Colour in the eyes of insects

Many insect species have darkly coloured eyes, but distinct colours or patterns are frequently featured. A number of exemplary cases of flies and butterflies are discussed to illustrate our present knowledge of the physical basis of eye colours, their functional background, and the implications for insect colour vision. The screening pigments in the pigment cells commonly determine the eye colour. The red screening pigments of fly eyes and the dorsal eye regions of dragonflies allow stray light to photochemically restore photoconverted visual pigments. A similar role is played by yellow pigment granules inside the photoreceptor cells which function as a light-controlling pupil. Most insect eyes contain black screening pigments which prevent stray light to produce background noise in the photoreceptors. The eyes of tabanid flies are marked by strong metallic colours, due to multilayers in the corneal facet lenses. The corneal multilayers in the gold-green eyes of the deer fly Chrysops relictus reduce the lens transmission in the orange-green, thus narrowing the sensitivity spectrum of photoreceptors having a green absorbing rhodopsin. The tapetum in the eyes of butterflies probably enhances the spectral sensitivity of proximal long-wavelength photoreceptors. Pigment granules lining the rhabdom fine-tune the sensitivity spectra.     

Rhabdom changes in the shrimp,Palaemonetes

The fine structure of the principal compound eye of the shrimp, Palaemonetes, was studied under conditions of light and dark adaptation. Ommatidium the situation in other decapod crustaceans. Light and dark adapted eyes differ in that the rhabdom changes its shape; morphological evidence suggests a possible sequence of events involving production, utilization, and degradation of photoreceptor membrane, a discontinuous process occurring only during changes from light to dark and dark to light. A hypothesis of membrane turnover is proposed.     

不同波长光照对三疣梭子蟹复眼超微结构的影响

三疣梭子蟹(Portunus tritubereulatus)经过30 min暗适应后,在不同波长的红光(750 nm),黄光(580 nm),绿光(560 nm),蓝光(400 nm)下,其光感受器形态和超微结构随不同波长光的适应而发生变化。在红光下感杆束直径大,微绒毛排列最整齐,内质网、线粒体等胞器较多,色素颗粒分布均匀,膜下储泡囊小;在蓝光下感杆束直径最小,微绒毛最凌乱,多囊体、板膜体、膜下储泡囊等胞器较多,色素颗粒位于细胞核周围。     

Intensity and polarization of the eyeshine in butterflies

The compound eyes of most diurnal butterflies have a reflecting tapetum below the retina. Light that enters the eye is guided down the rhabdom, reflected by the tapetum, and then guided back up the rhabdom. The light that is not absorbed by the rhabdom is reemitted and gives rise to an eyeshine. We have measured the fraction of the incident light that is re-emitted, and also the degree to which this light retains its original polarization. The following conclusions are drawn:

Interspecific variations in the morphology and ultrastructure of the rhabdoms of oplophorid shrimps

Interspecific variations in rhabdom structure between various oplophorid shrimps are described and the differences are related to the light environment at different depths within the mesopelagic zone. The ultrastructure of the distal rhabdom in these species is described for the first time. Quantitative measurements show that the proportion of the rhabdom layer occupied by the distal rhabdom varies from 3.5-25% in the dorsoventral plane of the eye of Systellaspis debilis. The distal rhabdom occupies less than 1% of the rhabdoms in the eye of Acanthephyra pelagica, where it can only be seen by using the electron microscope. It is suggested that the rhabdoms of those species that remain within the photic zone (such as S. debilis) are adapted to maximize contrast, whereas in those whose depth ranges extend into the aphotic zone (such as A. pelagica) they are adapted for maximum sensitivity.     

Superposition optics and the time of flight in onitine dung beetles

Dung beetles fly to fresh dung, with vision essential for flight navigation. The daily period of flight varies among different species: some beetles fly only in sunlight, others only when ambient light levels change rapidly during dusk or dawn and others in the constant dark of night. Measurements of the optical properties of the lenses, eye geometry and photoreceptor dimensions were used in a computer ray-tracing model to determine the optical performance of the superposition eyes of nine species of onitine dung beetles. Eye sensitivity to light is determined mainly by body size, by the refractive-index parameters and size of the crystalline cones, and by the photoreceptor dimensions. Based on the optics of the ommatidial lenses and absorption of light in the retina, the most sensitive eyes, found in the crepuscular-nocturnal beetles, are 85 times or nearly two log units more sensitive than the eyes of the diurnal beetles. Three possible criteria are considered to determine the best position for the retina: maximum amount of light absorbed in the target rhabdom; maximum amount of light falling on the target rhabdom (best focus); and maximum resolution. The structure and physiological optics of the superposition compound eyes of an onitine dung beetle are matched to the range of light intensities at which it flies. Accepted: 4 February 1998     

Involvement of ethylene in the abscission of flowers and petals of Leptospermum scoparium

The growth of cotyledons and primary leaves of I-day-old Sinapis alba L. plants were studied under various light conditions and action spectra produced. For both responses blue and red light are most effective and a strong fluence rate dependency can be observed. The red light effect appears to be mediated through phytochrome, that of blue light being due to a separate blue light receptor, although this receptor requires the presence of far-red absorbing phytochrome (P_fr) in order to be effective.     

The effect of light quality on the induction of efficient photosynthesis under low CO2 conditions in Chlamydomonas reinhardtii and Chlorella pyrenoidosa

The effect of blue and red light on the adaptation to low CO₂ conditions was studied in high-CO₂ grown cultures of Chlorella Pyrenoidosa (82T) and Chlamydomonas reinhardtii(137⁺) by measuring O₂ exchange under various inorganic carbon (Cⁱ) concentrations. At equal photosynthetic photon flux density (PPFD), blue light was more favourable for adaptation in both species, compared to red light. The difference in photosynthetic oxygen evolution between cells adapted to low C_iunder blue and red light was more pronounced when oxygen evolution was measured under low C_i compared to high C_i conditions. The effect of light quality on adaptation remained for several hours. The different effects caused by blue and red light was observed in C. pyrenoidosa over a wide range of PPFD with increasing differences at increasing PPFD. The maximal difference was obtained at a PPFD above 1 500 μmol m^?2s^?1. We found no difference in the extracellular carbonic anhydrase activity between blue- and red light adapted cells. The light quality effect recorded under C_i-limiting conditions in C. reinhardtii cells adapted to air, was only 37% less when instead of pure blue light red light containing 12.5% of blue light (similar PPFD as blue light) was used during adaptation to low carbon. This indicates that in addition to affecting photosynthesis, blue light affected a sensory system involved in algal adaptation to low C_i conditions. Since the affinity for C_i of C. Pyrenoidosa and C. reinhardtii cells adapted to air under blue light was higher than that of cells adapted under red light, we suggest that induction of some component(s) of the C_i accumulating mechanism is regulated by the light quality.     

Spectral sensitivity of the cod,Gadus morhua L.

The spectral sensitivity of the cod was determined under both dark adapted and light adapted conditions in the laboratory. Cod were trained by cardiac conditioning to detect a difference in radiance between an image of spots and the background radiance of a screen. Thresholds for this response were measured for a range of different wavelengths, and expressed as quantum adjusted values. Electroretino‐graphic studies were also performed on the eyes of cod, and spectral sensitivity curves prepared. Under dark adapted conditions both the behavioural and e.r.g. derived curves showed greatest sensitivity in the blue/green at 490 nm, matching the absorption curve for rhodopsin. A secondary peak in the behaviourally derived curve in the green/yellow at 550 nm indicated that a population of yellow cones may be implicated with the rods in scotopic vision. Under light adapted conditions the behavioural curves showed a shift to the blue, perhaps indicating an adaption to the high red content of the illuminating source. The e.r.g. curve showed greatest sensitivity to blue/green, as in the scotopic experiments but with an enhanced response at 550 nm, indicating greater cone activity. It is suggested that there is complex interaction between rods and cones in the cod retina, both types of receptor being active over a wide range of light intensities.     

Diminution and enlargement of the mosquito rhabdom in light and darkness

The rhabdoms of the larval ocelli of the mosquito Aedes aegypti undergo morphological light and dark adaptation over periods of hours. The rhabdom enlarges during dark adaptation and grows smaller during light adaptation. Diminution is exponential, enlargement linear, and rates of change are proportional to log light intensity. Rhabdoms maintained at a constant intensity level off at a constant volume proportional to log intensity. We argue that changes in rhabdom volume after changes in light intensity reflect an influence of light on the turnover of photoreceptro membrane, and that the volumes at which rhabdoms level off represent equilibria between opposed processes of membrane loss and renewal.     

Vision in hydrothermal vent shrimp

Bresiliid shrimp from hydrothermal vents on the Mid-Atlantic Ridge have non-imaging eyes adapted for photodetection in light environments of very low intensity. Comparison of retinal structures between both vent shrimp and surface-dwelling shrimp with imaging eyes, and between juvenile and adult vent shrimp, suggests that vent shrimp have evolved from ancestors that lived in a light environment with bright cyclic lighting. Whether the vent shrimp live in swarms and have large dorsal eyes or live in sparse groupings and have large anterior eyes, the basic retinal adaptations are the same across species. Retinal adaptations in adult vent shrimp include the loss of dioptrics, enlargement of both the rhabdomeral segment of the photoreceptors and the light-sensitive rhabdomere therein, attenuation of the arhabdomeral segment of the photoreceptors, reduction of black screening pigment, development of a white diffusing layer behind the photoreceptors, and the loss of rhabdom turnover.     

Degeneration of the compound eye of the termite Neotermes jouteli (Isoptera) in darkness during the phase of reproduction

Summary Long-term light deprivation of the royal pair of Neotermes jouteli during the phase of reproduction leads to a dramatic change in the organization within the compound eye. In a swarming alate, investigated with scanning and transmission electron microscopy, the eye consists of about 200 ommatidia. No differences between male and female eyes are observed. Each ommatidium is composed of a biconvex cornea, a cone of the eucone type, and a rhabdom which is located directly beneath the Semper cells. The rhabdom consists of eight rhabdomeres which are fused along the ommatidial axis. In the central part of the compound eye the rhabdom measures roughly 20 m in length. Concealed life of the imagines causes a dismantling of the cone and the rhabdom until complete destruction. This is accompanied by an increase in the number of pigment granules and a decrease in the number of mitochondria.     

Larval and adult eye of the Western Rock Lobster (Panulirus longipes)

A number of differences exists between the compound eyes of larval and adult rock lobsters, Panulirus longipes. The larval eye more closely resembles the apposition type of compound eye, in which retinula cells and rhabdom lie immediately below the cone cells. The adult eye, on the other hand, is a typical clear-zone photoreceptor in which cones and retinula cell layers are separated by a wide transparent region. The rhabdom of the larval eye, if cut longitudinally, exhibits a "banded" structure over its entire length; in the adult the banded part is confined to the distal end, and the rhabdom is tiered. Both eyes have in common an eighth, distally-located retinula cell, which possesses orthogonally-oriented microvilli, and a peculiar lens-shaped "crystal", which appears to focus light onto the narrow column of the distal rhabdom. Migration of screening pigment on dark-light adaptation is accompanied by changes in sensitivity and resolution of the eye. Retinula cells belonging to one ommatidium do not arrange into one single bundle of axons, but interweave with axons of four neighbouring facets in an extraordinarily regular fashion.     

Light induction of the Euglena chloroplast protein synthesis elongation factors: relative effectiveness of different wavelength ranges

The abilities of different wavelength ranges of light to promote the increase in the activities of the Euglena chloroplast protein synthesis elongation factors (EFs) during chloroplast biogenesis have been determined. Blue light was far more effective than either green light or red light in increasing the level of chloroplast EF-G, a nuclear encoded gene product. This observation suggests that the induction of EF-Gchl is under the control of the blue photoreceptor that has been identified in Euglena. Blue light was also the most effective wavelength range in facilitating the increase in EF-Ts, a nuclear gene product, and EF-Tu, a chloroplast gene product. However, red light and surprisingly green light were also effective. These results are not consistent with either of the known blue or blue/red photoreceptor systems in Euglena being the sole component involved in the light induction of these two factors and suggest that a green photoresponse may also be important in the development of the chloroplast. The specific activity of the Euglena mitochondrial protein biosynthetic translocase (EF-Gmt) decreased in cells exposed to light. Blue light caused an immediate decline in EF-Gmt activity; whereas, there was a temporal delay in the decrease in EF-Gmt activity when cells were exposed to either red or green light.     

Blue, red and blue plus red light control of chloroplast pigment and pigment-proteins in corn mesophyll cells: Irradiance level-quality interaction

Corn ( Zea mays L. cv. OP Golden Bantum) was grown under low irradiance blue, red or blue plus red light. Red was more effective than blue light for synthesis of Chl a, b and light-harvesting proteins (LHC-2) associated with photosystem 2(PS2). Blue light was slightly more effective for synthesis of light-harvesting proteins (LHC-1) associated with photosystem 1 (PS1), but below a fluence rate of 1 μmol m⁻² s⁻¹ the response to blue vs that to red depended on irradiance level. Blue light containing a small amount of red light was as effective as red light for Chl a and b synthesis, but no more effective than blue light for LHC-2 synthesis. Adding small amounts of blue light to red repressed the effect of red light on LHC-2 synthesis and produced irradiance response curves similar to those produced by blue alone for LHC-2 synthesis. This repression by blue light depended on the ratio of red to blue and the level of the blue light.     

Fine structure of the compound eye of Porcellio scaber in light and dark adaption.

The compound eyes of the terrestrial isopod Porcellio scaber comprises about 20 ommatidia. The dioptric apparatus of each ommatidia includes a biconvex corneal lens and a spherical crystalline cone that is secreted by two cone cells. The closed rhabdom is formed by the microvillar extensions of seven pigmented retinula cells and one apical eccentric cell. All retinular axons exit the eye in one bundle. During dark-adaption pigment granules in the retinula cells rapidly withdrew from around the rhabdom and the cell periphery, and migrated basally. Rhabdoms thickened because of movement of the microvilli, and mitochondria moved medially and basally. During light adaption these processes were reversed. Multivesicular bodies became less numerous and rough endoplasmic reticulum and ribosomes proliferated during the initial stages of light adaption.     

Photoreceptor spectral sensitivities of the Small White butterfly <Emphasis Type="Italic">Pieris rapae crucivora</Emphasis> interpreted with optical modeling

The compound eye of the Small White butterfly, Pieris rapae crucivora, has four classes of visual pigments, with peak absorption in the ultraviolet, violet, blue and green, but electrophysiological recordings yielded eight photoreceptors classes: an ultraviolet, violet, blue, double-peaked blue, green, blue-suppressed-green, pale-red and deep-red class. These photoreceptor classes were identified in three types of ommatidia, distinguishable by the different eye shine spectra and fluorescence; the latter only being present in the eyes of males. We present here two slightly different optical models that incorporate the various visual pigments, the light-filtering actions of the fluorescent, pale-red and deep-red screening pigment, located inside or adjacent to the rhabdom, and the reflectance spectrum of the tapetum that abuts the rhabdom proximally. The models serve to explain the photoreceptor spectral sensitivities as well as the eye shine.     

Insect pupil mechanisms

Summary The hypothesis that the glow observable in dark adapted butterfly eyes is extinguished upon light adaptation by the action of migrating retinula cell pigment granules (Stavenga, 1975a) has been investigated. Experimental procedures applying optical methods to intact, living animals were similar to those used previously to investigate the migration of retinula cell pigment granules in Hymenoptera (Stavenga and Kuiper, 1977). The data obtained from nymphalid butterflies and Hymenoptera show close parallels, favouring the pigment migration hypothesis.The retinula cell pigment granules control the light flux in the butterfly rhabdom and hence are part of a pupil mechanism. The range of action of this pupil mechanism is about 3 log units of light intensity. The speed of pupil closure is slowed down with longer dark adaptation times. The way in which pupil processes can be distinguished from photochemical processes of the visual pigment is discussed.     

LED不同光质对萝卜愈伤组织诱导、增殖和萝卜硫素含量的影响

以白水萝卜无菌苗及其愈伤组织为实验材料,研究其在LED白、红、黄、蓝、绿和蓝红6种光质下的愈伤诱导和增殖。结果表明：LED不同光质下胚轴愈伤组织的诱导效应不同,诱导率顺序依次为黄光〉红光〉蓝红光〉白光〉蓝光〉绿光;蓝光、黄光和红光有利于子叶愈伤组织的诱导;子叶诱导愈伤组织的效果较下胚轴好;LED红光下愈伤组织的增殖倍数和萝卜硫素含量均为最高。     

A comparison between the larval eyes of the dimly luminescent Keroplatus nipponicus and the brightly luminescent Arachnocampa luminosa (Diptera; Keroplatidae)

Larvae of the weakly blue‐luminescent fungus gnat Keroplatus nipponicus possess on either side of their heads a small black stemmatal eye with a plano‐convex lens approximately 25 μm in diameter. In total, 12–14 retinula cells give rise to a centrally fused rhabdom of up to 8 μm in diameter. The rhabdom's constituent microvilli, approximately 70 nm in width, are roughly orthogonally oriented, a requirement for polarization sensitivity. Screening pigment granules are abundant in the retinula cells and measure at least 1 μm in diameter. In comparison with the stemmatal eye of the brightly luminescent Arachnocampa luminosa, that of K. nipponicus is considerably smaller with a poorer developed lens and a rhabdom that is less voluminous, but possesses wider microvilli. Although the larval eye of K. nipponicus can be expected to be functional, as the larvae react to light with a behavioural response, the eyes are probably mainly involved in the detection of ambient light levels and not, as in A. luminosa, also in responding to the luminescence of nearby conspecifics.