females) oestrogen-suppressed moult. Finally, contrary to ideas that carotenoid ketolation rate mediates honest signalling of male quality, CYP2J19 expression was not related to plumage redness or male body condition.

Seasonal but not sex-biased gene expression of the carotenoid ketolase, CYP2J19, in the sexually dichromatic southern red bishop (Euplectes orix)

Intense red colours in birds are often owing to ketocarotenoids (KCs). In many land birds, KCs are oxidized from dietary yellow precursors, presumably by the avian carotenoid ketolase CYP2J19, the regulation and constraints of which have important implications for condition-dependence and honest signalling of carotenoid colour displays. We investigated hepatic CYP2J19 gene expression in the seasonally and sexually dichromatic southern red bishop (Euplectes orix) in relation to season, sex, progression of the prenuptial moult, testis size, body condition, redness and circulating sex steroids. A coloration function of CYP2J19 is supported by a seasonal upregulation prior to and during the carotenoid-depositing stage of the male prenuptial moult. However, CYP2J19 expression was similarly high in females (which do not moult prenuptially), and remained high in males after moult, suggesting additional or alternative roles of hepatic CYP2J19 or its products, such as detoxification or antioxidant functions. In males, the CYP2J19 upregulation preceded and was unrelated to the rise in plasma testosterone, but was correlated with androstenedione, probably of adrenal origin and compatible with luteinizing hormone-induced and (in females) oestrogen-suppressed moult. Finally, contrary to ideas that carotenoid ketolation rate mediates honest signalling of male quality, CYP2J19 expression was not related to plumage redness or male body condition.

Color variation in signal crayfish Pacifastacus leniusculus

External coloration in animals depends on the interaction of several different factors including the genetics and epigenetics processes that underlie the color expression, the mechanisms of color perception, and the general mechanisms controlling color evolution and function. Among all, camouflages from predators and conspicuousness are of particular interest because pose animal to choose between opposite adjustment in coloration. The external coloration of crustaceans is mainly due to the accumulation of carotenoids in the exoskeleton and the epidermal layer, and the trade-off between camouflage and communication had led to a variety of responses, involving signal partitioning, spectral sensibility, changing coloration, or signaling behavior. Here, we used digital images to explore intrapopulation variability of the external coloration of Pacifastacus leniusculus among body regions within an individual and between sexes. We found that 1) ventral coloration of claws are more saturated and brilliant than upper parts, 2) males express a more saturated and brightness coloration than females, especially on the lower portion of claws, 3) color intensity and brightness increases with size differently in different body regions, and 4) brightness is more variable in males than in females. All the above patterns support the hypothesis that color in this species could be the result of a compromise between camouflage from predators and conspicuousness for communication. The results of this study suggest that carotenoid might have something to do with intraspecific communication and perform more complex functions than that of a simple pigment.

Meral-Spot Reflectance Signals Weapon Performance in the Mantis Shrimp Neogonodactylus oerstedii (Stomatopoda)

During animal contests over resources, opponents often signal their fighting ability in an attempt to avoid escalating to physical attack. A reliable signal is beneficial to receivers because it allows them to avoid injuries from engaging in contests they are unlikely to win. However, a signaler could benefit from deceiving an opponent by signaling greater fighting ability or greater aggressive intent than the signaler possesses. Therefore, the reliability of agonistic signals has long intrigued researchers. We investigated whether a colored patch, the meral spot, signals weapon performance in the stomatopod Neogonodactylus oerstedii. During fights over possession of refuges, stomatopods can injure or even kill opponents with their ultrafast strike. We found that darker meral spots correlate with higher strike impulse, which reflects the total force integrated over time. Furthermore, we demonstrate that stomatopods that strike more often with both appendages have darker meral spots and that the first hit in a two-appendage strike has a greater mean strike impulse than that of a single-appendage strike. This indicates that stomatopods with darker meral spots tend to invest more energy in each strike. Our results provide evidence that stomatopods use total reflectance as an honest signal of weapon performance or aggressive intent. This improves our understanding of the evolution of agonistic signals.

A novel body coloration phenotype in Anolis sagrei: Implications for physiology, fitness, and predation

In animals, color signals that convey information about quality are often associated with costs linked to the expression of coloration and may therefore be honest signals of sender quality. Honest indicators are often seen in sexual signals that are used by males to advertise quality to females. Carotenoid and pterin pigments are responsible for yellow, orange, and red coloration in a variety of taxa, but can also serve important roles as antioxidants by reducing free radicals in the body. In this study, we test the effects of a novel full-bodied orange color phenotype of the brown anole, Anolis sagrei, on mate choice, physiology, and survival. We found no evidence that lizards expressing the orange phenotype were preferred by females. Additionally, they did not differ in immune function, running endurance, or maximum sprint speed from lizards that did not express the novel phenotype. Pigment extractions revealed that orange body coloration resulted from pterin pigments and not carotenoids. Visual models suggest that the orange phenotype is less conspicuous to bird predators than the brown phenotype and may provide an adaptive explanation for the persistence of this trait. Given its small, yet positive effect on fitness, we expect the orange color phenotype to increase in frequency in subsequent decades.

Carotenoid-based coloration in cichlid fishes

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.

Afternoon shedding of a new species of Isospora (Apicomplexa) in the endangered Regent Honeyeater (Xanthomyza phrygia)

The Regent Honeyeater (Xanthomyza phyrigia) is an endangered Australian bird species. Breeding populations have been established at Australian zoos in support of re-introduction programmes. This species is the host of a new species of Isospora (Apicomplexa). Oocysts are spherical, 25·8 (22·5-28·75) by 23·8 (20-26·25) μm with a colourless to pale yellow smooth wall undergoing rapid exogenous sporulation, 90% sporulated oocysts in 8 h at 20°C. Each oocyst contains 1 polar granule. Sporocysts are ovoid, 18·67 (17-19) by 9·49 (9-10) μm with a flat Stieda body and spherical substieda body devoid of a hyaline body. The asexual stages and sexual phase is within the enterocytes of the duodenum and jejunum. Faeces collected in the morning (AM, n=84) and in the afternoon (PM, n=90) revealed significant diurnal periodicity in oocyst shedding; 21% (18 of 84) of the AM were positive with the mean of 499 oocysts.g-1 compared to the PM with 91% (82 of 90) bird faeces positive with the mean of 129 723 oocysts.g-1. Therefore, parasite checks for these birds should be carried out in the afternoon to obtain an accurate result. The ecological significance of the high parasite burden in captive birds requires further investigation and comparison to the wild counterparts.

Condition-dependent expression of pre- and postcopulatory sexual traits in guppies

Female choice can impose persistent directional selection on male sexually selected traits, yet such traits often exhibit high levels of phenotypic variation. One explanation for this paradox is that if sexually selected traits are costly, only the fittest males are able to acquire and allocate the resources required for their expression. Furthermore, because male condition is dependent on resource allocation, condition dependence in sexual traits is expected to underlie trade-offs between reproduction and other life-history functions. In this study we test these ideas by experimentally manipulating diet quality (carotenoid levels) and quantity in the guppy (Poecilia reticulata), a livebearing freshwater fish that is an important model for understanding relationships between pre- and post-copulatory sexually selected traits. Specifically, we test for condition dependence in the expression of pre- and postcopulatory sexual traits (behavior, ornamentation, sperm traits) and determine whether diet manipulation mediates relationships among these traits. Consistent with prior work we found a significant effect of diet quantity on the expression of both pre- and postcopulatory male traits; diet-restricted males performed fewer sexual behaviors and exhibited significant reductions in color ornamentation, sperm quality, sperm number, and sperm length than those fed ad libitum. However, contrary to our expectations, we found no significant effect of carotenoid manipulation on the expression of any of these traits, and no evidence for a trade-off in resource allocation between pre- and postcopulatory episodes of sexual selection. Our results further underscore the sensitivity of behavioral, ornamental, and ejaculate traits to dietary stress, and highlight the important role of condition dependence in maintaining the high variability in male sexual traits.

Badge size and arrival time predict mating success of red-breasted flycatcher Ficedula parva males

Older red-breasted flycatcher males (after the second year) have an orange patch on the throat and breast. To date, the occurrence of this ornament has been explained in terms of male-male interactions. In this paper, we show that badge size also influences the mating success of red-breasted-flycatcher males. In addition to the size of the ornament, arrival time was a second factor related to the males' mating success, but no effects of body parameters such as wing length, tarsus length, and body mass were observed. Mated males arrived significantly earlier than unmated ones. The arrival time of males was negatively correlated to body mass and positively correlated to tarsus length but no relation to wing length or badge size was observed. No correlations between badge size and body parameters were observed. This ornament was evolved through sexual selection, with both male-male interaction and selection pressure arising from female preference for males with larger badges.

Independent sources of condition dependency and multiple pathways determine a composite trait: lessons from carotenoid-based plumage colouration

Many colour ornaments are composite traits consisting of at least four components, which themselves may be more complex, determined by independent evolutionary pathways, and potentially being under different environmental control. To date, little evidence exists that several different components of colour elaboration are condition dependent and no direct evidence exists that different ornamental components are affected by different sources of variation. For example, in carotenoid-based plumage colouration, one of the best-known condition-dependent ornaments, colour elaboration stems from both condition-dependent pigment concentration and structural components. Some environmental flexibility of these components has been suggested, but specifically which and how they are affected remains unknown. Here, we tested whether multiple colour components may be condition dependent, by using a comprehensive 3 × 2 experimental design, in which we carotenoid supplemented and immune challenged great tit nestlings (Parus major) and quantified effects on different components of colouration. Plumage colouration was affected by an interaction between carotenoid availability and immune challenge. Path analyses showed that carotenoid supplementation increased plumage saturation via feather carotenoid concentration and via mechanisms unrelated to carotenoid deposition, while immune challenge affected feather length, but not carotenoid concentration. Thus, independent condition-dependent pathways, affected by different sources of variation, determine colour elaboration. This provides opportunities for the evolution of multiple signals within components of ornamental traits. This finding indicates that the selective forces shaping the evolution of different components of a composite trait and the trait's signal content may be more complex than believed so far, and that holistic approaches are required for drawing comprehensive evolutionary conclusions.

Influence of canthaxanthin on broiler breeder reproduction, chick quality, and performance

To investigate the effect of canthaxanthin supplied via a maternal route on the production of both breeder hens and chickens, 270 Chinese Three-Yellow breeder hens were randomly divided into 2 groups consisting of 135 birds each (5 replicates of 27) for study. The breeder hens were fed either a basal diet or the basal diet supplemented with 6 mg of canthaxanthin/kg for 24 wk. At the end of the 24-wk breeder experiment, all hatching eggs laid in 5 consecutive days of each group were collected and incubated. For each breeder group, 100 newly hatched chicks (5 replicates of 20) were reared under environmentally controlled conditions for 21 d. Canthaxanthin supplementation resulted in the following outcomes: an enhancement of the serum total antioxidant capacity (TAC) of breeder hens (P = 0.029), a significant increase in the yolk colorimetric score of Roche Yolk Color Fan (RYCF; P < 0.001), and a significant improvement of the antioxidant status of the egg yolk (P < 0.05). The chicks that hatched from eggs laid by breeder hens fed the canthaxanthin supplementation diet demonstrated a higher pigmentation colorimetric score of RYCF for their shank skin (P < 0.05), and the antioxidant capacity of the newly hatched chicks was significantly increased (P < 0.05). Both of these positive effects on shank skin pigmentation colorimetric score of RYCF and antioxidant capacity were observed for at least 7 d posthatching, and the chicks that hatched from canthaxanthin-enriched eggs showed a lower mortality (0 vs. 4%) during the first 21 d posthatching. These findings support the hypothesis that canthaxanthin supplementation of the maternal diet enhances the protective capacity of tissues against oxidative stress in vivo, which might be beneficial for poultry producers.

Combined effects of agricultural activity and parasites on biomarkers in the bullfrog, Rana catasbeiana

Agricultural contaminants can have devastating impacts on amphibian survival and development, particularly considering their sensitivity to environmental perturbation. However, it is commonly overlooked that amphibians are infected with various parasites that can influence the overall health of the animal when exposed to a stressful environment. We investigated the interaction of agriculture and parasitism on the health of bullfrogs (Rana catesbeiana) in the field. Nine physiological and immunological biomarkers were related to naturally acquired parasite infections, along a gradient of agricultural activity. Most health biomarkers were affected by agriculture, parasitism, or both. Although bullfrogs residing in agricultural areas were infected with fewer parasite species, reflecting environmentally compromised ecosystems, certain persistent parasites interacted with agricultural disturbance to alter the physiology and immune competence of bullfrogs. The consequences of the combination for animal health highlight the importance of parasitism in ecotoxicological studies. Consideration of parasitism is warranted when evaluating the influence of anthropogenic disturbance on amphibian declines and environmental health.

Carotenoid trade-off between parasitic resistance and sexual display: an experimental study in the blackbird (Turdus merula)

Many parasites depress the expression of the carotenoid-based colour displays of their hosts, and it has been hypothesized that animals face a trade-off in carotenoid allocation between immune functions and 'degree of ornamentation'. While numerous correlative studies suggest that parasite infection decreases the intensity of carotenoid-based colour displays, the existence of this trade-off has never been demonstrated experimentally in a host-parasite model. In this study, we used the blackbird (Turdus merula) and Isospora (an intestinal parasite) to assess whether this trade-off does indeed exist. Blackbirds were supplemented with carotenoids while simultaneously being exposed to parasites. Supplemented males circulated more carotenoids in the blood and developed more brightly coloured bills than unsupplemented males. In addition, supplementation slowed down the replication rate of parasites. Supplementation with carotenoids enabled infected birds to maintain their bill coloration, whereas birds that were infected but not supplemented showed reduced bill coloration. At the same time, infection slowed carotenoid assimilation in the blood. Overall, we demonstrated that bill colour reflects a bird's health, and that only males with a carotenoid-rich diet are capable of coping with costs associated with parasitic infection. Carotenoids are thus traded off between host physiological response to parasites and secondary sexual traits. Further investigations are required to determine the physiological mechanisms that govern this trade-off.

Carotenoid Coloration in Greenfinches Is Individually Consistent Irrespective of Foraging Ability

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

Carotenoids, immune response and the expression of sexual ornaments in male greenfinches (Carduelis chloris)

Allocation trade-offs of carotenoids between their use in the immune system and production of sexual ornaments have been suggested as a proximate mechanism maintaining honesty of sexual signals. To test this idea, we experimentally examined whether carotenoid availability in the diet was related to variation in antibody response to novel antigens in male greenfinches (Carduelis chloris aurantiiventris), a species with extensive carotenoid-dependent plumage colouration. We also measured the cost of mounting a humoral response in terms of circulating carotenoids. Finally, we examined the relationship between plumage colour, immune response and circulating carotenoids. We found that males with carotenoid-supplemented diets showed stronger antibody response than non-supplemented birds. We also found that activation of the immune system significantly reduced circulating carotenoids (24.9% lower in immune-challenged birds than in control birds). Finally, intensity (chroma) of ventral plumage colouration of males, a character directly related to concentration of total carotenoids in feathers, was negatively correlated with the immune response and circulating carotenoids in winter. These results support the idea that carotenoids are a limiting resource and that males trade ornamental colouration against immune response.

Antioxidant protection, carotenoids and the costs of immune challenge in greenfinches

Costs accompanying immune challenges are believed to play an important role in life-history trade-offs and warranting the honesty of signal traits. We performed an experiment in captive greenfinches (Carduelis chlorisL.) in order to test whether and how humoral immune challenge with non-pathogenic antigen [sheep red blood cells (SRBC)] affects parameters of individual condition including intensity of coccidian infection, estimates of total antioxidant protection, plasma carotenoids and ability to mount a cell-mediated immune response. We also asked whether the potential costs of immune challenge can be alleviated by dietary carotenoid supplementation. None of the treatments affected intensity of coccidiosis. Humoral immune challenge suppressed the cell-mediated response to phytohemagglutinin (PHA), suggesting a trade-off between the uses of different arms of the immune system. Immune challenge reduced body-mass gain, but only among the carotenoid-depleted birds, indicating that certain somatic costs associated with immune system activation can be alleviated by carotenoids. No evidence for oxidative stress-induced immunopathological damages could be found because immune activation did not affect total antioxidant protection or carotenoid levels. Carotenoid supplementation inclined birds to fattening, indicating that lutein interfered with lipid metabolism. Altogether, our results support the hypotheses of biological importance of carotenoids and exemplify the overwhelming complexity of their integrated ecophysiological functions.

Do carotenoids and spleen size vary with helminth load in greylag geese?

It has been suggested that carotenoid-derived coloration serves as an indicator of parasite levels and (or) the general health of birds. We investigated relationships among spleen size (sometimes considered an indicator of the cellular immune response capacity of birds), carotenoid level, helminth load, and leg and bill coloration of greylag geese, Anser anser (L., 1758), from Doñana National Park (southwest Spain). Nematode abundance was positively related to spleen size and negatively to body condition, but only in males. Coloration of bill and legs was a reliable indicator of cestode but not nematode abundance. Individuals with many cestodes had greater carotenoid stores, suggesting that helminths do not limit carotenoid absorption. Rather, it suggests either that parasitized geese were accumulating more carotenoids to control parasite-induced damage, or that carotenoid-rich diets expose geese to more intermediate hosts of cestodes. Our results support the role of integumentary carotenoid-derived coloration as an indicator of parasitism, but only for particular taxonomic groups.

Individual colour patches as multicomponent signals

Colour patches are complex traits, the components of which may evolve independently through a variety of mechanisms. Although usually treated as simple, two-dimensional characters and classified as either structural or pigmentary, in reality colour patches are complicated, three-dimensional structures that often contain multiple pigment types and structural features. The basic dermal chromatophore unit of fishes, reptiles and amphibians consists of three contiguous cell layers. Xanthophores and erythrophores in the outermost layer contain carotenoid and pteridine pigments that absorb short-wave light; iridophores in the middle layer contain crystalline platelets that reflect light back through the xanthophores; and melanophores in the basal layer contain melanins that absorb light across the spectrum. Changes in any one component of a chromatophore unit can drastically alter the reflectance spectrum produced, and for any given adaptive outcome (e.g. an increase in visibility), there may be multiple biochemical or cellular routes that evolution could take, allowing for divergent responses by different populations or species to similar selection regimes. All of the mechanisms of signal evolution that previously have been applied to single ornaments (including whole colour patches) could potentially be applied to the individual components of colour patches. To reach a complete understanding of colour patch evolution, however, it may be necessary to take an explicitly multi-trait approach. Here, we review multiple trait evolution theory and the basic mechanisms of colour production in fishes, reptiles and amphibians, and use a combination of computer simulations and empirical examples to show how multiple trait evolution theory can be applied to the components of single colour patches. This integrative perspective on animal colouration opens up a host of new questions and hypotheses. We offer specific, testable functional hypotheses for the most common pigmentary (carotenoid, pteridine and melanin) and structural components of vertebrate colour patches.

Energetic and nutritional regulation of the adaptive immune response and trade-offs in ecological immunology

Ecological Immunology views immunocompetence as a costly process involving trade-off decisions among competing nutrient demands by different life-history traits. This review examines immunocompetence fitness costs in light of recent work on the role the energetic and nutritional status of the host plays in the regulation of the adaptive T-helper lymphocyte response. Three phenotypically distinct T-lymphocyte populations have been identified: the Th1 response, important in protecting against intracellular infections; the Th2 response, important in protecting against noninvasive infections such as helminthes; and the Th3 or Treg population, which downregulates polarized Th1 or Th2 responses. A strong Th1 response is protective against intracellular infections, while a Th2 response is protective against noninvasive infections. Adequate zinc and energy intake leads to a dominant Th1 response and a downregulated Th2 response, while deficiencies of either of these results in activation of the Th2 response and downregulation of the Th1 response. In contrast, adequate vitamin A intake leads to an activated Th2 response and downregulation of the Th1 response, while vitamin A deficiency reverses these patterns. These differential immune regulatory effects of energy and nutrient intake will have distinct effects on specific stages of the natural history of different pathogen infections where the protective roles of the Th1-Th2 responses are distinct. Accordingly, fitness costs of immunocompetence are more complex than currently proposed since trade-offs in energetic and nutritional resources produce cross-regulatory effects on immune system subcomponents.

Ecological, morphological and phylogenetic correlates of interspecific variation in plasma carotenoid concentration in birds

Carotenoids are important as pigments for bright coloration of animals, and as physiologically active compounds with a wide array of health-related benefits. However, the causes of variation in carotenoid acquisition and physiology among species are poorly known. We measured the concentration of carotenoids in the blood of 80 wild bird species differing in diet, body size and the extent of carotenoid-based traits. Preliminary analyses showed that diet significantly explains interspecific variability in plasma carotenoids. However, dietary influences were apparently overridden by phylogenetic relationships among species, which explained most (65%) of this variability. This phylogenetic effect could be due partly to its covariation with diet, but may also be caused by interspecific differences in carotenoid absorption from food to the blood stream, mediated, for example by endothelial carriers or gut parasites. Carotenoid concentrations also decreased with body size (which may be explained by the allometric relationship between ingestion rate and body mass), and correlated positively with the extent of carotenoid-dependent coloration of plumage and bare parts. Therefore, the acquisition of carotenoids from the diet and their use for both health and display functions seem to be constrained by ecological and physiological aspects linked to the phylogeny and size of the species.

Sex-specific effects of carotenoid intake on the immunological response to allografts in guppies (Poecilia reticulata)

Rarely are the evolutionary origins of mate preferences known, but, recently, the preference of female guppies (Poecilia reticulata) for males with carotenoid-based sexual coloration has been linked to a sensory bias that may have originally evolved for detecting carotenoid-rich fruits. If carotenoids enhance the immune systems of these fishes, as has been suggested for other species, this could explain the origin of the attraction to orange fruits as well as the maintenance of the female preference for orange males. We used the classic immunological technique of tissue grafting to assay a component of the immune response of guppies raised on two different dietary levels of carotenoids. Individual scales were transplanted between pairs of unrelated fishes, creating reciprocal allografts. Transplanted scales were scored on a six-point rejection scale every day for 10 days. Five days later, the same pairs of fishes received a second set of allografts and were scored again. Compared with low-carotenoid-diet males, high-carotenoid-diet males mounted a significantly stronger rejection response to the second allograft but not to the first allograft. High-carotenoid-diet females, however, showed no improvement in graft rejection compared with low-carotenoid-diet females. To our knowledge, this is the first experimental evidence for sex-specific effects of carotenoid consumption on the immune system of a species with carotenoid-based sexual coloration. These results are consistent with the hypothesis that the mate preference for carotenoid coloration is maintained by the benefits to females of choosing healthy mates, but they cast doubt on the idea that the benefits of carotenoid consumption, per se, could account for the origin of the preference. The sex-specificity of carotenoid effects on allograft rejection in guppies provides indirect support for the general hypothesis that males pay an immunological cost for sexual ornamentation.

Carotenoids, Immunocompetence, and the Information Content of Sexual Colors: An Experimental Test

Many male birds use carotenoid pigments to acquire brilliant colors that advertise their health and condition to prospective mates. The direct means by which the most colorful males achieve superior health has been debated, however. One hypothesis, based on studies of carotenoids as antioxidants in humans and other animals, is that carotenoids directly boost the immune system of colorful birds. We studied the relationship between carotenoid pigments, immune function, and sexual coloration in zebra finches (Taeniopygia guttata), a species in which males incorporate carotenoid pigments into their beak to attract mates. We tested the hypotheses that increased dietary carotenoid intake enhances immunocompetence in male zebra finches and that levels of carotenoids circulating in blood, which also determine beak coloration, directly predict the immune response of individuals. We experimentally supplemented captive finches with two common dietary carotenoid pigments (lutein and zeaxanthin) and measured cell-mediated and humoral immunity a month later. Supplemented males showed elevated blood-carotenoid levels, brighter beak coloration, and increased cell-mediated and humoral immune responses than did controls. Cell-mediated responses were predicted directly by changes in beak color and plasma carotenoid concentration of individual birds. These experimental findings suggest that carotenoid-based color signals in birds may directly signal male health via the immunostimulatory action of ingested and circulated carotenoid pigments.

Carotenoid concentration in barn swallow eggs is influenced by laying order, maternal infection and paternal ornamentation

Carotenoids are critical to embryonic development, immunity and protection from oxidative stress. Transmission of carotenoids to the eggs may affect development and maturation of immunity in offspring, but carotenoids may be available to females in limiting amounts. Females may thus transfer carotenoids to the eggs differentially in relation to the reproductive value of the offspring as affected by sexual ornamentation of their father. In this study of maternal allocation of carotenoids to the eggs in the barn swallow (Hirundo rustica), females whose immune system had been experimentally challenged with an antigen had smaller lutein concentrations in their eggs than controls. We manipulated the size of a secondary sexual character (tail length) of males, and analysed the effect of manipulation on allocation of lutein to eggs by their vaccinated mates. Contrary to our prediction based on parental allocation theory, mates of tail-shortened males had a larger lutein concentration in their eggs compared with those of control and tail-elongated males. According to previous studies, offspring of short-tailed males have larger exposure and/or susceptibility to parasites. A larger lutein concentration in the eggs of females mated to males with experimentally reduced ornaments may thus reflect adaptive maternal strategies to enhance offspring viability.