Turacoverdin
Encyclopedia
Turacoverdin is a unique copper
uroporphyrin
pigment
responsible for the bright green coloration of several bird
s of the family Musophagidae
, most notably the turaco. It is chemically related to turacin
, a red pigment also found almost exclusively in turacos. Turacoverdin is one of the only true green pigments found in birds, as the coloration that appears in most green feather
s is due to the unique properties of blue structural coloration in combination with yellow carotenoids. Turacoverdin and turacin were the first ever chemically characterized feather pigments, and turacoverdin was first isolated and described in 1882 by Dr. C.F.W. Krukenberg.
in basic
solution
s than its chemical cousin turacin. While originally thought to contain little copper by its discoverer, who instead believed it to be iron
-based, later spectroscopic
analysis demonstrated high copper (and low iron) content in pigment from the green feathers of the Knysna Turaco
and the Schalow's Turaco
. Moreau also demonstrated that the green coloration of turacos might actually be due to the combined effect of two different turacoverdin pigments that differ slightly in polarity
.
When extracted and exposed to light, oxygen, or strong bases, turacin has been shown to take on a green hue. This has caused several researchers to suggest that turacoverdin may be an oxidized
metabolite
of turacin. This has been supported by data comparing the absorption bands of the "altered turacin" with those of turacoverdin, which are shown to be very similar to one another. Several researchers have noted the chemical similarities between turacin and turacoverdin. This relationship has been supported by spectral properties, the fact that both pigments contain copper, their similar microscopic arrangement in feather cells, and the co-occurrence of the pigments: turacin and turacoverdin are always found together in the same species, and in many cases are also found in the same plumage
locations. The green appearance of turacoverdin can be derived from its absorbance curve, which peaks at blue wavelengths and in the long-wave range above yellow. Turacoverdin shows little UV reflectance.
, and are all notable for being mostly a vivid green.
Recent spectrophotometric
evidence suggests that turacoverdin may be closely related or identical to green pigments in the feathers of the Northern Jacana
(Jacana spinosa), the Blood Pheasant
(Ithaginis cruentus), and the Crested Wood-partridge (Rollulus rouloul). As Ithaginis and Rollulus are members of the order Galliformes
, this has led some researchers to assume support for a turacoverdin-bearing common ancestor of Musophagidae and Galliformes, making the presence of the pigment a symplesiomorphy
for these groups. The pigment data specifically suggests that turacos evolved from a group of galliform species, which is represented by the extant genera Ithaginis and Rollolus. Based on the appearance of its green feathers, researcher Jan Dyck speculates that Rollolus is closer to a possible ancestor than Ithaginis.
The Northern Jacana, on the other hand, is a member of the order Charadriiformes
, a group clearly not closely related to either Musophagidae or Galliformes. This makes it highly unlikely that turacoverdin in Jacana reflects common ancestry with either turacos or galliforms. If the green pigment in Jacana is truly turacoverdin, then the pigment must have evolved independently in this order. This is further supported by the fact that the pigment in Jacana is located only in the remiges, while in all musophagid and galliform species, the pigment is found mainly in body feathers.
s, flower
s, bud
s, and other plant matter. Church and Moreau estimated that 3 months' worth of fruit intake contribute to producing the pigment present in the newly grown plumage of the turaco species T. corythaix (the Knysna Turaco). It has also been observed that it takes young turacos around a year to acquire their colorful adult plumage, and some authors have speculated that they probably need that long to acquire the necessary copper. It has also been noted that turacos all live across Central Africa
, which corresponds geographically with one of the world's richest copperbelts. It is unknown whether turaco diets are especially rich in copper as compared to the diets of other birds, or whether turacos are especially effective at extracting copper from their foods. It is also unknown whether turaco species lacking turacin and turacoverdin-induced pigmentation have a comparatively copper-deficient diet, absorb less copper from their diet, or lack the enzymes required to synthesize the pigments.
Although no formal tests have been preformed investigating the functional significance of turacoverdin coloration, speculation abounds. Moreau in 1958 observed that turaco species inhabiting forests are more likely to be green in color than species inhabiting other environments, which may offer concealment from predators. In fact, it has been observed that the greener and denser a turaco's forest habitat, the deeper green its plumage, while non-forest-dwelling turaco species tend to be devoid of the green pigment. This claim has not been studied rigorously from a biochemical or phylogenetic
perspective, however, and awaits further research. Turacos may employ their unique green coloration for sexual or social advertisement, but again no spectrophotometric or biochemical studies have been conducted to test for sex differences
in coloration, and to limited human perception there appears to be none.
Other authors speculate that turacos and other birds employing the use of turacoverdin may derive a physiological and biochemical benefit from synthesizing the pigment. Copper, like porphyrins, can be damaging to birds when accumulated at high concentrations. Turacos may detoxify the high levels of copper ingested in a diet rich with porphyrins, thereby advertising the protection they've granted themselves by depositing the copper-rich pigments in their feathers. It also may be of some biological significance that turacos all seem to be pigmented with turacin and turacoverdin in exactly the same regions of the wing feathers.
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
uroporphyrin
Porphyrin
Porphyrins are a group of organic compounds, many naturally occurring. One of the best-known porphyrins is heme, the pigment in red blood cells; heme is a cofactor of the protein hemoglobin. Porphyrins are heterocyclic macrocycles composed of four modified pyrrole subunits interconnected at...
pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
responsible for the bright green coloration of several bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s of the family Musophagidae
Turaco
The turacos make up the bird family Musophagidae , which includes plantain-eaters and go-away-birds. In southern Africa both turacos and go-away-birds are commonly known as louries. They are semi-zygodactylous - the fourth toe can be switched back and forth...
, most notably the turaco. It is chemically related to turacin
Turacin
Turacin is a naturally occurring red pigment that is 6% copper complexed to uroporphyrin 111. Arthur Herbert Church discovered turacin in 1869.It is found only in the bird family Musophagidae, the turacos...
, a red pigment also found almost exclusively in turacos. Turacoverdin is one of the only true green pigments found in birds, as the coloration that appears in most green feather
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
s is due to the unique properties of blue structural coloration in combination with yellow carotenoids. Turacoverdin and turacin were the first ever chemically characterized feather pigments, and turacoverdin was first isolated and described in 1882 by Dr. C.F.W. Krukenberg.
Chemical properties
Few studies into the chemical nature of turacoverdin have been performed to date. Research by R.E. Moreau in the 1950s showed it to be less solubleSolubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...
in basic
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
s than its chemical cousin turacin. While originally thought to contain little copper by its discoverer, who instead believed it to be iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
-based, later spectroscopic
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
analysis demonstrated high copper (and low iron) content in pigment from the green feathers of the Knysna Turaco
Knysna Turaco
The Knysna Turaco , or, in South Africa, Knysna Lourie, is a large turaco, one of a group of African near-passerine birds. It is a resident breeder in the mature evergreen forests of southern and eastern South Africa, and Swaziland. It was formerly sometimes considered to be a subspecies of the...
and the Schalow's Turaco
Schalow's Turaco
The Schalow's Turaco is a frugivorous bird in the Musophagidae family. It is named after Herman Schalow. Mature birds have, on average, the longest crests of any turaco species....
. Moreau also demonstrated that the green coloration of turacos might actually be due to the combined effect of two different turacoverdin pigments that differ slightly in polarity
Polarity
In physics, polarity is a description of an attribute, typically a binary attribute , or a vector . For example:* An electric charge has a polarity of either positive or negative....
.
When extracted and exposed to light, oxygen, or strong bases, turacin has been shown to take on a green hue. This has caused several researchers to suggest that turacoverdin may be an oxidized
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
metabolite
Metabolite
Metabolites are the intermediates and products of metabolism. The term metabolite is usually restricted to small molecules. A primary metabolite is directly involved in normal growth, development, and reproduction. Alcohol is an example of a primary metabolite produced in large-scale by industrial...
of turacin. This has been supported by data comparing the absorption bands of the "altered turacin" with those of turacoverdin, which are shown to be very similar to one another. Several researchers have noted the chemical similarities between turacin and turacoverdin. This relationship has been supported by spectral properties, the fact that both pigments contain copper, their similar microscopic arrangement in feather cells, and the co-occurrence of the pigments: turacin and turacoverdin are always found together in the same species, and in many cases are also found in the same plumage
Plumage
Plumage refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage vary between species and subspecies and can also vary between different age classes, sexes, and season. Within species there can also be a...
locations. The green appearance of turacoverdin can be derived from its absorbance curve, which peaks at blue wavelengths and in the long-wave range above yellow. Turacoverdin shows little UV reflectance.
Phylogenetic evidence
Turacin and turacoverdin are both found in four of the six genera of turacos. The subfamily Criniferinae is typically regarded as being devoid of the brighter pigments, although the genus Corythaeola does have a small stripe of turacoverdin on its breast. The remaining turaco genera are placed in the subfamily Musophaginae and are referred to as the turacin-bearing turacos. More than half of turaco species belong to the genus TauracoTauraco
Tauraco is a genus of turacos. It contains the "typical" or green turacos; though their plumage is not always green all over, the presence of significant amounts of turacoverdin-colored plumage generally sets Turaco species apart from other Musophagidae...
, and are all notable for being mostly a vivid green.
Recent spectrophotometric
Spectrophotometry
In chemistry, spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength...
evidence suggests that turacoverdin may be closely related or identical to green pigments in the feathers of the Northern Jacana
Northern Jacana
The Northern Jacana or Northern Jaçana is a wader which is a resident breeder from coastal Mexico to western Panama, and on Cuba, Jamaica and Hispaniola. It sometimes breeds in Texas, USA, and has also been recorded on several occasions as a vagrant in Arizona...
(Jacana spinosa), the Blood Pheasant
Blood Pheasant
The Blood Pheasant is the only species in genus Ithaginis of the pheasant family. This relatively small, short-tailed pheasant is widespread and fairly common in northern Southasia...
(Ithaginis cruentus), and the Crested Wood-partridge (Rollulus rouloul). As Ithaginis and Rollulus are members of the order Galliformes
Galliformes
Galliformes are an order of heavy-bodied ground-feeding domestic or game bird, containing turkey, grouse, chicken, New and Old World Quail, ptarmigan, partridge, pheasant, and the Cracidae. Common names are gamefowl or gamebirds, landfowl, gallinaceous birds or galliforms...
, this has led some researchers to assume support for a turacoverdin-bearing common ancestor of Musophagidae and Galliformes, making the presence of the pigment a symplesiomorphy
Symplesiomorphy
In cladistics, a symplesiomorphy or symplesiomorphic character is a trait which is shared between two or more taxa, but which is also shared with other taxa which have an earlier last common ancestor with the taxa under consideration...
for these groups. The pigment data specifically suggests that turacos evolved from a group of galliform species, which is represented by the extant genera Ithaginis and Rollolus. Based on the appearance of its green feathers, researcher Jan Dyck speculates that Rollolus is closer to a possible ancestor than Ithaginis.
The Northern Jacana, on the other hand, is a member of the order Charadriiformes
Charadriiformes
Charadriiformes is a diverse order of small to medium-large birds. It includes about 350 species and has members in all parts of the world. Most Charadriiformes live near water and eat invertebrates or other small animals; however, some are pelagic , some occupy deserts and a few are found in thick...
, a group clearly not closely related to either Musophagidae or Galliformes. This makes it highly unlikely that turacoverdin in Jacana reflects common ancestry with either turacos or galliforms. If the green pigment in Jacana is truly turacoverdin, then the pigment must have evolved independently in this order. This is further supported by the fact that the pigment in Jacana is located only in the remiges, while in all musophagid and galliform species, the pigment is found mainly in body feathers.
Biological significance
Turacin and turacoverdin, being copper-based pigments, require large quantities of copper in order to be manufactured. As turacos are primarily arboreal species, they are able to accumulate copper through a diet rich in fruitFruit
In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...
s, flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
s, bud
Bud
In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of the stem. Once formed, a bud may remain for some time in a dormant condition, or it may form a shoot immediately. Buds may be specialized to develop flowers or short shoots, or may have...
s, and other plant matter. Church and Moreau estimated that 3 months' worth of fruit intake contribute to producing the pigment present in the newly grown plumage of the turaco species T. corythaix (the Knysna Turaco). It has also been observed that it takes young turacos around a year to acquire their colorful adult plumage, and some authors have speculated that they probably need that long to acquire the necessary copper. It has also been noted that turacos all live across Central Africa
Central Africa
Central Africa is a core region of the African continent which includes Burundi, the Central African Republic, Chad, the Democratic Republic of the Congo, and Rwanda....
, which corresponds geographically with one of the world's richest copperbelts. It is unknown whether turaco diets are especially rich in copper as compared to the diets of other birds, or whether turacos are especially effective at extracting copper from their foods. It is also unknown whether turaco species lacking turacin and turacoverdin-induced pigmentation have a comparatively copper-deficient diet, absorb less copper from their diet, or lack the enzymes required to synthesize the pigments.
Although no formal tests have been preformed investigating the functional significance of turacoverdin coloration, speculation abounds. Moreau in 1958 observed that turaco species inhabiting forests are more likely to be green in color than species inhabiting other environments, which may offer concealment from predators. In fact, it has been observed that the greener and denser a turaco's forest habitat, the deeper green its plumage, while non-forest-dwelling turaco species tend to be devoid of the green pigment. This claim has not been studied rigorously from a biochemical or phylogenetic
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
perspective, however, and awaits further research. Turacos may employ their unique green coloration for sexual or social advertisement, but again no spectrophotometric or biochemical studies have been conducted to test for sex differences
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
in coloration, and to limited human perception there appears to be none.
Other authors speculate that turacos and other birds employing the use of turacoverdin may derive a physiological and biochemical benefit from synthesizing the pigment. Copper, like porphyrins, can be damaging to birds when accumulated at high concentrations. Turacos may detoxify the high levels of copper ingested in a diet rich with porphyrins, thereby advertising the protection they've granted themselves by depositing the copper-rich pigments in their feathers. It also may be of some biological significance that turacos all seem to be pigmented with turacin and turacoverdin in exactly the same regions of the wing feathers.
See also
- TuracinTuracinTuracin is a naturally occurring red pigment that is 6% copper complexed to uroporphyrin 111. Arthur Herbert Church discovered turacin in 1869.It is found only in the bird family Musophagidae, the turacos...
, a red poryphrin pigment found almost exclusively in turacos - PsittacofulvinPsittacofulvinPsittacofulvin pigments cause the bright-red, orange, and yellow colours of parrots. Colourful feathers with high levels of psittacofulvin resist feather-degrading Bacillus licheniformis better than white ones....
, a brightly colored pigment unique to parrotParrotParrots, also known as psittacines , are birds of the roughly 372 species in 86 genera that make up the order Psittaciformes, found in most tropical and subtropical regions. The order is subdivided into three families: the Psittacidae , the Cacatuidae and the Strigopidae...
s - MelaninMelaninMelanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...
, a class of pigments responsible for a large range of coloration in many animal groups, and includes:- Phaeomelanin, a melanin pigment responsible for many russet, brown and tan hues in feathers
- Eumelanin, a melanin pigment responsible for the deep black common to flight feathers
- CarotenoidCarotenoidCarotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...
s, a class of pigments responsible for many of the yellow, orange and red hues found in birds, and includes:- AstaxanthinAstaxanthinAstaxanthin is a carotenoid. It belongs to a larger class of phytochemicals known as terpenes. It is classified as a xanthophyll, which means "yellow leaves". Like many carotenoids, it is a colorful, lipid-soluble pigment. Astaxanthin is found in microalgae, yeast, salmon, trout, krill, shrimp,...
, a red carotenoid pigment - RhodoxanthinRhodoxanthinRhodoxanthin is a xanthophyll pigment with a purple color that is found in small quantities in a variety plants including Taxus baccata. It is also found in the feathers of some birds...
, a purple-red carotenoid pigment - CanthaxanthinCanthaxanthinCanthaxanthin is a carotenoid pigment widely distributed in nature. Carotenoids belong to a larger class of phytochemicals known as terpenoids. The chemical formula of canthaxanthin is C40H52O2. It has E number E161g and is approved for use in the EU and USA however it is not approved for usage in...
, an orange-red carotenoid pigment - LuteinLuteinLutein is a xanthophyll and one of 600 known naturally occurring carotenoids. Lutein is synthesized only by plants and like other xanthophylls is found in high quantities in green leafy vegetables such as spinach and kale...
, a bright yellow carotenoid pigment
- Astaxanthin
- BiliverdinBiliverdinBiliverdin is a green tetrapyrrolic bile pigment, and is a product of heme catabolism. It is the pigment responsible for a greenish color sometimes seen in bruises.- Metabolism :...
, a blue bile pigment responsible for the bright blue eggshells of some birds