Sexual Dimorphism in the Compound Eye of Rhagophthalmus ohbai (Coleoptera: Rhagophthalmidae): I. Morphology and Ultrastructure

The eyes of the winged males and larvi-form, wingless females of the firefly Rhagophthalmus ohbai differ from each other in several respects. Compared with the eyes of the males, those of the females contain fewer (35 versus ca. 3500) and smaller (20 μm versus 24-31 μm) facets and anatomically they are of the apposition type. Their main function appears to be to detect light intensity changes from day to nighttime; resolving power of the female eye must be poor and e-vector discrimination would be absent. The eyes of the males consist of a smaller, dorsal region of ca. 500 om-matidia of about 250 μm length and a larger, ventral region of ca. 2000 ommatidia of about 640 urn length. The microvilli of the dorsal eye region are somewhat wider than those of the ventral region (55 nm versus 45 nm) and are less regularly arranged. A tapetal reflecting layer is only present in the dorsal eye region. The small clear-zone between dioptric apparatus and retina in the dorsal eye region would not allow as good a superposition image to be produced as in the ventral eye region with its 5 times wider clear-zone. The regular orientations of the microvilli in the rhabdoms and the lack of a proper tapetum in the ventral eye region suggest that e-vector discrimination should be possible.     

UV photoreceptors in the compound eye of Daphnia magna (Crustacea,Branchiopoda). A fourth spectral class in single ommatidia

Summary The spectral sensitivities of individually stimulated ommatidia in the compound eye of Daphnia magna were measured using a fast spectral scan voltage-clamp technique with extracellular recording. Chromatic adaptation was used to reveal the contributions of individual spectral classes of photoreceptors to the ommatidial sensitivity. Ommatidia in the dorsal and ventral regions of the compound eye were tested. Four spectral classes of photoreceptors were found in each ommatidium, among them a previously undetected class with peak sensitivity in the ultraviolet. The wavelengths of peak sensitivity were at 348, 434, 525, and 608 nm for the dorsal ommatidia. The three longer wavelength classes agreed well with those found previously by intracellular recording (Schehr 1984). Only small differences in wavelength and magnitude of peak sensitivity were found between the four classes in the dorsal versus ventral ommatidia.     

Spectral efficiency of the glasshouse whitefly Trialeurodes vaporariorum and Encarsia formosa its hymenopteran parasitoid

Using the electroretinogram (ERG) technique the spectral efficiency of the compound eye of the glasshouse whitefly Trialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae) and its main parasitoid Encarsia formosa (Gahan) (Hymenoptera: Aphelinidae) was measured at selected wavelengths between 340 nm and 670 nm. The form of the ERG for both T. vaporariorum and E. formosa was found to be monophasic in nature. For both male and female T. vaporariorum and female E. formosa a primary peak of efficiency occurred in the blue-green-yellow region, peak 520 nm and a secondary peak in the ultraviolet (UV) region. The compound eye of female E. formosa gave a significantly greater response in the UV region than either the dorsal or ventral regions of the compound eye of T. vaporariorum relative to the responses in the blue-green-yellow region. T. vaporariorum has divided compound eyes with distinct dorsal and ventral regions. In this study it was found that the percentage response in the UV, of the dorsal region of the eye, is significantly greater than that of the ventral region of the eye relative to the percentage response in the blue-green-yellow region and there is a significant shift in the blue-green yellow peak towards the right of the spectrum.     

Visual pigment processes and prolonged pupillary responses in insect photoreceptor cells

The visual pigment in the peripheral retinular cells of the hoverfly Syrphus balteatus was investigated by absorbance difference measurements. Different visual pigments were found in the dorsal versus the ventral part of the eye in the male, but not in the female. In the male in the dorsal part of the eye the visual pigment has an isosbestic point at 513 nm; in the ventral part this value is 490 nm. The latter value is found in the female in both parts of the eye.Prolonged pupillary responses were studied in the male Syrphus and appeared to be most marked in the ventral part of the eye. In both hoverfly and blowfly prolonged pupillary responses are induced by short wavelength light only; i.e., by light which excessively can convert rhodopsin into metarhodopsin. By contrast, in butterflies red light (and a long dark adaptation time) is necessary to evoke a prolonged pupillary response. It was demonstrated in both hoverfly and blowfly that long wavelength light, which reconverts metarhodopsin into rhodopsin, inhibits a prolonged pupillary response; or, accelerates pupil opening.Based on material presented at the European Neurosciences Meeting, Florence, September 1978     

Spectral sensitivity studies on the visual system of the praying mantis, Tenodera sinensis

In these studies a constant ERG response was used as a measure of visual sensitivity to different wavelengths of light. The dark-adapted compound eye of Tenodera sinensis is dominated by a single class of photoreceptors. with a major peak of sensitivity at about 510–520 nm, and with a minor peak of sensitivity in the near-ultraviolet region at about 370 nm. The dark-adapted dorsal ocellus does not contain a homogeneous population of sensory receptors. The sensitivity function of the dark-adapted ocellus to longer wavelength light (yellow and red) is determined by a single receptor with a major peak of sensitivity in the green at 510–520 nm with some sensitivity in the near-ultraviolet. Sensitivity at shorter wavelengths (near-ultraviolet and blue), however, involves the stimulation of both this and a near-ultraviolet-sensitive receptor with a maximum sensitivity at about 370 nm. Anatomically, the sensory cells of the dorsal ocellus of Tenodera were determined histologically to be grouped into two distinct regions, each group making its own separate contribution to the ocellar nerve. This may represent the separation of two different photoreceptor types in the ocellus of the mantis.     

The spectral sensitivity of eye movements in response to light flashes inDaphnia magna

Summary The crustaceanDaphnia magna responds to a flash of light with a ventral rotation of its compound eye; this behavior is termed eye flick. We determined the spectral sensitivity for the threshold of eye flick in response to light flashes having three different spatial characteristics: (1) full-field, extending 180° from dorsal to ventral in the animal's field of view; (2) dorsal, 30° wide and located in the dorsal region of the visual field; (3) ventral, same as dorsal but located ventrally. All three stimuli extended 30° to the right and to the left of the animal's midplane. We found that spectral sensitivity varies with the spatial characteristics of the stimulus. For full-field illumination, the relative sensitivity was maximal at 527 nm and between 365 nm and 400 nm, with a significant local minimum at 420 nm. For the dorsal stimulus, the relative sensitivity was greatest at 400 nm, but also showed local maxima at 440 nm and 517 nm. For the ventral stimulus, the relative sensitivity maxima occurred at the same wavelengths as those for the full-field stimulus. At wavelengths of 570 nm and longer, the responses to both dorsal and ventral stimuli showed lower relative sensitivity than the full-field stimulus. No circadian or other periodic changes in threshold spectral sensitivity were observed under our experimental conditions. Animals which had their nauplius eyes removed by means of laser microsurgery had the same spectral sensitivity to full-field illumination as normal animals. Our results are discussed in terms of our current knowledge of the spectral classes of photoreceptors found in theDaphnia compound eye.     

The dorsal eye of the dragonfly Sympetrum: specializations for prey detection against the blue sky

Dragonflies of the genus Sympetrum have compound eyes conspicuously divided into dorsal and ventral regions. Using anatomical, optical, electrophysiological, in-vivo photochemical and microspectrophotometrical methods, we have investigated the design and physiology of the dorsal part which is characterized by a pale yellow-orange screening pigment and extremely large facets. The upper part of the yellow dorsal region is a pronounced fovea with interommatidial angles approaching 0.3°, contrasting to the much larger values of 1.5°–2° in the rest of the eye. The dorsal eye part is exclusively sensitive to short wavelengths (below 520 nm). It contains predominantly blue-receptors with a sensitivity maximum at 420 nm, and a smaller amount of UV-receptors. The metarhodopsin of the blue-receptors absorbs maximally at 535 nm. The yellow screening pigment transmits longwavelength light (cut-on 580 nm), which increases the conversion rate from metarhodopsin to rhodopsin (see Fig. 11a). We demonstrate that because of the yellow pigment screen nearly all of the photopigment is in the rhodopsin state under natural conditions, thus maximizing sensitivity. Theoretical considerations show that the extremely long rhabdoms (1.1 mm) in the dorsal fovea are motivated for absorption reasons alone. A surprising consequence of the long rhabdoms is that the sensitivity gain, caused by pumping photopigment into the rhodopsin state, is small. To explain this puzzling fact we present arguments for a mechanism producing a gradient of rhodopsin concentration along the rhabdom, which would minimize saturation of transduction units, and hence improve the signal-to-noise ratio at high intensities. The latter is of special importance for the short integration time and high contrast sensitivity these animals need for spotting small prey at long distances.Abbreviations ERG electroretinogram - R rhodopsin - M metarhodopsin     

Spectral sensitivities of retinular cells measured in intact,living flies by an optical method

Summary The spectral sensitivity of the peripheral retinular cells R1–6 in nine species of intact flies was determined using non-invasive, optical measurements of the increase in reflectance that accompanies the pupillary response. Our technique is to chronically illuminate a localized region of the eye with a long wavelength beam, adjusted to bring pupillary scattering above threshold, then, after stabilization, to stimulate with monochromatic flashes. A criterion increase in scattering is achieved at each wavelength by adjusting flash intensity. Univariance of the pupillary response is demonstrated by Fig. 3.Action spectra measured with this optical method are essentially the same as the published spectral sensitivity functions measured with intracellular electrophysiological methods (Fig. 4 forCalliphora, Fig. 5 forDrosophila, Fig. 7 forEristalis, and Fig. 8 forMusca). This holds for both the long wavelength peak and the high sensitivity in the UV as was consistently found in all investigated fly species.Spectral sensitivity functions for R1–6 of hover flies (family Syrphidae) are quite different in different regions of the same eye. There can also be substantial differences between the two sexes of the same species. The ventral pole of the eye of femaleAllograpta (Fig. 10) contains receptors with a major peak at 450 nm, similar to those ofEristalis. However, the dorsal pole of the same eye contains receptors with a major peak at 495 nm, similar to those ofCalliphom. Both dorsal and ventral regions of the maleToxomerus eye, and the ventral region of the female eye, contain only the 450 nm type of R1-6 (see Fig. 12). However, the dorsal region of the female eye also contains another spectral type of receptor that is maximally sensitive at long wavelength. Eyes of both sexes ofAllograpta (Figs. 10 and 11) contain a mixture of spectral types of receptors R1-6.We thank Dr. Chris Maier of the Connecticut Agricultural Experiment Station, for determination of the Syrphidae. This work was supported by grants EY01140 and EY00785 from the National Eye Institute, U.S.P.H.S., (to GDB), by the Connecticut Lions Eye Research Foundation (to GDB), and by the Netherlands Organization for the Advancement of Pure Research (Z.W.O.), (to DGS).     

Sex and Caste-Specific Variation in Compound Eye Morphology of Five Honeybee Species

Ranging from dwarfs to giants, the species of honeybees show remarkable differences in body size that have placed evolutionary constrains on the size of sensory organs and the brain. Colonies comprise three adult phenotypes, drones and two female castes, the reproductive queen and sterile workers. The phenotypes differ with respect to tasks and thus selection pressures which additionally constrain the shape of sensory systems. In a first step to explore the variability and interaction between species size-limitations and sex and caste-specific selection pressures in sensory and neural structures in honeybees, we compared eye size, ommatidia number and distribution of facet lens diameters in drones, queens and workers of five species (Apis andreniformis, A. florea, A. dorsata, A. mellifera, A. cerana). In these species, male and female eyes show a consistent sex-specific organization with respect to eye size and regional specialization of facet diameters. Drones possess distinctly enlarged eyes with large dorsal facets. Aside from these general patterns, we found signs of unique adaptations in eyes of A. florea and A. dorsata drones. In both species, drone eyes are disproportionately enlarged. In A. dorsata the increased eye size results from enlarged facets, a likely adaptation to crepuscular mating flights. In contrast, the relative enlargement of A. florea drone eyes results from an increase in ommatidia number, suggesting strong selection for high spatial resolution. Comparison of eye morphology and published mating flight times indicates a correlation between overall light sensitivity and species-specific mating flight times. The correlation suggests an important role of ambient light intensities in the regulation of species-specific mating flight times and the evolution of the visual system. Our study further deepens insights into visual adaptations within the genus Apis and opens up future perspectives for research to better understand the timing mechanisms and sensory physiology of mating related signals.     

Electroretinogram Characteristics and the Spectral Mechanisms of the Median Ocellus and the Lateral Eye in Limulus polyphemus

Electrical responses (ERG) to light flashes of various wavelengths and energies were obtained from the dorsal median ocellus and lateral compound eye of Limulus under dark and chromatic light adaptation. Spectral mechanisms were studied by analyzing (a) response waveforms, e.g. response area, rise, and fall times as functions of amplitude, (b) slopes of amplitude-energy functions, and (c) spectral sensitivity functions obtained by the criterion amplitude method. The data for a single spectral mechanism in the lateral eye are (a) response waveforms independent of wavelength, (b) same slope for response-energy functions at all wavelengths, (c) a spectral sensitivity function with a single maximum near 520 mµ, and (d) spectral sensitivity invariance in chromatic adaptation experiments. The data for two spectral mechanisms in the median ocellus are (a) two waveform characteristics depending on wavelength, (b) slopes of response-energy functions steeper for short than for long wavelengths, (c) two spectral sensitivity peaks (360 and 530–535 mµ) when dark-adapted, and (d) selective depression of either spectral sensitivity peak by appropriate chromatic adaptation. The ocellus is 200–320 times more sensitive to UV than to visible light. Both UV and green spectral sensitivity curves agree with Dartnall's nomogram. The hypothesis is favored that the ocellus contains two visual pigments each in a different type of receptor, rather than (a) various absorption bands of a single visual pigment, (b) single visual pigment and a chromatic mask, or (c) fluorescence. With long duration light stimuli a steady-state level followed the transient peak in the ERG from both types of eyes.     

The photopic spectral sensitivity of the dorsal and ventral retinae of the chicken

Summary The relative spectral sensitivities of the dorsal and ventral chicken (Gallus gallus) retinae were determined under photopic conditions by means of electroretinography and compared with data from the pigeon (Columba livid). Differences in spectral sensitivity between the dorsal and ventral chicken retinae appear only in the short wavelength range. In the chicken the dorsal retina is more sensitive to near UV light than the ventral retina relative to long wavelengths (beyond 470 nm), but both retinal areas are less sensitive to near UV than in the pigeon. The variation in relative near UV sensitivity is discussed in relation to recent data on the retinal distribution of different types of oil droplets in birds. The adaptive significance of near UV sensitivity is also discussed.     

Wing colors of Chrysozephyrus butterflies (Lepidoptera; Lycaenidae): ultraviolet reflection by males

Wing colors of the four species of Chrysozephyrus butterflies were analyzed by a spectrophotometer. As the dorsal wing surface of males showed a strong reflectance when the specimen was tilted, measurements were made by the tilting method. The dorsal wing surface of males which appears green to the human eye reflected UV (315-350 nm) as well as green light (530-550 nm). The reflectance rate of UV to visible green light varied among species with a higher rate for C. hisamatsusanus and C. ataxus, and a lower rate for C. smaragdinus and C. brillantinus. The peak wavelength and the peak height did not shift when the specimen was exposed to direct sunlight at least for 16 hr. Artificial removal of scales by scratching the wing surface decreased reflectance. Blue marks on the forewings of C. brillantinus, C. hisamatsusanus and C. ataxus females reflected UV to visible light of short wavelength, and orange marks on the dorsal surface of the forewing and the ventral surface of the hindwing of C. samaragdinus females showed a higher reflectance at longer wavelengths.     

Spectral sensitivity in the eyes of male and female Lutzomyia longipalpissandflies

Abstract. Using electroretinogram recordings, the response of Lutzomyia longipalpis sandfly eyes to a range of wavelengths of light was measured, and spectral sensitivity determined. The eyes of both male and female adult sandflies were found to respond maximally to light in the ultraviolet region (at 340 nm) with a secondary peak in the blue-green-yellow region at 520 nm for females and 546 nm for males. The Mann-Whitney U test showed no significant differences between males and females at corresponding wavelengths.     

Morphologische regionale differenzierungen der retina und des facettenrasters vom komplexauge der pipunculidae (Diptera : Cyclorrhapha): ein neuartiges retinales muster der fliegen (brachycera)

The retinae of the compound eyes of several species of Pipunculidae (Diptera : Cyclorrhapha), belonging to the subfamilies Chalarinae and Pipunculinae, were investigated in semithin sections in both sexes of the representative species. Whereas the boundary of the dorsal and ventral retinular cells in a mirror-image configuration is at the equator in the male, in the female it is situated in the anterior region of the eye at the level of the upper frons, and is located above the equator only in the lateral region. In the frontal view, it constitutes a concave arch to frontofacial region. The facets of the corneal lenses are strikingly enlarged in the anterior region of the eyes, compared with those in the remainder of the eye in the female. This area with the large-faceted ommatidia, was determined in more detail in total views as well as in histological preparations and compared with the eye of the male. In the frontal region, the mirror-image boundary in the retina of the female coincides exactly with the boundary between the large-faceted central and small-faceted peripheral ommatidia.By examining the dichoptic eyes of the Chalarus male, it has been demonstrated that the arcuate mirror-image boundary in the retinae of females is not associated with their dichoptic eye position. This is an example of sexual dimorphism. The retinal pattern of the female described in this paper was not found in other 37 families of the flies investigated till now. This new type of the retina of the suborder Brachycera (including Cyclorrhapha) is to be subsumed under the synapomorphic ground plans of the Pipunculidae. At the same time, it proves to be an autapomorphic characteristic of the family.     

Spectral Sensitivity of Melanophores in the Primary Color Response of the Rose Bitterling, <Emphasis Type="Italic">Rhodeus ocellatus ocellatus</Emphasis>

Melanophores of young Rhodeus ocellatus ocellatus have the ability to respond by melanosome dispersion to the direct action of visible light. The effective wavelength within visible light region for inducing melanosome dispersion was investigated using melanophores located around the base of the dorsal fin of young fish set on the stage of a light microscope. The melano- -’ phores were exposed to light of various wavelengths (420–680 nm) but of the same intensity by placing interference filters under the condenser diaphragm. The most effective wavelength was about 420 nm. Longer wavelengths were less effective for the induction of melanosome dispersion.     

Action spectra of the female's response in the firefly Photinus pyralis (Coleoptera: Lampyridae): evidence for an achromatic detection of the bioluminescent optical signal

Behavioural action spectra of the threshold of the Photinus pyralis female response to light stimuli simulating the bioluminescent optical signal of the conspecific male firefly were determined in the laboratory. The action spectra (Fig. 1) were narrow and peaked in the yellow region of the spectrum. The females responded only to stimuli of wavelengths longer than 480 nm and not to stimuli in the blue (420-460 nm) part of the spectrum. The shape of the function corresponds with (a) the electroretinographic spectral sensitivity function in the long wavelength (520-660 nm) region of the spectrum, (b) the action spectrum of the female response (Fig. 1), (c) the species yellow bioluminescence emission spectrum and (d) the action spectrum of the intracellular response from single retinular cells (Fig. 2) of the compound eyes in the firefly. Such a correspondence suggests that the narrow yellow receptors of the female mediate the detection and processing of the optical signal of the conspecific male. Since the bioluminescent optical signal is processed exclusively by a single receptor class, signal detection is achromatic.     

Differential wavelength sensitivity in the receptive fields of sustaining fibers in the optic tract of the crayfishProcambarus

Summary Spike discharges were measured at 473 nm and at 573 nm in 40–50 individual sustaining fibers (slowly-adapting units signaling intensity levels over large receptive fields). The units belonged to five of the 14 classes of sustaining fibers recognized by Wiersma and Yamaguchi (1966) on the basis of the positions of their receptive fields. The test wavelengths were selected because they lie near the peaks of sensitivity of the two spectral types of receptor known to be present in the ommatida. Relative sensitivity was measured at 5 ° intervals as the test lights were moved around the eye on various arcs, and the receptive fields were described in terms of contours of equal sensitivity for each wavelength.No large differences in relative spectral sensitivity were observed as a function of position in the receptive field, but there was a consistent tendency for sensitivity to blue light to be relatively greater in the dorsal region of the eye. The difference was modest, generally being 0.5 log units or less. This effect could be caused either by regional variation in the population density of the blue and yellow-green receptors, or by weighting of inputs in the optic neuropile.This work was supported by USPHS research grant EY00222 to Yale University. A.E.R.W. was aided by a Fulbright-Hays travel grant.     

Spectral sensitivity differences in two Mysis sibling species (Crustacea, Mysida): Adaptation or phylogenetic constraints?

The variation in eye spectral sensitivities of the closely related mysid species Mysis relicta Lovén, 1862 and Mysis salemaai Audzijonyt? and Väinölä, 2005 was studied in sympatric and allopatric populations from the brackish Baltic Sea and from two lakes representing different light environments. In the Baltic Sea the maximum spectral sensitivity of M. relicta, measured by the electroretinogram (ERG) technique, was shifted by ca 20 nm to longer wavelengths than in M. salemaai (564 and 545 nm, respectively). The spectral sensitivity of M. salemaai was closer to that of marine mysid species, which is consistent with its broader euryhalinity and the presumed longer brackish-water history. The species-specific sensitivities in the Baltic Sea were not affected by regional differences in light environments. In two lake populations of M. relicta, the spectral sensitivity was further shifted by ca 28 nm towards the longer wavelengths compared with the conspecific Baltic Sea populations. The spectral sensitivities in the four M. relicta populations were not correlated to the current light conditions, but rather to the phylogeographic histories and fresh- vs. brackish-water environments. A framework to further explore factors affecting spectral sensitivities in Mysis is suggested.     

Navigation of Lutzomyia longipalpis (Diptera: Psychodidae) under dusk or starlight conditions

The responses of male and female Lutzomyia longipalpis (Lutz & Neiva) to different wavelengths of light was tested by presenting the sandflies with two light sources simultaneously, a series of test wavelengths between 350-670 nm and a 400 nm control. To test whether L. longipalpis could discriminate between the test and control, three sets of experiments were carried out in which the test wavelengths were presented at higher, equivalent or lower intensity than the control. In all three experiments, ultra-violet (350 nm) and blue-green-yellow (490-546 nm) light was more attractive to L. longipalpis than the control wavelength. However, at low intensity, UV was less attractive, than equivalent or higher intensity UV light. At intensities equivalent to or higher than the control wavelength, ultra-violet light was more attractive than blue-green. Furthermore, at low intensity, green-yellow (546 nm) light was more attractive to males whereas blue-green (490 nm) was more attractive to females. Blue-violet (400 nm) and orange-red (600-670 nm) light were least attractive in all three sets of experiments. Response function experiments indicated that the responses were dependent on both intensity and wavelength and that therefore more than one photoreceptor must be involved in the response. The results indicated that L. longipalpis can discriminate between different wavelengths at different intensities and thus have true colour vision. It also suggests that L. longipalpis may be able to navigate at dusk or under moonlight or starlight conditions using light in the blue-green-yellow part of the spectrum. The difference in response of males and females to light in this region is interesting and may indicate the different ecology of the sexes at night. Overall, these results may have important implications for sandfly trap design.