Carotenoid-based Coloration Research Articles

Plumage coloration, body condition and immunological status in Yellow-billed Cardinals (Paroaria capitata)

Plumage coloration deriving from carotenoid and melanin pigments can be a quality signal in birds, and can be under conspecific inspection in social interactions. For example, parasite load and immune system status can be inferred through plumage color intensity, and can influence the choice of sexual partners. Here, we evaluated two plumage ornaments in the Yellow-billed Cardinal [Paroaria capitata (d’Orbigny & Lafresnaye 1837)]: the carotenoid-based coloration of the cap and the melanin-based coloration of the bib. We evaluated whether these ornaments were related to blood parasite burden, immunological status and body condition, and whether they could reveal individual sex and age. Cardinals were mist-netted in a Brazilian wetland, and 12 individuals were infected with malaria parasites. Both carotenoid and melanin colorations were related to age, but only carotenoids reflected immunological status. Adult cardinals presented redder caps and darker bibs in comparison to juveniles, and redder caps were associated with low values of heterophil to lymphocyte ratio (H/L, indicating lower stress level). Plumage coloration did not indicate individual sex or parasite infection. Taken together, these results demonstrated that both melanin- and carotenoid-based coloration in cardinals can potentially reflect significant information for social interactions, such as individual age and experience, but apparently only carotenoid coloration is condition-dependent and could reliably indicate quality.

Carotenoid profile and vitamins in the combs of the red grouse (Lagopus lagopus scoticus): implications for the honesty of a sexual signal

The carotenoid-based ornaments displayed by many birds often play key roles in social and sexual signalling, revealing information about individual quality. However, the proximate regulation of the honesty of sexual traits remains controversial. Understanding the mechanisms of coloured trait production and maintenance requires an accurate description of their chemical composition and of the physiological pathways involved in pigment production and deposition in the ornaments. Carotenoid-based colouration has been extensively studied in birds, but such information is often lacking for coloured integuments other than feathers, such as fleshy carotenoid-based ornaments. Here we report the carotenoid composition of the combs of the red grouse (Lagopus lagopus scoticus), a sexual trait that honestly reveals individual quality. In the present study, we also investigated blood carotenoid content, as well as associations between carotenoids, retinol and tocopherol (the active forms of vitamin A and E, respectively) within the ornament. We found that comb pigmentation was primarily the result of two red ketocarotenoids (astaxanthin and papilioerythrinone), which are synthesised from their dietary precursors (zeaxanthin and lutein) directly at the comb integument. These red ketocarotenoids are largely deposited esterified with fatty acids. Astaxanthin concentration in the comb was found to negatively correlate with retinol levels but positively correlate with tocopherol levels. Considering evidence from this and other studied species, we suggest that carotenoid esterification is a characteristic of coloured fleshy integuments, probably affecting pigment stability and colouration in living tissues, with subsequent effects on their signalling role and maintenance costs. We found little evidence that the honesty of this signal would result from a direct connection with vitamin A metabolism, as recently proposed. Rather, honest signalling via comb colouration appears more related to potential allocation trade-offs of some specific dietary precursors or to the capacity of individuals to manage the redox reactions interfering with carotenoid metabolism.

Metal exposure influences the melanin and carotenoid-based colorations in great tits

Metals are naturally found in the environment but are also emitted through anthropogenic activities, raising some concerns about the potential deleterious effects of these elements on wildlife. The potential effects of metals on bird coloration have been the focus of several recent studies since animal colored-signals often reflect the physiology of their bearers and are thus used by animals to assess the quality of another individual as a mate or competitor. These studies have shown that the melanin pigmentation seems to be positively associated and the carotenoid-based coloration negatively associated with metal exposure in wild birds. Although these studies have been very useful to show the associations between metal exposure and coloration, only few of them have actually quantified the levels of metal exposure at the individual level; always focusing on one or two of them. Here, we measured the concentrations of eight metals in great tits' feathers and then assessed how these levels of metals were associated with the carotenoid and melanin-based colorations. We found that the melanin pigmentation was positively associated with the copper concentration and negatively correlated with the chromium concentration in feathers. In addition, we have shown that the carotenoid-based coloration was negatively associated with the feather's mercury concentration. This study is the first one to identify some metals that might affect positively and negatively the deposition of melanin and carotenoid into the plumage of wild birds.

High Concentrations of Ketocarotenoids in Hepatic Mitochondria of Haemorhous mexicanus.

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.

Carotenoids increase immunity and sex specifically affect color and redox homeostasis in a monochromatic seabird

Carotenoid-based integument coloration is extremely widespread in animals and commonly used as an honest signal of condition in sexual selection. Besides being used for color expression, carotenoids have antioxidant and immunomodulatory activity. Being a limited resource, carotenoid allocation to competing demands generates a trade-off. Recent studies, however, suggest that the antioxidant role of carotenoids might not be as important as previously thought. To shed light on the mechanism maintaining carotenoid-based signal honesty in the black-legged kittiwake (Rissa tridactyla), we supplemented males and females with dietary yellow xanthophylls (lutein and zeaxanthin) during the chick-rearing period, when male coloration may be a good indicator of future reproductive success. The supplementation affected plasma carotenoid levels similarly in males and females, i.e., it increased the levels of lutein but decreased the levels of total astaxanthin, one of the main pigments coloring integuments in this species. Supplemented adults and their chicks had stronger immune response than controls, suggesting that yellow xanthophylls enhance the innate immune system in kittiwakes. However, supplementation caused sex-specific effects on integument coloration and oxidative stress. Supplemented males had duller integuments, but similar oxidative damages compared to control males, while supplemented females had more colorful integuments, but higher oxidative damages than control females. Because the increase in lutein was associated with a decrease in other potential antioxidants (i.e., astaxanthin and vitamin A), the role of carotenoids as antioxidants in kittiwakes remains undetermined. Our results, however, indicate that the trade-off responses to carotenoid availability are sex-specific in kittiwakes.

Effects of carotenoid supplementation and oxidative challenges on physiological parameters and carotenoid-based coloration in an urbanization context

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.

Bill color characteristics and body mass of the great tit (Parus major) nestling

This study was conducted to examine the bill color and body mass of great tit (Parus major) nestlings in artificial nest boxes. In this study, the nestlings with yellow bills had a higher body mass on the second and eighth day after hatching. Moreover, the brightness values of the color of the bill on the eighth day after hatching were negatively correlated with the body mass of the chicks. Our experiment shows that the color of the bill of the nestling could accurately signal the quality of the chick. Moreover, carotenoid-based colors play an important role in avian communication. Study of carotenoid-based colors in the great tit would be required in the future.

Sublethal Pb exposure produces season-dependent effects on immune response, oxidative balance and investment in carotenoid-based coloration in red-legged partridges.

Ingestion of lead (Pb) shot pellets constitutes the main cause of Pb poisoning in avifauna. We studied the effects of sublethal Pb exposure on immunity, carotenoid-based coloration, oxidative stress and trade-offs among these types of responses during spring and autumn in red-legged partridges (Alectoris rufa). We evaluated constitutive immunity testing lysozyme and natural antibody levels, and blood bactericidal and phagocytic activities. We studied induced immunity by testing PHA and humoral responses. We analyzed fecal parasite and bacterial abundance and oxidative stress biomarkers. Pb exposure in spring reduced natural antibody levels, whereas in autumn, it reduced lysozyme levels and increased phagocytic activity. Pb exposure increased PHA response in both seasons, and decreased T-independent humoral response in autumn. Pb exposure also increased noncoliform and decreased coliform Gram-negative gut bacteria. In spring, Pb exposure decreased antioxidant levels and increased coloration in males, whereas in autumn, it increased retinol levels but reduced coloration in both genders. Our results suggest that in spring, Pb-exposed females used antioxidants to cope with oxidative stress at the expense of coloration, whereas Pb-exposed males increased coloration, which may reflect an increased breeding investment. In autumn, both genders prioritized oxidative balance maintenance at the expense of coloration.

Age-related change in carotenoid-based plumage of the American Redstart (Setophaga ruticilla)

Plumage colouration serves a variety of functions for birds, including conspecific signalling, crypsis, and predator–prey interactions. Though much research has been conducted on colour changes in species with delayed plumage maturation, where birds do not exhibit definitive adult plumage until their second breeding season or later, relatively few studies have examined how plumage colour changes once definitive adult plumage has been attained. In this study on male and female American Redstarts (Setophaga ruticilla), which exhibit male delayed plumage maturation, we used reflectance spectrometry to evaluate carotenoid-based tail colour changes over 11 breeding seasons, examining both within-individual and population-level changes. At a population level, males in their first breeding season in definitive adult plumage had a feather hue that was more orange-shifted than birds in their second year in adult plumage, and marginally, but not significantly, more orange-shifted than birds in their third year in adult plumage. Within-individual analysis of males recaptured in subsequent seasons also revealed a shift away from orange towards a more yellow feather hue as individuals aged. Within individuals, red chroma was highest for males in their second year in adult plumage, but it showed no population-level effects. At the population level, female redstarts in their first breeding season displayed plumage with a higher red chroma and a lower brightness than birds in their second breeding season, potentially as a result of differences in the timing and conditions of moult (first-year bird tail feathers were grown in the nest). For adult males and females, there was no difference in plumage colouration between birds that returned to the study site compared to those that failed to return. Together, our results suggest that within-individual change rather than differential survival best explains our findings. We suggest that studies examining age-related colour changes are critical for understanding the evolution of complex signalling systems, such as that of American Redstarts.

A de novo transcriptome of the noble scallop, Chlamys nobilis, focusing on mining transcripts for carotenoid-based coloration

BackgroundThe noble scallop Chlamys nobilis Reeve displays polymorphism in shell and muscle colors. Previous research showed that the orange scallops with orange shell and muscle had a significantly higher carotenoid content than the brown ones with brown shell and white muscle. There is currently a need to identify candidate genes associated with carotenoid-based coloration.ResultsIn the present study, 454 GS-FLX sequencing of noble scallop transcriptome yielded 1,181,060 clean sequence reads, which were assembled into 49,717 isotigs, leaving 110,158 reads as the singletons. Of the 159,875 unique sequences, 11.84% isotigs and 9.35% singletons were annotated. Moreover, 3,844 SSRs and over 120,000 high confidence variants (SNPs and INDELs) were identified. Especially, one class B scavenge receptor termed SRB-like-3 was discovered to express only in orange scallops and absent in brown ones, suggesting a significant association with high carotenoid content. Down-regulation of SRB-like-3 mRNA by RNA interference remarkably decreased blood carotenoid, providing compelling evidence that SRB-like-3 is an ideal candidate gene controlling carotenoid deposition and determining orange coloration.ConclusionTranscriptome analysis of noble scallop reveals a novel scavenger receptor significantly associated with orange scallop rich in carotenoid content. Our findings pave the way for further functional elucidation of this gene and molecular basis of carotenoid deposition in orange scallop.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1241-x) contains supplementary material, which is available to authorized users.

What is the value of a yellow patch? Assessing the signalling role of yellow colouration in the European serin

Sexual selection promotes the evolution of signals, many of which can reliably indicate condition, health or good genes of individuals. In order to be evolutionarily stable, indicator signals must be costly to produce. Carotenoid colouration evolved in many species by sexual selection. Carotenoids besides acting as pigments have been implicated in immune defence and antioxidation which makes them likely candidates for honest signalling. A trade-off for carotenoid availability was proposed as the basis for signal honesty. Alternatively, it was suggested that carotenoid colouration is not advertising the presence of the pigment per se, but the quality of antioxidant resources which then affect carotenoid concentration. One possibility is that carotenoid-based colouration could signal colourless antioxidant mechanisms, which are partially regulated by vitamins. β-Carotene is one of the most common precursors of vitamin A and, although present in bird diet, is not available for feather colouration. If an indirect association exists between carotenoid signal and condition, then manipulation of β-carotene concentration could reveal that this link is indirect. We tested this by conditioning the availability of β-carotene in the diet of a cardueline finch with yellow carotenoid colouration during moult. β-Carotene-supplemented males had higher plasma carotenoid concentration and higher response to a cellular immunity challenge (phytohaemagglutinin (PHA)) than control males. β-Carotene-supplemented males also had more saturated plumage colouration and were preferred by females in a mate choice test. Our results support the possibility of an indirect role for yellow carotenoid colouration.

Carotenoid-based bill coloration functions as a social, not sexual, signal in songbirds (Aves: Passeriformes).

Many animals use coloration to communicate with other individuals. Although the signalling role of avian plumage colour is relatively well studied, there has been much less research on coloration in avian bare parts. However, bare parts could be highly informative signals as they can show rapid changes in coloration. We measured bill colour (a ubiquitous bare part) in over 1600 passerine species and tested whether interspecific variation in carotenoid-based coloration is consistent with signalling to potential mates or signalling to potential rivals in a competitive context. Our results suggest that carotenoid bill coloration primarily evolved as a signal of dominance, as this type of coloration is more common in species that live in social groups in the nonbreeding season, and species that nest in colonies; two socio-ecological conditions that promote frequent agonistic interactions with numerous and/or unfamiliar individuals. Additionally, our study suggests that carotenoid bill coloration is independent of the intensity of past sexual selection, as it is not related to either sexual dichromatism or sexual size dimorphism. These results pose a significant challenge to the conventional view that carotenoid-based avian coloration has evolved as a developmentally costly, condition-dependent sexual signal. We also suggest that bare part ornamentation may often signal different information than plumage ornaments.

Is oxidative status influenced by dietary carotenoid and physical activity after moult in the great tit (Parus major)?

In the context of sexual and natural selection, an allocation trade-off for carotenoid pigments may exist because of their obligate dietary origin and their role both in the antioxidant and immune systems and in the production of coloured signals in various taxa, particularly birds. When birds have expended large amounts of carotenoids to feather growth such as after autumn moult, bird health and oxidative status might be more constrained. We tested this hypothesis in a bird species with carotenoid-based plumage colour, by manipulating dietary carotenoids and physical activity, which can decrease antioxidant capacity and increase reactive oxygen metabolite (ROM) concentration. Great tits were captured after moult and kept in aviaries, under three treatments: physical handicap and dietary supplementation with carotenoids, physical handicap and control diet, and no handicap and control diet. We measured plasma composition (antioxidant capacity, ROM concentration, and vitamin A, vitamin E and total carotenoid concentrations), immune system activation (blood sedimentation) and stress response (heterophil/lymphocyte ratio) and predicted that handicap treatment should influence these negatively and carotenoid supplementation positively. Coloration of yellow feathers was also measured. Carotenoid supplementation increased total plasma carotenoid concentration, decreased feather carotenoid chroma and marginally increased ROM concentration. Handicap increased blood sedimentation only in males but had no clear influence on oxidative stress, which contradicted previous studies. Further studies are needed to investigate how physical activity and carotenoid availability might interact and influence oxidative stress outside the moult period, and their combined potential influence on attractiveness and reproductive investment later during the breeding season.

Carotenoids, birdsong and oxidative status: administration of dietary lutein is associated with an increase in song rate and circulating antioxidants (albumin and cholesterol) and a decrease in oxidative damage.

Despite the appealing hypothesis that carotenoid-based colouration signals oxidative status, evidence supporting the antioxidant function of these pigments is scarce. Recent studies have shown that lutein, the most common carotenoid used by birds, can enhance the expression of non-visual traits, such as birdsong. Nevertheless, the underlying physiological mechanisms remain unclear. In this study we hypothesized that male European starlings (Sturnus vulgaris) fed extra lutein increase their song rate as a consequence of an improved oxidative status. Although birdsong may be especially sensitive to the redox status, this has, to the best of our knowledge, never been tested. Together with the determination of circulating oxidative damage (ROMs, reactive oxygen metabolites), we quantified uric acid, albumin, total proteins, cholesterol, and testosterone, which are physiological parameters potentially sensitive to oxidation and/or related to both carotenoid functions and birdsong expression. We found that the birds fed extra lutein sang more frequently than control birds and showed an increase of albumin and cholesterol together with a decrease of oxidative damage. Moreover, we could show that song rate was associated with high levels of albumin and cholesterol and low levels of oxidative damage, independently from testosterone levels. Our study shows for the first time that song rate honestly signals the oxidative status of males and that dietary lutein is associated with the circulation of albumin and cholesterol in birds, providing a novel insight to the theoretical framework related to the honest signalling of carotenoid-based traits.

Genetic basis and fitness correlates of dynamic carotenoid-based ornamental coloration in male and female common kestrels Falco tinnunculus.

Knowledge of the genetic basis of sexual ornaments is essential to understand their evolution through sexual selection. Although carotenoid-based ornaments have been instrumental in the study of sexual selection, given the inability of animals to synthesize carotenoids de novo, they are generally assumed to be influenced solely by environmental variation. However, very few studies have directly estimated the role of genes and the environment in shaping variation in carotenoid-based traits. Using long-term individual-based data, we here explore the evolutionary potential of a dynamic, carotenoid-based ornament (namely skin coloration), in male and female common kestrels. We first estimate the amount of genetic variation underlying variation in hue, chroma and brightness. After correcting for sex differences, the chroma of the orange-yellow eye ring coloration was significantly heritable (h2±SE=0.40±0.17), whereas neither hue (h2=0) nor brightness (h2=0.02) was heritable. Second, we estimate the strength and shape of selection acting upon chromatic (hue and chroma) and achromatic (brightness) variation and show positive and negative directional selection on female but not male chroma and hue, respectively, whereas brightness was unrelated to fitness in both sexes. This suggests that different components of carotenoid-based signals traits may show different evolutionary dynamics. Overall, we show that carotenoid-based coloration is a complex and multifaceted trait. If we are to gain a better understanding of the processes responsible for the generation and maintenance of variation in carotenoid-based coloration, these complexities need to be taken into account.

Inter-annual variation in American redstart (Setophaga ruticilla) plumage colour is associated with rainfall and temperature during moult: an 11-year study.

Carotenoid-based colouration plays an important role in sexual signaling in animals as an honest indicator of individual quality during mate choice and competitive interactions. However, few studies have examined how natural variation in weather conditions influences inter-annual variation in the expression of ornamentation, potentially through affecting the dietary availability of carotenoids. In this study, we examine variation in the expression of carotenoid-based plumage colouration in relation to temperature and rainfall during the pre-moulting and moulting period over 11 years in a population of American redstarts, Setophaga ruticilla, breeding in eastern Canada. We used reflectance spectrometry of tail feathers collected from male and female redstarts to relate feather colour with weather conditions the previous breeding season during the months over which redstarts are likely to moult (June-September). At a population level, birds expressed feathers with higher red chroma and lower brightness in years following high July rainfall and low August temperature. The pattern was stronger in males, but was generally consistent across ages and sexes. Analyses of feathers from repeatedly captured birds indicated that the above patterns could be explained by individual change in feather colour. We suggest that higher rainfall during the moulting period may increase insect abundance and the availability of dietary carotenoids. This is among the first studies to show effects of weather conditions on a sexual signalling trait, which may have important consequences for sexual selection, mate choice, and the reliability of putative signals.

Imidacloprid-treated seed ingestion has lethal effect on adult partridges and reduces both breeding investment and offspring immunity

The ingestion of imidacloprid treated seeds by farmland birds may result in exposure to toxic amounts of this insecticide. Here we report on the effects that the exposure to the recommended application rate and to 20% of that rate may produce on birds feeding on treated seeds. Experimental exposure to imidacloprid treated seeds was performed on red-legged partridges (Alectoris rufa) (n=15 pairs per treatment group: control, 20% or 100% of the recommended application rate) during two periods that corresponded to the autumn (duration of exposure: 25 days) and late winter (10 days) cereal sowing times in Spanish farmlands. We studied effects on the survival, body condition, oxidative stress biomarkers, plasma biochemistry, carotenoid-based coloration, T-cell mediated immune response and reproduction of exposed adult partridges, and on the survival and T-cell immune response of their chicks. The high dose (recommended application rate) killed all partridges, with mortality occurring faster in females than in males. The low dose (20% the recommended application rate) had no effect on mortality, but reduced levels of plasma biochemistry parameters (glucose, magnesium and lactate dehydrogenase), increased blood superoxide dismutase activity, produced changes in carotenoid-based integument coloration, reduced the clutch size, delayed the first egg lay date, increased egg yolk vitamins and carotenoids and depressed T-cell immune response of chicks. Moreover, the analysis of the livers of dead partridges revealed an accumulation of imidacloprid during exposure time. Despite the moratorium on the use of neonicotinoids in the European Union, birds may still be at high risk of poisoning by these pesticides through direct sources of exposure to coated seeds in autumn and winter.

Habitat structure and prey composition generate contrasting effects on carotenoid-based coloration of great titParus majornestlings

Carotenoid-based coloration of nestling plumage is generally considered a reliable signal of quality and has consistently been related to habitat structure. The main hypothesis proposed to explain this correlation is that high quality habitats contain high quality food, which in return affects the expression of carotenoid-based plumage. It therefore assumes that, at the population level, the link between habitat structure and food composition is consistent and more relevant than inter-individual differences in foraging ability or parental investment. In addition, it is assumed by default that food and habitat produce concordant effects on nestling coloration. In this work we evaluated habitat structure and prey composition in addition to several measures of parental investment. We investigated their relative effect on carotenoid-based plumage coloration (lightness, chroma and hue) of great tit Parus major nestlings. We found a low correlation between carotenoid-based coloration of nestlings and that of their parents. Nestling coloration, especially lightness and chroma, increased with the intake of more spiders. The time of breeding was positively correlated with lightness and chroma and negatively correlated with hue. Finally, the maturity of oak trees surrounding nest-boxes correlated negatively with lightness, and the size of all tree species surrounding nest-boxes correlated positively with hue of chick plumage. Our findings support the view that habitat structure and prey composition may produce divergent effects on feather pigmentation, and that prey proportions and variables related to parental investment should be assessed when considering carotenoid-based coloration of chicks.

Carotenoid-based coloration is associated with predation risk, competition, and breeding status in female convict cichlids (Amatitlania siquia) under field conditions

The signaling function of carotenoid-based orange ventral coloration expressed by female convict cichlids (A. siquia) is still largely unknown. This field study examined the relationship between breeding female A. siquia orange coloration and predation stress, territorial competition, and offspring developmental stage. Female orange coloration decreased significantly with increased behavioral interactions with predators and heterospecific competitors, and the presence of wrigglers, fry, or juveniles was significantly associated with a lack of orange coloration. Multiple alternative explanations for these observations are discussed, including body carotenoid re-allocation and variation in environmental characteristics.

Elaborate visual and acoustic signals evolve independently in a large, phenotypically diverse radiation of songbirds.

The concept of a macroevolutionary trade-off among sexual signals has a storied history in evolutionary biology. Theory predicts that if multiple sexual signals are costly for males to produce or maintain and females prefer a single, sexually selected trait, then an inverse correlation between sexual signal elaborations is expected among species. However, empirical evidence for what has been termed the 'transfer hypothesis' is mixed, which may reflect different selective pressures among lineages, evolutionary covariates or methodological differences among studies. Here, we examine interspecific correlations between song and plumage elaboration in a phenotypically diverse, widespread radiation of songbirds, the tanagers. The tanagers (Thraupidae) are the largest family of songbirds, representing nearly 10% of all songbirds. We assess variation in song and plumage elaboration across 301 species, representing the largest scale comparative study of multimodal sexual signalling to date. We consider whether evolutionary covariates, including habitat, structural and carotenoid-based coloration, and subfamily groupings influence the relationship between song and plumage elaboration. We find that song and plumage elaboration are uncorrelated when considering all tanagers, although the relationship between song and plumage complexity varies among subfamilies. Taken together, we find that elaborate visual and vocal sexual signals evolve independently among tanagers.