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Si S, Xu X, Zhuang Y, Gao X, Zhang H, Zou Z, Luo SJ. The genetics and evolution of eye color in domestic pigeons (Columba livia). PLoS Genet 2021; 17:e1009770. [PMID: 34460822 PMCID: PMC8432899 DOI: 10.1371/journal.pgen.1009770] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Revised: 09/10/2021] [Accepted: 08/10/2021] [Indexed: 11/18/2022] Open
Abstract
The eye color of birds, generally referring to the color of the iris, results from both pigmentation and structural coloration. Avian iris colors exhibit striking interspecific and intraspecific variations that correspond to unique evolutionary and ecological histories. Here, we identified the genetic basis of pearl (white) iris color in domestic pigeons (Columba livia) to explore the largely unknown genetic mechanism underlying the evolution of avian iris coloration. Using a genome-wide association study (GWAS) approach in 92 pigeons, we mapped the pearl iris trait to a 9 kb region containing the facilitative glucose transporter gene SLC2A11B. A nonsense mutation (W49X) leading to a premature stop codon in SLC2A11B was identified as the causal variant. Transcriptome analysis suggested that SLC2A11B loss of function may downregulate the xanthophore-differentiation gene CSF1R and the key pteridine biosynthesis gene GCH1, thus resulting in the pearl iris phenotype. Coalescence and phylogenetic analyses indicated that the mutation originated approximately 5,400 years ago, coinciding with the onset of pigeon domestication, while positive selection was likely associated with artificial breeding. Within Aves, potentially impaired SLC2A11B was found in six species from six distinct lineages, four of which associated with their signature brown or blue eyes and lack of pteridine. Analysis of vertebrate SLC2A11B orthologs revealed relaxed selection in the avian clade, consistent with the scenario that during and after avian divergence from the reptilian ancestor, the SLC2A11B-involved development of dermal chromatophores likely degenerated in the presence of feather coverage. Our findings provide new insight into the mechanism of avian iris color variations and the evolution of pigmentation in vertebrates.
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Affiliation(s)
- Si Si
- The State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China
- Peking-Tsinghua Center for Life Sciences, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China
| | - Xiao Xu
- The State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China
- Peking-Tsinghua Center for Life Sciences, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China
| | - Yan Zhuang
- The State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China
- Peking-Tsinghua Center for Life Sciences, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China
| | - Xiaodong Gao
- College of Life Sciences, Qufu Normal University, Qufu, Shandong, China
| | - Honghai Zhang
- College of Life Sciences, Qufu Normal University, Qufu, Shandong, China
| | - Zhengting Zou
- Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
| | - Shu-Jin Luo
- The State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China
- Peking-Tsinghua Center for Life Sciences, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China
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Brejcha J, Bataller JV, Bosáková Z, Geryk J, Havlíková M, Kleisner K, Maršík P, Font E. Body coloration and mechanisms of colour production in Archelosauria: the case of deirocheline turtles. ROYAL SOCIETY OPEN SCIENCE 2019; 6:190319. [PMID: 31417734 PMCID: PMC6689573 DOI: 10.1098/rsos.190319] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2019] [Accepted: 06/28/2019] [Indexed: 05/11/2023]
Abstract
Animal body coloration is a complex trait resulting from the interplay of multiple mechanisms. While many studies address the functions of animal coloration, the mechanisms of colour production still remain unknown in most taxa. Here we compare reflectance spectra, cellular, ultra- and nano-structure of colour-producing elements, and pigment types in two freshwater turtles with contrasting courtship behaviour, Trachemys scripta and Pseudemys concinna. The two species differ in the distribution of pigment cell-types and in pigment diversity. We found xanthophores, melanocytes, abundant iridophores and dermal collagen fibres in stripes of both species. The yellow chin and forelimb stripes of both P. concinna and T. scripta contain xanthophores and iridophores, but the post-orbital regions of the two species differ in cell-type distribution. The yellow post-orbital region of P. concinna contains both xanthophores and iridophores, while T. scripta has only xanthophores in the yellow-red postorbital/zygomatic regions. Moreover, in both species, the xanthophores colouring the yellow-red skin contain carotenoids, pterins and riboflavin, but T. scripta has a higher diversity of pigments than P. concinna. Trachemys s. elegans is sexually dichromatic. Differences in the distribution of pigment cell types across body regions in the two species may be related to visual signalling but do not match predictions based on courtship position. Our results demonstrate that archelosaurs share some colour production mechanisms with amphibians and lepidosaurs (i.e. vertical layering/stacking of different pigment cell types and interplay of carotenoids and pterins), but also employ novel mechanisms (i.e. nano-organization of dermal collagen) shared with mammals.
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Affiliation(s)
- Jindřich Brejcha
- Department of Philosophy and History of Science, Faculty of Science, Charles University, Viničná 7, Prague 2, 128 00, Czech Republic
- Department of Zoology, Natural History Museum, National Museum, Václavské nám. 68, Prague 1, 110 00, Czech Republic
- Department of Biophysical Chemistry, J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, Dolejškova 3, Prague 8, 18223, Czech Republic
| | - José Vicente Bataller
- Centro de Conservación de Especies Dulceacuícolas de la Comunidad Valenciana. VAERSA-Generalitat Valenciana, El Palmar, València, 46012, Spain
| | - Zuzana Bosáková
- Department of Analytical Chemistry, Faculty of Science, Charles University, Hlavova 8, Prague 2, 128 43, Czech Republic
| | - Jan Geryk
- Department of Biology and Medical Genetics, 2nd Faculty of Medicine, Charles University and University Hospital Motol, V Úvalu 84, 150 06 Prague, Czech Republic
| | - Martina Havlíková
- Department of Analytical Chemistry, Faculty of Science, Charles University, Hlavova 8, Prague 2, 128 43, Czech Republic
| | - Karel Kleisner
- Department of Philosophy and History of Science, Faculty of Science, Charles University, Viničná 7, Prague 2, 128 00, Czech Republic
| | - Petr Maršík
- Department of Food Science, Faculty of Agrobiology, Food, and Natural Resources, Czech University of Life Sciences Prague, Kamýcká 129, Prague 6, 165 00, Czech Republic
| | - Enrique Font
- Ethology Lab, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, C/ Catedrátic José Beltrán Martinez 2, Paterna, València, 46980, Spain
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Schartl M, Larue L, Goda M, Bosenberg MW, Hashimoto H, Kelsh RN. What is a vertebrate pigment cell? Pigment Cell Melanoma Res 2015; 29:8-14. [DOI: 10.1111/pcmr.12409] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2015] [Accepted: 07/17/2015] [Indexed: 12/11/2022]
Affiliation(s)
- Manfred Schartl
- Department Physiological Chemistry, Biocenter and Comprehensive Cancer Center Mainfranken; University of Würzburg; University Clinic Würzburg; Würzburg Germany
| | - Lionel Larue
- Institut Curie; Normal and Pathological Development of Melanocytes CNRS UMR3347 INSERM U1021 Equipe labellisée - Ligue Nationale contre le Cancer; Orsay France
| | - Makoto Goda
- Cellular and Structural Physiology Institute; Nagoya University; Nagoya Japan
| | - Marcus W. Bosenberg
- Departments of Dermatology and Pathology; Yale University School of Medicine; New Haven CT USA
| | - Hisashi Hashimoto
- Bioscience and Biotechnology Center; Nagoya University; Nagoya Japan
| | - Robert N. Kelsh
- Department of Biology & Biochemistry and Centre for Regenerative Medicine; University of Bath; Claverton Down Bath UK
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Prum RO, Torres R. Structural colouration of avian skin: convergent evolution of coherently scattering dermal collagen arrays. J Exp Biol 2003; 206:2409-29. [PMID: 12796458 DOI: 10.1242/jeb.00431] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Structural colours of avian skin have long been hypothesized to be produced by incoherent (Rayleigh/Tyndall) scattering. We investigated the colour, anatomy, nanostructure and biophysics of structurally coloured skin, ramphotheca and podotheca from 31 species of birds from 17 families in 10 orders from across Aves. Integumentary structural colours of birds include ultraviolet, dark blue, light blue, green and yellow hues. The discrete peaks in reflectance spectra do not conform to the inverse fourth power relationship predicted by Rayleigh scattering. The dermis of structurally coloured skin consists of a thick (100-500 micro m) layer of collagen that is usually underlain by a layer of melanin granules. Transmission electron micrographs (TEMs) of this colour-producing dermal collagen layer revealed quasi-ordered arrays of parallel collagen fibres. Two-dimensional (2-D) Fourier analysis of TEMs of the collagen arrays revealed a ring of peak spatial frequencies in the spatial variation in refractive index that are the appropriate size to make the observed ultraviolet-yellow colours by coherent scattering alone. One species, Philepitta castanea (Eurylaimidae), has exceptionally ordered, hexagonal arrays of collagen fibres that produce a hexagonal pattern of spatial frequency peaks in the power spectra. Ultraviolet, blue, green and yellow structural colours of avian skin are produced by coherent scattering (i.e. constructive interference) by arrays of collagen fibres in the dermis. Some yellow and orange skin colours are produced with a combination of structural and pigmentary mechanisms. These combined colours can have reflectance spectra with discrete peaks that are more saturated than hues produced by carotenoid pigments alone. Bluish facial skin from two species of Neotropical antbirds (Thamnophilidae) are nanostructurally too small to produce visible light by coherent scattering, and the colour production mechanism in these species remains unknown. Based on the phylogenetic distribution of structurally coloured skin in Aves, this mechanism of colour production has evolved convergently more than 50 independent times within extant birds.
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Affiliation(s)
- Richard O Prum
- Department of Ecology and Evolutionary Biology, and Natural History Museum, Dyche Hall, University of Kansas, Lawrence, KS 66045-7561, USA.
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Hudon J, Muir AD. Characterization of the reflective materials and organelles in the bright irides of North American blackbirds (Icterinae). PIGMENT CELL RESEARCH 1996; 9:96-104. [PMID: 8857673 DOI: 10.1111/j.1600-0749.1996.tb00096.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The reflective materials in the iris stroma of bright-irised American blackbirds (Icterinae, Emberizidae) and the red-eyed vireo (vireo olivaceus) (Vireonidae) were characterized using high-performance liquid chromatography (HPLC) and diode-array detection. Two purines, guanine and hypoxanthine, and two pteridines, leucopterin and xanthopterin, were detected in large amounts in all bright irides. The brown iris of the red-winged blackbird (Agelaius phoeniceus) by comparison contained only small amounts of these and additional unidentified compounds. The absolute and relative amounts of light-absorbing compounds in the iris varied somewhat among species of blackbirds with bright irides, and markedly within one species (brewer's blackbird, Euphagus cyanocephalus) between sexes and age classes that very in eye color. Differences in the types, numbers, and sizes of pigment organelles in the irides appeared to underlie the differences in amounts of light-absorbing compounds. Guanine was the most abundant light-absorbing compound in all bright irides, accounting for about 90% of the total absorption at 250 nm. A wide range of concentrations of guanine, from 96 to 9 micrograms per iris, produced bright irides. The primary pigment organelles of pigment cells in bright irides were reflecting platelets, which typically appeared as open spaces on electron micrographs. In the red-eyed vireo there were in addition red pterinosome-like pigment organelles in the pigment cells on the anterior surface of the iris stroma. Guanine was present even in irides with no overt reflecting platelets.
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Affiliation(s)
- J Hudon
- Department of Veterinary Anatomy, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada
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Oliphant LW, Hudon J. Pteridines as reflecting pigments and components of reflecting organelles in vertebrates. PIGMENT CELL RESEARCH 1993; 6:205-8. [PMID: 8248017 DOI: 10.1111/j.1600-0749.1993.tb00603.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
This paper reviews evidence for the presence of pteridines in iridophores, leucophores, and xanthophores in a wide variety of vertebrate chromatophores, and argues that the chemical and functional distinction between pterinosomes and reflecting platelets is not as clear-cut as previously believed. Observations indicate that: (1) Pteridines may, either alone or in conjunction with purines, form pigment granules that reflect light, (2) these pigment granules are highly variable ranging from fibrous pterinosomes to typical reflecting platelets and may be colored, reflect white light, or be iridescent, and (3) many "leucophores" probably contain typical pterinosomes and presumed associated colorless pteridines and are therefore more closely related to erythrophores and xanthophores than to iridophores with which they are usually classified. We propose that the classification of pigment cells should be modified to reflect these facts.
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Affiliation(s)
- L W Oliphant
- Department of Veterinary Anatomy, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada
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Oliphant LW, Hudon J, Bagnara JT. Pigment cell refugia in homeotherms--the unique evolutionary position of the iris. PIGMENT CELL RESEARCH 1992; 5:367-71. [PMID: 1492070 DOI: 10.1111/j.1600-0749.1992.tb00564.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Homeotherms are generally considered to lack classical active dermal pigment cells (chromatophores) in their integument, attributable to the development of an outer covering coat of hair or feathers. However, bright colored dermal pigment cells, comparable to chromatophores of lower vertebrates, are found in the irides of many birds. We propose that, because of its exposed location, the iris is an area in which color from pigment cells has sustained a selective advantage and appears to have evolved independently of the general integument. In birds, the iris appears to have retained the potential for the complete expression of all dermal chromatophore types. Differences in cell morphology and the presence of unusual pigments in birds are suggested to be the result of evolutionary changes that followed the divergence of birds from reptiles. By comparison, mammals appear to have lost the potential for producing iridophores, xanthophores, or erythrophores comparable to those of lower vertebrates, even though some species possess brightly colored irides. It is proposed that at least one species of mammal (the domestic cat) has recruited a novel iridial reflecting pigment organelle originally developed in the choroidal tapetum lucidum. The potential presence of classical chromatophores in mammals remains open, as few species with bright irides have been examined.
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Affiliation(s)
- L W Oliphant
- Department of Veterinary Anatomy, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada
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Abstract
There are three genetically controlled iris types found in the pigeon, two of which contain stromal pigment cells, the third lacks pigment cells. The yellow (gravel) and white (pearl) iris types have pigment cells that contain birefringent pigment granules (crystals) and are ultrastructurally similar to iridophores of poikilothermic vertebrates. Both these iris types contain guanine as a major "pigment" and, in addition, the yellow iris contains at least two yellow fluorescing pigments that are tentatively identified as pteridines. The pigment cells of the yellow and white irises are structurally identical differing only in the presence or absence of these yellow pigments. The stromal pigment cells of the white iris correspond in structure and pigment chemistry to classical iridophores although they lack strong irridescence and are therefore perhaps best considered leucophores. The pigment cells of the yellow iris can be considered "reflecting xanthophores" having the combined properties of both classical xanthophores and iridophore/leucophores.
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Affiliation(s)
- L W Oliphant
- Department of Veterinary Anatomy, College of Veterinary Medicine, University of Saskatchewan, Saskatoon
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Abstract
Stromal pigments from the irises of 28 species of birds having brightly colored eyes were extracted and analyzed. Carotenoids were present in six species and they were the sole bright pigment in only two of these. The iris pigments of the majority of the birds examined were soluble in 0.1 M NaOH and chromatographic analysis indicated they were primarily pteridines and purines. The pteridines often occurred in a crystalline state, either alone or, more commonly, in conjunction with purines.
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Affiliation(s)
- L W Oliphant
- Department of Veterinary Anatomy, Western College of Veterinary Medicine, University of Saskatchewan, Canada
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Oliphant LW, Johnson MR, Murphy C, Howland H. The musculature and pupillary response of the great horned owl iris. Exp Eye Res 1983; 37:583-95. [PMID: 6662207 DOI: 10.1016/0014-4835(83)90134-3] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
There is considerable confusion in the literature regarding the nature of the musculature of the avian iris. The most commonly held view is that both the sphincter and dilator are striated. The iris of the Great Horned Owl (Bubo virginianus) has a complex iridial musculature consisting of three circumferential components (a myoepithelium, smooth muscle and striated muscle) and two radial components (a well-developed myoepithelium and a few striated fibers). On the basis of the anatomy and relative development of these components, and a quantitative analysis of the pupillary reflex, it is proposed that the circumferential striated muscle is the primary pupillary constrictor and radial myoepithelium is the primary dilator. The annular band of smooth muscle may play an important role in maintaining pupillary size.
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