Specific receptor input into spectral preference inDrosophila

Summary Drosophila have 3 types of retinal receptors, R1–6, R7 and R8. Using visual mutant strains lacking function in one or two receptor types, spectral preference in walking fast (30 s) phototaxis was measured. High correlations for intensity-response functions were obtained (Fig. 2 and 5). With a 467 nm choice standard, which could saturate R1–6, white-eyed strains with only R8 or with R1–6 plus R8 functional exhibited similar spectral sensitivities with a broad peak at visible wavelengths (Fig. 3) not unlike the electrophysiological characterization of R8 (Fig. 1). Strains with R7 plus R8 or with all receptors intact exhibited similar functions with a high ultraviolet (UV) peak (Fig. 4), like the electrophysiological characterization of R7 plus R8. The presence of R1–6 did not alter the profiles mediated by R8 alone or by R7 plus R8.With a 572 nm standard, which should maintain R1–6 function, white- and red-eyed wild-type strains with all receptors intact exhibited similar UV dominated spectral sensitivities, probably from R7 plus R8, with weak visible secondary peaks possibly from R1–6 or R8 (Fig. 6). However, even with a very dim 572 nm standard or with no standard at all, unequivocal evidence for R1–6 input was not found and intensity-response function correlations were low. This finding and other recent studies suggest that specific phototactic or optomotor tasks and conditions (e.g., adaptation level) determine the extent to which each receptor input is utilized.Spectral preference with a bright 365 nm standard was difficult to measure because of the strong UV preference in phototaxis. In pilot studies, an ocelliless strain showed strong fast phototaxis.Supported by NSF grants BMS-74-12817 and BNS-76-11921. We thank D. Lakin, A. Ivanyshyn, R. Greenberg, M. Chapin, D. Fritzberg, and W. Hamilton for technical assistance. We also thank R. Schümperli for suggestions, for his permission to redraw his data and for confirming the conversions we made.     

Phototaxis in Drosophila: R1–6 input and interaction among ocellar and compound eye receptors

All 3 photoreceptor types in the compound eye of Drosophila can evoke positive phototaxis. Here we describe input from R1–6 receptors which are very sensitive. Previous reports in this series of studies described input from R7 and R8, the other less sensitive receptors. Here we studied fast-walking phototaxis using extremely dim stimuli. We also studied input from the simple ocellar eyes. Thus, we can now summarize a complete synthesis of inputs and interactions among all compound eye and ocellar receptor types. Receptor-deficient mutants were used to establish receptor-specific input. Two other findings are presented: (1) eye colour pigments affect the spectral sensitivity for phototaxis; and (2) the ocelli interact to facilitate input from the compound eye receptor types. Possible mechanisms of receptor interaction are discussed in the light of these findings of positive input from all photoreceptor types in Drosophila.     

Simulations of a model for transmitter kinetics

The influence of the internal water balance on the phototactic behaviour in the walking female fly (Calliphora erythrocephala Meig.) was investigated. The phototactic reaction depends on the age of the flies and the duration of water withdrawal. In young blowflies with progressive dehydration, the strength of the light reaction varies considerably from fly to fly. From the 4th. day of life onwards up to day 21 the flies respond much more homogeneously and elicit a reproduceable temporal pattern of reaction (Figs. 2 and 3). All the following statements refer to the behaviour of 10-day-old, virgin females, which, under optimal humidity conditions, have been shown to be spontancously photonegative (Meyer, 1978). The phototactic reaction of progressively dehydrated flies depends in a characteristic manner on the illumination conditions during the intervals between tests. If the flies are kept in darkness during these intervals, the light reaction varies rhythmically, with a period of almost exactly 12 h (Figs. 4a and 5). Under the test conditions this rhythm is found not to vary with the time of day (Fig.4a), or with the length of the between-test intervals, for intervals up to 4h long (Fig. 6). If the flies are kept under illumination during the intervals between tests, the light reaction becomes arhythmical. After an initial maximum after 2–4h of dehydration, further photopositive responses are severely suppressed (Fig. 4b). When the ocelli are covered, the between-test illumination no longer influences the mean response to light. The arhythmic dehydrationtime vs. light-reaction curve in this case is characterised by a strong sustained enhancement of runs towards the light after 10h of dehydration (Fig. 7). A preliminary model of a possible control system for this moisture-dependent phototactic switching is presented, from which all essential results can be deduced. This system determines the phototactic turning direction from the ocelli afferences. These afferences act upon the central nervous system in two ways: directly and also indirectly via the internal water regulation.This work was supported by the DFG-(Me417/4)     

Photomovement of the red alga Porphyridium cruentum (Ag.) Naegeli

Phototaxis of the unicellular red alga Porphyridium cruentum was studied by staining the slime tracks of individual cells as well as with the aid of a population method. Because of the increased straightness of the movement the mean linear velocity of a unilaterally illuminated population exceeds considerably that of an only photokinetically stimulated one. In white light the phototactic reaction is saturated already at 100 lx. The zero threshold lies at about 1 lx. Spectral sensitivity curves of phototaxis obtained at high photon fluence rates (>=10^–11 mol cm^–2 s^–1) display two main peaks which shift against each other at intermediate irradiances and, finally, form a single maximum in the blue range (443 nm) at low photon fluence rates (10^–12 and 10^–13 mol cm^–2 s^–1). Photon fluence rate-response curves reveal that supraoptimal irradiances decrease the phototactic reaction, especially in the range of the highest sensitivity of the cells. The action spectrum of phototaxis was calculated on the basis of the photon fluence rate-response curves. It shows a maximum at 443 nm and shoulder at 416 nm and between 467 and 477 nm. Wavelengths longer than 540 nm are phototactically inactive even at very high irradiances (25 W m^–2). Thus, this is the first phototactic action spectrum of a biliprotein-containing organism which does not indicate the participation of biliproteins in the absorption of phototactically active light. DCMU and potassium iodide have no specific effects on phototaxis.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

T-maze phototaxis ofDrosophila melanogaster and several mutants in the visual systems

Summary T-maze phototaxis ofDrosophila melanogaster and several of its mutants was investigated as function of the light illuminating the mazes. For visible light the response curves of thewildtype are quite complex and nonmonotonic functions of the light intensity. The data are interpreted as a result of an interaction between visual subsystems: the system which receives inputs from receptor cells R1-R6 is inhibited by the system of receptor cells R7 and R8, probably by R8 alone.We wish to thank E. Kreutzer, E. Brutzer and A. Emanns for excellent technical assistance. Discussions with Drs. M. Heisenberg and N. Franceschini, R. Schümperli and K. Kirschfeld are gratefully acknowledged. This work was supported by funds of the SFB 46.     

Convergence of antennal and ocellar inputs in the insect brain

Summary Unitary responses were recorded from the brain of the fleshfly, Boettcherisca peregrina, during olfactory or mechanical stimulation of the antenna, and simultaneous photic stimulation of the ocelli. Convergence from the two inputs, the antenna and the ocelli, was observed. The response to antennal stimulation was facilitated by photic stimulation in most units. The responses to the antennal stimuli were facilitated greatly at the peak of the photic response. Some units responded both to ocellar illumination and antennal stimulation. Their response to antennal stimulation seemed independent of the light-condition during the light-adapted state, but was facilitated at the onset of the ocellar illumination, and occluded just after its cessation. In addition, there were some units which responded to antennal stimulation but not to the ocellar illumination; some of them also showed facilitation of the response to antennal stimulation during ocellar illumination.     

Ocellar optics in nocturnal and diurnal bees and wasps

Nocturnal bees, wasps and ants have considerably larger ocelli than their diurnal relatives, suggesting an active role in vision at night. In a first step to understanding what this role might be, the morphology and physiological optics of ocelli were investigated in three tropical rainforest species – the nocturnal sweat bee Megalopta genalis, the nocturnal paper wasp Apoica pallens and the diurnal paper wasp Polistes occidentalis – using hanging-drop techniques and standard histological methods. Ocellar image quality, in addition to lens focal length and back focal distance, was determined in all three species. During flight, the ocellar receptive fields of both nocturnal species are centred very dorsally, possibly in order to maximise sensitivity to the narrow dorsal field of light that enters through gaps in the rainforest canopy. Since all ocelli investigated had a slightly oval shape, images were found to be astigmatic: images formed by the major axis of the ocellus were located further from the proximal surface of the lens than images formed by the minor axis. Despite being astigmatic, images formed at either focal plane were reasonably sharp in all ocelli investigated. When compared to the position of the retina below the lens, measurements of back focal distance reveal that the ocelli of Megalopta are highly underfocused and unable to resolve spatial detail. This together with their very large and tightly packed rhabdoms suggests a role in making sensitive measurements of ambient light intensity. In contrast, the ocelli of the two wasps form images near the proximal boundary of the retina, suggesting the potential for modest resolving power. In light of these results, possible roles for ocelli in nocturnal bees and wasps are discussed, including the hypothesis that they might be involved in nocturnal homing and navigation, using two main cues: the spatial pattern of bright patches of daylight visible through the rainforest canopy, and compass information obtained from polarised skylight (from the setting sun or the moon) that penetrates these patches.     

Investigations on the phototactic orientation of Anabaena variabilis

Phototaxis of the blue-green alga Anabaena variabilis was studied using both population method and observation of single trichomes by microscope. The trichomes react positively at low and negatively at high illuminance. The inversion point lies at about 1000 1x. The action spectrum of positive phototaxis indicates that the photosynthetic pigments chlorophyll a, C-phycocyanin and allo-phycocyanin are involved in the absorption of the active light. The same range of wavelengths is active in negative phototaxis, but in addition, wavelengths between 500 and 560 nm and between 700 and 750 nm are also effective. Obviously pigments of unknown chemical nature are sharing in light absorption. Two alternatives are discussed. Since inhibitors of photosynthesis such as DCMU and DBMIB do not affect phototactic orientation, a direct coupling of phototaxis with photosynthesis can be excluded.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DBMIB Dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) Presented in part at the International Symposium on Photosynthetic Prokaryotes: August 22–28, 1976, Dundee, Scotland     

Optical properties of the ocelli of Calliphora erythrocephala and their role in the dorsal light response

The 3 ocelli of the blowfly Calliphora erythrocephala, grouped close together on the top of the head (Fig. 1), have large, extensively overlapping visual fields. Together they view the entire upper hemisphere of the surroundings plus part of the lower hemisphere (Figs. 5, 7). It is shown for the lateral ocelli that despite the underfocussing of the ocellar lens large patterns are imaged on the receptor mosaic. Because of the astigmatism of the lens, patterns in longitudinal orientations are more accurately represented than in others (Fig. 3). Nevertheless, an artifical horizon rotated around the long axis of the animal does not elicit head roll. Likewise, changes of overall brightness in the visual field of the median and one lateral ocellus elicit only weak phasic-tonic dorsal light responses of the animal which supplement the tonic dorsal light responses mediated by the compound eyes (Figs. 9, 10). Our results show that, in Calliphora, the ocelli have little influence on head orientation during flight, and must be assumed to serve other functions.Abbreviations body pitch angle - head-tilt angle - DNOVS descending neuron of the ocellar and vertical cell systems - HR head roll - spatial wavelength - R roll angle - SD standard deviation     

Phototaxis by the Dinoflagellate Gymnodinium splendens Lebour*

A microscope-television system was used to monitor quantitatively the behavior of Gymnodinium splendens Lebour in response to light. The predominant behavioral sequence upon stimulation is (a) an initial 2–5 sec cessation of movement (stop-response) followed by (b) positive phototaxis. The action spectra for each response are identical, having maxima at 450 and 280 nm. Upon measuring the percent response to a range of stimulus intensities, it is apparent that a stop-response is not a behavioral prerequisite for phototaxis. An identical circadian rhythm in photoresponsiveness is observed for phototaxis and for the stop-response with greatest light sensitivity occurring during the first 4 hr of the entrained light period. The implication of phototactic sensitivity and the phototactic circadian rhythm in diurnal vertical migration is discussed.     

Effect of rest deprivation on motor activity of fish

Summary The rest-activity behavior of two fish species,Cichlosoma nigrofasciatum andCarassius auratus kept under 12-h light-12-h dim condition was investigated. Rest and activity were determined from continuous time-lapse video recordings. Three states were discriminated based on the degree of motor activity. Both species exhibited a clear rest-activity rhythm with activity predominating during the light period (Figs. 1, 2). Rest deprivation was carried out in perch during the habitual dim period by exposing the animals to either 12 h continuous light or to 6 h intermittent light (1 h light — 1 h dim for 12 h). Both light schedules enhanced activity and reduced rest (Fig. 3). Light-induced activation was followed by an increase in low activity and rest behavior which prevailed for 12 h following continuous light, and for 6 h following intermittent light (Figs. 3, 4). The results indicate that homeostatic mechanisms are involved in the regulation of rest and activity in fish. These mechanisms may be similar to those underlying sleep regulation in mammals.Abbreviations Ldim light-dim - EEG electroencephalogram - REM rapid eye movements     

Phototactic behaviour in Aphidius gifuensis (Hymenoptera:Braconidae)

We investigated the spectral sensitivity and response to light intensity of Aphidius gifuensis (Hymenoptera: Braconidae), a key natural enemy of the green peach aphid, Myzus persicae (Hemiptera: Aphididae). We used 15 monochromatic lights (emitting various specific wavelengths from 340 to 689 nm) and white light. Monochromatic light of different wavelengths and white light elicited photopositive behaviour from A. gifuensis. The strongest response was stimulated by blue light (492 nm), which induced a movement of 43.5 cm, a response that differed from all other groups. This was followed by green light (568 nm) and UV-light (380 nm). There was no significant response to orange light (601 nm) or red light (649, 668 and 689 nm) from A. gifuensis. The response intensity curve for A. gifuensis to monochromatic light (492 nm) decreased as light intensity increased. At 568 nm, the phototactic response showed an ‘S’ shaped curve. But at 628 nm, the phototactic response rose continuously with increasing intensity. We report here that the visual system of A. gifuensis is composed of three spectrum receptors, attuned to UV, blue and green light. While light intensity is a key factor in determining the photopositive response of A. gifuensis, the effect of intensity varies by wavelength.     

Photomovement in Dunaliella salina: Fluence rate-response curves and action spectra

We determined the action spectra of the photophobic responses as well as the phototactic response in Dunaliella salina (Volvocales) using both single cells and populations. The action spectra of the photophobic responses have maxima at 510 nm, the spectrum for phototaxis has a maximum at 450–460 nm. These action spectra are not compatible with the hypothesis that flavoproteins are the photoreceptor pigments, and we suggest that carotenoproteins or rhodopsins act as the photoreceptor pigments. We also conclude that the phototactic response in Dunaliella is an elementary response, quite independent of the step-up and step-down photophobic responses. We also determined the action spectra of the photoaccumulation response in populations of cells adapted to two different salt conditions. Both action spectra have a peak a 490 nm. The photoaccumulation response may be a complex response composed of the phototactic and photophobic responses. Blue or blue-green light does not elicit a photokinetic response in Dunaliella.Diagrams of the optical set-ups used for measuring the responses at the single-cell level and of the plans for building the phototaxometer described in this paper are available to the interested readerWe thank Mr. M. Kubota for a tremendous amount of technical assistance and Mr. R. Nagy for building the phototaxometer. We thank T. Kondo, Professor H. Imaseki and the members of the Laboratory of Biological Regulation, NIBB, for their help and support in various aspects of this research. This research was supported, in part, from grants from the Okazaki Large Spectrograph (Project Nos. 86-535, 87-518, 88-523), the Japanese Society for the Promotion of Science, and the College of Agriculture and Life Sciences at Cornell University to R. W.     

Phototaxis in a dinoflagellate: Action spectra as evidence for a two-pigment system

Summary Action spectra were determined in the UV region of the spectrum for the first phase of the phototactic response (stop response) and for the phytochrome pigment associated with this response in the dinoflagellate Gyrodinium dorsum Kofoid. Differences between these action spectra indicate the participation of two pigments in phototaxis. Following R (620 nm) irradiation of the phytochrome, the stop response maxima occur at 470 and 280-nm; after FR irradiation they shift to 490 and 300–310 nm. These maxima suggest that the photoreceptor pigment for phototaxis is a carotenoprotein. The action spectrum shift following the different phytochrome conversions may represent a trans to cis isomer change by the carotenoid. The absorption maximum of P_R in the UV appears to be at 320 nm, which is consistent with the shift of the R absorption maximum to shorter wavelengths (620 nm) as compared to higher plants. The P_FR absorption maximum appears as a broad band between 360 and 390 nm. Comparison of P_R to P_FR conversions by different intensities of 620-nm and 320-nm light indicates that at lower intensities the logarithm of the threshold for the stop response is inversely proportional to the logarithm of the intensity of the sensitizing light. The ratio of response activation by R and UV light is about 4:1.Abbreviations FR far-red - R red - P_FR far-red-absorbing form of phytochrome - P_R red-absorbing form of phytochrome - UV ultraviolet     

Phototropin Influence on Eyespot Development and Regulation of Phototactic Behavior in Chlamydomonas reinhardtii

The eyespot of Chlamydomonas reinhardtii is a light-sensitive organelle important for phototactic orientation of the alga. Here, we found that eyespot size is strain specific and downregulated in light. In a strain in which the blue light photoreceptor phototropin was deleted by homologous recombination, the light regulation of the eyespot size was affected. We restored this dysfunction in different phototropin complementation experiments. Complementation with the phototropin kinase fragment reduced the eyespot size, independent of light. Interestingly, overexpression of the N-terminal light, oxygen or voltage sensing domains (LOV1+LOV2) alone also affected eyespot size and phototaxis, suggesting that aside from activation of the kinase domain, they fulfill an independent signaling function in the cell. Moreover, phototropin is involved in adjusting the level of channelrhodopsin-1, the dominant primary receptor for phototaxis within the eyespot. Both the level of channelrhodopsin-1 at the onset of illumination and its steady state level during the light period are downregulated by phototropin, whereas the level of channelrhodopsin-2 is not significantly altered. Furthermore, a light intensity–dependent formation of a C-terminal truncated phototropin form was observed. We propose that phototropin is a light regulator of phototaxis that desensitizes the eyespot when blue light intensities increase.     

Multiple light inputs control phototaxis in Synechocystis sp. strain PCC6803

The phototactic behavior of individual cells of the cyanobacterium Synechocystis sp. strain PCC6803 was studied with a glass slide-based phototaxis assay. Data from fluence rate-response curves and action spectra suggested that there were at least two light input pathways regulating phototaxis. We observed that positive phototaxis in wild-type cells was a low fluence response, with peak spectral sensitivity at 645 and 704 nm. This red-light-induced phototaxis was inhibited or photoreversible by infrared light (760 nm). Previous work demonstrated that a taxD1 mutant (Cyanobase accession no. sll0041; also called pisJ1) lacked positive but maintained negative phototaxis. Therefore, the TaxD1 protein, which has domains that are similar to sequences found in both bacteriophytochrome and the methyl-accepting chemoreceptor protein, is likely to be the photoreceptor that mediates positive phototaxis. Wild-type cells exhibited negative phototaxis under high-intensity broad-spectrum light. This phenomenon is predominantly blue light responsive, with a maximum sensitivity at approximately 470 nm. A weakly negative phototactic response was also observed in the spectral region between 600 and 700 nm. A deltataxD1 mutant, which exhibits negative phototaxis even under low-fluence light, has a similar action maximum in the blue region of the spectrum, with minor peaks from green to infrared (500 to 740 nm). These results suggest that while positive phototaxis is controlled by the red light photoreceptor TaxD1, negative phototaxis in Synechocystis sp. strain PCC6803 is mediated by one or more (as yet) unidentified blue light photoreceptors.     

The comparative photobehavior of laboratory-hatched and plankton-caught Balanus improvisus (Darwin) nauplii and the effects of 24-hour starvation

Stage II nauplii of Balanus improvisus (Darwin) were obtained from laboratory-maintained adult barnacles. The immediate phototactic and photokinetic response of laboratory nauplii to light stimuli of known wavelength (460–540 nm) and quantal intensity was determined through use of closed-circuit videotape recordings quantified for computer analysis. Spectral and light intensity responses were compared with previous results using nauplii collected from the plankton. In both cases, nauplii exhibit a primary peak response to light near 480 nm and a secondary peak near 520 nm. Although the spectral response and basic patterns of photobehavior remain similar in field and laboratory nauplii, sensitivity to light intensity is significantly reduced in laboratory nauplii. Responses of fed and 24-h starved laboratory nauplii were also compared at three salinities (15, 20, 30‰). Starvation for 24 h, although inducing no major change in photopositive and photokinetic response of nauplii, can slightly depress spontaneous swimming speed and raise the threshold of intensity response for phototaxis.     

The role of retinula cell types in fixation behaviour of walkingDrosophila melanogaster

Summary Fixation behaviour of free walking wild typeDrosophila and various retinal mutants was tested in a circular arena. Optomotor response was also measured as a test of the function of R1-6.ora andsev,ora do not fixate a narrow stripe (10° or 20°, Fig. 1) but are able to orient towards broad stripes (110° or 180°, Fig. 1). The behaviour ofsev is not different from wild type. Fixation behaviour ofw rdgB is similar toora (Figs. 5, 6). The mutantora has a maximum optomotor response at low contrast frequencies (Fig. 2), but the threshold for this response is at least one log unit higher than in wild type orsev (Fig. 8). The light intensity threshold at 550 nm of fixation to a broad stripe (110°) is 1–2 log units higher inora than in wildtype, and 4 log units higher insev,ora and the structural brain mutantVam (Fig. 7).The conclusions are that retinula cells R1-6 mediate fixation to a narrow stripe at high and low ambient light intensities, and to a broad stripe at low ambient light levels. R8, possibly in conjunction with R1-6, contributes to orientation towards broad stripes at high light intensities. This hypothesis is supported by evidence that blue-adapted white-eyed flies are able to orient towards a broad stripe at high blue light intensities (Figs. 9 and 12). Blue adaptation totally eliminates the optomotor response (Figs. 10, 11) and so the optomotor response observed inora at low contrast frequencies (Figs. 2 and 8) is most likely due to the small remnants of the rhabdomeres of R1-6 that remain.Abbreviations PDA prolonged depolarising afterpotential - ERG electroretinogram     

Lateral ocellar nerve projections in the dragonfly brain

Summary The central projections of the lateral ocellar neurons of the dragonfly were examined using whole nerve cobalt iontophoresis, supplemented by sectioning of the nerve and brain for inspection in the light and electron microscopes. At E.M. level the presence of cobalt in filled axon profiles and cell bodies was confirmed by analysis of X-ray energy spectra in the microscope.The pathways, cell body sites and terminal arborizations of four large (7–25 m diameter) lateral ocellar neurons are described. Two of these fibers arborize in the ipsilateral posterior neuropil of the protocerebrum and two cross the brain and arborize in the contralateral posterior neuropil. Within each half of the posterior neuropil, two spatially separated regions of ocellar input have been identified. These regions receive median ocellar input plus input from either the ipsi- or contralateral ocellus, but not both. The arborizations of the contralateral fibers are more extensive than those of the ipsilateral fibers.One of the contralateral neurons crosses the brain in the region of the protocerebral bridge giving off a collateral in that region before descending to the posterior neuropil. This collateral arborizes almost immediately in a region receiving input from arborizations of a number of small ocellar neurons (those less than 5 m in diameter) from the ipsilateral ocellar nerve, together with small neurons from the median ocellar nerve, forming a region in each half of the brain which receives input from all three ocelli. The small lateral ocellar neurons associated with these arborizations have cell bodies adjacent to the lateral ocellar tracts.This work was supported in part by National Institute of Health Grants 2 RO1 EY-00777 and 1 KO4 EY-00040     

The role of the ocelli in the phototactic behaviour of the haematophagous bug Triatoma infestans

In addition to compound eyes, most adult insects posses two or three simple eyes, the ocelli. The function of these photoreceptors remains elusive in most cases. Triatomine bugs posses two well-developed ocelli, located in a latero-dorsal position, behind the compound eyes. We tested the role of the ocelli in the phototactic behaviour of Triatoma infestans, by measuring the time spent by adult males in the dark half of an experimental arena, which had the other half illuminated. The occlusion of the ocelli or the compound eyes alone had little effect on the phototactic response of the bugs. Only those insects which had both their ocelli and compound eyes occluded showed a significant reduction in their negative response to light. The ability of the ocelli of T. infestans to mediate the phototactic response by themselves (i.e., not through the modulation of compound eyes sensitivity) constitutes the first report on this function in insects.