**3.3 Pigmentary coloration in animals**

Pigments are very common in insects where they are responsible of almost all yellow, orange, red, brown and blacks. A blue pigmented hue is however very rare and can mainly be obtained by bile pigments such as pterobilin, phorcabilin and sarpedobilin. The two last names are coming from the species from which they were first extracted: Papilio phorcas and Graphium sarpedon (Barbier, 1990; Vuillaume & Barbier, 1969; Choussy et al., 1975).

Light induce cyclisation in bile pigments and transforms pterobilin into phorcabilin which in turn converts to sarpedobilin. In butterflies, pterobilin is widely distributed while the phorcabilin and sarpedobilin remain rare (Barbier, 1981).

Pigmented blue are mainly seen in two genera: *Papilio* (*Papilio weiskei*, *Papilio phorcas*) and *Graphium* where almost all the species contain blue pigments. In the *Graphium* species (*G. agamemnon*, *G. doson*, *G. antiphates*, *G. sarpedon*), pterobilin is responsible of the blue coloration. In the *Graphium sarpedon*, pterobilin is located in the wing membrane. Moreover, the transparent scales of the ventral side of the wing improve this blue coloration by further diffusing and polarizing light (Stavenga et al., 2010). This situation is rare among butterflies. Generally, the coloration of the wing originates from the scales covering the wing. Pigments can be embedded in the scales, absorbing part of the visible light spectrum. Alternatively or in addition, interferences can provoke structural coloration or modify pigmentary colors, as explained in the next section.

Fig. 4. Swordtail *Graphium sarpedon*. The blue coloration comes from the bile pigment sarpedobilin.

Pigmented blue is also seen in the dull blue stripes of the *Nessaea* genus (Nimphalidae). This coloration has been attributed to pterobilin (Vane-Wright, 1979).

the leave surface cells can help absorption by increasing high angle incident light to be transmitted through the leave or by focusing light in the pigmentary region. For example, in the velvet-leaved anthurium (*Anthurium warocqueanum*), the surface cells are convexly curved to focus light at some internal distance, just onto chloroplasts area (Lee, 2007).

Pigments are very common in insects where they are responsible of almost all yellow, orange, red, brown and blacks. A blue pigmented hue is however very rare and can mainly be obtained by bile pigments such as pterobilin, phorcabilin and sarpedobilin. The two last names are coming from the species from which they were first extracted: Papilio phorcas and Graphium sarpedon (Barbier, 1990; Vuillaume & Barbier, 1969; Choussy et al., 1975).

Light induce cyclisation in bile pigments and transforms pterobilin into phorcabilin which in turn converts to sarpedobilin. In butterflies, pterobilin is widely distributed while the

Pigmented blue are mainly seen in two genera: *Papilio* (*Papilio weiskei*, *Papilio phorcas*) and *Graphium* where almost all the species contain blue pigments. In the *Graphium* species (*G. agamemnon*, *G. doson*, *G. antiphates*, *G. sarpedon*), pterobilin is responsible of the blue coloration. In the *Graphium sarpedon*, pterobilin is located in the wing membrane. Moreover, the transparent scales of the ventral side of the wing improve this blue coloration by further diffusing and polarizing light (Stavenga et al., 2010). This situation is rare among butterflies. Generally, the coloration of the wing originates from the scales covering the wing. Pigments can be embedded in the scales, absorbing part of the visible light spectrum. Alternatively or in addition, interferences can provoke structural coloration or modify pigmentary colors, as

Fig. 4. Swordtail *Graphium sarpedon*. The blue coloration comes from the bile pigment

coloration has been attributed to pterobilin (Vane-Wright, 1979).

Pigmented blue is also seen in the dull blue stripes of the *Nessaea* genus (Nimphalidae). This

**3.3 Pigmentary coloration in animals** 

explained in the next section.

sarpedobilin.

phorcabilin and sarpedobilin remain rare (Barbier, 1981).

To our knowledge, pigmented blue has not been found in mammals and in other insects. However, the presence of blue pigment remains very difficult to prove, partly because of their weak solubility. Extracting and characterizing very weakly soluble pigments is a complex task that restraints the possibilities of analysis. Moreover, determining the concentrations and localization of pigments within the tissues is still a real challenge.

Pigments in bird feathers are assumed to be present since the ages of dinosaurs. Studies on a *Sinosauropterix* (125 million years old), showed that their feathers would be filled with melanosomes and thus should appear dark (Vinther et al. 2008, Zhang et al., 2010). This work was, however, taken with cautious and discussions (Lingham-Soliar, 2011).
