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Transient receptor potential ankyrin 1 (TRPA1) channel is an ion channel whose gating is controlled by agonists, such as allyl isothiocyanate (AITC), and temperature. Since TRPA1 is associated with various disease symptoms and chemotherapeutic side effects, it is a frequent target of drug development. To facilitate the screening of TRPA1 agonists and antagonists, this study aimed to develop a simple bioassay for TRPA1 activity. To this end, transgenic Chlamydomonas reinhardtii expressing human TRPA1 was constructed. The transformants exhibited positive phototaxis at high temperatures (≥20°C) but negative phototaxis at low temperatures (≤15°C); wild-type cells showed positive phototaxis at all temperatures examined. In the transgenic cells, negative phototaxis was inhibited by TRPA1 antagonists, such as HC030031, A-967079, and AP18, at low temperatures. Negative phototaxis was induced by TRPA1 agonists, such as icilin and AITC, at high temperatures. The effects of these agonists were blocked by TRPA1 antagonists. In wild-type cells, none of these substances had any effects on phototaxis. These results indicate that the action of TRPA1 agonists and antagonists can be readily assessed using the behavior of C. reinhardtii expressing human TRPA1 as an assessment tool.

Autonomous nanomotors have become the new paradigm for current research as they are expected to shift the momentum in the development of next‐generation technologies. However, there is a grand challenge in gaining control over the nanomotors’ motion, speed, directionality, and using biocompatible fuels to power them. Currently, light is recognized for powering micromotors with advancement in using visible light for driving motion at the nanoscale regime. In this context, micron‐scaled motors are fabricated but they contain metal surfaces and fabrication is quite laborious. Herein, encapsulation of plant organelles into supramolecular assemblies for active motion is conducted to fabricate bio‐nanomotors, utilizing the natural photosynthesis process for powering motion at the nanoscale. The oxygen produced by the water‐splitting reaction by plant organelles in visible light and the photophoresis effect due to the transparent nature of the supramolecular assembly are the main driving forces for bio‐nanomotors. The bio‐nanomotors are observed to have propelled motion with speed reaching up to 120.42 ± 12 μm s−1, together with on‐demand reversible on/off motion and real‐time control over change in directionality at the nanoscale. The observed results shift the momentum toward harnessing energy from natural processes to power nanosystems for varied applications.

Cyanobacteria have evolved various strategies to sense and adapt to biotic and abiotic stresses including active movement. Motility in cyanobacteria utilizing the type IV pili (TFP) is useful to cope with changing environmental conditions. The model cyanobacterium Synechocystis sp. PCC 6803 (hereafter named Synechocystis) exhibits motility via TFP called thick pili, and uses it to seek out favorable light/nutrition or escape from unfavorable conditions. Recently, a number of studies on Synechocystis thick pili have been undertaken. Molecular approaches support the role of the pilin in motility, cell adhesion, metal utilization, and natural competence in Synechocystis. This review summarizes the most recent studies on the function of thick pili as well as their formation and regulation in this cyanobacterium.

The green algae Chlamydomonas reinhardtii is a model system for motility in unicellular organisms. Photo-, gravi-, and chemotaxis have previously been associated with C. reinhardtii, and observing the extent of these responses within a population of cells is crucial for refining our understanding of how this organism responds to changing environmental conditions. However, manually tracking and modeling a statistically viable number of samples of these microorganisms is an unreasonable task. We hypothesized that automated particle tracking systems are now sufficiently advanced to effectively characterize such populations. Here, we present an automated method to observe C. reinhardtii motility that allows us to identify individual cells as well as global information on direction, speed, and size. Nutrient availability effects on wild-type C. reinhardtii swimming speeds, as well as changes in speed and directionality in response to light, were characterized using this method. We also provide for the first time the swimming speeds of several motility-deficient mutant lines. While our present effort is focused around the unicellular green algae, C. reinhardtii, we confirm the general utility of this approach using Chlamydomonas moewusii, another member of this genus which contains over 300 species. Our work provides new tools for evaluating and modeling motility in this model organism and establishes the methodology for conducting similar experiments on other unicellular microorganisms.

Bridging brain-scale circuit dynamics and organism-scale behavior is a central challenge in neuroscience. It requires the concurrent development of minimal behavioral and neural circuit models that can quantitatively capture basic sensorimotor operations. Here, we focus on light-seeking navigation in zebrafish larvae. Using a virtual reality assay, we first characterize how motor and visual stimulation sequences govern the selection of discrete swim-bout events that subserve the fish navigation in the presence of a distant light source. These mechanisms are combined into a comprehensive Markov-chain model of navigation that quantitatively predicts the stationary distribution of the fish’s body orientation under any given illumination profile. We then map this behavioral description onto a neuronal model of the ARTR, a small neural circuit involved in the orientation-selection of swim bouts. We demonstrate that this visually-biased decision-making circuit can capture the statistics of both spontaneous and contrast-driven navigation.

Optimization of light-based fish passage facilities has attracted extensive attention, but studies under the influence of various environmental factors are scarce. We established a novel experimental method to measure the phototactic behavior of Schizothorax waltoni. The results showed that S. waltoni preferred the four light colors in the order green, blue, red, and yellow. The increased flow velocity intensified the positive and negative phototaxis of fish under different light environments, while an increase in the water temperature aroused the escape behavior. The escape behavior of fish in red and yellow light and the phototaxis behavior in green and blue light intensified as the light intensity exceeded the phototaxis threshold and continued to increase. Thus, red or yellow light greater than the phototaxis threshold can be used to move fish away from high-turbulent flows or polluted waters, while green or blue light can be used to guide them to fish passage entrance or ideal habitats. This study provides scientific evidence and application value for restoring fish habitats, fish passages, and fisheries.

Copyright of Xinjiang Agricultural Sciences is the property of Xinjiang Agricultural Sciences Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Controllable self‐propelled droplet robots show great potential to be used as carriers, sensors and actuators in biological medicine and oil exploration. Current research mainly focuses on studying oil droplet robots floating in water phase which has limited application. Different from the previous robots, a light‐driven self‐propelled water‐phase droplet micro robot, which is doped with Fe2O3 nanoparticles, moving in oil solvent is proposed. Unlike light‐driven oil droplets, the water drop robot is constantly diving towards the light source like a submarine moving in oil environment under blue laser irradiation. Numerical simulations are performed to investigate the water/oil interface behavior and the motion mechanism of micro robots. It is found that a photocatalytic Fenton reaction occurs on the irradiated Fe2O3 nanoparticles of water droplet robot, which causes uneven ion concentration to change the interfacial tension distribution of the water drop generating Marangoni flow. In addition to phototaxis behavior, further experiments confirmed that multiple water droplet micro robots show collective behavior under the control of surface light source. The proposed water droplet micro robot provides new possibilities for the development of targeted drug delivery, oil‐water separation as well as oil pollution treatment. [ABSTRACT FROM AUTHOR]

The geomagnetic field (GMF) is an environmental cue that provides directional information for animals. The intensity of GMF is varied over space and time. Variations in the GMF intensity affect the navigation of animals and their physiology. In this study, the phototaxis of the migratory insect rice planthopper Nilaparvata lugens (N. lugens) and frataxin in N. lugens (Nl‐fh), which is a mitochondrial protein required for cellular iron homeostasis and iron‐sulfur cluster assembly, were investigated by using different intensities of magnetic field. From the results, individuals of N. lugens showed decreased phototaxis when reared and tested in a behavioral arena under a strong magnetic field. Besides the reduction in performance, an accompanying effect of the strong magnetic field condition was a reduced level of Nl‐fh‐messenger RNA, and a Nl‐fh knockdown indeed impaired the phototactic behavior in a tested sample of insects. This leads to the conclusion that the expression of frataxin is dependent on the strength of the surrounding magnetic field and that functional frataxin facilitates phototactic behavior in N. lugens. [ABSTRACT FROM AUTHOR]

Photoreceptor cells in the eyes of Bilateria are often classified into microvillar cells with rhabdomeric opsin and ciliary cells with ciliary opsin, each type having specialized molecular components and physiology. First data on the recently discovered xenopsin point towards a more complex situation in protostomes. In this study, we provide clear evidence that xenopsin enters cilia in the eye of the larval bryozoan Tricellaria inopinata and triggers phototaxis. As reported from a mollusc, we find xenopsin coexpressed with rhabdomeric-opsin in eye photoreceptor cells bearing both microvilli and cilia in larva of the annelid Malacoceros fuliginosus. This is the first organism known to have both xenopsin and ciliary opsin, showing that these opsins are not necessarily mutually exclusive. Compiling existing data, we propose that xenopsin may play an important role in many protostome eyes and provides new insights into the function, evolution, and possible plasticity of animal eye photoreceptor cells. [ABSTRACT FROM AUTHOR]

We studied phototaxis, the directional movement relative to light, in the bumble bee Bombus terrestris. We first developed and validated a MATLAB-based system enabling reliable high-resolution tracking of a bee and a measurement of her distance relative to a changing LED light source. Using this system, we found in all our experiments that workers show positive phototaxis. The strength of the phototactic response was influenced by body size but not age, and this effect was significant when the light source was weak. In a separate experiment, foragers showed stronger phototactic response compared with nurses only in one of two trials in which they were larger and tested with weak light intensity. The evidence that phototaxis is associated with size-based division of labor in the bumble bee and with age-related division of labor in the honey bee lends credence to response threshold models implicating the response to light in the organization of division of labor in cavity dwelling social insects. [ABSTRACT FROM AUTHOR]

Transient receptor potential ankyrin 1 (TRPA1) channel is an ion channel whose gating is controlled by agonists, such as allyl isothiocyanate (AITC), and temperature. Since TRPA1 is associated with various disease symptoms and chemotherapeutic side effects, it is a frequent target of drug development. To facilitate the screening of TRPA1 agonists and antagonists, this study aimed to develop a simple bioassay for TRPA1 activity. To this end, transgenic Chlamydomonas reinhardtii expressing human TRPA1 was constructed. The transformants exhibited positive phototaxis at high temperatures (≥20°C) but negative phototaxis at low temperatures (≤15°C); wild-type cells showed positive phototaxis at all temperatures examined. In the transgenic cells, negative phototaxis was inhibited by TRPA1 antagonists, such as HC030031, A-967079, and AP18, at low temperatures. Negative phototaxis was induced by TRPA1 agonists, such as icilin and AITC, at high temperatures. The effects of these agonists were blocked by TRPA1 antagonists. In wild-type cells, none of these substances had any effects on phototaxis. These results indicate that the action of TRPA1 agonists and antagonists can be readily assessed using the behavior of C. reinhardtii expressing human TRPA1 as an assessment tool. [ABSTRACT FROM AUTHOR]

The persistent motility of individual constituents in microbial suspensions represents a prime example of the so-called active matter systems. Cells consume energy, exert forces and move, overall releasing the constraints of equilibrium statistical mechanics of passive elements and allowing for complex spatio-temporal patterns to emerge. Moreover, when subject to physico-chemical stimuli their collective behaviour often drives large-scale instabilities of a hydrodynamic nature, with implications for biomixing in natural environments and incipient industrial applications. In turn, our ability to exert external control of these driving stimuli could be used to govern the emerging patterns. Light, being easily manipulable and, at the same time, an important stimulus for a wide variety of microorganisms, is particularly well suited to this end. In this paper, we will discuss the current state, developments and some of the emerging advances in the fundamentals and applications of light-induced bioconvection with a focus on recent experimental realizations and modelling efforts. [ABSTRACT FROM AUTHOR]

The giant freshwater prawn Macrobrachium rosenbergii larvae have apposition eyes and are positively phototactic, whereas the postlarvae (PL) have superposition eyes and are negatively phototactic. M. rosenbergii has colour vision as early as larval stage. We discovered that M. rosenbergii alters background colour preference after metamorphosis from larvae to PL in association with nature of phototaxis. The test circular glass aquaria covered with a pair of two‐colour papers contained with a group of 100 larvae or 20 Pl, and the number of individuals in each colour background was recorded five times for each colour pair. The background colours tested were light blue, green, yellow, red, white and black. The numbers of larvae or PL in each colour background of different pairs were analysed by the Thurstone's law of comparative judgment. In the larvae, significant bias towards yellow was evident. In the PL, of the four pairings of black with other colours, all biased to black. The mean z‐scores were highest for yellow in the larvae, and for black in the PL. To determine the possible background brightness preference of the larvae and PL, six different colour backgrounds were presented in pairs. The larvae significantly preferred light blue over dark blue, white over yellow and white over black. The PL exhibited reversed preference. The relationship between z‐scores and light reflectance levels of five colour papers was significantly positive in the larvae and negative in the PL. The observed background colour preference was probably due to relative brightness rather than chromaticity difference. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Tea Science is the property of Journal of Tea Science Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Henan Agricultural Sciences is the property of Editorial Board of Journal of Henan Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cold weather is one of the biggest challenges in establishing a large-scale microalgae culture facility in temperate regions. In order to develop a strain that is resistant to low temperatures and still maintains high photosynthetic efficiency, transgenic studies have been conducted targeting many genes. Early light-inducible proteins (ELIPs) located in thylakoid membranes are known to protect photosynthetic machinery from various environmental stresses in higher plants. An ELIP homolog was identified from Chlamydomonas reinhardtii and named ELIP3. The role of the gene was analyzed in terms of photosynthetic CO2 assimilation under cold stress. Western blot results showed a significant accumulation of ELIP3 when the cells were exposed to cold stress (4°C). High light stress alone did not induce the accumulation of the protein. Enhanced expression of ELIP3 helped survival of the cell under photo-oxidative stress. The influx of CO2 to the photobioreactor induced strong accumulation of ELIP3, and enhanced survival of the cell under high light and cold stress. When the oxidative stress was reduced by adding a ROS quencher, TEMPOL, to the media the expression of ELIP3 was reduced. A knockdown mutant showed much lower photosynthetic efficiency than wild type in low temperature, and died rapidly when it was exposed to high light and cold stress. The overexpression mutant survived significantly longer in the same conditions. Interestingly, knockdown mutants showed negative phototaxis, while the overexpression mutant showed positive phototaxis. These results suggest that ELIP3 may be involved in the regulation of the redox state of the cell and takes important role in protecting the photosystem under photooxidative stress in low temperatures. [ABSTRACT FROM AUTHOR]

The detection of light intensity and subsequent phototaxis are essential for the fitness of sea urchins in intertidal and shallow subtidal waters, where light intensity varies in accordance with the depth and other hydrographic conditions. The molecular basis of photoresponse, however, remains largely unknown. We compared the expression of SiOpsin4, SiPax6, and SiOpsin5 among tube feet, coelomocytes, gonads, and gut of the sea urchin Strongylocentrotus intermedius. All three genes showed the significantly highest expression in tube feet. To test whether r‐opsin genes (for example, Opsin4) and Pax6 in tube feet, rather than chaopsin genes (for example, Opsin5), are involved in the molecular responses to light intensity, we investigated the expression of Opsin4, Pax6, and Opsin5 among four light intensities. Both Opsin4 and Pax6 expressions were significantly higher in the sea urchins at 1,500 lx than at 100, 300, and 700 lx, indicating a co‐upregulation of Opsin4 and Pax6 expressions in sea urchins exposed to the high light intensity (for example, 1,500 lx). However, there was no significant difference of SiOpsin5 expression among the four light intensity groups. Consistent with our hypothesis, there was no significant difference in either Opsin4 or Pax6 expression between the two light intensity environments (low light intensity environment: 50–100 lx; high light intensity environment: 330–1400 lx). This indicates that positive phototaxis and negative phototaxis probably regulate the expression of Opsin4 and Pax6 to a similar level when sea urchins are exposed to the high and low light intensities, respectively. The present study provides new insights into the molecular basis of light intensity detection and subsequent phototaxis of eyeless species. [ABSTRACT FROM AUTHOR]

Jaw malformations are a serious problem in fingerlings of the greater amberjack, Seriola dumerili. To establish a countermeasure against these malformations, we conducted a larval behavioural test to identify their root cause, and we investigated the ability of low‐brightness rearing tank walls to control their occurrence. Larval distribution was examined in a horizontally illuminated rectangular transparent aquarium (20 cm × 100 cm × 25 cm), and their distribution was biased towards the light source after this lighting was provided from 3 to 13 days post hatching (dph), indicating positive phototaxis; this response disappeared on 22 dph (there are no data between 13 and 22 dph). Larvae were observed to swim phototactically towards the light source and repeatedly collided with the tank wall (walling behaviour). To investigate the ability of wall brightness to control the incidence of jaw malformations, we compared their incidence in a rearing trial with different Munsell colour values for the tank walls: 2.11 (black), 5.85 (grey) and 9.52 (white). The incidence rate of jaw malformations at 25 dph was significantly lower in the tanks with lower‐brightness walls, that is, 5.8%, 22.5% and 26.8% for black, grey and white respectively. Larval walling behaviour was most intense for white, followed in order by grey and black. These results indicate that positive phototaxis elicits larval walling behaviour, causing jaw malformations, and that low‐brightness tank walls control this process. [ABSTRACT FROM AUTHOR]

Copyright of Österreichische Wasser- und Abfallwirtschaft is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Light pollution is increasing and artificial light sources have great impacts on animals. For migrating birds, collisions caused by artificial light pollution are a significant source of mortality. Laboratory studies have demonstrated that birds have different visual sensitivities to different colors of light, but few field experiments have compared birds′ responses to light of different wavelengths. We used 3 monochromatic lights (red, green, and blue) and polychromatic yellow light to study the impact of wavelength on phototaxis at 2 gathering sites of nocturnally migrating birds in Southwest China. For both sites, short-wavelength blue light caused the strongest phototactic response. In contrast, birds were rarely attracted to long-wavelength red light. The attractive effect of blue light was greatest during nights with fog and headwinds. As rapid urbanization and industrialization cause an increase in artificial light, we suggest that switching to longer wavelength lights is a convenient and economically effective way to reduce bird collisions. [ABSTRACT FROM AUTHOR]

The CORL family of CNS-specific proteins share a Smad-binding region with mammalian SnoN and c-Ski protooncogenes. In this family Drosophila CORL has two mouse and two human relatives. Roles for the mouse and human CORL proteins are largely unknown. Based on genome-wide association studies linking the human CORL proteins Fussel15 and Fussel18 with ataxia, we tested the hypothesis that dCORL mutations will cause adult movement disorders. For our initial tests, we conducted side by side studies of adults with the small deletion Df(4)dCORL and eight control strains. We found that deletion mutants exhibit three types of behavioral plasticity. First, significant climbing defects attributable to loss of dCORL are eliminated by age. Second, significant phototaxis defects due to loss of dCORL are partially ameliorated by age and are not due to faulty photoreceptors. Third, Df(4)dCORL males raised in groups have a lower courtship index than males raised as singles though this defect is not due to loss of dCORL. Subsequent tests showed that the climbing and phototaxis defects were phenocpied by dCORL21B and dCORL23C two CRISPR generated mutations. Overall, the finding that adult movement defects due to loss of dCORL are subject to age-dependent plasticity suggests new hypotheses for CORL functions in flies and mammals. [ABSTRACT FROM AUTHOR]

Given the recent extensive synthesis and application of ionic liquids (ILs), finding a sensitive and visual indicator to provide a fast-initial risk assessment of IL use has become a pressing issue. In this study, we verified that the phototaxis of Chlamydomonas reinhardtii is a valid indicator of the environmental risk associated with chiral ILs L-(+)- and D-(−)-1-butyl-3-methylimidazolium lactate (BMIM L). Briefly, C. reinhardtii was exposed to a 4000-lx side light source for varying lengths of time. Following the allotted exposure time, the algae aggregation was photographed, and then quantitative analysis was conducted using Image-J software to obtain the corresponding relationship between IL stimulation and C. reinhardtii phototaxis. The gray areas from each treatment were measured and the percentage was calculated. After 16 h of side lighting, for control, the percentage of gray areas was − 22%, while for L-(+)- and D-(−)- BMIM L were 17% and 33%, respectively. Then, after 8 h of darkness, where D-(−)-BMIM L and the control showed the positive phototaxis, but the L-(+)-BMIM L-treated group showed virtually no change. This phenomenon is consistent with excessive production of reactive oxygen species (ROS). Moreover, atomic force microscope (AFM) results indicated distinct aggregation between D-(−)- and L-(+)-BMIM L, which caused changes in cell permeability that induced a change in ROS transfer. Furthermore, relationship between phototaxis and changes in cell ultrastructure and photosynthetic efficiency was also investigated. This work demonstrates the potential of phototaxis to serve as a sensitive, convenient, and cost effective qualitative assessment of ILs' toxic impact, with the understanding that quantitative evaluation requires further improvement. [ABSTRACT FROM AUTHOR]

Autonomous nanomotors have become the new paradigm for current research as they are expected to shift the momentum in the development of next‐generation technologies. However, there is a grand challenge in gaining control over the nanomotors' motion, speed, directionality, and using biocompatible fuels to power them. Currently, light is recognized for powering micromotors with advancement in using visible light for driving motion at the nanoscale regime. In this context, micron‐scaled motors are fabricated but they contain metal surfaces and fabrication is quite laborious. Herein, encapsulation of plant organelles into supramolecular assemblies for active motion is conducted to fabricate bio‐nanomotors, utilizing the natural photosynthesis process for powering motion at the nanoscale. The oxygen produced by the water‐splitting reaction by plant organelles in visible light and the photophoresis effect due to the transparent nature of the supramolecular assembly are the main driving forces for bio‐nanomotors. The bio‐nanomotors are observed to have propelled motion with speed reaching up to 120.42 ± 12 μm s−1, together with on‐demand reversible on/off motion and real‐time control over change in directionality at the nanoscale. The observed results shift the momentum toward harnessing energy from natural processes to power nanosystems for varied applications. [ABSTRACT FROM AUTHOR]

Cells in microbial colonies integrate information across multiple spatial and temporal scales while sensing environmental cues. A number of photosynthetic cyanobacteria respond in a directional manner to incident light, resulting in the phototaxis of individual cells. Colonies of such bacteria exhibit large-scale changes in morphology, arising from cell-cell interactions, during phototaxis. These interactions occur through type IV pili-mediated physical contacts between cells, as well as through the secretion of complex polysaccharides ('slime') that facilitates cell motion. Here, we describe a computational model for such collective behaviour in colonies of the cyanobacterium Synechocystis. The model is designed to replicate observations from recent experiments on the emergent response of the colonies to varied light regimes. It predicts the complex colony morphologies that arise as a result. We ask if changes in colony morphology during phototaxis can be used to infer if cells integrate information from multiple light sources simultaneously, or respond to these light sources separately at each instant of time. We find that these two scenarios cannot be distinguished from the shapes of colonies alone. However, we show that tracking the trajectories of individual cyanobacteria provides a way of determining their mode of response. Our model allows us to address the emergent nature of this class of collective bacterial motion, linking individual cell response to the dynamics of colony shape. Author summary: Microbial colonies in the wild often consist of large groups of heterogeneous cells that coordinate and integrate information across multiple spatio-temporal scales. We describe a computational model for one such collective behaviour, phototaxis, in colonies of the cyanobacterium Synechocystis that move in response to light. The model replicates experimental observations the response of cyanobacterial colonies to varied light regimes, and predicts the complex colony morphologies that arise as a result. The results suggest that tracking the trajectories of individual cyanobacteria may provide a way of determining their mode of information integration. Our model allows us to address the emergent nature of this class of collective bacterial motion, linking individual cell response to the large scale dynamics of the colony. [ABSTRACT FROM AUTHOR]

Swarming micro/nanomotors can self‐organize into cohesive groups to execute cooperative tasks. To date, research work has focused on the construction of egalitarian microswarms composed of similar individuals. The construction and collective behaviors of hierarchical leader–follower‐like microswarms are demonstrated. By inducing converging electrohydrodynamic flows under an AC electric field, dielectric microparticles with different sizes and dielectric properties can hierarchically self‐organize into leader–follower‐like microswarms under attractive electrohydrodynamic interactions, and show novel emergent collective behaviors. First, different from immobile single constituents or egalitarian clusters, the hierarchical microswarms autonomously move with tunable speed. Second, they exhibit multimode collective photoresponses emerging from different behaviors of the constituents in response to light signals. With a vertical UV signal, the photoresponsive followers tend to surround the leader and stop the microswarm. In response to sidewise UV signals, the constituents with stronger phototaxis would migrate to the position away from light stimuli, and thus the microswarms reorient parallel/antiparallel to the light direction and perform collective positive/negative phototaxis. Due to differential roles and huge design spaces of constituents, the hierarchical microswarms are envisioned to possess merits of high‐efficiency, multiresponsiveness, and multifunctions, and may serve as intelligent micro/nanorobot systems for biomedicine and microengineering. [ABSTRACT FROM AUTHOR]

Mimicking the intelligence of biological organisms in artificial systems to design smart actuators that act autonomously in response to constant environmental stimuli is crucial to the construction of intelligent biomimetic robots and devices, but remains a great challenge. Here, a light‐driven autonomous carbon‐nanotube‐based bimorph actuator is developed through an elaborate structural design. This curled droplet‐shaped actuator can be simply driven by constant white light irradiation, self‐propelled by a light‐mechanical negative feedback loop created by light‐driven actuation, time delay in the photothermal response along the actuator, and good elasticity from the curled structure, performing a continuously self‐oscillating motion in a wavelike fashion, which mimics the human sit‐up motion. Moreover, this autonomous self‐oscillating motion can be further tuned by controlling the intensity and direction of the incident light. The autonomous actuator with continuous wavelike oscillating motion shows immense potential in light‐driven biomimetic soft robots and optical‐energy‐harvesting devices. Furthermore, a self‐locomotive artificial snake with phototaxis is constructed, which autonomously and continuously crawls toward the light source in a wave‐propagating manner under constant light irradiation. This snake can be placed on a substrate made of triboelectric materials to realize continuous electric output when exposed to constant light illumination. [ABSTRACT FROM AUTHOR]

Cyanobacteria have evolved various strategies to sense and adapt to biotic and abiotic stresses including active movement. Motility in cyanobacteria utilizing the type IV pili (TFP) is useful to cope with changing environmental conditions. The model cyanobacterium Synechocystis sp. PCC 6803 (hereafter named Synechocystis) exhibits motility via TFP called thick pili, and uses it to seek out favorable light/nutrition or escape from unfavorable conditions. Recently, a number of studies on Synechocystis thick pili have been undertaken. Molecular approaches support the role of the pilin in motility, cell adhesion, metal utilization, and natural competence in Synechocystis. This review summarizes the most recent studies on the function of thick pili as well as their formation and regulation in this cyanobacterium. [ABSTRACT FROM AUTHOR]

Summary: Carotenoids are the most universal and most widespread pigments in nature. They have played pivotal roles in the evolution of photosensing mechanisms in microbes and of vision in animals. Several groups of phytoflagellates developed a photoreceptive organelle called the eyespot apparatus (EA) consisting of two separable components: the eyespot, a cluster of carotenoid‐rich globules that acts as a reflector device, and actual photoreceptors for photobehaviors. Unlike other algal eyespots, the eyespot of Euglenophyta lacks reflective properties and is generally considered to act as a shading device for the photoreceptor (paraflagellar body, PFB) for major photomovements. However, the function of the eyespot of Euglenophyta has not yet been fully proven. Here, we report that the blocking carotenoid biosynthesis in Euglena gracilis by suppressing the phytoene synthase gene (crtB) caused a defect in eyespot function resulting in a loss of phototaxis. Raman spectroscopy and transmission electron microscopy suggested that EgcrtB‐suppressed cells formed eyespot globules but had a defect in the accumulation of carotenoids in those packets. Motion analysis revealed the loss of phototaxis in EgcrtB‐suppressed cells: a defect in the initiation of turning movements immediately after a change in light direction, rather than a defect in the termination of cell turning at the appropriate position due to a loss of the shading effect on the PFB. This study revealed that carotenoids are essential for light perception by the EA for the initiation of phototactic movement by E. gracilis, suggesting one possible photosensory role of carotenoids in the EA for the phototaxis. Significance Statement: The eyespot apparatus (EA) of Euglena gracilis consists of a cluster of cytosolic carotenoid‐rich globules, called the eyespot, and the actual photoreceptive organelle, the paraflagellar body (PFB). The eyespot of this alga has been speculated to be just a shading device for the PFB. This study revealed by single‐cell tracking techniques that the eyespot is necessary for phototaxis of this alga and that carotenoids participate in light perception by the EA to initiate phototactic movement. [ABSTRACT FROM AUTHOR]

We assess the potentiality of several geometries of metallic nanodimers (one of the simplest thermoplasmonic systems) as candidates for active particles (nanoswimmers) propelled and controlled by light (phototaxis). The studied nanodimers are formed by two spherical nanoparticles of gold, silver, or copper with radii ranging from 20 to 100 nm. Contrary to most proposals, which assume the asymmetry of the systems as a requirement for self-propulsion, our results show that nanodimers made of identical nanoparticles are excellent candidates for phototactic self-thermophoretic systems. Nonsymmetrical nanodimers, although having a tunable effective diffusion, possess much lower or negligible average thermophoretic forces. We show that the effective diffusion and the net thermophoretic force in both types of systems depend strongly on the wavelength of the incident light, which makes these properties highly tunable. Our study may be useful for the design of simple-to-make but controllable self-propelled nanoparticles. This can find numerous applications ranging from autonomous drug-carrying to controlling the self-assembly of complex nanomaterials. [ABSTRACT FROM AUTHOR]

The cyanobacterium Synechocystis sp. PCC 6803 can move directionally on a moist surface toward or away from a light source to reach optimal light conditions for its photosynthetic lifestyle. This behavior, called phototaxis, is mediated by type IV pili (T4P), which can pull a single cell into a certain direction. Several photoreceptors and their downstream signal transduction elements are involved in the control of phototaxis. However, the critical steps of local pilus assembly in positive and negative phototaxis remain elusive. One of the photoreceptors controlling negative phototaxis in Synechocystis is the blue-light sensor PixD. PixD forms a complex with the CheY-like response regulator PixE that dissociates upon illumination with blue light. In this study, we investigate the phototactic behavior of pixE deletion and overexpression mutants in response to unidirectional red light with or without additional bluelight irradiation. Furthermore, we show that PixD and PixE partly localize in spots close to the cytoplasmic membrane. Interaction studies of PixE with the motor ATPase PilB1, demonstrated by in vivo colocalization, yeast two-hybrid and coimmunoprecipitation analysis, suggest that the PixD–PixE signal transduction system targets the T4P directly, thereby controlling blue-light-dependent negative phototaxis. An intriguing feature of PixE is its distinctive structure with a PATAN (PatA N-terminus) domain. This domain is found in several other regulators, which are known to control directional phototaxis. As our PilB1 coimmunoprecipitation analysis revealed an enrichment of PATAN domain response regulators in the eluate, we suggest that multiple environmental signals can be integrated via these regulators to control pilus function. [ABSTRACT FROM AUTHOR]

The relationship between cnidarians and their micro-algal symbionts is crucial for normal animal function and the formation of coral reefs. We used the sea anemone Exaiptasia pallida (Aiptasia) as a model cnidarian–dinoflagellate system to determine the effects of white, blue and red light on photo-movement. In white light, phototropism and phototaxis of Aiptasia were dependent on the presence of symbionts; anemones with symbionts bent and moved toward the light, whereas aposymbiotic anemones (lacking algal symbionts) moved, but without strong directionality. Phototaxis and phototropism also occurred in blue light, but to a lesser extent than in white light, with no apparent response to red light. Phototactic behavior was also sensitive to the specific anemone–symbiont pairing. The ability to sense and move in response to light would presumably allow for selection of favorable habitats. Overall, this study demonstrates that the algal symbiont is required for photo-movement of the host and that the extent of movement is influenced by the different anemone–symbiont associations. [ABSTRACT FROM AUTHOR]

In the present study, colour selection and phototaxis experiments were performed on wild subadult Schizothorax oconnori Lloyd. The experimental variables included: five light colours: red, yellow, green, blue, and dark (no light conditions—control), and two flow rates of 0 and 0.3 m/s. Colour selection experiments were conducted to study the preference of S. oconnori to different colours of light in still water and at 10 lx of light intensity. The results showed that the distribution time of S. oconnori in the yellow and green light areas were significantly longer than those in the red and blue light areas (p <.05), and the order of preference for the five colours was: green > yellow > black > blue > red. In the phototaxis experiment, the phototactic behaviour of S. oconnori was studied when the light intensity was at 20 lx and the water velocity was at 0 and 0.3 m/s, respectively. The results showed that in both still and dynamic water conditions, S. oconnori displayed positive phototaxis for yellow and green light, and negative phototaxis for red and blue light. S. oconnori displayed weak phototaxis with a light intensity threshold of 0.65 lx–0.80 lx and 1.50 lx–3.05 lx for yellow and green light, respectively. The results suggest that low‐intensity green light could be used for light trapping of S. oconnori. The research may be helpful in the management of fish passage facilities and fisheries. [ABSTRACT FROM AUTHOR]

The minute pirate bug Orius sauteri (Poppius) (Heteroptera: Anthocoridae) is a major natural enemy of micro-pests and is expected to be an effective pest-control agent in Asia. Recently, the violet wavelength has been found to attract several natural enemies, and we proved that violet illumination can increase the O. sauteri population and decrease the pest populations on crops. To optimize this attraction strategy for natural enemies, knowledge of their daily activity rhythm is indispensable. In this study, we examined the daily distribution of O. sauteri activity and determined the lighting time appropriate for selective attraction. Under artificial light–dark cycles, O. sauteri displayed a typical diurnal rhythm that peaked from 9 to 12 h after light-on and declined after light-off, regardless of the photoperiod. A similar activity rhythm was confirmed under natural light. Importantly, the activity remained for around 2 h after sunset, even in complete darkness. Considering the diurnality of micro-pests, we conclude that the most efficient lighting time for the selective attraction of this natural enemy to crops is during the 2 h after sunset. [ABSTRACT FROM AUTHOR]

The term "bioconvection" describes hydrodynamic instabilities and patterns in suspensions of biased swimming microorganisms. Hydrodynamic instabilities arise from coupling between cell swimming behaviors; physical properties of the cells, such as density; and fluid flows. For instance, a combination of viscous and gravitational torques can lead to cells swimming toward downwelling fluid. If the cells are more dense than the fluid, then a gyrotactic instability results. Phototaxis describes the directed response of cells to light, which can also lead to instability. Bioconvection represents a classic system where macroscopic phenomena arise from microscopic cellular behavior in relatively dilute systems. There are ecological consequences for bioconvection and the mechanisms involved as well as potential for industrial exploitation. The focus of this review is on progress measuring and modeling gyrotactic and phototactic bioconvection. It builds on two earlier reviews of bioconvection and recent interest in active matter, describing progress and highlighting open problems. [ABSTRACT FROM AUTHOR]

The recruitment process of planktic larvae of the nereidid polychaete Hediste diadroma, which has a catadromous life cycle, was examined in an estuary in Kagoshima Bay, Southern Japan. Our laboratory experiments showed that the phototaxis of the planktic larvae changed drastically from positive to negative during the 3-chaetiger nectochaeta, 3.5-4.0 days after fertilization. During this stage, the prostomial antennae, first peristomial cirri, and anal cirri appeared and the ciliary bands used for swimming were reduced; these results suggest that larvae shifted from pelagic to demersal stage at approximately 4.0 days after fertilization. Field sampling took place in the estuary, where reproductive swarming of mature adults was observed in late February to April; planktic larvae of, mainly, 5- to 8-chaetiger stages were collected in evening high tides during the spring tides of April and May 1989, 2013, and 2015. During the same period, 5- or higher chaetiger benthic juveniles were collected at low tide from intertidal flats from a wide area of the estuary where adults inhabited. The morphology of benthic juveniles of 5- and 6-chaetiger stages differed from that of planktic larvae of the same stages in the following characteristics: (1) the long larva-specific spinigers were lost; (2) the second peristomial cirri, originating from the parapodial lobes of chaetiger 1 of the planktic larvae, appeared; and (3) the anal cirri were elongated. Our results indicate that 5- to 8-chaetiger nectochaeta are critical phases for the successful settlement of planktic larvae, which come back into an estuary with rising tides. [ABSTRACT FROM AUTHOR]

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The planarian flatworm has become one of the leading animal model systems for studying stem cell behavior and tissue regeneration. Recent studies have shown that components of the circadian clockwork have important roles in tissue homeostasis and repair. However, it remains unknown whether planarians exhibit circadian or diurnal rhythms in physiology or behavior. Here, we developed a behavioral assay to evaluate diurnal activity in planarians based upon their well-established propensity to swim away from light (negative phototaxis). We show evidence that the planarian Schmidtea mediterranea has diurnal variability in negative phototaxis as a function of daily variation in motility. We also demonstrate that variation in planarian motility over 48 h occurs with 24-h periodicity. Our data suggest that S. mediterranea may be a useful model for studying the interplay between the circadian system and tissue regeneration. [ABSTRACT FROM AUTHOR]

Human activity is rapidly increasing the radiance and geographic extent of artificial light at night (ALAN) leading to alterations in the development, behavior, and physiological state of many organisms. A limited number of community-scale studies investigating the effects of ALAN have allowed for spatial aggregation through positive phototaxis, the commonly observed phenomenon of arthropod movement toward light. We performed an open field study (without restricted arthropod access) to determine the effects of ALAN on local arthropod community composition, plant traits, and local herbivory and predation rates. We found strong positive phototaxis in 10 orders of arthropods, with increased (159% higher) overall arthropod abundance under ALAN compared to unlit controls. The arthropod community under ALAN was more diverse and contained a higher proportion of predaceous arthropods (15% vs 8%). Predation of immobilized flies occurred 3.6 times faster under ALAN; this effect was not observed during the day. Contrary to expectations, we also observed a 6% increase in herbivory under ALAN. Our results highlight the importance of open experimental field studies in determining community-level effects of ALAN. [ABSTRACT FROM AUTHOR]

Many insects, especially nocturnal insects, exhibit positive phototaxis to artificial lights. Light traps are currently used to monitor and manage insect pest populations, and play a crucial role in physical pest control. Efficient use of light traps to attract target insect pests is an important topic in the application of integrated pest management (IPM). Phototactic responses of insects vary among species, light characteristics and the physiological status of the insects. In addition, light can cause several biological responses, including biochemical, physiological, molecular and fitness changes in insects. In this review, we discuss several hypotheses on insect phototaxis, factors affecting insect phototaxis, insect‐sensitive wavelengths, biological responses of insects to light, and countermeasures for conserving beneficial insects and increasing the effect of trapping. In addition, we provide information on the different sensitivities to wavelengths causing positive phototactic behavior in > 70 insect pest and beneficial insect species. The use of advanced light traps equipped with superior light sources, such as light‐emitting diodes (LEDs), will make physical pest control in IPM more efficient. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The behavior and neuronal ganglia integrity of Drosophila melanogaster larvae exposed to Bisphenol F (BPF) and Bisphenol S (BPS) (0.25, 0.5 and 1 mM) was evaluated. Larvae exposed to BPF and BPS (0.5 and 1 mM) showed hyperactivity, reduced decision-making capacity and were not responsive to touch (no sensitivity to physical stimuli). There was also a reduction in the tunneling capacity induced by 1 mM of BPF and BPS (innate behaviors for survival). Behaviors resulting from changes in neuronal functioning, thermotaxis and phototaxis showed that BPS was more harmful compared to BPF. Furthermore, the concentration of 1 mM BPS generated greater damage to neuronal ganglia when compared to BPF. This difference may be related to the LC 50 of the 10.04 mM BPS and 15.07 mM BPF. However, these behavioral changes presented by the larvae here are characteristic of those presented in neurodevelopmental disorders. Our findings are novel and refute the possibility that BPF and BPS are safer alternatives. [ABSTRACT FROM AUTHOR]

[Display omitted] • Rotifer reproduction control in open microalgae ponds poses a serious challenge for industries. • Light-induced phototaxis combined by electroshocking removed ratifiers effectively. • Positive and negative phototropism phototaxis rates were 66.7% and −78.8% with blue and red light. • The best electroshock config. employed 1200 V/cm, 15 min, 1-second cycle time, and 10 % duty cycle. • Rotifer removal rate was observed at 75.0% without impacting microalgae growth. Rotifer reproduction control in open microalgae cultivation systems poses a significant challenge for large-scale industries. Conventional methods, such as electric, meshing, and chemical techniques, are often expensive, ineffective, and may have adverse environmental-health impacts. This study investigated a promising control technique through light-induced phototaxis to concentrate rotifers in a specific spot, where they were electroshocked by local-limited exposure dose. The results showed that the rotifers had the most pronounced positive and negative phototropism with phototaxis rates of 66.7 % and −78.8 %, respectively, at blue-light irradiation of 30 µmol∙m−2∙s−1 and red-light irradiation of 22.5 µmol∙m−2∙s−1 for 20 min. The most effective electroshock configuration employed 1200 V/cm for 15 min with a 1-second cycle time and a 10 % duty cycle, resulting in a 75.0 % rotifer removal rate without impacting microalgae growth. The combination of the two light beams could effectively lead rotifers to designated areas where they were electrocuted successfully. [ABSTRACT FROM AUTHOR]

In recent years, studies have shown that different light wavelengths have varying effects on aquaculture species. This indicates that exposure to light can significantly influence the health and development of aquatic organisms. This study investigated the effects of different visible light spectra on the behavior and physiological responses of sea cucumbers. Under blue LED and white LED illumination, the sea cucumbers exhibited shelter-seeking behavior. A phototaxis experiment found that the blue LED light elicited the strongest negative phototaxis, followed by the white LED. However, the red LED light elicited no obvious response. In the bottom zone preference experiment, blue LED and white LED illumination affected the bottom preference behaviors of some individuals compared to the control group. By measuring the mean photon flux density (MPFD) values at different illumination distances, the individuals in each group tended to stop moving when they were close to a similar MPFD value. Next, this study examined the physiological effects of red LED and blue LED illumination on sea cucumbers. Interestingly, the blue LED group exhibited higher oxygen consumption rates and thinner connective tissue in the respiratory tree during the early stage of the experiment. In contrast, no significant differences in coelomocyte phagocytosis were observed between the blue LED and red LED groups. Our findings suggested that the behaviors and physiological responses elicited by the blue or white LED light are likely caused by the number of photons in a specific time and area received by photoreceptors on the integument of sea cucumbers. Furthermore, neither long- nor short-wavelength spectra caused significant stress or damage to sea cucumbers in this study. The results obtained from this data will be beneficial for lighting usage in aquaculture environments in the future. • The short-wavelength light environment produces avoidance and negative phototaxis movement behavior respectively for sea cucumbers. • The short-wavelength light environment will disturb the original selectivity of sea cucumbers to dark and bright substrates. • The behavior of sea cucumbers is affected by the light intensity (photon flux density) contained in different spectra exposed to the surface of sea cucumbers. • Acute red and blue LED light illumination does not cause stress or significant physiological injury to sea cucumbers. [ABSTRACT FROM AUTHOR]

Developing efficient, sustainable microalgae harvesting methods is vital to enable microalgae as renewable feedstock for food and functional nutrients. Conventional techniques face barriers in efficiency, cost, scalability, and compatibility with food processing. While extensive reviews exist on individual harvesting mechanisms, this critical review uniquely focuses on emerging, gentler technologies compatible with food-grade microalgae production, including bioflocculation, electrolytic coagulation, ultrasonic aggregation, magnetic separation and phototaxis. Novel hybrid approaches combining these mechanisms are also discussed. Focus is placed on potential advantages in separation performance, energy input, scalability and compatibility with food-grade production. Considerations for continued development like materials optimization, large-scale operation, process monitoring, and technoeconomic analysis are outlined. Bioflocculation using microbes or algal biopolymers can achieve high, selective recovery without chemicals. Electroflocculation electrolytically generates coagulants, enabling rapid, controlled destabilization and aggregation. Ultrasound/hydrodynamic cavitation disrupts cells to release coagulating organics. Magnetic nanoparticles give excellent, scalable separation under low magnetic field gradients. Phototaxis exploits directional swimming of motile species towards light. Hybrid systems integrate advantages of individual mechanisms. Continuous separation systems like electrolytic coagulation combined with flotation minimize processing steps but require holistic optimization. By avoiding toxic chemicals and reducing energy input, advanced bio-based and low-energy harvesting technologies can enhance the sustainability of microalgae production for food ingredients. This review emphasizes green technologies and their integration potential, stimulating innovation towards eco-friendly microalgae harvesting, while aligning process development with sustainable design principles. • Bioflocculation with microbes/algae gives high, selective recovery without chemicals. • Electroflocculation's precision dosing enhances control over microalgae recovery. • Magnetic nanoparticles enable excellent separation under low magnetic fields. • Phototaxis exploits directional motility of microalgae towards LED light. • Hybrid systems integrate mechanisms to improve efficiency over individual methods. [ABSTRACT FROM AUTHOR]

Studying the behavior of animals roaming the deep-sea is challenging and is driven by technological developments. The next step to further understand the interactions between predators and prey in the deep sea may be aided by animal-borne camera tags. However, in the darkness of the deep sea, obtaining useful footage requires a light source, which may affect the animal carrying the tag as well as other nearby organisms such as prey. Here we have tested whether the presence of camera associated white light affects the foraging behavior of sperm whales in the Eastern Caribbean Sea. Based on a small dataset of 7 foraging dives with camera lights on, we observed no changes in diving behavior and overall biosonar search behavior. However, we did observed indications of fewer prey capture attempts, which may be due to light induced prey deterrence. For short camera tag deployments this likely does not affect the long term fitness of the whales. However, this effect should be considered and monitored for longer camera tag deployments. Importantly, different deep-sea communities may react differently, we therefore wish to highlight the importance of testing whether research equipment affects the studied animal and its surroundings. • Light-aided camera-tags can yield novel insight on the foraging of deep-diving whales. • Light in the deep sea may affect whales and their prey. • Sperm whales do not alter diving and echolocation behavior in the presence of light. • With light, sperm whales catch less prey, but this is within typical range. • Testing for impacts of research equipment is of great importance. [ABSTRACT FROM AUTHOR]

Microalgae have a high potential for application in different industries including renewable energy production from light and atmospheric CO 2. Biotechnologies should provide high production rates while using the mass and energy resources in a restrained manner. Often, mixing and gas provision are combined to minimize the energetic requirements of photobioreactors. Recent studies suggest that bioconvective patterns naturally developed in suspensions of motile microorganisms may provide biomixing. In this paper we report a study of the phototactic response of Chlamydomonas reinhardtii to induce biomixing in a small bioreactor at macro-scale. By exploiting the phototactic mechanism, we stimulated the microalgae to swim in opposite directions repeatedly in cycles of 40 min (20′ left, 20′ right) in the photobioreactor. The resulting Phototactic Oscillatory Motion (POM) lasted 7 days and maintained an amplitude close to the width of the bioreactor. Phototaxis allowed algae to remain in suspension without the use of any mechanical stirring system. We have demonstrated that light can be controlled to effectively provide mixing and ensure access to nutrients in form of an oscillatory motion at no extra energetic costs. This strategy can replace mechanical agitation in the manner of a 'phototactic stirring' under certain circumstances in pursuit of energetic sobriety. [ABSTRACT FROM AUTHOR]

Danionella cerebrum (DC) is a promising vertebrate animal model for systems neuroscience due to its small adult brain volume and inherent optical transparency, but the scope of their cognitive abilities remains an area of active research. In this work, we established a behavioral paradigm to study visual spatial navigation in DC and investigate their navigational capabilities and strategies. We initially observed that adult DC exhibit strong negative phototaxis in groups but less so as individuals. Using their dark preference as a motivator, we designed a spatial navigation task inspired by the Morris water maze. Through a series of environmental cue manipulations, we found that DC utilize visual cues to anticipate a reward location and found evidence for landmark-based navigational strategies wherein DC could use both proximal and distal visual cues. When subsets of proximal visual cues were occluded, DC were capable of using distant contextual visual information to solve the task, providing evidence for allocentric spatial navigation. Without proximal visual cues, DC tended to seek out a direct line of sight with at least one distal visual cue while maintaining a positional bias toward the reward location. In total, our behavioral results suggest that DC can be used to study the neural mechanisms underlying spatial navigation with cellular resolution imaging across an adult vertebrate brain. • Adult Danionella cerebrum (DC) exhibit strong negative phototaxis • DC are capable of learning a Morris water maze-like spatial navigation task • DC use environmental visual cues to solve the spatial navigation task • Performance in this task is modulated by the visual environmental context The translucent fish Danionella cerebrum (DC) are a promising systems neuroscience animal model. Lee and Briggman show that adult DC exhibit negative phototaxis and apply this as a motivator in a Morris water maze-like spatial navigation task. DC use visual cues to learn this task; their performance is modulated by the environmental visual context. [ABSTRACT FROM AUTHOR]

• Daphnia 's swimming behaviour is a good indicator of the state of the environment. • Phototaxis is a result of a complex decision-making process. • Environment affects phototaxis and the studies using it for ecological research. • Predator presence, food, light conditions, pigmentation etc. must be considered. [Display omitted] Animal-based sensors have been increasingly applied to many water monitoring systems and ecological studies. One of the staple organisms used as living sensors for such systems is Daphnia. This organism has been extensively studied and, with time, used in many toxicological and pharmaceutical bioassays, often used for exploring the ecology of freshwater communities. One of its behaviours used for evaluating the state of the aquatic environment is phototaxis. A disruption in the predicted behaviour is interpreted as a sign of stress and forms the basis for further investigation. However, phototaxis is a result of complex processes counteracting and interacting with each other. Predator presence, food quality, body pigmentation and other factors can greatly affect the predicted phototactic response, hampering its reliability as a bioindicator. Therefore, a holistic approach and meticulous documentation of the methods are needed for the correct interpretation of this behavioural indicator. In this review, we present the current methods used for studying phototaxis, the factors affecting it and proposed ways to optimise the reliability of the results. [ABSTRACT FROM AUTHOR]

The biogenic amines octopamine and tyramine are important neurotransmitters in insects and other protostomes. They play a pivotal role in the sensory responses, learning and memory and social organisation of honeybees. Generally, octopamine and tyramine are believed to fulfil similar roles as their deuterostome counterparts epinephrine and norepinephrine. In some cases opposing functions of both amines have been observed. In this study, we examined the functions of tyramine and octopamine in honeybee responses to light. As a first step, electroretinography was used to analyse the effect of both amines on sensory sensitivity at the photoreceptor level. Here, the maximum receptor response was increased by octopamine and decreased by tyramine. As a second step, phototaxis experiments were performed to quantify the behavioural responses to light following treatment with either amine. Octopamine increased the walking speed towards different light sources while tyramine decreased it. This was independent of locomotor activity. Our results indicate that tyramine and octopamine act as functional opposites in processing responses to light.