Papiliochrome II pigment reduces the angle dependency of structural wing colouration innireusgroup papilionids

Abstract

SUMMARYThe wings of four papilionid butterfly species of the nireus group, Papilio bromius, P.epiphorbas, P.nireus and P.oribazus, are marked by blue-green coloured bands surrounded by black margins. The cover scales in the coloured bands contain a violetabsorbing, blue-fluorescing pigment. The fluorescence and absorbance spectra of the nireus group wings are very similar to those of the wings of the Japanese yellow swallowtail, Papilio xuthus, and thus the pigment is presumably papiliochromeII. The scale structures of P. xuthus are arranged irregularly, and both the fluorescence and light reflection are diffuse. In the nireus papilionids, the spatial fluorescence distribution of the scales is also diffuse, but the reflection is specular. The scales have a multilayered structure, consisting of two main laminae. We show that the papiliochromeII pigment in the upper lamina of the scales functions as a violet-blocking long-pass filter in front of the lower lamina, thus limiting the reflectance spectrum to the blue-green wavelength range. Optical modelling showed that the papiliochromeII filter effectively removes the angle dependency of the reflectance spectra -that is, it reduces the wing iridescence. The contribution of the fluorescence signal to the visual appearance is minor.

Colouration principles of nymphaline butterflies - thin films, melanin, ommochromes and wing scale stacking

“…Those scales consist of two collapsed layers, each with a thickness of about 200 nm . The same thickness value was concluded for the lower lamina of the green scales of P. nireus butterflies (Trzeciak et al, 2012;Wilts et al, 2012b). However, rather different values exist in other cases; for instance, the thickness of the lower lamina of Argyrophorus argenteus scales is 120 nm (Vukusic et al, 2009), and the small white [Pieris rapae; see fig.…”

“…The crossribs of these scales form a thick upper lamina, which contains the violet-absorbing pigment papiliochrome II. The upper lamina acts twice as an effective spectral filter for a broad-band white light beam, incident from the abwing side, which is reflected by the lower lamina, thus causing a narrow-band blue-green reflection (Trzeciak et al, 2012;Wilts et al, 2012b).…”

“…White scales may be presumed to be unpigmented, but the white scales of pierids contain leucopterin, a purely UV-absorbing pigment, whereas the yellow, orange and red scales of pierids contain the violet-and blue-absorbing xanthopterin and/or erythropterin (Kayser, 1985;Wijnen et al, 2007). The pigments of the coloured scales of papilionids contain another pigment class, the papiliochromes, derived from the precursor kynurenine (Umebachi, 1985;Wilts et al, 2012b), which is also used by nymphalids to produce 3-hydroxy-kynurenine (3-OH-kynurenine) and various ommochromes, pigments that predominantly determine their wing coloration (Nijhout, 1997;Takeuchi et al, 2005;Nijhout, 2010). In a few cases, bile pigments and carotenoids colour butterfly wings (Barbier, 1981;Stavenga et al, 2010).…”

“…The lower lamina of the scales in the blue-green bands acts as a thin film, reflecting broad-band blue light. The thick upper lamina contains the violet-absorbing pigment papiliochrome II, and thus acts as an optical band-filter, limiting the reflected light to the blue-green wavelength range (Trzeciak et al, 2012;Wilts et al, 2012b). In the opposite way, in several pierid butterflies, in the short-wavelength range, where the wing pigments strongly absorb, ridge interference reflectors contribute to the reflectance (Rutowski et al, 2005;Stavenga et al, 2006).…”

How does the blue-ringed octopus (Hapalochlaena lunulata) flash its blue rings?

“…Morpho butterflies, for example, use their wings to give a blue iridescent warning flash that deters predators (Young, 1971) and there are other examples of birds and butterflies pairing iridescent colors with dark pigmented colors to maximize contrast (e.g. Frith and Beehler, 1998;Stavenga et al, 2004;Wilts et al, 2012). Cephalopod skin, in particular that of cuttlefish and octopus, is highly elastic and muscular, lending these animals the unique ability to give their skin 3-dimensional texture for camouflage and signaling (Hanlon, 2007).…”