Blue Iridescence Research Articles

Hyperspectral optical imaging of two different species of lepidoptera

In this article, we report a hyperspectral optical imaging application for measurement of the reflectance spectra of photonic structures that produce structural colors with high spatial resolution. The measurement of the spectral reflectance function is exemplified in the butterfly wings of two different species of Lepidoptera: the blue iridescence reflected by the nymphalid Morpho didius and the green iridescence of the papilionid Papilio palinurus. Color coordinates from reflectance spectra were calculated taking into account human spectral sensitivity. For each butterfly wing, the observed color is described by a characteristic color map in the chromaticity diagram and spreads over a limited volume in the color space. The results suggest that variability in the reflectance spectra is correlated with different random arrangements in the spatial distribution of the scales that cover the wing membranes. Hyperspectral optical imaging opens new ways for the non-invasive study and classification of different forms of irregularity in structural colors.

Iridescent hindwing patches in the Pipevine Swallowtail: differences in dorsal and ventral surfaces relate to signal function and context

Summary 1. Iridescent colour signals are directional but, like diffusely reflected colours, vary within and among species in ways that may be adaptations to specific types of receivers in specific light environments. 2. The hindwings of pipevine swallowtail butterflies exhibit brilliant blue and iridescent colour patches on the ventral surface in both sexes and on the dorsal wing surface in males. Evidence suggests that the ventral iridescent blue is a component of the warning coloration of this distasteful species, while the dorsal blue iridescent wing area is a sexual signal. Given differences in the function and ecological context of signal production, we analysed reflectance spectra from the iridescent blue areas of both field‐caught and laboratory‐reared animals to test several predictions about the iridescent colour patches on these wing surfaces. 3. The ventral blue patches in the warning coloration of males and females should be most visible early and late in the day, due to wing orientation relative to sun angle. We therefore predicted that these iridescent colour patches would be brighter and of longer wavelengths than the male dorsal blue patch displayed during midday courtships. The prediction about reflectance intensity was supported but the prediction about hue was not. 4. We predicted that the sexually selected dorsal hindwing iridescence of males would be more variable among individuals and condition dependent than the naturally selected ventral iridescent colour patches. To assess variation and condition dependence, laboratory‐reared and field‐captured individuals were compared. The prediction about variation was not supported, but only the dorsal wing surfaces showed evidence of being condition dependent. 5. We investigated whether development of dorsal and ventral blue iridescence was coupled by determining correlations in colour properties between the wing surfaces. Our finding of positive correlations indicated a potential developmental constraint in the evolution of colour differences between the two wing surfaces. 6. Results of this study suggest that some properties of iridescent coloration on the hindwing of the pipevine swallowtail (especially intensity) may have been fine‐tuned by evolution in response to prevailing ambient light conditions and viewing perspectives that differ among types of signal receivers.

Function of blue iridescence in tropical understorey plants

The blue colouration seen in the leaves of Selaginella willdenowii is shown to be iridescent. Transmission electron microscopy studies confirm the presence of a layered lamellar structure of the upper cuticle of iridescent leaves. Modelling of these multi-layer structures suggests that they are responsible for the blue iridescence, confirming the link between the observed lamellae and the recorded optical properties. Comparison of blue and green leaves from the same plant indicates that the loss of the blue iridescence corresponds to a loss of the multi-layer structure. The results reported here do not support the idea that iridescence in plants acts to enhance light capture of photosynthetically important wavelengths. The reflectance of light in the range 600-700 nm is very similar for both iridescent and non-iridescent leaves. However, owing to the occurrence of blue colouration in a wide variety of shade dwelling plants it is probable that this iridescence has some adaptive benefit. Possible adaptive advantages of the blue iridescence in these plants are discussed.

Austrolebias paucisquama (Cyprinodontiformes: Rivulidae), a new species of annual killifish from southern Brazil

Austrolebias paucisquama is described from the rio Vacacaí drainage, a tributary to the rio Jacuí, Rio Grande do Sul, Brazil. The new species belongs to the Austrolebias alexandri species-group, by sharing the apomorphic bright blue iridescence and dark gray pectoral fins in males. It is distinguished from other species of this group by having fewer scales around caudal peduncle (12) and fewer dorsal-fin rays in males (17-21). The lack of contact organs on the inner surface of the pectoral fin in males and the color pattern of females - ground color light brownish, sides of body with a variable number of relatively large dark black spots distributed mostly on posterior portion of body - distinguish A. paucisquama from all other species of the genus.

Malleable skin coloration in cephalopods: selective reflectance, transmission and absorbance of light by chromatophores and iridophores

Nature's best-known example of colorful, changeable, and diverse skin patterning is found in cephalopods. Color and pattern changes in squid skin are mediated by the action of thousands of pigmented chromatophore organs in combination with subjacent light-reflecting iridophore cells. Chromatophores (brown, red, yellow pigment) are innervated directly by the brain and can quickly expand and retract over underlying iridophore cells (red, orange, yellow, green, blue iridescence). Here, we present the first spectral account of the colors that are produced by the interaction between chromatophores and iridophores in squid (Loligo pealeii). Using a spectrometer, we have acquired highly focused reflectance measurements of chromatophores, iridophores, and the quality and quantity of light reflected when both interact. Results indicate that the light reflected from iridophores can be filtered by the chromatophores, enhancing their appearance. We have also measured polarization aspects of iridophores and chromatophores and show that, whereas structurally reflecting iridophores polarize light at certain angles, pigmentary chromatophores do not. We have further measured the reflectance change that iridophores undergo during physiological activity, from "off" to various degrees of "on", revealing specifically the way that colors shift from the longer end (infra-red and red) to the shorter (blue) end of the spectrum. By demonstrating that three color classes of pigments, combined with a single type of reflective cell, produce colors that envelop the whole of the visible spectrum, this study provides an insight into the optical mechanisms employed by the elaborate skin of cephalopods to give the extreme diversity that enables their dynamic camouflage and signaling.

Natural layer-by-layer photonic structure in the squamae ofHoplia coerulea(Coleoptera)

The microscopic structure of the hard external parts of the body of the iridescent blue-violet chaffer beetle Hoplia coerulea is studied using scanning electron microscopy. The blue iridescence is shown to originate from the structure of the squamae within scales covering the dorsal side of the beetle. The internal structure of the scales shows a stack of planar sheets, separated by a well-organized network of spacers, a structure which belongs to the family of the layer-by-layer photonic crystals. The blue iridescence is easily explained by a planar multilayer approximation model, deduced from the observed three-dimensional structure.

Morphological and Molecular Characterization of a Cypovirus ( Reoviridae ) from the Mosquito Uranotaenia sapphirina (Diptera: Culicidae)

A novel cypovirus has been isolated from the mosquito Uranotaenia sapphirina (UsCPV) and shown to cause a chronic infection confined to the cytoplasm of epithelial cells of the gastric ceca and posterior stomach. The production of large numbers of virions and inclusion bodies and their arrangement into paracrystalline arrays gives the gut of infected insects a distinctive blue iridescence. The virions, which were examined by electron microscopy, are icosahedral (55 to 65 nm in diameter) with a central core that is surrounded by a single capsid layer. They are usually packaged individually within cubic inclusion bodies (polyhedra, approximately 100 nm across), although two to eight virus particles were sometimes occluded together. The virus was experimentally transmitted per os to several mosquito species. The transmission rate was enhanced by the presence of magnesium ions but was inhibited by calcium ions. Most of the infected larvae survived to adulthood, and the adults retained the infection. Electrophoretic analysis of the UsCPV genome segments (using 1% agarose gels) generated a migration pattern (electropherotype) that is different from those of the 16 Cypovirus species already recognized. UsCPV genome segment 10 (Seg-10) showed no significant nucleotide sequence similarity to the corresponding segment of the other cypoviruses that have previously been analyzed, and it has different "conserved" termini. A BLAST search of the UsCPV deduced amino acid sequence also showed little similarity to Antheraea mylitta CPV-4 (67 of 290 [23%]) or Choristoneura fumiferana CPV-16 (33 of 111 [29%]). We conclude that UsCPV should be recognized as a member of a new Cypovirus species (Cypovirus 17, strain UsCPV-17).

Spectral imaging, reflectivity measurements, and modeling of iridescent butterfly scale structures

An innovative device for spectral imaging and reflectivity measurements is developed to study iridescent butterfly scales. Of par- ticular interest is the bright blue Morpho menelaus butterfly. The device called the microscale reflectance spectrometer (MicroRS) is used to measure spectral reflectivity for the M. menelaus between 400 and 900 nm. Different optical effects such as thin-film interference, scattering, and diffraction are examined in an attempt to understand the microstructure of an M. menelaus iridescent butterfly scale. The MicroRS apparatus uses a modified microscope and CCD camera to examine spectral re- flectivity of areas as small as 0.348 30.348 mm 2 . Some individual fea- tures of an M. menelaus scale are found to be of the same order of magnitude or smaller than the resolution of the MicroRS device. As a result, individual pixel analysis is used to determine only that the scale structure produced high reflectivity, 40 to 70%, between 450 and 550 nm and very low reflectivity, less than 8%, above 600 nm. An average reflec- tivity over a larger area is taken, resulting in a peak of 68% at 500 nm. This explains the bright blue iridescence seen from the M. menelaus wing. Results are used in conjunction with a thin-film numerical program to develop a complex model of the butterfly scale structure. The structure includes 24 alternating layers of chitin and air. A complex combination of an effective index of refraction and effective area model is used to match the reflectivity of an M. menelaus butterfly scale. © 2001 Society of Photo-

Colour mixing in wing scales of a butterfly.

Green coloration in the animal kingdom, as seen in birds' feathers and reptile integument, is often an additive mixture of structurally effected blue and pigmentary yellow1. Here we investigate the origin of the bright green coloration of the wing scales of the Indonesian male Papilio palinurus butterfly, the microstructure of which generates an extraordinary combination of both yellow and blue iridescence. The dual colour arises from a modulation imposed on the multilayer, producing the blue component as a result of a previously undiscovered retro-reflection process.

Confined blue iridescence by a diffracting microstructure: an optical investigation of the Cynandra opis butterfly

When illuminated and viewed along certain well-defined directions, segments on the wings of the butterfly Cynandra opis shows a striking violet-blue to blue-green. We quantify the spectral and the directional properties of these areas of the wings of the insect. Electron microscopy shows that wing scales from these iridescent regions of the wings contain two gratinglike microstructures crossed at right angles. Application of the diffraction theory, as formulated by the Stratton-Silver-Chu integral, to the microstructure can explain all the important features observed experimentally.

An iridescent virus fromPopillia japonica (Col.: Scarabaeidae)

A very low incidence (<0.01%) of a blue iridovirus (IV) was found in larvae of the Japanese beetle,Popillia japonica Newman, that were sampled over a two year period on Terceira Island (Azores, Portugal). In the most heavily infected larvae, a deep blue iridescence was observed, particularly in the fat body. Transmission electron microscopy revealed the characteristic crystalline arrays of the hexagonal virus particles in the cytoplasm of fat body cells, tracheal matrix, muscle, hypodermis and blood cells. Crystals of the virus particles were also observed freely circulating in the hemolymph. The average diameter of negatively stained purified virus particles was 157 nm. Similarities and differences with other IVs found in the Scarabaeidae are discussed. Considering the broad host range of some of the iridescent viruses, the relatively recent invasion of Terceira byP. japonica, and the rarity of the virus in the beetle, it is probable that the infection was the result of transmission from another species of soil-inhabiting arthropod. Its value as a potential biological control agent ofP. japonica is negligible.

Iridescence: a useful criterion to sort gametophytes from sporophytes in the red algaChondrus crispus

Carrageenan analyses ofChondrus crispus Stackhouse from Brittany, France, showed that the iridescent fronds always were kappa-carrageenan dominant and that the non-iridescent ones were lambda-carrageenan dominant, whatever their sizes and their vegetative or reproductive stages. Evidence is presented that the blue iridescence is independent of both the morphology of the fronds and their ecological situation (shelter, exposure). It is suggested that iridescence might be used to sort rapidly the kappa-carrageenan containingChondrus crispus (gametophytes) from the lambda-carrageenan containing ones (tetrasporophytes).

Covert iridovirus infection of blackfly larvae

Iridovirus infections are typically isolated at extremely low frequencies from invertebrate species in moist or aquatic habitats. Crystalline arrangements of virus particles in heavily infected tissues cause an iridescent hue obvious to the naked eye; diagnosis of iridovirus infection has traditionally occurred when the host appeared bright lilac or blue. Evidence is presented here to show that there are two forms of iridovirus infection in larval blackfly (Diptera: Simuliidae) populations: (i) the classical patent form which causes larvae to develop blue iridescence before death; and (ii) a covert (inapparent) form which is not lethal. Patent infections are extremely rare in Simulium populations from the River Ystwyth, Wales ( ca . 1 in 10 6 ). However, a large proportion of the population harbours the disease without obvious symptoms. Covert iridovirus infection was shown by using two techniques. First, tissue homogenates from 8 out of 30 apparently healthy Simulium larvae produced patent iridovirus infections when injected into a permissive lepidopteran host species. The DNA restriction profiles from these covert isolates showed very close similarities in fragment pattern and variability to isolates causing patent infections in the same River Ystwyth populations. Second, the presence of iridovirus DNA in host tissues was confirmed by using the polymerase chain reaction (PCR) targeted at the iridovirus major structural protein gene. The frequency of PCR-positive larvae taken from the River Ystwyth in April 1992 varied between 17% and 37%, depending on site.

Physical and Ultrastructural Basis of Blue Leaf Iridescence in Two Neotropical Ferns

Physical and Ultrastructural Basis of Blue Leaf Iridescence in Two Neotropical Ferns

Laurencia iridescens sp. nov. (Rhodomelaceae, Ceramiales) from the Caribbean Sea

Laurencia iridescens sp. nov. (Rhodophyta), a repent species, described from Guadeloupe (French West Indies) and Puerto Rico, is distinguished by the following set of characters: a perpendicular arrangement of its tetrasporangia, the presence of secondary pit connections between epidermal cells, the highly concrescent axes displaying a brilliant blue iridescence, and the absence of both ‘corps en cerise’ in the cortical cells and lenticular thickenings in the walls of the medullary cells.

Ultrastructural Basis and Developmental Control of Blue Iridescence in Selaginella Leaves

The iridescent blue color of several Selaginella species is caused by a physical effect, thin-film interference. Predictions for a model film have been confirmed by electron microscopy of S. willdenowii and S. uncinata. For the latter species iridescence contributes to leaf absorption at wavelengths above 450 nm and develops in environments enriched with far-red (730 nm) light. This evidence supports the involvement of phytochrome in the developmental control of iridescence.

Blue fleck corneal iridescence: an occasional feature of Cogan's microcystic corneal dystrophy.

Flecks consisting of brilliant reflective blue dots and streaks were a prominent biomicroscopical feature in three patients with Cogan's microcystic corneal dystrophy. Two patients required epithelial debridement. We used the material obtained to investigate their histology and ultrastructure. A subepithelial accumulation of basement membrane-like material composed of ultrastructurally fine granules was deposited in alternating layers of compaction and rarefaction. The layers lie mostly parallel to the anterior corneal surface, but in some places they are folded. Such foldings are possibly the sites of multilaminar reflection and constructive interference, giving rise to the blue iridescence.

THE IDENTITY OF IRIDOMYRMEX PURPUREUS FORM VIRIDIAENEUS VIEHMEYER (HYMENOPTERA: FORMICIDAE)

AbstractIn the past 2 dark‐coloured forms of the meat ant, Iridomyrmex purpureus (F. Smith), occurring in arid and semi‐arid areas of Australia have been confused under the name viridiueneus Viehmeyer. This name properly applies only to a form in which the workers are dark brown to black with green and pinkish violet iridescence. The other form, distinguished by blue iridescence, is undescribed.

Chemical Evidence for Exsolution in a Labradorite

The plagioclase feldspars are important constituents and genetic indicators in most metamorphic and plutonic rocks. Complete solid solution exists between the end members, albite (Ab), NaAlSi3O8 and anorthite (An), CaAl2SiO8 at high temperatures, but considerable evidence has been accumulated for the presence of limited solid solubility at the low temperatures representative of near-equilibrium conditions in plutonic and metamorphic rocks. Electron microscopic investigations of specimens of various bulk compositions show lamellar textures a few tens to hundreds of nm in thickness indicative of exsolution (phase separation) into two phases. In addition, doubled X-ray and electron diffraction spots have been obtained from samples in the composition ranges An2-An15 (known as peristerites)1−5 and An67–An83 (the bytownites)6–9. The characteristic faint blue iridescence or “schiller” displayed by peristerites was shown to be the result of Bragg diffraction of light from the boundaries between the two phases10. Similar but more intense colours covering the whole visible spectrum are produced by labradorites (An42-An58) from coarsely crystalline anorthosites11 and this has led to speculations about the existence of “reflecting planes”12 and hence the possibility of a solubility gap13 similar to that which occurs in the peristerite and bytownite composition fields.

Crystals in the lens.

Crystal formation in the lens in both the young and the aged has been reported by various observers from time to time. The morphology and the chemical nature of the crystals are also of varied nature; for example, Goulden12and other observers have described crystalline opacities in the lens showing green and blue iridescence in morbid conditions such as thyroid dysfunction, postoperative tetany, mongolian idiocy, and myotonia atrophica. Vogt26as mentioned by Parker22has described a spear cataract consisting of shiny crystalline needles. Riad24has reported a pedigree with lens crystals which looked like tiny broken glass fragments, rectangular in shape, with a notch at one corner. Verhoeff reported a case in which protein crystals produced the picture of coralliform cataract.30Among the varied chemical constituents of the crystals, cholesterol is frequently found in different types of senile, traumatic, and complicated cataracts. The spear cataract