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For as long as dinosaurs have been known to exist, there has been speculation about their appearance. Fossil feathers can preserve the morphology of color-imparting melanosomes, which allow color patterns in feathered dinosaurs to be reconstructed. Here, we have mapped feather color patterns in a Late Jurassic basal paravian theropod dinosaur. Quantitative comparisons with melanosome shape and density in extant feathers indicate that the body was gray and dark and the face had rufous speckles. The crown was rufous, and the long limb feathers were white with distal black spangles. The evolution of melanin-based within-feather pigmentation patterns may coincide with that of elongate pennaceous feathers in the common ancestor of Maniraptora, before active powered flight. Feathers may thus have played a role in sexual selection or other communication. [ABSTRACT FROM AUTHOR]

The osprey (Pandion haliaetus) is a cosmopolitan and long-distant migrant, found at all thermal extremes ranging from polar to tropical climates. Since ospreys may have an unusually flexible thermal physiology due to their migration over, and use of, a wide range of habitats, they represent an interesting study system to explore thermoregulatory adaptations in a raptor. In this study, we investigated the efficiency of heat exchange between body and environment in ospreys using micro-computed tomography (μ-CT), infrared thermography and behavioral observations. μ-CT revealed that the osprey bill has its largest potential for heat exchange at the proximal bill region, where arteries are situated most closely under the surface. However, thermal images of 10 juvenile ospreys showed that the bill contributes to only 0.3% of the bird's total heat exchange. The long legs and protruding claws played a more prominent role as heat dissipation areas with a contribution of 6% and 7%, respectively. Operative thresholds, i.e. the ambient temperature below which heat is lost, were high (>38.5 °C) in these body parts. However, we found no indication of active regulation of heat exchange. Instead we observed multiple behavioral adaptations starting at relatively low ambient temperatures. At 26.3 °C ospreys had a 50% probability of showing panting behavior and above 27.9 °C they additionally spread their wings to enable heat dissipation from the less insulated ventral side. The thermal images revealed that at an ambient temperature of 32.1 °C ospreys had a 50% probability of developing a ≥2 °C and up to 7.5 °C colder stripe on the head, which was likely caused by cutaneous evaporation. Our observations suggest that ospreys more strongly rely on behavioral mechanisms than on active thermal windows to cope with heat stress. This study not only improves our understanding of the role of different body parts in ospreys' total heat exchange with the environment but further provides an insight about additional adaptations of this raptor to cope with heat stress. • Legs, claws and bill in ospreys function as heat dissipation areas. • We found no indications for an active control of heat exchange through these areas. • Behavioral adaptations to cope with heat stress included panting and wing spreading. • With thermography we visualized cutaneous evaporation as a cooling mechanism. [ABSTRACT FROM AUTHOR]

Several ecogeographical 'rules' have been proposed to explain colour variation at broad spatial and phylogenetic scales but these rarely consider whether colours are based on pigments or structural colours. However, mechanism can have profound effects on the function and evolution of colours. Here, we combine geographic information, climate data and colour mechanism at broad phylogenetic (9,409 species) and spatial scales (global) to determine how transitions between pigmentary and structural colours influence speciation dynamics and range distributions in birds. Among structurally coloured species, we find that rapid dispersal into tropical regions drove the accumulation of iridescent species, whereas the build-up of non-iridescent species in the tropics was driven by a combination of dispersal and faster in situ evolution in the tropics. These results could be explained by pleiotropic links between colouration and dispersal behaviour or ecological factors influencing colonization success. These data elucidate geographic patterns of colouration at a global scale and provide testable hypotheses for future work on birds and other animals with structural colours., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Colors are well studied in bird plumage but not in other integumentary structures. In particular, iridescent colors from structures other than plumage are undescribed in birds. Here, we show that a multilayer of keratin and lipids is sufficient to produce the iridescent bill of Spermophaga haematina . Furthermore, that the male bill is presented to the female under different angles during display provides support for the hypothesis that iridescence evolved in response to sexual selection. This is the first report of an iridescent bill, and only the second instance of iridescence in birds in which melanosomes are not involved. Furthermore, an investigation of museum specimens of an additional 98 species, showed that this evolved once, possibly twice. These results are promising, as they suggest that birds utilize a wider array of physical phenomena to produce coloration and should further stimulate research on nonplumage integumentary colors., (© The Author(s) 2024. Published by Oxford University Press on behalf of National Academy of Sciences.)

Evolutionary biologists have long been interested in understanding the factors that promote diversification in organisms, often focussing on distinct and/or conspicuous phenotypes with direct effects on natural or sexual selection such as body size and plumage coloration. However, multiple traits that potentially influence net diversification are not conspicuous and/or might be concealed. One such trait, the dark, melanin-rich skin concealed beneath the feathers, evolved more than 100 times during avian evolution, frequently in association with white feathers on the crown and UV-rich environments, suggesting that it is a UV-photoprotective adaptation. Furthermore, multiple species are polymorphic, having both light and dark skin potentially aiding occupation in different UV radiation environments. As such these polymorphisms are predicted to occur in species with large latitudinal variation in their distribution. Furthermore, by alleviating evolutionary constraints on feather colour, the evolution of dark skin may promote net diversification. Here, using an expanded dataset on bird skin coloration of 3033 species we found that more than 19% of species had dark skin. In contrast to our prediction, dark skinned birds have smaller distribution ranges. Furthermore, both dark skin and polymorphism in skin coloration promote net diversification. These results suggest that even concealed traits can influence large scale evolutionary events such as diversification in birds.

Colour is often not a static trait but can change over time either through biotic or abiotic factors. Humidity-dependent colour change can occur through either morphological change (e.g. to feather barbules in birds) or by the replacement of air by water causing a shift in refractive index, as seen in arthropod multi-layer cuticles or scales. The scaled springtail Lepidocyrtus cyaneus has scales that produce colour largely via thin film interference from their lamina. We observed a marked colour change from golden to violet/purple coloration in humid conditions. Light microscopy, micro-spectrophotometry, contact angle goniometry and optical modelling indicate that the formation of a thin film of water on top of the hydrophilic scales increases their laminar thin film thickness, causing a shift towards violet/purple colour. Evaporation of the water film causes the metallic golden colour to return. This constitutes a remarkably rapid colour change (in the order of seconds), only limited by the speed of water film condensation and evaporation, that may serve as inspiration for new dynamically coloured materials and sensors.

The bright, saturated iridescent colours of feathers are commonly produced by single and multi-layers of nanostructured melanin granules (melanosomes), air and keratin matrices, surrounded by an outer keratin cortex of varying thicknesses. The role of the keratin cortex in colour production remains unclear, despite its potential to act as a thin film or absorbing layer. We use electron microscopy, optical simulations and oxygen plasma-mediated experimental cortex removal to show that differences in keratin cortex thickness play a significant role in producing colours. The results indicate that keratin cortex thickness determines the position of the major reflectance peak (hue) from nanostructured melanosomes of common pheasant ( Phasianus colchicus ) feathers. Specifically, the common pheasant has appropriate keratin cortex thickness to produce blue and green structural colours. This finding identifies a general principle of structural colour production and sheds light on the processes that shaped the evolution of brilliant iridescent colours in the common pheasant., (© 2023 The Authors.)

Remarkably well-preserved soft tissues in Mesozoic fossils have yielded substantial insights into the evolution of feathers 1 . New evidence of branched feathers in pterosaurs suggests that feathers originated in the avemetatarsalian ancestor of pterosaurs and dinosaurs in the Early Triassic 2 , but the homology of these pterosaur structures with feathers is controversial 3,4 . Reports of pterosaur feathers with homogeneous ovoid melanosome geometries 2,5 suggest that they exhibited limited variation in colour, supporting hypotheses that early feathers functioned primarily in thermoregulation 6 . Here we report the presence of diverse melanosome geometries in the skin and simple and branched feathers of a tapejarid pterosaur from the Early Cretaceous found in Brazil. The melanosomes form distinct populations in different feather types and the skin, a feature previously known only in theropod dinosaurs, including birds. These tissue-specific melanosome geometries in pterosaurs indicate that manipulation of feather colour-and thus functions of feathers in visual communication-has deep evolutionary origins. These features show that genetic regulation of melanosome chemistry and shape 7-9 was active early in feather evolution., (© 2022. The Author(s).)

Cleidoic eggs possess very efficient and orchestrated systems to protect the embryo from external microbes until hatch. The cuticle is a proteinaceous layer on the shell surface in many bird and some reptile species. An intact cuticle forms a pore plug to occlude respiratory pores and is an effective physical and chemical barrier against microbial penetration. The interior of the egg is assumed to be normally sterile, while the outer eggshell cuticle hosts microbes. The diversity of the eggshell microbiome is derived from both maternal microbiota and those of the nesting environment. The surface characteristics of the egg, outer moisture layer and the presence of antimicrobial molecules composing the cuticle dictate constituents of the microbial communities on the eggshell surface. The avian cuticle affects eggshell wettability, water vapor conductance and regulates ultraviolet reflectance in various ground-nesting species; moreover, its composition, thickness and degree of coverage are dependent on species, hen age, and physiological stressors. Studies in domestic avian species have demonstrated that changes in the cuticle affect the food safety of eggs with respect to the risk of contamination by bacterial pathogens such as Salmonella and Escherichia coli . Moreover, preventing contamination of internal egg components is crucial to optimize hatching success in bird species. In chickens there is moderate heritability (38%) of cuticle deposition with a potential for genetic improvement. However, much less is known about other bird or reptile cuticles. This review synthesizes current knowledge of eggshell cuticle and provides insight into its evolution in the clade reptilia. The origin, composition and regulation of the eggshell microbiome and the potential function of the cuticle as the first barrier of egg defense are discussed in detail. We evaluate how changes in the cuticle affect the food safety of table eggs and vertical transmission of pathogens in the production chain with respect to the risk of contamination. Thus, this review provides insight into the physiological and microbiological characteristics of eggshell cuticle in relation to its protective function (innate immunity) in egg-laying birds and reptiles., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Kulshreshtha, D’Alba, Dunn, Rehault-Godbert, Rodriguez-Navarro and Hincke.)

Amniotic eggs are multifunctional structures that enabled early tetrapods to colonize the land millions of years ago, and are now the reproductive mode of over 70% of all terrestrial amniotes. Eggshell morphology is at the core of animal survival, mediating the interactions between embryos and their environment, and has evolved into a massive diversity of forms and functions in modern reptiles. These functions are critical to embryonic survival and may serve as models for new antimicrobial and/or breathable membranes. However, we still lack critical data on the basic structural and functional properties of eggs, particularly of reptiles. Here, we first characterized egg shape, shell thickness, porosity, and mineralization of eggs from 91 reptile species using optical images, scanning electron microscopy, and micro computed tomography, and collected data on nesting ecology from the literature. We then used comparative analyses to test hypotheses on the selective pressures driving their evolution. We hypothesized that eggshell morphology has evolved to protect shells from physical damage and desiccation, and, in support, found a positive relationship between thickness and precipitation, and a negative relationship between porosity and temperature. Although mineralization varied extensively, it was not correlated with nesting ecology variables. Ancestral state reconstructions show thinning and increased porosity over evolutionary time in squamates, but the opposite in turtles and crocodilians. Egg shape, size, porosity and calcification were correlated, suggesting potential structural or developmental tradeoffs. This study provides new data and insights into the morphology and evolution of reptile eggs, and raises numerous questions for additional research., (© 2021 Wiley Periodicals LLC.)

With functions as diverse as communication, protection and thermoregulation, coloration is one of the most important traits in lizards. The ability to change colour as a function of varying social and environmental conditions is thus an important innovation. While colour change is present in animals ranging from squids, to fish and reptiles, not much is known about the mechanisms behind it. Traditionally, colour change was attributed to migration of pigments, in particular melanin. More recent work has shown that the changes in nanostructural configuration inside iridophores are able to produce a wide palette of colours. However, the genetic mechanisms underlying colour, and colour change in particular, remain unstudied. Here we use a combination of transcriptomic and microscopic data to show that melanin, iridophores and pteridines are the main colour-producing mechanisms in Agama atra, and provide molecular and structural data suggesting that rapid colour change is achieved via melanin dispersal in combination with iridophore organization. This work demonstrates the power of combining genotypic (gene expression) and phenotypic (microscopy) information for addressing physiological questions, providing a basis for future studies of colour change., (© 2021 John Wiley & Sons Ltd.)

The thermal environment can affect the evolution of morpho-behavioral adaptations of ectotherms. Heat is transferred from substrates to organisms by conduction and reflected radiation. Because brightness influences the degree of heat absorption, substrates could affect the evolution of integumentary optical properties. Here, we show that vipers (Squamata:Viperidae) inhabiting hot, highly radiative and superficially conductive substrates have evolved bright ventra for efficient heat transfer. We analyzed the brightness of 4161 publicly available images from 126 species, and we found that substrate type, alongside latitude and body mass, strongly influences ventral brightness. Substrate type also significantly affects dorsal brightness, but this is associated with different selective forces: activity-pattern and altitude. Ancestral estimation analysis suggests that the ancestral ventral condition was likely moderately bright and, following divergence events, some species convergently increased their brightness. Vipers diversified during the Miocene and the enhancement of ventral brightness may have facilitated the exploitation of arid grounds. We provide evidence that integument brightness can impact the behavioral ecology of ectotherms.

Plumage is among the most well-studied components of integumentary colouration. However, plumage conceals most skin in birds, and as a result the presence, evolution and function of skin colour remains unexplored. Here we show, using a database of 2259 species encompassing >99% of bird genera, that melanin-rich, black skin is found in a small but sizeable percentage (~5%) of birds, and that it evolved over 100 times. The spatial distribution of black skin follows Gloger's rule, which states that pigmentation of endothermic animals increases towards the equator. Furthermore, most black-skinned birds inhabit high irradiation regions, and tend to be bald and/or have white feathers. Thus, taken together, our results suggest that melanin-rich, black skin helps to protect birds against ultraviolet irradiation. More generally, our results illustrate that feathered skin colour varies taxonomically, ontogenetically and temporally, providing an additional dimension for avian colour research.

White colouration is a common and important component of animal visual signalling and camouflage, but how and why it varies across species is poorly understood. White is produced by wavelength-independent and diffuse scattering of light by the internal structures of materials, where the degree of brightness is related to the amount of light scattered. Here, we investigated the morphological basis of brightness differences among unpigmented pennaceous regions of white body feathers across 61 bird species. Using phylogenetically controlled comparisons of reflectance and morphometric measurements, we show that brighter white feathers had larger and internally more complex barbs than duller white feathers. Higher brightness was also associated with more closely packed barbs and barbules, thicker and longer barbules, and rounder and less hollow barbs. Larger species tended to have brighter white feathers than smaller species because they had thicker and more complex barbs, but aquatic species were not significantly brighter than terrestrial species. As similar light scattering principals affect the brightness of chromatic signals, not just white colours, these findings help broaden our general understanding of the mechanisms that affect plumage brightness. Future studies should examine how feather layering on a bird's body contributes to differences between brightness of white plumage patches within and across species.

The visible spectrum represents a fraction of the sun's radiation, a large portion of which is within the near infrared (NIR). However, wavelengths outside of the visible spectrum that are reflected by coloured tissues have rarely been considered, despite their potential significance to thermal effects. Here, we report the reflectivity from 300 to 2100 nm of differently coloured feathers. We measured reflectivity across the UV-Vis-NIR spectra of different (a) body parts, (b) colour-producing mechanisms and (c) sexes for 252 individuals of 68 sunbird (family: Nectariniidae) species. Breast plumage was the most reflective and cap plumage the least. Female plumage had greater reflectivity than males. Carotenoid-based colours had the greatest reflectivity, followed by non-iridescent and iridescent melanin-based colours. As ordered arrays of melanin-filled organelles (melanosomes) produce iridescent colours, this suggests that nanostructuring may affect reflectance across the spectrum. Our results indicate that differently coloured feathers consistently vary in their thermal, as well as obvious visual, properties.

Animal integumentary coloration plays a crucial role in visual communication and camouflage, and varies extensively among and within species and populations. To understand the pressures underlying such diversity, it is essential to elucidate the mechanisms by which animals have created novel integumentary coloration. Colours can be produced by selective absorption of light by skin pigments, through light scattering by structured or unstructured tissues, or by a combination of pigments and nanostructures. In this review, we highlight our current understanding of the interactions between pigments and structural integumentary tissues and molecules. We analyse the available evidence suggesting that these combined mechanisms are capable of creating colours and optical properties unachievable by either mechanism alone, thereby effectively expanding the animal colour palette. Moreover, structural and pigmentary colour mechanisms frequently interact in unexpected and overlooked ways, suggesting that classification of colours as being of any particular type may be difficult. Finally, we discuss how these mixtures are useful for investigating the largely unknown genetic, developmental and physical processes generating phenotypic diversity.This article is part of the themed issue 'Animal coloration: production, perception, function and application'., (© 2017 The Author(s).)

Avian eggs are at risk of microbial infection prior to and during incubation. A large number of defence mechanisms have evolved in response to the severe costs imposed by these infections. The eggshell's cuticle is an important component of antimicrobial defence, and its role in preventing contamination by microorganisms in domestic chickens is well known. Nanometer-scale cuticular spheres that reduce microbial attachment and penetration have recently been identified on eggs of several wild avian species. However, whether these spheres have evolved specifically for antimicrobial defence is unknown. Here, we use comparative data on eggshell cuticular structure and nesting ecology to test the hypothesis that birds nesting in habitats with higher risk of infection (e.g. wetter and warmer) are more likely to evolve cuticular nanospheres on their eggshells than those nesting in less risky habitats. We found that nanostructuring, present in 54 of 296 analysed species, is the ancestral condition of avian eggshells and has been retained more often in taxa that nest in humid infection-prone environments, suggesting that they serve critical roles in antimicrobial egg defence., (© 2016 The Author(s).)

Stressful conditions early in life can give rise to exaggerated stress responses, which, while beneficial in the short term, chronically increase lifetime exposure to stress hormones and elevate disease risk later in life. Using zebra finches Taeniopygia guttata, we show here that individuals whose glucocorticoid stress hormones were experimentally increased for only a brief period in early post-natal life, inducing increased stress sensitivity, had reduced adult lifespans. Remarkably, the breeding partners of such exposed individuals also died at a younger age. This negative effect on partner longevity was the same for both sexes; it occurred irrespective of the partner's own early stress exposure and was in addition to any longevity reduction arising from this. Furthermore, this partner effect continued even after the breeding partnership was terminated. Only 5 per cent of control birds with control partners had died after 3 years, compared with over 40 per cent in early stress-early stress pairs. In contrast, reproductive capability appeared unaffected by the early stress treatment, even when breeding in stressful environmental circumstances. Our results clearly show that increased exposure to glucocorticoids early in life can markedly reduce adult life expectancy, and that pairing with such exposed partners carries an additional and substantial lifespan penalty.

Colours in feathers are produced by pigments or by nanostructurally organized tissues that interact with light. One of the simplest nanostructures is a single layer of keratin overlying a linearly organized layer of melanosomes that create iridescent colours of feather barbules through thin-film interference. Recently, it has been hypothesized that glossy (i.e. high specular reflectance) black feathers may be evolutionarily intermediate between matte black and iridescent feathers, and thus have a smooth keratin layer that produces gloss, but not the layered organization of melanosomes needed for iridescence. However, the morphological bases of glossiness remain unknown. Here, we use a theoretical approach to generate predictions about morphological differences between matte and glossy feathers that we then empirically test. Thin-film models predicted that glossy spectra would result from a keratin layer 110-180 nm thick and a melanin layer greater than 115 nm thick. Transmission electron microscopy data show that nanostructure of glossy barbules falls well within that range, but that of matte barbules does not. Further, glossy barbules had a thinner and more regular keratin cortex, as well as a more continuous underlying melanin layer, than matte barbules. Thus, their quasi-ordered nanostructures are morphologically intermediate between matte black and iridescent feathers, and perceived gloss may be a form of weakly chromatic iridescence.

Avian incubation dramatically reduces the abundance and diversity of microbial assemblages on eggshells, and this effect has been hypothesized as an adaptive explanation for partial incubation, the bouts of incubation that some birds perform during the egg-laying period. However, the mechanisms for these antimicrobial effects are largely unknown. In this study, we hypothesized that microbial inhibition is partly achieved through removal of liquid water, which generally enhances microbial growth, from eggshells, and experimentally tested this hypothesis in two ways. First, we placed the first- and second-laid eggs of tree swallow (Tachycineta bicolor) clutches in unincubated holding nests with either ambient or increased water on eggshells. Second, we added water to eggshells in naturally partially incubated nests. We compared microbial growth on shells during a 5-day experimental period and found that, as predicted, both unincubated groups had higher microbial growth than naturally partially incubated controls, and that only in the absence of incubation did wetted eggs have higher microbial growth than unwetted eggs. Thus, we have shown that water increases microbial growth on eggshells and that incubation nullifies these effects, suggesting that removal of water from egg surfaces is one proximate mechanism for the antimicrobial effects of incubation.

Complete androgen insensitivity syndrome (CAIS) is a genetic disease caused by mutations in the androgen receptor gene. CAIS patients are individuals with a 46, XY karyotype. The phenotype consists in female external genitalia, short vagina, absent mullerian structures, and abdominal, inguinal or intralabial testes. Our aim is to describe a group of CAIS patients in our centre and identify the difficulties in the diagnosis. The amount of patients with inguinal hernia in childhood was remarkable (83%). Interestingly, the diagnosis was suspected later when patients presented primary amenorrhea. CAIS must be suspected every time a female child shows inguinal hernia. Early diagnosis is very important for a correct genetic counseling.

Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is a disorder which can adopt three clinical expressions: two classical forms -salt-wasting (SW), with residual enzymatic activity (EA) < or = 1% and simple virilizing (SV), with EA 1-2%- and a mild late onset or nonclassical (NC) form, with EA 10-60%. Our objective is to describe clinical characteristics, growth, and bone mass in a group of patients affected by 21-hydroxylase deficiency. Besides, molecular genetics studies were performed in patients, and also when available in their parents and siblings. Nine patients with neonatal diagnosis and 8 with pre or postpubertal diagnosis were studied. Analyses of 10-point mutations in the CYP21A2 gene were performed. We found that all the patients with the classical expression, except one with a de novo mutation R356W in one allele, were fully genotyped with predictive < 2% EA mutations. Signs of hyperandrogenism were present in 5/6 NC patients; one was diagnosed by searching for mutations in asymptomatic siblings. All the NC patients were compound heterozygotes carrying V281L mutation in one allele and a predictive low EA in the other, except for one not yet determined. In patients with neonatal diagnosis, mean height was low at one year of age, though it showed a significant increase before the onset of puberty. We conclude that neonatal diagnosis of classical CAH allows an adequate follow up enhancing growth. Molecular analyses of all members of an affected family may disclose asymptomatic patients. The presence of de novo mutations, as well as, the presence of mutations with low predicted EA in NC patients reinforces the importance of genotyping for appropriate genetic counseling. In fully genotyped NC patients, the lowest value of ACTH-stimulated 17OHP was 14 ng/ml. Lower cut-off values might overestimate the diagnosis of the NC form.