Enhanced photothermal absorption in iridescent feathers

Rogalla, Svana; Patil, Anvay; Dhinojwala, Ali; Shawkey, Matthew D.; D’Alba, Liliana

doi:10.1098/rsif.2021.0252

Cited by 17 publications

(32 citation statements)

References 65 publications

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“…It is Previous mechanistic studies have identified various morphological structures as potential thermal radiators, including bare skin patches 12 and external appendages, such as the ears of elephants 9 , the enlarged claws of fiddler crabs 29 and the beaks of birds 10,11,30 . In addition, secondary sexual signaling characters involving melanin or structural iridescent colors can also have cascading effects on body temperature, and be either beneficial in cold environments or to decrease risk of overheating in hot environments [31][32][33] . While these previous mechanistic studies have provided compelling evidence for the thermoregulatory consequences of various morphological traits, they have not provided direct evidence for their fitness consequences, plasticity, and underlying genetic variation.…”

Section: Discussionmentioning

confidence: 99%

Heritable variation in thermoregulation is associated with reproductive success in the world’s largest bird

Svensson

Schou

Melgar

et al. 2022

Preprint

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Organisms inhabiting extreme thermal environments, such as desert birds, have evolved various adaptations to thermoregulate during hot days and cold nights. However, our knowledge of selection acting on thermoregulatory traits and their evolutionary potential is limited, particularly for large organisms experiencing extreme temperature fluctuations. Here we show, using thermal imaging that the featherless neck of the ostrich (Struthio camelus) acts as a ‘thermal radiator’, protecting the head from overheating during hot conditions and conserving heat during cool conditions. We found substantial individual variation in thermal plasticity of the neck to dissipate heat away from the head that was associated with increased egg-laying rates during high ambient temperatures. Combined with low, but significant, heritability estimates of individual thermal profiles, these findings suggest that the ostrich neck functions as an adaptive thermal radiator with evolutionary potential. There were also signatures of past selection, since ostriches originating from more volatile climatic regions and females that incubate during hot daytime conditions exhibited especially high thermal plasticity. Taken together our results indicate that morphological adaptations involved in ostrich thermoregulation, such as the neck, are experiencing ongoing selection and are crucial for successfully reproducing under fluctuating climatic conditions.

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Section: Discussionmentioning

confidence: 99%

Heritable variation in thermoregulation is associated with reproductive success in the world’s largest bird

Svensson

Schou

Melgar

et al. 2022

Preprint

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“…Coloration also affects the thermal properties of plumage. Variation in reflectance and absorption of light affect the heating of the feather surface (Wolf & Walsberg 2000, Rogalla et al 2021a. When the plumage surface is heated by the sun under cold conditions, the temperature gradient between the skin and the feathers is reduced, which in return decreases heat loss to the environment (Fig.…”

Section: Functions Of Avian Plumagementioning

confidence: 99%

“…3). Concurrently, melanin-based colours reflect less light than carotenoid-based colours (Rogalla et al 2021a).…”

Section: Determinants Of Plumage Coloration and Their Thermal Propertiesmentioning

confidence: 99%

“…Larger font/symbol sizes are used to visualize increasing intensities. This figure was originally published in Rogalla et al (2021a).…”

Section: Metabolic Effects Of Plumage Colorationmentioning

confidence: 99%

“…A recent study of the thermal properties of sunbird (Nectariniidae) feather coloration showed that nanostructured, melanin‐based, iridescent feathers (green, purple, blue) reflected less light and heated more than unstructured melanin‐based colours (grey, brown, black), carotenoid‐based colours (yellow, orange, red) and non‐pigmented whites (Rogalla et al . 2021a). The higher heating rates of iridescent feathers were linked to greater melanin content within feather barbules and, to a minor extent, to the shape of the melanosomes, with higher aspect‐ratio (i.e.…”

Section: Determinants Of Plumage Coloration and Their Thermal Propertiesmentioning

confidence: 99%

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Thermal effects of plumage coloration

Rogalla

Shawkey

D’Alba

2022

Ibis

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Plumage coloration can have substantial effects on a bird's energy budget. This is because different colours reflect and absorb light differently, affecting the heat loads acquired from solar radiation. We examine the thermal effects of feather coloration on solar heat gain and flight performance and discuss the potential role of plumage colour on a bird's energy budget. Early investigations of the effects of plumage colour on thermoregulation revealed complex interactions between environmental conditions and physical properties of the plumage that may have led to diverse behavioural and physiological adaptations of birds to their thermal environment. While darker feather surfaces absorb more light, and heat more, than light‐coloured surfaces under exposure to the sun, this relationship is not always straightforward when considering heat transfer to the skin. Heat transfer through plumage varies depending on multiple factors, such as feather density and transmission of light. For instance, higher transmissivity of light‐coloured plumage can increase heat loads reaching skin level, while conduction and convection transfer heat from the surface of dark feathers to the skin. Solar heating can affect the metabolic costs of maintaining a constant body temperature, and depending on environmental conditions, colours can have either a positive or negative effect on a bird's energy budget. More specifically, solar heating can be advantageous in the cold but may increase the energetic costs associated with thermoregulation when ambient temperature is high. More recent studies have further suggested that the thermal properties of feather coloration might reduce the energetic costs of flight. This is because surface heating can affect the ratio between lift and drag on a wing. As concluding remarks, we provide future directions for new lines of research that will aid in improving our understanding of the thermal effects of feather coloration on a bird's energy budget, which can potentially explain factors driving colour evolution and distribution patterns in birds.

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Structural Color Production in Melanin‐Based Disordered Colloidal Nanoparticle Assemblies in Spherical Confinement

Patil

Heil

Vanthournout

et al. 2021

Advanced Optical Materials

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Melanin is a ubiquitous natural pigment that exhibits broadband absorption and high refractive index. Despite its widespread use in structural color production, how the absorbing material, melanin, affects the generated color is unknown. Using a combined molecular dynamics and finite‐difference time‐domain computational approach, this paper investigates structural color generation in one‐component melanin nanoparticle‐based supraparticles (called supraballs) as well as binary mixtures of melanin and silica (nonabsorbing) nanoparticle‐based supraballs. Experimentally produced one‐component melanin and one‐component silica supraballs, with thoroughly characterized primary particle characteristics using neutron scattering, produce reflectance profiles similar to the computational analogs, confirming that the computational approach correctly simulates both absorption and multiple scattering from the self‐assembled nanoparticles. These combined approaches demonstrate that melanin's broadband absorption increases the primary reflectance peak wavelength, increases saturation, and decreases lightness factor. In addition, the dispersity of nanoparticle size more strongly influences the optical properties of supraballs than packing fraction, as evidenced by the production of a larger range of colors when size dispersity is varied versus packing fraction. For binary melanin and silica supraballs, the chemistry‐based stratification allows for more diverse color generation and finer saturation tuning than does the degree of mixing/demixing between the two chemistries.

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Enhanced photothermal absorption in iridescent feathers

Cited by 17 publications

References 65 publications

Heritable variation in thermoregulation is associated with reproductive success in the world’s largest bird

Heritable variation in thermoregulation is associated with reproductive success in the world’s largest bird

Thermal effects of plumage coloration

Structural Color Production in Melanin‐Based Disordered Colloidal Nanoparticle Assemblies in Spherical Confinement

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