Butterfly blues and greens caused by subtractive colour mixing of carotenoids and bile pigments

Butterflies often have conspicuously patterned wings, due to pigmentary and/or structurally wing scales that cover the wing membrane. The wing membrane of several butterfly species is also pigmentary coloured, notably by the bile pigments pterobilin, pharcobilin and sarpedobilin. The absorption spectra of the bilins have bands in the ultraviolet and red wavelength range, resulting in blue-cyan colours. Here, a survey of papilionoid and nymphalid butterflies reveals that several species with wings containing bile pigments combine them with carotenoids and other short-wavelength absorbing pigments, e.g., papiliochrome II, ommochromes and flavonoids, which creates green-coloured patterns. Various uncharacterized, long-wavelength absorbing wing pigments were encountered, particularly in heliconiines. The wings thus exhibit quite variable reflectance spectra, extending the enormous pigmentary and structural colouration richness of butterflies.

Polarized iridescence of the tropical carpenter bee, Xylocopa latipes

The tropical carpenter bee, Xylocopa latipes, has metallic-reflecting, iridescent wings. The wing reflectance spectra for TE- and TM-polarized light depend on the angle of light incidence in a way characteristic for dielectric multilayers. Anatomy indicates the presence of melanin multilayers in the wing's chitinous matrix. A simple optical model of melanin multilayers explains the angle dependence of the wing reflectance spectra. The wing reflections that occur upon oblique illumination exhibit colourful and strongly polarized light patterns, which may mediate intraspecific signaling and mutual recognition by conspecifics.

Pigmentary colouration of hairy carpenter bees, genus Xylocopa

Carpenter bees can display distinct colouration patterns due to structural coloured wings and/or coloured hairs on their bodies. Females of the sexually dichromatic Xylocopa caerulea are marked by strongly blue-pigmented hairs on the head, thorax and abdomen. The thorax of female X. confusa is covered by yellow-pigmented hairs. The diffuse pigmentary colouration of the blue and yellow hairs is effectively enhanced by strongly scattering granules. The absorption spectrum of the blue pigment of X. caerulea has a maximum at 605 nm and is probably a bilin (a bile pigment). The absorption spectrum of the yellow pigment of X. confusa has a maximum at 445 nm and may be a pterin. The thoracic hairs of female X. confusa contain also a minor amount of the bilin. The reflectance spectra of the pigmented hairs suggest that the pigments are tuned to the spectral sensitivity of the bees' photoreceptors and provide spectral contrast with a green background.

Substractive colour mixing with bile pigments creates the rich wing palette of Graphium weiskei butterflies

The wings of the Purple spotted swallowtail Graphium weiskei are marked by an unusual bright colour pattern. Spectrophotometry on G. weiskei wings demonstrated the presence of a pigment with an absorption spectrum (peak wavelength λmax=676 nm), similar to that of the bile pigment sarpedobilin in the wings of the congeneric G. sarpedon (λmax=672 nm). Sarpedobilin alone causes cyan-blue wing areas, but the green-coloured areas of G. sarpedon wings result from subtractive colour mixing with the carotenoid lutein. Reflectance spectra of the blue-coloured areas of G. weiskei wings indicate that the sarpedobilin is mixed with the short-wavelength absorbing papiliochrome II. An enigmatic pigment, tentatively called weiskeipigment (λmax=580 nm) enhances the saturation of the blue colour. The weiskeipigment causes a purple colour in areas where the sarpedobilin concentration is low. The wings of the related papilionid Papilio phorcas contain the bile pigment pharcobilin (λmax=604 nm), as well as another sarpedobilin (λmax=663 nm). The cyan to greenish wings of P. phorcas are due to phorcabilin and sarpedobilin mixed with papiliochrome II. A survey of known subspecies of G. weiskei as well as of congeneric Graphium species of the 'weiskei' group shows various degrees of subtractive colour mixing of bilins and short-wavelength absorbers (carotenoids and/or papiliochromes) in their wings. This study illuminates the underestimated role of bile pigments in butterfly wing colouration.

Identification and characteristic analysis of urban vegetation spectra under different dust deposition

Urban atmospheric environmental problems have raised increasing attention in recent years. To confirm the impact of plant dust deposition capacity on urban atmosphere and spectral characteristics, this study carried out experiments in Xuhui District and Minhang District of Shanghai, and 4 common greening species were selected as research objects. In order to explore the changes in vegetation spectral characteristics, ASD FieldSpec 3 Spectrometer and 1/10000 electronic balance were used to measure the spectral data and dust data of samples. The results show as follows: (1) 380-680 nm and 750-1350 nm are the best spectral wavelengths to analyze the influence of dust deposition on spectrum. (2) The canopy reflectance spectra of tree species decrease with the increase of dust deposition, especially in the wavelength range of 750-1350 nm. (3) The first derivative and the second derivative are beneficial to observe the spectral changes and judge the position of the red edge. The red edge position of some tree species is easy to move under the interference of dust deposition. (4) Among the four tree species, the spectrum of Osmanthus fragrans is relatively undisturbed by dust deposition, and Osmanthus fragrans is a great tree species for urban greening. The research made a foundation for the future use of spectral information to estimate vegetation dust.

The wing scales of the mother-of-pearl butterfly, Protogoniomorpha parhassus, are thin film reflectors causing strong iridescence and polarization

The dorsal wings of the mother-of-pearl butterfly, Protogoniomorpha parhassus, display an angle-dependent pink, structural color. This effect is created by light interference in the lower lamina of the wing scales, which acts as an optical thin film. The scales feature extremely large windows that enhance the scale reflectance, because the upper lamina of ridges and cross-ribs is very sparse. Characteristic for thin film reflectors, the spectral shape of the reflected light strongly depends on the angle of light incidence, shifting from pink to yellow when changing the angles of illumination and observation from normal to skew, and also the degree of polarization strongly varies. The simultaneous spectral and polarization changes serve a possibly widespread, highly effective system among butterflies for intraspecific communication during flight.

Summary: The dorsal wings of the mother-of-pearl butterfly, Protogoniomorpha parhassus, show characteristics of thin film reflectors, allowing simultaneous spectral and polarization changes, which may be important in intraspecific communication.

Lamelloplasts and minichloroplasts in Begoniaceae: iridescence and photosynthetic functioning

Iridoplasts (modified plastids in adaxial epidermal cells) reported from Begonia were originally hypothesized to cause iridescence, which was broadly accepted for decades. However, several species of Begonia with iridoplasts are not iridescent causing confusion. Here chloroplast ultrastructure was observed in 40 taxa of Begoniaceae to explore the phenomenon of iridescence. However, 22 Begonias and Hillebrandia were found to have iridoplasts, but only nine display visually iridescent blue to blue-green leaves. Unexpectedly, a new type of plastid, a 'minichloroplast,' was found in the abaxial epidermal cells of all taxa, but was present in adaxial epidermal cells only if iridoplasts were absent. Comparative ultrastructural study of iridoplasts and a shading experiment of selected taxa show that a taxon with iridoplasts does not inevitably have visual iridescence, but iridescence is greatly affected by the spacing between thylakoid lamellae (stoma spacing). Thus, we propose instead the name 'lamelloplast' for plastids filled entirely with regular lamellae to avoid prejudging their function. To evaluate photosynthetic performance, chlorophyll fluorescence (F _v /F _m ) was measured separately from the chloroplasts in the adaxial epidermis and lower leaf tissues by using leaf dermal peels. Lamelloplasts and minichloroplasts have much lower photosynthetic efficiency than mesophyll chloroplasts. Nevertheless, photosynthetic proteins (psbA protein of PSII, RuBisCo and ATPase) were detected in both plastids as well as mesophyll chloroplasts in an immunogold labeling. Spectrometry revealed additional blue to blue-green peaks in visually iridescent leaves. Micro-spectrometry detected a blue peak from single blue spots in adaxial epidermal cells confirming that the color is derived from lamelloplasts. Presence of lamelloplasts or minichloroplasts is species specific and exclusive. High prevalence of lamelloplasts in Begoniaceae, including the basal clade Hillebrandia, highlights a unique evolutionary development. These new findings clarify the association between iridescence and lamelloplasts, and with implications for new directions in the study of plastid morphogenesis.