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Sexual dimorphism in melanin pigmentation, feather coloration and its heritability in the barn swallow (Hirundo rustica).

Saino N, Romano M, Rubolini D, Teplitsky C, Ambrosini R, Caprioli M, Canova L, Wakamatsu K - PLoS ONE (2013)

Bottom Line: The relative concentration of either melanin (Pheo:Eu) differed between sexes in throat but not in belly feathers, and the concentrations in males compared to females were larger in belly than in throat feathers.Finally, we found high heritability of color of throat feathers.Melanization was found to differ from that recorded in Hirundo rustica rustica from Scotland or from H. r. erythrogaster from North America.

View Article: PubMed Central - PubMed

Affiliation: Department of Biosciences, University of Milan, Milan, Italy. nicola.saino@unimi.it

ABSTRACT
Melanin is the main pigment in animal coloration and considerable variation in the concentrations of the two melanin forms (pheo- and eumlanin) in pigmented tissues exists among populations and individuals. Melanin-based coloration is receiving increasing attention particularly in socio-sexual communication contexts because the melanocortin system has been hypothesized to provide a mechanistic basis for covariation between coloration and fitness traits. However, with few notable exceptions, little detailed information is available on inter-individual and inter-population variation in melanin pigmentation and on its environmental, genetic and ontogenetic components. Here, we investigate melanin-based coloration in an Italian population of a passerine bird, the barn swallow (Hirundo rustica rustica), its sex- and age-related variation, and heritability. The concentrations of eu- and pheomelanin in the throat (brown) and belly (white-to-brownish) feathers differed between sexes but not according to age. The relative concentration of either melanin (Pheo:Eu) differed between sexes in throat but not in belly feathers, and the concentrations in males compared to females were larger in belly than in throat feathers. There were weak correlations between the concentrations of melanins within as well as among plumage regions. Coloration of belly feathers was predicted by the concentration of both melanins whereas coloration of throat feathers was only predicted by pheomelanin in females. In addition, Pheo:Eu predicted coloration of throat feathers in females and that of belly feathers in males. Finally, we found high heritability of color of throat feathers. Melanization was found to differ from that recorded in Hirundo rustica rustica from Scotland or from H. r. erythrogaster from North America. Hence, present results show that pigmentation strategies vary in a complex manner according to sex and plumage region, and also among geographical populations, potentially reflecting adaptation to different natural and sexual selection regimes, and that some coloration components seem to be highly heritable.

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Reflectance spectra of belly or throat feathers with relative pale or dark color.
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pone-0058024-g001: Reflectance spectra of belly or throat feathers with relative pale or dark color.

Mentions: We quantified feather reflectance by means of spectrophotometric measurements using an Avantes DH-2000 spectrometer in a dark chamber (Fig. 1). Illumination was provided by a combined deuterium-tungsten halogen light source. Two repeated measurements were obtained from three overlain throat feathers or one belly feather. Reflectance of the samples was always referred to white and black standards. The illuminated field covered an area of 2.5 mm2 centered approximately 1.5 mm from the distal end of the throat feathers (i.e. in the terminal brown part of the feather) and 2.5 mm from the distal end of the belly feather (i.e. in a white-to-brownish region). Reflectance spectra were processed to quantify coloration using the tetrachromatic color space model [62] using TetraColorSpace program (Version 1a; [47]) run in MATLAB 7 (MathWorks, Natick, MA). This approach has the advantage of incorporating information on both plumage reflectance spectra and bird cone sensitivity functions. This allows to estimate the relative stimulation of the retinal cones and thus to better model the color perceived by birds. As this model has been recently adopted in a number of studies of tetrachromatic vertebrates (e.g. [47], [63]), we will only briefly describe the rationale of the method here. According to Goldsmith and co-workers [62], the idealized stimulus QI of each retinal cone type by the reflectance of a color patch can be estimated as:where R(λ) is the color reflectance spectrum, Cr(λ) is the spectral sensitivity function of cone type r. We assumed UVS cone type-retina and used spectral sensitivity of the blue tit (Cyanistes caeruleus) because this is the species more phylogenetically close to the barn swallow for which spectral sensitivity information is implemented in TetraColorSpace program. However, correlation analysis of θ and φ color components (see below) obtained by assuming blue tit or, respectively average bird UVS spectral sensitivities disclosed an extremely high association (details not shown). This implies that the results were robust to the effect of the particular spectral sensitivity profile chosen among those typical of UVS birds. Idealized stimulation of the four cones were normalized to a sum of 1, so that each color patch can be described in the tetrahedral color space by a vector of {uv, s, m, l} values representing the relative stimulations of the ultraviolet-, short-wavelength-, medium-wavelength-, and long-wavelength-sensitive cones, respectively. Each color vector in the tetrahedral color space is then transformed to Cartesian coordinates that are subsequently converted into the spherical coordinates θ, φ, and r (see [47], [63]). θ and φ that we used here to quantify hue roughly represent the red-green-blue (θ) or the ultraviolet (φ) components of hue, while r is a measure of color saturation (or chroma). In the range of colors of barn swallow throat and belly feathers, increasing θ values indicate paler, whitish coloration. No verbal description can be provided for variation in φ because this mainly reflects ultraviolet hue components which cannot be sensed by the human eye. Because the color space is a tetrahedron and not a sphere, different hues vary in their maximum potential chroma (rmax) [47]. Thus, in the analyses we used the ‘achieved chroma’, computed as rA = r/rmax.


Sexual dimorphism in melanin pigmentation, feather coloration and its heritability in the barn swallow (Hirundo rustica).

Saino N, Romano M, Rubolini D, Teplitsky C, Ambrosini R, Caprioli M, Canova L, Wakamatsu K - PLoS ONE (2013)

Reflectance spectra of belly or throat feathers with relative pale or dark color.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585210&req=5

pone-0058024-g001: Reflectance spectra of belly or throat feathers with relative pale or dark color.
Mentions: We quantified feather reflectance by means of spectrophotometric measurements using an Avantes DH-2000 spectrometer in a dark chamber (Fig. 1). Illumination was provided by a combined deuterium-tungsten halogen light source. Two repeated measurements were obtained from three overlain throat feathers or one belly feather. Reflectance of the samples was always referred to white and black standards. The illuminated field covered an area of 2.5 mm2 centered approximately 1.5 mm from the distal end of the throat feathers (i.e. in the terminal brown part of the feather) and 2.5 mm from the distal end of the belly feather (i.e. in a white-to-brownish region). Reflectance spectra were processed to quantify coloration using the tetrachromatic color space model [62] using TetraColorSpace program (Version 1a; [47]) run in MATLAB 7 (MathWorks, Natick, MA). This approach has the advantage of incorporating information on both plumage reflectance spectra and bird cone sensitivity functions. This allows to estimate the relative stimulation of the retinal cones and thus to better model the color perceived by birds. As this model has been recently adopted in a number of studies of tetrachromatic vertebrates (e.g. [47], [63]), we will only briefly describe the rationale of the method here. According to Goldsmith and co-workers [62], the idealized stimulus QI of each retinal cone type by the reflectance of a color patch can be estimated as:where R(λ) is the color reflectance spectrum, Cr(λ) is the spectral sensitivity function of cone type r. We assumed UVS cone type-retina and used spectral sensitivity of the blue tit (Cyanistes caeruleus) because this is the species more phylogenetically close to the barn swallow for which spectral sensitivity information is implemented in TetraColorSpace program. However, correlation analysis of θ and φ color components (see below) obtained by assuming blue tit or, respectively average bird UVS spectral sensitivities disclosed an extremely high association (details not shown). This implies that the results were robust to the effect of the particular spectral sensitivity profile chosen among those typical of UVS birds. Idealized stimulation of the four cones were normalized to a sum of 1, so that each color patch can be described in the tetrahedral color space by a vector of {uv, s, m, l} values representing the relative stimulations of the ultraviolet-, short-wavelength-, medium-wavelength-, and long-wavelength-sensitive cones, respectively. Each color vector in the tetrahedral color space is then transformed to Cartesian coordinates that are subsequently converted into the spherical coordinates θ, φ, and r (see [47], [63]). θ and φ that we used here to quantify hue roughly represent the red-green-blue (θ) or the ultraviolet (φ) components of hue, while r is a measure of color saturation (or chroma). In the range of colors of barn swallow throat and belly feathers, increasing θ values indicate paler, whitish coloration. No verbal description can be provided for variation in φ because this mainly reflects ultraviolet hue components which cannot be sensed by the human eye. Because the color space is a tetrahedron and not a sphere, different hues vary in their maximum potential chroma (rmax) [47]. Thus, in the analyses we used the ‘achieved chroma’, computed as rA = r/rmax.

Bottom Line: The relative concentration of either melanin (Pheo:Eu) differed between sexes in throat but not in belly feathers, and the concentrations in males compared to females were larger in belly than in throat feathers.Finally, we found high heritability of color of throat feathers.Melanization was found to differ from that recorded in Hirundo rustica rustica from Scotland or from H. r. erythrogaster from North America.

View Article: PubMed Central - PubMed

Affiliation: Department of Biosciences, University of Milan, Milan, Italy. nicola.saino@unimi.it

ABSTRACT
Melanin is the main pigment in animal coloration and considerable variation in the concentrations of the two melanin forms (pheo- and eumlanin) in pigmented tissues exists among populations and individuals. Melanin-based coloration is receiving increasing attention particularly in socio-sexual communication contexts because the melanocortin system has been hypothesized to provide a mechanistic basis for covariation between coloration and fitness traits. However, with few notable exceptions, little detailed information is available on inter-individual and inter-population variation in melanin pigmentation and on its environmental, genetic and ontogenetic components. Here, we investigate melanin-based coloration in an Italian population of a passerine bird, the barn swallow (Hirundo rustica rustica), its sex- and age-related variation, and heritability. The concentrations of eu- and pheomelanin in the throat (brown) and belly (white-to-brownish) feathers differed between sexes but not according to age. The relative concentration of either melanin (Pheo:Eu) differed between sexes in throat but not in belly feathers, and the concentrations in males compared to females were larger in belly than in throat feathers. There were weak correlations between the concentrations of melanins within as well as among plumage regions. Coloration of belly feathers was predicted by the concentration of both melanins whereas coloration of throat feathers was only predicted by pheomelanin in females. In addition, Pheo:Eu predicted coloration of throat feathers in females and that of belly feathers in males. Finally, we found high heritability of color of throat feathers. Melanization was found to differ from that recorded in Hirundo rustica rustica from Scotland or from H. r. erythrogaster from North America. Hence, present results show that pigmentation strategies vary in a complex manner according to sex and plumage region, and also among geographical populations, potentially reflecting adaptation to different natural and sexual selection regimes, and that some coloration components seem to be highly heritable.

Show MeSH
Related in: MedlinePlus