Turacoverdin

Source: Wikipedia, the free encyclopedia.
The Guinea turaco's green coloration is due to the pigment turacoverdin

Turacoverdin is a unique

carotenoids.[2] 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.[3]

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 soluble in basic solutions 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.[4]

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.[4][5] 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.[6] 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.[4]

Phylogenetic evidence

The green in the wings of the northern jacana may be due to turacoverdin

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 Tauraco, and are all notable for being mostly a vivid green.[7]

Recent

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.[6]

The northern jacana, on the other hand, is a member of the order

remiges, while in all musophagid and galliform species, the pigment is found mainly in body feathers.[6]

Biological significance

Turacin and turacoverdin, being copper-based pigments, require large quantities of copper in order to be manufactured. As turacos are primarily

enzymes required to synthesize the pigments.[4]

A Knysna turaco displaying its bright colors

Although no formal tests have been performed 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.[9] 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.[10] 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.[4]

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.[11] 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.[12] 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.[4]

See also

  • Turacin, a red poryphrin pigment found almost exclusively in turacos
  • Psittacofulvin, a brightly colored pigment unique to parrots
  • Melanin, 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
  • Carotenoids, a class of pigments responsible for many of the yellow, orange and red hues found in birds, and includes:
  • bile pigment
    responsible for the bright blue eggshells of some birds

References

  1. ISBN 978-0-7167-4983-7
  2. ISBN 978-1-4262-0571-2
  3. ^ Newton, Alfred; et al. (1899), A dictionary of birds, Part 1, A. and C. Black, p. 982
  4. ^
    ISBN 978-0-674-02176-1
  5. doi:10.1098/rsta.1892.0013
    .
  6. ^
    JSTOR 4088197
    .
  7. doi:10.1111/j.1474-919x.2000.tb04441.x
    .
  8. ISBN 978-0-307-34205-8
    .
  9. doi:10.1111/j.1474-919x.1958.tb00367.x
    .
  10. ISBN 978-0-8018-8429-0
  11. ISBN 0-85199-219-6
  12. PMID 14454853
    .
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