Phototaxis and adaptation of the eyeless Drosophila melanogaster line]

An artificial selection on positive and negative phototaxis of eyeless (ey) Drosophila melanogaster line was carried out. Expression of the ey trait in imago was estimating during the selection. The fitness of the "+" and "-" selected lines was evaluated by such components as heat resistance, life span, fertility of flies. The genetic analysis of phototaxis inheritance was carried out. It was found that phototaxis selection results in changes of fertility whereas it doesn't affect other indices of fitness to environmental conditions as well as the ey expression. The main polygenic systems of phototaxis inheritance are located in chromosome 2 and chromosome 3.     

Phototaxis in the flagellates,Euglena gracilis and Ochromonas danica

Oriented movement with respect to laterally impinging white light of the flagellates Euglena gracilis and Ochromonas danica has been analyzed in an individual cell study with a microvideographic technique. Using the deviation of track segments (in given time intervals of 1 s) from the light direction as raw data allowed a computer based analysis of the direction distribution. A number of statistical methods employed to test the significance of the obtained results demonstrated an obvious phototactic orientation in Ochromonas which was positive (toward the light source) in low illuminance (1.25 lx=5.3×10^-3 Wm^-2) and negative in higher illuminance (>12.5 lx=5.3×10^-2 Wm^-2). Since in this flagellate the threshold for negative phototaxis is much lower than that for the step-up photophobic response, the hypothesis that negative phototaxis may be brought about by repetitive step-up phobic responses can be rejected for at least this organism. In Euglena positive phototaxis was observed in 50 lx (=0.21 Wm^-2), while an illuminance of 500 lx (=2.1 Wm^-2) caused a negative phototaxis.The experiments were carried out in this laboratory     

Phototaxis inEuglena gracilis: Effect of sodium azide and triphenylmethyl phosphonium ion on the photosensory transduction chain

Phototaxis in the flagellateEuglena gracilis was studied by means of a microvideographic analysis, and the light-induced directional movement was determined by computer-based statistical treatments. Lateral white light with an illuminance of 25 lx (0.105 Wm^–2) caused the cells to preferentially swim toward the light source (positive phototaxis), while an illuminance of 1,000 lx (4.2 Wm^–2) induced negative phototaxis. The lipophilic membranepenetrating cation triphenylmethyl phosphonium ion (TPMP⁺) specifically inhibited positive phototaxis, while it hardly affected negative phototaxis. The uncoupler sodium azide, on the other hand, impaired negative phototaxis substantially.     

Responses of Echinostoma caproni miracidia to gravity, light, and chemicals.

In a four-tube vertical system, Echinostoma caproni miracidia exhibited a strong negative geotaxis which was dominated by a positive phototaxis. In horizontal chambers a positive phototactic response was also demonstrated. These miracidia showed a positive chemoresponse, as determined in phi-chambers, to glutamic and aspartic acids but not leucine. Positive responses were also elicited to snail-conditioned water and sulfuric and acetic acids. Ammonia, Mg2+, and HCl produced no significant reactions. Responses of E. caproni and Schistosoma mansoni miracidia, both of which develop in Biomphalaria glabrata snails, were similar providing further evidence that miracidia mimic the behavioral patterns of compatible snail species.     

The role of two plant-derived volatiles in the foraging movement of 1st instar Helicoverpa armigera (Hübner): time to stop and smell the flowers

Positive phototaxis and negative geotaxis are behaviours that 1st instar Helicoverpa armigera use to direct their foraging movement upward towards nutritious new plant growth and reproductive structures. Odours emitted by fruits or seeds can attract larvae directly via chemotaxis. In this study we clarify the effect of leaf and flower odours on foraging 1st instar H. armigera. Using a Y-tube olfactometer we tested for chemotaxis towards two plant volatiles and found larvae were not attracted. Bioassays for phototaxis towards UV, blue, green and white light showed that a green leaf volatile ((Z)-3-hexenyl acetate) and a flower volatile (phenylacetaldehyde) reduced larval phototaxis towards blue light. Feeding on a host plant reduced phototaxis towards blue and green light. We concluded that the upward movement of 1st instars on plants is largely due to phototaxis towards the blue wavelengths of skylight. Plant attributes such as volatile chemicals affect the expression of phototaxis and therefore, indirectly influence larval movement to locate food resources. Handling Editor: Anna-Karin Borg-Karlson     

The effect of temperature on phototaxis and geotaxis by larvae of the crab Rhithropanopeus harrisi (Gould)

Investigations of the effect of sudden temperature change on the phototaxis of Stage I and IV zoeae upon stimulation from horizontal and vertical directions with 500-nm light indicate a temperature-induced geotactic response in larvae of the crab Rhithropanopeus harrisi (Gould). For the horizontal tests both zoea stages were reared at 20 °C. Stage I showed positive phototaxis at temperatures between 15 ° and 35 °C, while Stage IV responded over the range of 10–30 °C. For the vertical tests, larvae, reared at 25 °C, were stimulated with overhead lights. Stage I zoeae ascended at 15 °, 20 ° and 25 °C and descended at 5 °, 10 °, 30 ° and 35 °C. Stage IV zoeae ascended at 20 ° and 25 °C and descended at 5 °, 10 °, 15 °, 30 ° and 35 °C. Although the descent at high temperatures could result from a negative phototaxis, a reversal in phototactic sign at high temperatures was not found in the horizontal experiments and the same vertical movement pattern is observed in total darkness. Upon exposure to high temperatures near the water surface, larvae would descend by means of a positive geotaxis rather than a negative phototaxis. This response involves active swimming by Stage IV larvae and passive sinking by Stage I.     

Where to from here? The mechanisms enabling the movement of first instar caterpillars on whole plants using Helicoverpa armigera (Hübner)

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is an economically-important, polyphagous herbivore in Old World countries. The distribution of larvae within various host plants has been described, but few studies have tried to determine the behavioural mechanisms by which the given distributions arose. Our aim was to determine the mechanisms which enable larval movement on pea plants, starting with first instars. Observations and bioassays determined larval movement in response to light and angled surfaces, as well as the effect of feeding and plant volatiles on these responses. The majority (68–72%) of 1st instars were positively phototactic towards blue, green and white light and 42% towards UV light. In the dark, larvae showed negative geotaxis. The angle of their substrate also had a kinetic effect on larvae; the steeper the angle from horizontal the more larvae moved under all conditions. Phenylacetaldehyde (a flower volatile) suppressed larval movement except at 90°. (Z)-3-Hexenyl acetate (a green leaf volatile) reversed the direction of movement at the flattest angle. Feeding lessened the probability of moving. We suggest that phototaxis and geotaxis are behaviours common to larval lepidopterans (caterpillars), and that these basic behaviours are modulated by environmental, larval, and plant factors to give observed distributions. Using a multinomial model approach, we created a flow chart to qualitatively and quantitatively represent the decision-making process of first instar H. armigera in response to the factors influencing movement.     

The responses of Philophthalmus gralli and P. megalurus miracidia to light, gravity and magnetic fields

Miracida of an eyefluke of birds, Philophthalmus gralli, which are positively geotactic, exhibited a positive north-seeking magnetotaxis when subjected to magnetic field strengths from 3 × 10^?4 to 2 × 10^?2 T. A closely-related species, P. megalurus, which is positively geotactic only in complete darkness, exhibited no magnetotaxis under similar conditions. A positive phototactic response overrode the north-seeking magnetotaxis when P. gralli miracidia were subjected to both stimuli in a competing system. No detector mechanisms for magnetic fields are known in miracidia of digenetic trematodes. The order of responsiveness for P. gralli miracidia then is: geotaxis > phototaxis > magnetotaxis.     

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.     

Photoresponses of second-instar Chaoborus larvae

The diel vertical migration of Chaoborus larvae varies with larval instar. Although light is involved in the control of vertical migration the contribution of larval photoresponses is unknown. In order to describe ontogenetic changes in larval photoresponses we measured photoresponses of second-instar Chaoborus punctipennis larvae in the laboratory. The response spectrum of these larvae had peaks in sensitivity at 420 and 620 nm with a wide plateau of lower sensitivity from 460 to 600 and 640 to 680 nm. Dark adapted larvae were positively phototactic at intensities from 10^?7 to 10¹ Wm^?2 at 420 nm. The level of response decreased somewhat above 10^?4 Wm^?2, and above 10^?2 Wm^?2 a small proportion of larvae shifted to a negative phototaxis. At 420 nm the threshold intensity was about 10^?7 Wm^?2 for positive phototaxis and 10^?2 Wm^?2 for negative phototaxis. Light adaptation increased the threshold intensity for positive phototaxis. The differences in larval photoresponses between second- and fourth-instar larvae suggests that the young instars are adapted to the photoenvironment of the water column and older larvae are adapted to avoid the water column except at very low light intensities. These predictions match the diel distribution of these larvae.     

Sudden reversal of phototaxis during the development of nestling birds

Starling, Sturnus vulgaris, nestlings from about 10 days of age moved away from light, i.e. they were negatively phototactic. However, several days before fledging, they changed to move towards light, probably a necessary prerequisite for fledging. The phototactic reversal was correlated with physical development and the ability to fly. In contrast to most studies or newly acquired behaviour, there was no change in response time associated with the reversal. However, hunger reduced the response time of hand-reared nestlings. It is suggested that a positive phototaxis for strong fliers or negative phototaxis for flightless young is an adaptive escape response. The reversal of phototaxis is probably a general feature of avian development.     

Photoresponses of Chaoborus larvae

The diel vertical migration of Chaoborus larvae is a well known phenomenon. In order to quantify the ability of larvae to utilize underwater light cues in their migration, we measured photoresponses of fourth-instar Chaoborus punctipennis larvae in the laboratory. The action spectrum for these larvae was characterized by a maximum in sensitivity at 400 nm, a plateau at a lower sensitivity from 480 to 560 nm, and a region of much lower sensitivity at wavelengths longer than 620 nm. Dark-adapted larvae exhibited a positive phototaxis at low light intensity which shifted to a negative phototaxix as light intensity increased. At 540 nm the threshold intensity was 1.5 × 10^?9 W/m² for positive phototaxis and about 10^?6 W/m² for negative phototaxis. Light adaptation decreased sensitivity and altered the phototactic pattern. Larvae have a clear circadian rhythm in negative phototaxis, in which greatest responsiveness occurs early in the day. We suggest that the rhythm in photoresponsiveness primarily controls the timing of the downward migration at dawn.     

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.     

锈赤扁谷盗成虫趋光行为研究

【目的】研究灯光诱捕技术防治锈赤扁谷盗Cryptolestes ferrugineus(Stephens)的可行性。【方法】在实验室条件下测定了锈赤扁谷盗成虫对不同光源的趋光反应。【结果】锈赤扁谷盗成虫对实验所选取的光源都有一定的趋性。在可见光中,对主波长为575 nm的光源的趋性最强,对430、495、620、530和450 nm光源的趋性依次降低。在紫外光中,对主波长为385 nm的光源的趋性显著高于对主波长为365、375和395 nm的光源;1~10日龄的锈赤扁谷盗成虫,随日龄的增加,成虫趋光性先增强后有所减弱;雌虫的趋光性高于雄虫,且交配状态会影响雌虫和雄虫的趋光性。交配会抑制雄虫的趋光性,但是交配后的雌虫的趋光性增强;短期饥饿处理和灯光经历对害虫趋光性无显著影响。【结论】锈赤扁谷盗成虫对光波长的选择偏好性证实了其灯光诱捕技术的可行性。     

Maintenance of Motility Bias during Cyanobacterial Phototaxis

Signal transduction in bacteria is complex, ranging across scales from molecular signal detectors and effectors to cellular and community responses to stimuli. The unicellular, photosynthetic cyanobacterium Synechocystis sp. PCC6803 transduces a light stimulus into directional movement known as phototaxis. This response occurs via a biased random walk toward or away from a directional light source, which is sensed by intracellular photoreceptors and mediated by Type IV pili. It is unknown how quickly cells can respond to changes in the presence or directionality of light, or how photoreceptors affect single-cell motility behavior. In this study, we use time-lapse microscopy coupled with quantitative single-cell tracking to investigate the timescale of the cellular response to various light conditions and to characterize the contribution of the photoreceptor TaxD1 (PixJ1) to phototaxis. We first demonstrate that a community of cells exhibits both spatial and population heterogeneity in its phototactic response. We then show that individual cells respond within minutes to changes in light conditions, and that movement directionality is conferred only by the current light directionality, rather than by a long-term memory of previous conditions. Our measurements indicate that motility bias likely results from the polarization of pilus activity, yielding variable levels of movement in different directions. Experiments with a photoreceptor (taxD1) mutant suggest a supplementary role of TaxD1 in enhancing movement directionality, in addition to its previously identified role in promoting positive phototaxis. Motivated by the behavior of the taxD1 mutant, we demonstrate using a reaction-diffusion model that diffusion anisotropy is sufficient to produce the observed changes in the pattern of collective motility. Taken together, our results establish that single-cell tracking can be used to determine the factors that affect motility bias, which can then be coupled with biophysical simulations to connect changes in motility behaviors at the cellular scale with group dynamics.     

Behavioral dissection of Drosophila larval phototaxis

A behavior generally comprises multiple processes. Analyzing these processes helps to reveal more characteristics of the behavior. In this report, light/dark choice-based Drosophila larval phototaxis is analyzed with a simplistic mathematical model to reveal a fast phase and a slow phase response that are involved. Larvae of the strain w¹¹¹⁸, which is photophobic in phototaxis tests, prefer darkness to light in an immediate light/dark boundary passing test and demonstrate a significant reduction in motility in the dark condition during phototaxis tests. For tim⁰¹ larvae, which show neutral performance in phototaxis tests, larvae unexpectedly prefer light to darkness in the immediate light/dark boundary passing test and demonstrate no significant motility alteration in the dark condition. It is proposed that Drosophila larval phototaxis is determined by a fast phase immediate light/dark choice and an independent slow phase light/dark-induced motility alteration that follows.     

Effects of gravity on positive phototaxis in fruit fly Drosophila melanogaster

Geotaxis and phototaxis are movements in response to gravity and light, respectively, and are commonly observed in nature. The interactions between these two types of movement have been shown to confer ecological advantages to many taxa. Although several studies have been conducted on phototaxis and geotaxis in various organisms, reports on the interactions between positive phototaxis and negative geotaxis are lacking. In the fruit fly, Drosophila melanogaster, any direct interactions that exist between positive phototaxis and negative geotaxis are yet to be determined and the ecological significance of such interactions remains unclear. In the present study, the effects of gravity on positive phototaxis in a Y‐maze were investigated using the Canton‐S wild type and gravity‐sensing‐deficient pyx³ mutant fruit flies. Gravity sensing was not necessary for horizontal positive phototaxis, but was required for vertical positive phototaxis. These results suggest that gravitoreception may selectively modulate positive phototaxis depending on the vertical and horizontal movements of the fruit flies.     

Baculovirus infection triggers a positive phototactic response in caterpillars to induce ‘tree-top’ disease

Many parasites manipulate host behaviour to enhance parasite transmission and survival. A fascinating example is baculoviruses, which often induce death in caterpillar hosts at elevated positions (‘tree-top’ disease). To date, little is known about the underlying processes leading to this adaptive host manipulation. Here, we show that the baculovirus Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) triggers a positive phototactic response in S. exigua larvae prior to death and causes the caterpillars to die at elevated positions. This light-dependent climbing behaviour is specific for infected larvae, as movement of uninfected caterpillars during larval development was light-independent. We hypothesize that upon infection, SeMNPV captures a host pathway involved in phototaxis and/or light perception to induce this remarkable behavioural change.     

Gametic behavior in a marine green alga, Monostroma angicava: an effect of phototaxis on mating efficiency

The role of phototactic behavior of gametes was tested experimentally in the slightly anisogamous marine green alga Monostroma angicava Kjellman, and the effect of phototaxis on mating efficiency was discovered. Both male and female gametes showed positive phototaxis in response to a white light source. In contrast, they did not respond to a red light source. Their swimming velocity did not differ between these two illuminating light sources. It was, therefore, suggested that the search ability of the gamete itself might not vary between phototactic and non-phototactic conditions. The number of zygotes formed during the mating process may be expressed as the product of the number of encounters between male and female gametes and the fraction of encounters that result in sexual fusion. In this study, with high densities of male and female gametes mixed in test tubes, almost all minor (fewer in number) gametes fused sexually within 10 min. After dilution of the gamete suspensions by half, mating efficiency in test tubes illuminated by white light from above was higher than that in dark controls. This suggests that male and female gametes gathered at the water surface through their positive phototaxis, thus increasing the rate of encounters. Mating efficiency also decreased if the test tubes were illuminated from above by white light and also shaken. Since negative phototaxis is clearly shown in planozygotes, we suggest that positive phototaxis of male and female gametes in M. angicava is an adaptive trait for increasing the rate of gametic encounters rather than for the dispersal of zygotes as previously reported for zoospores of some marine algae. Received: 12 February 1999 / Revision accepted: 24 May 1999