Daily changes of structure,function and rhodopsin content in the compound eye of the crabHemigrapsus sanguineus

The compound eye of the crab hemigrapsus sanguineus undergoes daily changes in morphology as determined by light and electron microscopy, both in the quantity of chromophore substances studied by HPLC and in visual sensitivity as shown by electrophysiological techniques. 1. At a temperature of 20 degrees C, the rhabdom occupation ratio (ROR) of an ommatidial retinula was 11.6% (maximum) at midnight, 8.0 times larger than the minimum value at midday (1.4%). 2. Observations by freeze-fracture revealed that the densities of intra-membranous particles (9-11 nm in diameter) of rhabdomeric membrane were ca. 2000/microns 2 and ca. 3000/microns 2 for night and daytime compound eyes, respectively. 3. Screening pigment granules migrated longitudinally and aggregated at night, but dispersed during the day. Reflecting pigment granules migrate transversally in the proximal half of the reticula layer i.e. cytoplasmic extensions containing reflecting pigment granules squeeze between neighbouring retinula cells causing optical isolation (Fig. 4). Thus the screening pigment granules within the retinula cells show longitudinal migration and radial movement so that the daytime rhabdoms are closely surrounded by the pigment granules. 4. At 20 degrees C, the total amount of chromophore of the visual pigment (11-cis and all-trans-retinal) was 1.4 times larger at night than during the day i.e. 46.6 pmol/eye at midnight and 33.2 pmol/eye at midday. Calculations of the total surface area of rhabdomeric membrane, total number of intra-membranous particles in rhabdomeric membrane and the total number of chromophore molecules in a compound eye, indicate that a considerable amount of chromophore-protein complex exists outside the rhabdom during the day. 5. The change in rhabdom size and quantity of chromophore were highly dependent on temperature. At 10 degrees C both rhabdom size and amount of chromophore stayed close to daytime levels throughout the 24 hours. 6. The intracellularly determined relative sensitivity of the dark adapted night eye to a point source of light was about twice as high as the dark-adapted day eye. Most of the increase in the sensitivity is attributed primarily to the effect of reflecting pigment migration around the basement membrane and, secondarily, to the changes in the amount and properties of the photoreceptive membrane. The results form the basis of a detailed discussion as to how an apposition eye can function possibly as a night-eye.     

The nauplius eye complex in 'conchostracans'(Crustacea, Branchiopoda: Laevicaudata, Spinicaudata, Cyclestherida) and its phylogenetic implications

The nauplius eye in Cyclestherida, Laevicaudata and Spinicaudata (previously collectively termed Conchostraca) consists of four cups of inverse sensory cells separated by a pigment layer and a tapetum layer. There are two lateral and two medial cups, a ventral medial cup and a posterior medial cup. The pigment and tapetum layers contain two different kinds of pigment granules, the inner pigment layer relatively large, dark (and electron dense) granules, and the outer tapetum layer light, reflective pigment granules. The presence of four cups and two different kinds of pigment granules are interpreted as autapomorphies of Phyllopoda. The position and shape of the nauplius eye in Spinicaudata is very distinct and herein interpreted as an autapomorphy of this taxon.Additional frontal eyes might be present dorsally or ventrally in varying proximity to the nauplius eye, but they have separate nerves from their sensory cells to the nauplius eye centre in the protocerebrum. Rhabdomeric structures are present in all these frontal eyes, evidencing their light sensitivity. In Lynceus biformis and L. tatei (Laevicaudata), two pairs of frontal eyes were found. In Cyclestheria hislopi (Cyclestherida), an unpaired ventral frontal eye is present. We did not find additional frontal eyes in Limnadopsis parvispinus and Caenestheriella sp. (Spinicaudata).     

夜蛾复眼转化速度与光暗适应的时间关系

夜行蛾类的复眼,随光、暗适应时间而逐步转化,这种转化是可逆的.以屏蔽色素分布范围的大小为指标来判断复眼的转化速度得以下结果:1.从亮眼到暗眼:亮眼进入暗适应后其屏蔽色素随暗适应时间的增加而逐步向远心端方向集中.屏蔽色素的移动是减速进行的.暗适应开始后的前3分钟,每分钟移动百分率为10.7,当暗到10—15分钟时每分钟移动百分率为4.6,再暗到60—150分钟时每分钟移动百分率为0.7.屏蔽色素移动的速度个体间差异较大,完成全过程大多数个体需150分钟,少数个体只需60分钟,另有个别个体经过270分钟暗适应仍尚未完成全过程.2.从暗眼到亮眼:暗眼受光后,其屏蔽色素随光适应时间的增加而向近心端方向扩散,色素移动速度随时间的增加而减缓.转化全过程约需60分钟.     

黑翅土白蚁有翅成虫复眼的形态结构

采用组织切片法光镜下观察黑翅土白蚁Odontotermes formosanus(Shiraki)有翅成虫的复眼形态结构及光、暗适应条件下色素颗粒移动的规律。结果如下:(1)头正前方观,复眼外部形态略呈圆形。(2)有翅成虫复眼类型属于并列像眼,每只复眼约由360个小眼组成。(3)每个小眼是由1套屈光器(1个角膜和1个晶锥)、小网膜色素细胞、视杆和基细胞等几部分组成。小网膜色素细胞内均含有丰富的色素颗粒。(4)在光适应条件状态下,屈光器及视杆周围的色素颗粒主要分布在视杆部位的上侧,暗度适应条件状态时则较均匀地分布于视杆两侧上下;性别对色素颗粒分布无明显影响。     

Investigations of pigment granule transport systems in Gonodactylus oerstedii (Crustacea: Hoplocarida: Stomatopoda)

Compound eyes of the stomatopod, Gonodactylus oerstedii, exhibit pupillary reflection responses which arise from migration of retinular cell pigment granules. In the light, reflectance from the eye increases as pigment granules accumulate around light-sensitive rhabdoms and scatter incoming light back out of the eye (pupillary closure). At dark onset, reflectance diminishes as pigment granules disperse centrifugally, enhancing photon capture by the rhabdom. We investigated the mechanisms of the pupillary response in intact animals by measuring reflectance from the eye under different temperature conditions. Lowering the temperature from 27° to 7 °C caused an increase in reflectance of infrared light in the absence of visible-light stimuli, indicating pupillary closure. When given light stimuli as temperature decreased, the eye continued to produce reflection increases which decreased in amplitude as the between stimulus reflectance level increased. All low-temperature effects were reversed when temperature was increased to normal. The rate of pupillary closure was insensitive to temperature, with a temperature quotient (Q₁₀) of 0.8 ± 0.1 s.e.m, while pupillary opening was extremely temperature sensitive (Q₁₀ of 5.4 ± 0.4). Different temperature sensitivities for pupillary opening and closing suggest that these processes involve different mechanisms.Abbreviations IOP intracelllular optical physiology - Q₁₀ temperature quotient     

The effects of hypophysectomy on the retinomotor responses of the killifish, Fundulus heteroclitus

This paper presents the results of an investigation concerned with the effects of long-term hypophysectomy on the retinomotor responses of the euryhaline killifish, Fundulus heteroclitus: 1. The eye of hypophysectomised Fundulus heteroclitus responds to light and dark in the same manner as that of intact controls: the retina is not in a state of permanent light-adaptation as claimed by Vilter (1942) for the hypophysectomised eel. 2. There is no evidence of a persistent circadian rhythm during continous darkness. 3. Unilateral illumination of the eye of intact fish results in dispersion of retinal pigment in both illuminated and unilluminated eyes, as in the goldfish (Ali, 1964), but no such contralateral response was evident after hypophysectomy. The cones are unresponsive.     

Eye color pigment granules in Drosophila mauritiana: mosaics produced by excision of a transposable element

Compound eyes of the white-peach (wpch) mutant strain of Drosophila mauritiana have some pigment and receptor cells with wild-type eye color pigmentation. These eyes are mosaic, because excision of a transposable element reverts wpch to wild type during the development of somatic cells. Wild-type patches have three types of pigment granule residing in three respective cell types: primary pigment cells, secondary pigment cells, and retinula (visual receptor) cells. Most aspects of these granules, as well as all other aspects of compound eye ultrastructure, are exactly as in the better studied sibling species D. melanogaster. In the wpch parts of the eye, small and giant unpigmented "pigment granules" reside in secondary pigment cells. These white granules are just like the corresponding granules of w mutant D. melanogaster. Small vs. large patches of pigmented cells likely represent excision events occurring late vs. early respectively during development. Mosaics of eye color markers have been important in developmental analyses; the ease of constructing mosaics of D. mauritiana gives this preparation advantages for mosaic analyses.     

Effects of energy deprivation on the fly pupil mechanism: evidence for a rigor state

The energy dependence of the pupil pigment-migrations in the fly Musca domestica was studied in live animals, using optical techniques and nitrogen-gas induced anoxia. The results obtained can be summarized in 3 points:

1. Energy deficiency can make the pupil mechanism stop in any state, extreme or intermediate.
2. Anoxia induced during intermittent stimulation makes the pupil stop in the closed state (aggregated pigment granules).
3. During long-term anoxia the pupil very slowly opens (dispersal of pigment granules), irrespective of ambient intensity.

The slow anoxic opening (point 3) is more than 1000 times slower than that predicted for free diffusion of pigment granules in water. Assuming realistic values of cytoplasm viscosity, this implies that anoxia causes the pigment granules to attach to rigid structures in the cells, in analogy with the rigor state in anoxic muscles. The rigor phenomenon in the pupil mechanism prevents experimental discrimination between active and passive processes of pigment migration. Normal pupil opening has a time course which agrees reasonably with a passive diffusion process, but it is argued that an active transportation of granules away from the rhabdom is more likely in the dark adapted eye.     

Physiological colour changes in Odonata eyes. A comparison between eye and epidermal chromatophore pigment migrations

Pigment migration in the eyes of Austrolestes annulosus and Ischnura heterosticta cause pronounced colour changes which superficially resemble those of Odonata epidermal chromatophores. In both species, the migratory pigment is confined to the distal pigment cells of dorsal ommatidia. When the pigment is concentrated around the base of the crystalline cones, a dense layer of Tyndall blue bodies produce bright ‘blue phase’ colours. Distal migration of the pigment disrupts the Tyndall effect and produces ‘dark phase’ (grey-brown) colours. As in chromatophores, eye pigments consist of a mixture of xanthommatin and dihydroxanthommatin together with an additional pigment, possibly ommin A, not found in chromatophores.As with chromatophores, eye pigments respond to change in temperature only, change in light intensity having no effect. The change from blue to dark phase (at 8°C) occurs at the same rate as in chromatophores, whereas the reverse change (at 20°C) is significantly slower. Equilibrium colours at constant temperature are variable but significantly different from those of chromatophores at 12°C and above. There is no diurnal variation in responsiveness as is found in chromatophores.Isolated dark phase eyes or undamaged pieces of eye are able to change to blue phase after temperature increase. Isolated blue phase eyes show little response to temperature decrease, isolated undamaged pieces show no response. A temperature difference between the eyes of the same intact insect may result in minor colour differences. Ablation of the optic tract or of tissue posterior to the optic tract prevents normal colour change from blue to dark phase. The above results indicate that eye pigment cells are structurally similar to Odonata chromatophores and are under similar environmental and physiological control.     

Studies on the Relation between the Pigment Migration and the Sensitivity Changes during Dark Adaptation in Diurnal and Nocturnal Lepidoptera

The functional significance of the pigment migration in the compound insect eye during dark adaptation has been studied in diurnal and nocturnal Lepidoptera. Measurements of the photomechanical changes were made on sections of eyes which had been dark-adapted for varying periods of time. In some experiments the sensitivity changes during dark adaptation were first determined before the eye was placed in the fixation solution. No change in the position of the retinal pigment occurred in Cerapteryx graminis until the eye had been dark-adapted for about 5 minutes. The start of the migration was accompanied by the appearance of a break in the dark adaptation curve. During longer periods of dark adaptation the outward movement of the pigment proceeded in parallel with the change in sensitivity, the migration as well as the adaptive process being completed within about 30 minutes. In the diurnal insects chosen for the present study (Erebia, Argynnis) the positional changes of the retinal pigment were insignificant in comparison with the movement of the distal pigment in Cerapteryx graminis. On the basis of these observations the tentative hypothesis is put forward that the second phase of adaptive change in nocturnal Lepidoptera is mediated by the migration of the retinal pigment while the first phase is assumed to be produced by the resynthesis of some photochemical substance. In diurnal insects which have no appreciable pigment migration the biochemical events alone appear to be responsible for the increase in sensitivity during dark adaptation.     

Quantitative Studies on Pigment Migration and Light Sensitivity in the Compound Eye at Different Light Intensities

Comparative electrophysiological and histological studies were made on the functional significance of the secondary iris pigment migration for the sensitivity of the eye in the noctuid moth Cerapteryx graminis. The pigment position at different adapting light intensities was studied as well as the influence of different positions on the sensitivity of the eye. Adapting light intensities above a certain value hold the pigment in light position. At a 3 log units lower intensity the pigment is brought into dark position and at light intensities between these limiting values the pigment attains intermediate positions. The results indicate that at light intensities between the limiting values the pigment shifts closely follow the changes in intensity of the environmental light. With the pigment in dark position the eye is about 1000 times more sensitive than when the pigment is in light position, there being a close relationship between the sensitivity of the eye and the position of the pigment at intermediate positions.     

The physical and morphological properties of the pigment screen in the compound eye of a shrimp (Crustacea)

Summary The pigment cells of the compound eye of the shrimps (Crangon crangon andC. allmani) were studied by electron microscopy (SEM and TEM) and microspectrophotometry. The compound eyes of these species contain light-absorbing and -reflecting pigments contained in granules, located in 5 different cells. The light absorbing pigment granules (light screen) are situated in (1) the distal pigment cells, (2) the retinular cells, (3) the basal pigment cells. The reflecting pigment granules are located in (4) the distal, and (5) the proximal reflecting pigment cells. Another innominate cell type investing the ommatidia contains vacuoles without pigment content. The innominate cell type, and the basal absorbing pigment cell (3) listed above, have not earlier been reported for a crustacean species. Measurements of the spectral absorption on sliced and squashed ommatidia show that all components of the light screen have an increased absorption in the wavelength regions 400–450 nm and 530–570 nm, probably due to xanthommatin and ommin. The spectral absorbancy of the reflecting pigment cells were not determined. Similar cells in other species are known to contain pteridines.We thank Prof. Dr. Langer, Bochum, Germany, for his kind help. The work was supported by funds from the Karolinska Institutet to Doc. G. Struwe, and grant NFR No. 2760-007 to Doc. R. Elofsson.     

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.     

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.     

Light-adapting migration of the screening-pigment in crayfish photoreceptors is a two-stage movement comprising an all-or-nothing initial phase

The light-adapting response of the screening-pigment in crayfish retinal photoreceptors, previously described as a monophasic movement, was found to consist of two stages with different properties: (1) a rapid initial expansion that once started proceeds for at least half of the full distance, and (2) a slower and more variable continuation of the movement. The two components were resolved in isolated eyes stimulated under conditions expected to restrict Na+ influx into the photoreceptors. Only the second stage of the response to light was inhibited when Na+ was substituted with choline, or if the normal saline contained amiloride, a diuretic that hinders Na+ entry across many cell membranes. Amiloride in a medium without Na+ delayed, but did not curb, the first stage, whereas the rest of the movement was markedly restrained. Partial replacement of Na+ with Li+ blocked the second stage without affecting the rapid initial shift triggered by light. Exposure of dark-adapted eyes to high Na+ levels or to ouabain in the presence of Na+ in the dark also elicited a two-staged pigment dispersion to the light-adapted position. Low Na+ concentrations or amiloride affected the latency, but not the rate or extent, of the first stage of migration in ouabain-treated eyes. Consistent though less significant results were obtained with cyanide and the Na+ ionophore monensin. These observations suggest a differential control of pigment position over two defined domains along the photoreceptors, probably to integrate a double mechanism of light-adaptation: an all-or-nothing partial shift of the pigment screen as a safety factor against overexposure, followed by a regulated adjustment according to stimulation intensity.     

Ultrastructural evidence for the origin of the subretinal pigment shield in the compound eye of Drosophila melanogaster

Little morphological information is available about subretinal pigment shields in insect compound eyes, especially ultrastructural information. The latter is however needed in order to detect possible smallest projections that emanate from pigment-granule-bearing cells and pass through the basal matrix (BM), but that are not visible in light micrographs. Previous work on the subretinal pigment shield in Drosophila melanogaster suggests that the pigment cell population located below the BM is closely associated with secondary and tertiary pigment cells. Whether these cells stay in connection throughout life with the subretinal regions via thin projections that pass through the fenestrae of the BM, or whether the subretinal parts later become separated during eye development remained so far unknown. Our investigation of the periphery of the BM by three-dimensional reconstruction based on serial-sectioning transmission electron microscopy has revealed that the secondary and tertiary pigment cells possess thin projections that pass through the fenestrae of the BM and thus connect the cellular regions above and below the BM in the adult compound eye. The subretinal pigment shield of D. melanogaster is therefore of retinal origin and is not composed of additional subretinal pigment cells. The maintained bond allows the active displacement of pigment granules below the BM during the process of dark and light adaptation of the compound eye.     

Calcium-activated Myosin V closes the Drosophila pupil

Approximately 40 years ago, an elegant automatic-gain control was revealed in compound eye photoreceptors: In bright light, an assembly of small pigment granules migrates to the cytoplasmic face of the photosensitive membrane organelle, the rhabdomere, where they attenuate waveguide propagation along the rhabdomere. This migration results in a "longitudinal pupil" that reduces rhodopsin exposure by a factor of 0.8 log units. Light-induced elevation of cytosolic free Ca(2+) triggers the migration of pigment granules, and pigment granules fail to migrate in a mutant deficient in photoactivated TRP calcium channels. However, the mechanism that moves photoreceptor pigment granules remains elusive. Are the granules actively pulled toward the rhabdomere upon light, or are they instead actively pulled into the cytoplasm in the absence of light? Here we show that Ca(2+)-activated Myosin V (MyoV) pulls pigment granules to the rhabdomere. Thus, one of MyoV's several functions is also as a sensory-adaptation motor. In vitro, Ca(2+) both activates and inhibits MyoV motility; in vivo, its role is undetermined. This first demonstration of an in vivo role for Ca(2+) in MyoV activity shows that in Drosophila photoreceptors, Ca(2+) stimulates MyoV motility.     

The eyes of Macrosoma sp. (Lepidoptera: Hedyloidea): a nocturnal butterfly with superposition optics

The visual system of nocturnal Hedyloidea butterflies was investigated for the first time, using light and electron microscopy. This study was undertaken to determine whether hedylids possess the classic superposition eye design characteristic of most moths, or apposition eyes of true butterflies (Papilionoidea), and, to gain insights into the sensory ecology of the Hedyloidea. We show that Macrosoma heliconiaria possesses a superposition-type visual mechanism, characterized by long cylindrical crystalline cones, a lack of corneal processes, 8 constricted retinular sense cells, rhabdoms separated from the crystalline cones forming a translucent 'clear zone', and tight networks of trachea that form a tapetum proximal to the retina and which also surround the rhabdoms to form a tracheal sheath. Dark-adapted individuals of M. heliconiaria, M. conifera, and M. rubidinarea exhibited distal retinular pigment migration, forming an eye glow. Correspondingly, light-exposure induced pigment to migrate proximally, causing the eye glow to be replaced by a dark pseudopupil. Other characteristics of the visual system, including relative eye size, facet size, and external morphology of the optic lobes, are mostly 'moth like' and correlate with an active, nocturnal lifestyle. The results are discussed in relation to the evolution of lepidopteran eyes, and the sensory ecology of this poorly understood butterfly superfamily.