Search

In Chlamydomonas, the directly light‐gated, plasma membrane‐localized cation channels channelrhodopsins ChR1 and ChR2 are the primary photoreceptors for phototaxis. Their targeting and abundance is essential for optimal movement responses. However, our knowledge how Chlamydomonas achieves this is still at its infancy. Here we show that ChR1 internalization occurs via light‐stimulated endocytosis. Prior or during endocytosis ChR1 is modified and forms high molecular mass complexes. These are the solely detectable ChR1 forms in extracellular vesicles and their abundance therein dynamically changes upon illumination. The ChR1‐containing extracellular vesicles are secreted via the plasma membrane and/or the ciliary base. In line with this, ciliogenesis mutants exhibit increased ChR1 degradation rates. Further, we establish involvement of the cysteine protease CEP1, a member of the papain‐type C1A subfamily. ΔCEP1‐knockout strains lack light‐induced ChR1 degradation, whereas ChR2 degradation was unaffected. Low light stimulates CEP1 expression, which is regulated via phototropin, a SPA1 E3 ubiquitin ligase and cyclic AMP. Further, mutant and inhibitor analyses revealed involvement of the small GTPase ARL11 and SUMOylation in ChR1 targeting to the eyespot and cilia. Our study thus defines the degradation pathway of this central photoreceptor of Chlamydomonas and identifies novel elements involved in its homoeostasis and targeting. Summary Statement: How Chlamydomonas targets and controls the level of its main photoreceptor for photomovement responses is largely unknown. Here we show involvement of light‐stimulated endocytosis, cilia, a small GTPase, and a phototropin E3 ubiquitin ligase‐ and cAMP‐controlled cysteine protease in these processes. [ABSTRACT FROM AUTHOR]

Zoosporic fungi, also called chytrids, produce single-celled motile spores with flagellar swimming tails (zoospores). 1,2 These fungi are key components of aquatic food webs, acting as pathogens, saprotrophs, and prey. 3,4,5,6,7,8 Little is known about the swimming behavior of fungal zoospores, a crucial factor governing dispersal, biogeographical range, ecological function, and infection dynamics. 6,9 Here, we track the swimming patterns of zoospores from 12 evolutionarily divergent species of zoosporic fungi from across seven orders of the Chytridiomycota and the Blastocladiomycota. We report two major swimming patterns that correlate with the cytoskeletal ultrastructure of these zoospores. Specifically, we show that species without major cytoplasmic tubulin components swim in a circular fashion, while species with prominent cytoplasmic tubulin structures swim in a pattern akin to a random walk (move-stop-redirect-move). We confirm cytoskeletal architecture by performing fluorescence confocal microscopy across all 12 species. We then treat representative species with variant swimming behaviors and cytoplasmic-cytoskeletal arrangements with tubulin-stabilizing (Taxol) and depolymerizing (nocodazole) pharmacological compounds. We observed that when treating the "random walk" species with nocodazole, their swimming behavior changed to a circular-swimming pattern. Confocal imaging of the nocodazole-treated zoospores demonstrates that these cells maintain flagellum tubulin structures but lack their characteristic cytoplasmic tubulin structures. Our data demonstrate that the capability of zoospores to perform "complex" random-walk movement is linked to the presence of prominent cytoplasmic tubulin structures and suggest a link between cytology, sensory systems, and swimming behavior in a diversity of zoosporic fungi. [Display omitted] • Fungal zoospores swim using either a random-walk or a circular pattern • The random walk is linked with the presence of major cytoplasmic tubulin structures • Nocodazole-treated random-walk zoospores transform into circular swimmers • In Blastocladiella, ultrastructure, movement, and light-sensing organelles are linked Galindo et al. find that fungal zoospores swim in either circular or random-walk patterns, the latter being linked with the presence of major cytoplasmic tubulin structures. Random-walk zoospores treated with a tubulin-depolymerizing drug turn into circular swimmers. They note a relationship between cytology, movement, and light-sensing organelles. [ABSTRACT FROM AUTHOR]

Despite the recent wide investigation on active cancer drug delivery, there are still strong medical unmet needs for active tumor‐environment responsive cancer drug delivery in terms of spatiotemporal control. Herein, a biohybrid system of pH‐responsive peptide nanotubes (PNTs)‐coated microalgae for active cancer drug delivery in response to the tumor‐environment is developed. The amphiphilic PNTs are effectively used to encapsulate cancer drugs and coat the living microalgae of C. reinhardtii by electrostatic interactions. The drug‐loaded PNTs‐based biohybrid microalgae maintain agile movement with phototaxis behavior. After in vitro characterization and cytotoxicity assessment, it is shown that the biohybrid microalgae could be phototactically localized to the cancer cells and pH‐responsively disassembled to release cancer drugs in a controlled manner. Finally, with the encapsulation of paclitaxel, the statistically significant suppression of tumor growth in xenograft tumor model animals is successfully demonstrated. Taken together, the feasibility of the multifunctional microrobotic platform for advanced cancer therapy is confirmed. [ABSTRACT FROM AUTHOR]

Evaluating artificial light as a bycatch reduction device (bycatch reduction light, "BRL") requires a multidisciplinary approach that applies knowledge of fisheries science, fishing technology, engineering, physics, optics, vision biology, oceanography, animal behavior, economics, and social science. To support the continued evaluation of BRL, these guidelines were developed for conducting standardized and systematic studies. The guidelines highlight how information from those fields of study contributes to the efficacy of study design and the evaluation of results. The guidance is focused on four core areas: (i) defining the objective of using a BRL; (ii) understanding the context in which the BRL is applied and considering the base knowledge that is needed; (iii) selecting an appropriate study design (including selection and placement of the BRL) and analytical methods for measuring both behavioral responses and catch outcomes from using the BRL; and (iv) interpreting the data through the lens of the base knowledge, context, and study design, and evaluating the results against an established definition of success and variables that affect adoption. The purpose of these guidelines is to increase the ability of researchers and managers to determine if BRL is appropriate for a fishery and to encourage consistency in data collection among studies to support future meta-analyses and inter-study comparison. In addition, suggestions are provided on where more research and technology development are needed to support this rapidly emerging field of research. [ABSTRACT FROM AUTHOR]

The ways in which animals sense the world changes throughout development. For example, young of many species have limited visual capabilities, but still make social decisions, likely based on information gathered through other sensory modalities. Poison frog tadpoles display complex social behaviors that have been suggested to rely on vision despite a century of research indicating tadpoles have poorly-developed visual systems relative to adults. Alternatively, other sensory modalities, such as the lateral line system, are functional at hatching in frogs and may guide social decisions while other sensory systems mature. Here, we examined development of the mechanosensory lateral line and visual systems in tadpoles of the mimic poison frog (Ranitomeya imitator) that use vibrational begging displays to stimulate egg feeding from their mothers. We found that tadpoles hatch with a fully developed lateral line system. While begging behavior increases with development, ablating the lateral line system inhibited begging in pre-metamorphic tadpoles, but not in metamorphic tadpoles. We also found that the increase in begging and decrease in reliance on the lateral line co-occurs with increased retinal neural activity and gene expression associated with eye development. Using the neural tracer neurobiotin, we found that axonal innervations from the eye to the brain proliferate during metamorphosis, with few retinotectal connections in recently-hatched tadpoles. We then tested visual function in a phototaxis assay and found tadpoles prefer darker environments. The strength of this preference increased with developmental stage, but eyes were not required for this behavior, possibly indicating a role for the pineal gland. Together, these data suggest that tadpoles rely on different sensory modalities for social interactions across development and that the development of sensory systems in socially complex poison frog tadpoles is similar to that of other frog species. [Display omitted] • Ranitomeya imitator tadpoles hatch with fully developed lateral line systems. • Use of mechanosensory stimuli for begging is dependent on developmental stage. • The visual system of R. imitator tadpoles continues to develop through metamorphosis. • When visual capabilities are poor, tadpoles rely more on mechanosensory inputs. [ABSTRACT FROM AUTHOR]

It has long been hypothesized that benthic motile pennate diatoms use phototaxis to optimize photosynthesis and minimize photoinhibitory damage by adjusting their position within vertical light gradients in coastal benthic sediments. However, experimental evidence to test this hypothesis remains inconclusive, mainly due to methodological difficulties in studying cell behavior and photosynthesis over realistic spatial microscale gradients of irradiance and cell position. In this study, a novel experimental approach was developed and used to test the hypothesis of photosynthesis optimization through motility, based on the combination of single-cell in vivo chlorophyll fluorometry and microfluidic chips. The approach allows the concurrent study of behavior and photosynthetic activity of individual cells of the epipelic diatom species Craspedostauros britannicus exposed to a light microgradient of realistic dimensions, simulating the irradiance and distance scales of light microgradients in benthic sediments. Following exposure to light, (i) cells explored their light environment before initiating light-directed motility; (ii) cells used motility to lower their light dose, when exposed to the highest light intensities; and (iii) motility was combined with reversible non-photochemical quenching, to allow cells to avoid photoinhibition. The results of this proof-of-concept study not only strongly support the photoprotective nature of photobehavior in the studied species but also revealed considerable variability in how individual cells reacted to a light microgradient. The experimental setup can be readily applied to study motility and photosynthetic light responses of other diatom species or natural assemblages, as well as other photoautotrophic motile microorganisms, broadening the toolset for experimental microbial ecology research. [ABSTRACT FROM AUTHOR]

Cyanobacteria move by gliding motility on surfaces toward the light or away from it. It is as yet unclear how the light direction is sensed on the molecular level. Diverse photoreceptor knockout mutants have a stronger response toward the light than the wild type. Either the light direction is sensed by multiple photoreceptors or by photosystems. In a study on photophobotaxis of the filamentous cyanobacterium Phormidium lacuna, broad spectral sensitivity, inhibition by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), and a highly sensitive response speaks for photosystems as light direction sensors. Here, it is discussed whether the photosystem theory could hold for phototaxis of other cyanobacteria. [ABSTRACT FROM AUTHOR]

The behaviour and welfare of animals in captivity is of great importance to zoological collections, captive breeding programmes, food production and keepers of companion animals. Artificial lighting is commonly deficient in UV wavelengths, and use of such lighting for indoor animal enclosures could have significant impacts on the behaviour and welfare of animals to which UV wavelengths are visible. This includes birds, reptiles and fish, but also insects. Here we investigated the effect of UV-present and UV-absent light environments on the behaviour of Vanessa cardui , a butterfly that possesses a trichromatic visual system typical of many insects. We conducted behavioural experiments using a free-flight arena divided in half, where each half could be subjected to UV+ or UV− illumination. When lighting conditions for the two arena halves were the same, we found no significant differences in activity between UV+ and UV− light environments. However when lighting conditions for the two arena halves were different, butterflies showed a significant preference for the UV+ over the UV− half. This remained the case even when the overall intensity of UV+ illumination was less than that of UV− illumination. Our results suggest that UV-deficient artificial lighting conditions do not themselves affect the activity of butterflies, but that given a choice, butterflies prefer lighting that contains UV. Based on these findings, captive light environments can be designed that use supplementary lighting or filters to improve the welfare of captive insects, and the visitor experience. • Artificial light often lacks ultraviolet wavelengths that many animals use. • This may impact animal welfare in captivity. • Butterfly activity did not differ under UV-present and UV-absent lighting. • However, butterflies were attracted to UV-present lighting when given a choice. • These findings can inform the design of lighting for butterfly houses. [ABSTRACT FROM AUTHOR]

In robotics, achieving adaptivity in complex environments is challenging. Traditional robotic systems use stiff materials and computationally expensive centralized controllers, while nature often favors soft materials and embodied intelligence. Inspired by nature's distributed intelligence, this study explores a decentralized approach for robust behavior in soft robotic systems without knowledge of their shape or environment. It is demonstrated that only a few basic rules implemented in identical modules that shape the soft robotic system can enable whole‐body phototaxis, navigating on a surface toward a light source, without explicit communication between modules or prior system knowledge. The results reveal the method's effectiveness in generating robust and adaptive behavior in dynamic and challenging environments. Moreover, the approach's simplicity makes it possible to illustrate and understand the underlying mechanism of the observed behavior, paying particular attention to the geometry of the assembled system and the effect of learning parameters. Consequently, the findings offer insights into the development of adaptive, autonomous robotic systems with minimal computational power, paving the way for robust and useful behavior in soft and microscale robots, as well as robotic matter, that operate in real‐world environments. [ABSTRACT FROM AUTHOR]

Simple Summary: The flea beetle Asiophrida xanthospilota (Baly, 1881) is a serious forest pest specifically damaging the common smoketree Cotinus coggygria. To understand how this beetle sees the world, we used scanning electron microscopy, transmission electron microscopy, micro-computed tomography, and three-dimensional reconstruction to investigate the external morphology and internal ultrastructure of the compound eye. The examination showed that of Asi. xanthospilota has apposition eye like other leaf beetles, consisting of a subplano-convex cornea, an acone of four cone cells, eight retinular cells along with an open rhabdom, as well as two primary pigment cells and about 23 secondary pigment cells. Interestingly, retinular cell 8 does not contribute to the rhabdom. We also investigated the spectral sensitivity by electroretinogram tests and phototropism experiments. Electroretinogram tests showed that Asi. xanthospilota exhibits the strongest sensitivity to blue and green lights but the weakest to red light. Phototropism experiments also revealed that this beetle has the strongest reaction to blue light. In this study, the morphology and ultrastructure of the compound eye of Asi. xanthospilota were examined by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), micro-computed tomography (μCT), and 3D reconstruction. Spectral sensitivity was investigated by electroretinogram (ERG) tests and phototropism experiments. The compound eye of Asi. xanthospilota is of the apposition type, consisting of 611.00 ± 17.53 ommatidia in males and 634.8 0 ± 24.73 ommatidia in females. Each ommatidium is composed of a subplano-convex cornea, an acone consisting of four cone cells, eight retinular cells along with the rhabdom, two primary pigment cells, and about 23 secondary pigment cells. The open type of rhabdom in Asi. xanthospilota consists of six peripheral rhabdomeres contributed by the six peripheral retinular cells (R1~R6) and two distally attached rhabdomeric segments generated solely by R7, while R8 do not contribute to the rhabdom. The orientation of microvilli indicates that Asi. xanthospilota is unlikely to be a polarization-sensitive species. ERG testing showed that both males and females reacted to stimuli from red, yellow, green, blue, and ultraviolet light. Both males and females exhibited strong responses to blue and green light but weak responses to red light. The phototropism experiments showed that both males and females exhibited positive phototaxis to all five lights, with blue light significantly stronger than the others. [ABSTRACT FROM AUTHOR]

Artificial light at night (ALAN) is negatively impacting numerous species of nocturnally active birds. Nocturnal positive phototaxis, the movement towards ALAN, is exhibited by many marine birds and can result in stranding on land. Seabird species facing major population declines may be most at risk. Leach's Storm-Petrels (Hydrobates leucorhous) are small, threatened seabirds with an extensive breeding range in the North Atlantic and North Pacific Oceans. The Atlantic population, which represents approximately 40–48% of the global population, is declining sharply. Nocturnal positive phototaxis is considered to be a key contributing factor. The Leach's Storm-Petrel is the seabird species most often found stranded around ALAN in the North Atlantic, though there is little experimental evidence that reduction of ALAN decreases the occurrence of stranded storm-petrels. During a two-year study at a large, brightly illuminated seafood processing plant adjacent to the Leach's Storm-Petrel's largest colony, we compared the number of birds that stranded when the lights at the plant were on versus significantly reduced. We recorded survival, counted carcasses of adults and juveniles, and released any rescued individuals. Daily morning surveys revealed that reducing ALAN decreased strandings by 57.11% (95% CI: 39.29% - 83.01%) per night and night surveys revealed that reducing ALAN decreased stranding of adult birds by 11.94% (95% CI: 3.47% - 41.13%) per night. The peak stranding period occurred from 25 September to 28 October, and 94.9% of the birds found during this period were fledglings. These results provide evidence to support the implementation of widespread reduction and modification of coastal artificial light as a conservation strategy, especially during avian fledging and migration periods. [ABSTRACT FROM AUTHOR]

Nesidiocoris tenuis (Reuter) is an important omnivorous insect in tobacco fields. It is of practical scientific significance to regulate the population of N. tenuis by employing insect lure strategies with specific light spectra. In this study, the phototactic behavior of N. tenuis adults and nymphs to 15 kinds of monochromatic lights was examined. N. tenuis adults have a higher response rate and a longer displacement to different light spectra and different light intensities compared with nymphs. N. tenuis adults were more attractived by monochromatic lights at 628, 504, 568 and 589 nm among the 15 monochromatic lights. While N. tenuis nymphs were more attractived by monochromatic lights at 628, 549 and 577 nm, and there was no significant difference between the nymphs' response displacements to monochromatic lights except for red light at 628 nm and darkness treatments. The light intensity significantly affected the phototactic behavior of N. tenuis adults but not nymphs. These results suggested that insect traps with a red light at 628 nm, blue-green light at 504 nm, yellow-green light at 568 nm and yellow-green light at 589 nm can be used to monitor and regulate N. tenuis population. [ABSTRACT FROM AUTHOR]

Simple Summary: The tomato leaf miner Phthorimaea absoluta is a harmful invasive pest first reported in China in 2017. As an alternative to chemical methods for pest control, recent research has focused on green prevention, specifically light-induced control. However, current light-trapping technology is non-specific, attracting both pests and non-target organisms. Our study aimed to understand the phototactic behavior of P. absoluta and to develop a targeted light-trapping technology. Using in situ hybridization, we found widespread opsin expression throughout the insect body. We also investigated tropism using a wavelength-lamp experiment, revealing that 365 ± 5 nm light accurately traps P. absoluta without affecting natural enemies. Additionally, we found that long-wavelength opsin gene mutants (LW2−/−) and short-wavelength opsin gene mutants (BL−/−) showed significant differences in phototactic behavior. The LW2(−/−) strain was attracted to light at 390 ± 5 nm, whereas the BL(−/−) strain was unresponsive. Our findings contribute to the development of precise light-trapping technology for controlling the tomato leaf miner, contributing to our understanding of pest population dynamics and the protection of crops from natural enemies. Phthorimaea absoluta (Meyrick) is an invasive pest that has caused damage to tomatoes and other crops in China since 2017. Pest control is mainly based on chemical methods that pose significant threats to food safety and environmental and ecological security. Light-induced control, a green prevention and control technology, has gained attention recently. However, current light-trapping technology is non-specific, attracting targeted pests alongside natural enemies and non-target organisms. In this study, we characterized the phototactic behavior of tomato leaf miners for the development a specific light-trapping technology for pest control. In situ hybridization revealed opsin expression throughout the body. Furthermore, we investigated the tropism of pests (wild T. absoluta, Toxoptera graminum, and Bemisia tabaci) and natural enemies (Nesidiocoris tenuis and Trichogramma pintoi) using a wavelength-lamp tropism experiment. We found that 365 ± 5 nm light could accurately trap wild P. absoluta without trapping natural enemies and other insects. Finally, we analyzed the phototactic behavior of the mutant strains LW2(−/−) and BL(−/−). LW2 and BL mutants showed significant differences in phototactic behavior. The LW2(−/−) strain was attracted to light at 390 ± 5 nm and the BL(−/−) strain was unresponsive to any light. Our findings will help to develop specific light-trapping technology for controlling tomato leaf miners, providing a basis for understanding pest population dynamics and protecting crops against natural enemies. [ABSTRACT FROM AUTHOR]

Simple Summary: Personality and light are crucial to ensure the welfare of aquatic animals. To understand how personality affects the light color selection of fish, we tested the behaviors with different personalities under six colors of light: violet (410–420 nm), yellow (580–590 nm), green (550–560 nm), red (620–630 nm), blue (470–480 nm), and white. In this study, the yellow catfish Pelteobagrus fulvidraco preferred the yellow and green light over the other light colors. After identifying their preferred light colors, bold individuals reduced their frequency of exploration. The results showed that bold individuals could make a quick decision for light color selection. This study provides a reference for the welfare of juvenile yellow catfish in aquaculture. Personality, which matters for animal welfare, demonstrates behavioral differences. Light is one of the most important factors in aquaculture. However, how fish personality affects light color selection is unclear. In this study, we tested the personality of yellow catfish Pelteobagrus fulvidraco juveniles and then quantified the selective behaviors of different personalities under six light colors: violet (410–420 nm), yellow (580–590 nm), green (550–560 nm), red (620–630 nm), blue (470–480 nm), and white. The results showed that juveniles preferred the yellow and green light over the other colors of light, probably due to different reasons. The average cumulative dwell time in yellow (32.81 ± 5.22%), green (21.81 ± 3.58%), and red (26.36 ± 4.89%) lights was significantly longer than the other light colors, and the average visit frequency in green light (32.00 ± 4.93%) was the most. Juveniles had the longest total moved distance in green light. Moreover, the results demonstrated that shy and bold individuals had the same preference for the green light. Bold individuals could find the preferred light colors rapidly and make quick decisions for light color selection. After identifying the preferred light colors, bold individuals reduced the frequency of exploration. This study provides a theoretical basis for the welfare of juvenile yellow catfish in aquaculture. [ABSTRACT FROM AUTHOR]

Simple Summary: This research aims to explore the phototactic behavior and key opsin genes associated with Vespinae. The results showed that the two species, Vespula germanica and Vespa analis, exhibited varying photophilic rates under different wavelengths of light, suggesting that light wavelength significantly affects their phototactic behavior. Additionally, the opsin genes of the most aggressive hornet, Vespa basalis, have been sequenced. There are only two opsin genes, one for UV light and the other for blue light, and Vespa basalis lacks long-wavelength visual proteins. However, they exhibit peak phototaxis for long-wavelength light and instead have the lowest phototropism for UV light. This suggests that the visual protein genes have a complex regulatory mechanism for phototactic behavior in Vespinae. Our findings provide a sound theoretical basis for further investigation of visual expression patterns and phototactic mechanisms in Vespinae. The phototactic behavior of insects is commonly used to manage pest populations in practical production. However, this elusive behavior is not yet fully understood. Investigating whether the opsin genes play a crucial role in phototaxis is an intriguing topic. Vespinae (Hymenoptera: Vespidae) are a common group of social wasps that are closely associated with human activities. Efficiently controlling wasp populations while maintaining ecological balance is a pressing global challenge that still has to be resolved. This research aims to explore the phototactic behavior and key opsin genes associated with Vespinae. We found significant differences in the photophilic rates of Vespula germanica and Vespa analis under 14 different light conditions, indicating that their phototactic behavior is rhythmic. The results also showed that the two species exhibited varying photophilic rates under different wavelengths of light, suggesting that light wavelength significantly affects their phototactic behavior. Additionally, the opsin genes of the most aggressive hornet, Vespa basalis, have been sequenced. There are only two opsin genes, one for UV light and the other for blue light, and Vespa basalis lacks long-wavelength visual proteins. However, they exhibit peak phototaxis for long-wavelength light and instead have the lowest phototaxis for UV light. This suggests that the visual protein genes have a complex regulatory mechanism for phototactic behavior in Vespinae. Additionally, visual protein sequences have a high degree of homology among Hymenoptera. Despite the hypotheses put forward by some scholars regarding phototaxis, a clear and complete explanation of insect phototaxis is still lacking to date. Our findings provide a strong theoretical basis for further investigation of visual expression patterns and phototactic mechanisms in Vespinae. [ABSTRACT FROM AUTHOR]

Techniques to control the phototactic behaviour of fish have expanded with progress in LED lights. However, the phototaxis direction of fish could be reversible at some light intensities, and thus it is necessary to evaluate the light-intensity levels that will induce repulsion or attraction behaviour to understand the transition. This study determined the light intensities of white LED light required to induce repulsion or attraction behaviour from a dark place, and the degree of dark-adapted visual sensitivity in juvenile of two salmon species. Oncorhynchus keta smolts showed negative phototaxis under intense light intensity, but positive phototaxis was not observed. The range of light intensities under which O. masou exhibited positive phototaxis changed with the life stage (from pre-smolts to smolts). Notably, the light intensities that elicited positive phototaxis were relatively low and narrow for pre-smolts, whereas smolts responded to a greater range of intensities. Positive phototaxis disappeared in O. masou pre-smolts under intense light intensity, but not in O. masou smolts under the most-intense light intensity tested here. Negative phototaxis was not observed in O. masou pre-smolts or smolts. The appropriate light intensity indicated here may be used to either guide juvenile O. masou from the dam reservoir to fishways or bypass channels, or to repel O. keta smolts from the water intakes of agricultural diversion weirs or hydropower dams. [ABSTRACT FROM AUTHOR]

Background: Various morphological adaptations are associated with symbiotic relationships between organisms. One such adaptation is seen in the nemertean genus Malacobdella. All species in the genus are commensals of molluscan hosts, attaching to the surface of host mantles with a terminal sucker. Malacobdella possesses several unique characteristics within the order Monostilifera, exhibiting the terminal sucker and the absence of eyes and apical/cerebral organs, which are related to their adaptation to a commensal lifestyle. Nevertheless, the developmental processes that give rise to these morphological characteristics during their transition from free-living larvae to commensal adults remain uncertain. Results: In the present study, therefore, we visualized the developmental processes of the internal morphologies during postembryonic larval stages using fluorescent molecular markers. We demonstrated the developmental processes, including the formation of the sucker primordium and the functional sucker. Furthermore, our data revealed that sensory organs, including apical/cerebral organs, formed in embryonic and early postembryonic stages but degenerated in the late postembryonic stage prior to settlement within their host using a terminal sucker. Conclusions: This study reveals the formation of the terminal sucker through tissue invagination, shedding light on its adhesion mechanism. Sucker muscle development likely originates from body wall muscles. Notably, M. japonica exhibits negative phototaxis despite lacking larval ocelli. This observation suggests a potential role for other sensory mechanisms, such as the apical and cerebral organs identified in the larvae, in facilitating settlement and adhesive behaviors. The loss of sensory organs during larval development might reflect a transition from planktonic feeding to a stable, host-associated lifestyle. This study also emphasizes the need for further studies to explore the phylogenetic relationships within the infraorder Amphiporiina and investigate the postembryonic development of neuromuscular systems in closely related taxa to gain a more comprehensive understanding of ecological adaptations in Nemertea. [ABSTRACT FROM AUTHOR]

Monostroma nitidum, a monostromatic green algae (MGA) with high economic value, is distributed worldwide. Life cycle often serves as a fundamental criterion for taxonomic classification. Most researchers consider the life cycle of M. nitidum to involve dimorphic alternation of generations, although the possibility of a monomorphic asexual life cycle remains unclear. In this study, tufA and 18S rDNA sequences were employed as molecular markers, complemented by morphological analysis, to classify and identify MGA in two distinct habitats: Hailing Island reefs (YJ) and Naozhou Island reefs (ZJ). The results of tufA and 18S rDNA sequence analysis revealed that all samples from YJ and ZJ clustered to the same branch (M. nitidum clade) with high bootstrap support and genetic distances of less than 0.000 and 0.005, respectively. However, morphological observations indicated significant differences in the external morphology of the YJ and ZJ samples, although both initially exhibited a filament‐blade form during early development. The life cycle of the ZJ samples exhibited typical dimorphic alternation of generations, whereas the YJ samples only produced biflagellate asexual gametes with negative phototaxis. Gametes of the YJ samples directly developed into new gametophytes without undergoing the sporophyte stage. Consequently, the YJ and ZJ samples were classified as monomorphic asexual and dimorphic sexual M. nitidum, respectively. These findings provide evidence supporting the monomorphic asexual life cycle of M. nitidum for the classification of MGA. [ABSTRACT FROM AUTHOR]

In this study, we proposed a model for modular robots in which autonomous decentralized modules adaptively organize their behavior. The phototaxis of Gonium pectorale, a species of volvocine algae, was modeled as a modular system, and a fault-tolerant modular control method of phototaxis was proposed for it. The proposed method was based on the rotation phase of the colony and adaptively adjusted an internal response-related parameter to enhance the fault tolerance of the system. Compared to a constant parameter approach, the simulation results demonstrated a significant improvement in the phototaxis time for positive and negative phototaxis during module failures. This method contributes to achieving autonomous, decentralized, and purposeful mediation of the modules necessary for controlling modular robots. [ABSTRACT FROM AUTHOR]

Age-dependent changes in the transcription levels of 5-day-old Euglena gracilis cells, which showed positive gravitaxis, 6-day-old cells without gravitactic orientation, and older cells (9- and 11-day-old, which displayed a precise negative gravitaxis) were determined through microarray analysis. Hierarchical clustering of four independent cell cultures revealed pronounced similarities in transcription levels at the same culture age, which proves the reproducibility of the cultivation method. Employing the non-oriented cells from the 6-day-old culture as a reference, about 2779 transcripts were found to be differentially expressed. While positively gravitactic cells (5-day-old culture) showed only minor differences in gene expression compared to the 6-day reference, pronounced changes of mRNAs (mainly an increase) were found in older cells compared to the reference culture. Among others, genes coding for adenylyl cyclases, photosynthesis, and metabolic enzymes were identified to be differentially expressed. The investigated cells were grown in batch cultures, so variations in transcription levels most likely account for factors such as nutrient depletion in the medium and self-shading. Based on these findings, a particular transcript (e.g., transcript 19556) was downregulated using the RNA interference technique. Gravitaxis and phototaxis were impaired in the transformants, indicating the role of this transcript in signal transduction. Results of the experiment are discussed regarding the increasing importance of E. gracilis in biotechnology as a source of valuable products and the possible application of E. gracilis in life-support systems. [ABSTRACT FROM AUTHOR]

The brown marmorated stink bug (Halyomorpha halys) is an invasive pest insect species, which was recently introduced from Asia to America and then to Europe. Besides causing serious damage in agriculture, this species also represents a source of intense annoyance for humans in residential areas, because large amounts of individuals can aggregate on buildings while seeking shelter before overwintering. Taking into account the need for pesticide-free pest management methods, for example light trapping, we measured the spectral sensitivity of the compound eyes of H. halys with electroretinography (ERG). In behavioural experiments, we also quantified the attraction of H. halys to 14 quasi-monochromatic light stimuli in the 368–743 nm spectral range. The dark-adapted compound eyes were mostly sensitive to the green range, but a minor sensitivity peak in the UV region was also identified. Recordings on chromatic-adapted eye preparations unequivocally revealed the presence of only a green- and a UV-sensitive photoreceptor type, with sensitivity maxima at 519 nm and 367 nm, respectively. No sign of any blue-sensitive receptor was detected, and thus only a receptor set allowing dichromatic vision was found. Based on the results of the behavioural experiments, we established that the attraction of H. halys to light is increasing with decreasing wavelength, and thus we emphasize the importance of short wavelength lights (368–455 nm) when phototactic attraction of H. halys is the aim. [ABSTRACT FROM AUTHOR]

The tidal occurrence of larval fishes was investigated in the permanently open Kowie Estuary on the warm-temperate coast of South Africa. Larval fishes were sampled in the mouth region using two drifting light traps deployed on the ebb and flood tides every second night for two consecutive 14-day periods, coinciding with the dark moon phase. A total of 553 larval fishes were caught, representing nine families and 26 species, of which Blenniidae and Clupeidae dominated. The prevalence of different estuarine association fish guilds was also tide-specific. Marine and estuarine species, such as Omobranchus woodi, were more dominant during flood tides, while marine straggler species, such as Sardinops sagax, which are not dependent on estuaries, were dominant on the ebb tide. Marine estuarine-dependents were only present during flood tides, potentially indicating ingress and entrainment within the estuary. The results confirm that light trap catches yield a different composition of species compared to towed ichthyoplankton net studies. Additionally, drifting light traps allow for better targeting of species with a phototactic response and reduction of incidental catch. Consequently, a mixture of gear is encouraged for more comprehensive surveys of larval fish occurrence. [ABSTRACT FROM AUTHOR]

The modern concept of the genus Chloromonas includes a subclade of species found exclusively in snow. We describe Chloromonas (Cr.) fuhrii sp. nov., a new member of this clade, which is closely related to Cr. muramotoi from Japan. The new species is characterised by the absence of a stigma, pyrenoid, and defined papilla, ready loss of flagella in culture, and a single lobed chloroplast. Strains of Cr. fuhrii have been sourced from green, orange, and pink/red snow. The species has been found in Svalbard, Antarctica, and New Zealand, with most genetic variation occurring in Svalbard. The minimal variation present in New Zealand strains suggests a relatively recent arrival. Secondary structure models for ITS2 in the new species demonstrate a separation from Cr. muramotoi due to one CBC. The nine New Zealand strains isolated showed no variation in ITS2 but four variable base positions in ITS1. Inclusion of the single Antarctic and four Svalbard strains resulted in 14 variable positions in ITS2 and 69 in ITS1, with the sequences remaining alignable. The ITS data showed a strong biogeographic signal, both in total in an unrooted tree, and using ITS2 alone with Cr. muramotoi as an outgroup. The absence of a stigma in this species prompted a survey of the literature, showing that stigma absence in Chloromonas is strongly associated with the snow habitat, occurring at about 10 times the rate observed in other habitats, perhaps owing to the difficulty of phototaxis in snow with abundant reflected light. [ABSTRACT FROM AUTHOR]

Photosynthesizers face a trade-off regarding light: they need enough to maintain high photosynthetic rates, yet excess leads to oxidative stress. Despite this, light and its detrimental effects are chronically underestimated. Solar-powered sea slugs (Sacoglossa: Gastropoda) provide the ideal lens with which to study this trade-off, since they steal chloroplasts from algae but do not inherit photoacclimation and photorepair capacities. We collected three slug species in Curaçao during March and December 2022, comparing the amount of light they received in nature to their optimal light intensities for photosynthesis, and their preferred light intensities. We then investigated behavioral and physiological photoprotection mechanisms to determine if and how they limit light. Finally, we examined oxidative activity under optimal and excess light. All three species were naturally exposed to more light (> 1000 µmol m−2 s−1) than is optimal or preferred. Elysia crispata (kleptoplast retention for > 3 months) is fully exposed to light in nature but reduces the light reaching its kleptoplasts via parapodial shading. Elysia velutinus retains kleptoplasts for ~ 2 weeks and hides in its macroalgal food, limiting light exposure. Both species displayed low amounts of oxidative activity under optimal light, which increased slightly under excess light. Elysia ornata retained chloroplasts for ~ 3 days, lacked observable photoprotection and always displayed high levels of oxidative activity, potentially explaining its limited capacity for kleptoplast retention. Furthermore, both E. velutinus and E. ornata display strong light-avoidance behaviors. This study clearly demonstrates links between high light intensities, photoprotection, and oxidative stress, highlighting the need for future studies that examine aquatic photosynthesizers under natural lighting. [ABSTRACT FROM AUTHOR]

Insect odorant binding proteins (OBPs) were initially regarded as carriers of the odorants involved in chemosensation. However, it had been observed that a growing number of OBP genes exhibited broad expression patterns beyond chemosensory tissues. Here, an OBP gene (OBP31) was found to be highly expressed in the larval ventral nerve cord, adult brain and male reproductive organ of Spodoptera frugiperda. An OBP31 knockout strain (OBP31−/−) was generated by CRISPR/Cas9 mutagenesis. For OBP31−/−, the larvae needed longer time to pupate, but there was no difference in the pupal weight between OBP31−/− and wild type (WT). OBP31−/− larvae showed stronger phototaxis than the WT larvae, indicating the importance of OBP31 in light perception. For mating rhythm of adults, OBP31−/− moths displayed an earlier second mating peak. In the cross‐pairing of OBP31−/− and WT moths, the mating duration was longer, and hatchability was lower in OBP31−/− group and OBP31+/−♂ group than that in the WT group. These results suggested that OBP31 played a vital role in larval light perception and male reproductive process and could provide valuable insights into understanding the biological functions of OBPs that were not specific in chemosensory tissues. [ABSTRACT FROM AUTHOR]

Symsagittifera roscoffensis forms a photosymbiotic relationship with the alga Tetraselmis convolutae within the intertidal zone. Juveniles lack algal symbionts at birth and acquire them from the environment. Requiring light for photosynthesis, they position themselves within the water column while also balancing the risk of being washed away. To understand their behavioural adaptations, we conducted experiments on their movement in response to algal cues (chemotaxis), light gradients (phototaxis), and mechanical vibrations. Aposymbiotic juveniles showed three times more positive displacement towards algae. Adults exhibited positive phototaxis but retreated from high light intensity. When introduced to a column with a light source, the worms remained just below the surface. In the mechanical vibration experiment, worms only descended when vibrations exceeded a threshold. These findings suggest that S. roscoffensis has chemotactic abilities crucial for acquiring algae and acquires light for photosynthesis while minimizing dispersal risk and photoinhibition, facilitating its life cycle in the intertidal zone. [ABSTRACT FROM AUTHOR]

SUMMARY: The spatial arrangement of cell fusion sites and eyespots of the gametes in vis‐à‐vis mating pairs of Chlamydomonas eugametos, corresponding to the swimming zygote of Chlamydomonas reinhardtii, were studied using field emission scanning electron microscopy and light microscopy, respectively. After the adhesion of mt+ and mt− gametes, each of which has one eyespot and two flagella elongated from the cell anterior, gamete–gamete fusion occurred at the anterior papilla on the cell apex of each gamete, leading to the formation of a vis‐à‐vis mating pair, indicating that the cell fusion site is arranged symmetrically relative to the flagellar beat plane. In vis‐à‐vis mating pairs, two eyespots could be seen on the same or on opposite sides of the cell. As only the mt+ flagella and eyespot are functional for swimming and phototaxis in the vis‐à‐vis mating pair of C. eugametos, it is suggested that coordinated alignment of the parental gamete flagella and eyespots in the swimming zygote and asymmetric positioning of the gamete mating structure/cell fusion sites, which is prevalent in C. reinhardtii and other chlorophytes, is not necessary for C. eugametos. [ABSTRACT FROM AUTHOR]

In central Japan, adult Patanga japonica (Bolívar) grasshoppers overwinter as adults while in reproductive diapause. At this local, February nights fall as low as -7°C, whereas days can exceed 16°C. Adults respond to the diel thermal cycle with daily vertical movements out of and back into leaf litter. This paper documents and discusses the significance of this interesting winter behavior. Temperature strongly influenced the daily vertical movements. Time of morning emergence, duration of aboveground occupancy, and number of adults emerging all highly correlated with current and maximum daily temperatures. In January, adults were immobile at < -1°C but could stand up when their body temperatures reached ~3.7°C. In contrast, adults held outdoors in semi-natural conditions emerged from the litter at ~14°C, suggesting threshold temperatures of ~14°C for morning emergence. The numbers of adults emerging or hiding varied over the winter season. Light also influenced movements. Adults held in horizontal transparent tubes, each with half covered with black paper (D-area) and the other half exposed to light (L-area), moved into the L-area during the day and returned to the D-area in the afternoon. In both cases, movement was into a colder microhabitat, implying that the direction of daily movements was possibly via phototaxis, not thermotaxis. Further experiments suggested that increasing temperatures elicited positive phototaxis, and decreasing temperatures elicited negative phototaxis and that the phototaxis was controlled by the direction, magnitude, and absolute range of the temperature change in P. japonica. [ABSTRACT FROM AUTHOR]

Drone flies, Eristalis tenax (Diptera: Syrphidae), are important generalist pollinators and visit flowers globally that range widely in color. The flies' photoreceptors allow them to sense light wavelengths between 300-600 nm and E. tenax exhibit a positive phototactic response. To understand the effects of light on E. tenax movement, we conducted two- choice behavioral tests to determine their phototactic response to different wavelengths of light across the spectrum (ultraviolet to red light, plus full spectrum white light). The drone flies moved most and quickest toward sunlight, with almost twice the percentage of flies moving toward sunlight than toward black and purple light (short wavelength sources), which elicited the second strongest phototactic responses. Eristalis tenax moved minimally toward green and red light sources. When increasing air temperature by 6°C, the percent of E. tenax moving toward fluorescent white light increased by a factor of four. They also moved toward a food source in light but not dark conditions. Our findings may be useful for managing E. tenax populations in the lab or for increasing crop pollination. [ABSTRACT FROM AUTHOR]

Simple Summary: The division of labor among workers is one of the predominant characteristics of social insects, which simply means that workers perform different tasks, such as caring for the brood inside the nest and foraging outside the nest, and which is essential for colony maintenance and development. Previous studies on honeybees have demonstrated that the regulation of behavioral transitions can be influenced by juvenile hormone (JH). The red imported fire ant (RIFA), Solenopsis invicta, is a typical social pest that poses a significant risk to biodiversity, ecosystems, and public health in invaded areas. Understanding the effects of JH on the behavioral transitions of RIFA is necessary, as it may provide valuable experimental data for pest control. In this study, we simulated JH elevation using the juvenile hormone analogue (JHA) methoprene application and evaluated its effect on activity levels, brood care behavior, phototaxis, and threat responsiveness of nurse workers. Our study indicates that the application of JHA reduced brood care behavior and enhanced phototaxis in nurse workers, thereby revealing the role of JH in facilitating behavioral transitions in RIFA from intranidal tasks to extranidal activity. These findings may contribute to a better understanding of the underlying mechanisms behind the division of labor in social insects. The division of labor among workers is a defining characteristic of social insects and plays a pivotal role in enhancing the competitive advantage of their colony. Juvenile hormone (JH) has long been hypothesized to be the essential driver in regulating the division of labor due to its ability to accelerate behavioral transitions in social insects, such as honeybees. The regulation of behavioral transitions by JH in the red imported fire ant (RIFA), Solenopsis invicta, a typical social pest, is unclear. Through video capture and analysis, we investigated the effects of the juvenile hormone analogue (JHA) methoprene on brood care, phototaxis behavior, and threat responsiveness of RIFA nurse workers. Our results showed that the JHA application significantly reduced the time and frequency of brood care behavior by nurse workers while increasing their walking distance and activity time in the light area. Additionally, the application of JHA made ants become excited, indicating a significant improvement in their activity level (movement distance, time, and speed). Furthermore, it was observed that the application of JHA did not affect the threat responsiveness of nurse workers towards stimuli (nestmates or non-nestmates). Our study demonstrates that the application of JHA reduced brood care behavior and enhanced phototaxis in nurse workers, which may reveal the role of JH in facilitating behavioral transitions in RIFA from intranidal tasks to extranidal activity. This study provides an experimental basis for further elucidating the mechanism underlying the division of labor in social insects. [ABSTRACT FROM AUTHOR]

Impacts of artificial light at night on wildlife are well documented, yet specific effects on parasitism in aquatic systems are largely unknown. Circadian patterns in animal physiology and behaviour are light-driven, as is host-searching by many infective stages. This can be impacted by artificial light at night. Attraction of hosts and infective stages to light sources can result in aggregations that promote direct infection by infective stages and high levels of trophic transmission. I hypothesise that temporal fluctuations in infection risk disappear as day–night differences in lighting are reduced, that areas exposed to light at night act as hotspots of transmission, and that altered photoperiod exerts strong selective pressures. Known effects of light on host–parasite interactions must be considered when designing measures to reduce the impact of artificial light on wildlife. With growing human populations living along freshwater shores and marine coastlines, aquatic ecosystems are experiencing rising levels of light pollution. Through its effects on hosts and parasites, anthropogenic light at night can disrupt host–parasite interactions evolved under a normal photoperiod. Yet its impact on aquatic parasites has been ignored to date. Here, I discuss the direct effects of light on the physiology and behaviour of parasite infective stages and their hosts. I argue that night-time lights can change the spatiotemporal dynamics of infection risk and drive the rapid evolution of parasites. I then highlight knowledge gaps and how impacts on parasitic diseases should be incorporated into the design of measures aimed at mitigating the impact of anthropogenic light on wildlife. [ABSTRACT FROM AUTHOR]

Photosymbiotic cnidarians generally seek bright environments so that their symbionts can be photosynthetically active. However, excess light may result in a breakdown of symbiosis due to the accumulation of photodamage in symbionts causing symbiont loss (bleaching). It is currently unknown if photosymbiotic cnidarians sense light only to regulate spawning time and to facilitate predation, or whether they also use their light-sensing capacities to protect their symbionts from photodamage. In this study, we examined how the sea anemone Aiptasia changes its behaviour when exposed to excess light. We reveal that Aiptasia polyps, when carrying symbionts, contract their bodies when exposed to high light intensities and subsequently migrate away in a direction perpendicular to the light source. Interestingly, this negative phototaxis was only evident under blue light and absent upon UV, green and red light exposure. Non-symbiotic Aiptasia did not exhibit this light response. Our study demonstrates that photosymbiotic Aiptasia polyps display negative phototactic behaviour in response to blue light, and that they also can perceive its direction, despite lacking specialized eye structures. We postulate that Aiptasia uses blue light, which penetrates seawater efficiently, as a general proxy for sunlight exposure to protect its symbionts from photodamage. [ABSTRACT FROM AUTHOR]

Light provides a widely abundant energy source and valuable sensory cue in nature. Most animals exposed to light have photoreceptor cells and in addition to eyes, there are many extraocular strategies for light sensing. Here, we review how these simpler forms of detecting light can mediate rapid behavioural responses in animals. Examples of these behaviours include photophobic (light avoidance) or scotophobic (shadow) responses, photokinesis, phototaxis and wavelength discrimination. We review the cells and response mechanisms in these forms of elementary light detection, focusing on aquatic invertebrates with some protist and terrestrial examples to illustrate the general principles. Light cues can be used very efficiently by these simple photosensitive systems to effectively guide animal behaviours without investment in complex and energetically expensive visual structures. [ABSTRACT FROM AUTHOR]

Simple Summary: Ants fulfill an important ecological function, not only serving as one of the main decomposers but also playing a role in improving soil fertility. Ants may conflict with humans as a pest species in homes and living facilities (e.g., closets, wardrobes, cabinets, and tables), as well as in outdoor facilities (e.g., tables, chairs, and benches). In addition, ants and humans can come into conflict in green spaces (including parks, gardens, and tourist attractions) and can seriously interfere with outdoor leisure and the life and entertainment activities of people (especially children). Therefore, it is a matter of public health and environmental protection to ensure ant prevention by adopting green control technology and not merely by spraying pesticides to kill them. This review mainly focuses on the species and diversity of ants, especially in China, and the research progress of ant tropism regarding phototaxis, chromotaxis, and chemotaxis (i.e., 3-tropisms). Moreover, current research on repellent substances is also summarized, analyzed, and discussed in order to help the application of green prevention and control technology for ant diversity protection and conservation, especially in daily home life and entertainment activities. This field of research is related to ensuring the healthy life of the public and the protection of the ecological environment. Ants are one of the largest insect groups, with the most species and individuals in the world, and they have an important ecological function. Ants are not only an important part of the food chains but are also one of the main decomposers on the Earth; they can also improve soil fertility, etc. However, some species of ants are harmful to human beings, which leads to people's panic or worry about coming into contact with these insects during their daily home life or in their tourism or leisure activities. The presence of ants in indoor living facilities and in outdoor green spaces, parks, gardens, and tourist attractions seriously interferes with the leisure life and entertainment activities of all people (especially children). How can we control ants in these environments? Do we kill them by spraying insecticides, or do we adopt green prevention and control technology for the ecological management of ants? This topic is related to healthy life for the public and the protection of the ecological environment. In this paper, the species and diversity of ants are introduced, and research progress regarding ant tropism is introduced according to the three aspects of phototaxis, chromotaxis, and chemotaxis (i.e., "3-tropisms"). The research on repellent substances from plants and insects and the related ant attractants are also summarized, analyzed, and discussed, in order to help the research and application of green prevention and control technology for ant diversity protection and conservation. [ABSTRACT FROM AUTHOR]

Photosymbiotic cnidarians generally seek bright environments so that their symbionts can be photosynthetically active. However, excess light may result in a breakdown of symbiosis due to the accumulation of photodamage in symbionts causing symbiont loss (bleaching). It is currently unknown if photosymbiotic cnidarians sense light only to regulate spawning time and to facilitate predation, or whether they also use their light-sensing capacities to protect their symbionts from photodamage. In this study, we examined how the sea anemone Aiptasia changes its behaviour when exposed to excess light. We reveal that Aiptasia polyps, when carrying symbionts, contract their bodies when exposed to high light intensities and subsequently migrate away in a direction perpendicular to the light source. Interestingly, this negative phototaxis was only evident under blue light and absent upon UV, green and red light exposure. Non-symbiotic Aiptasia did not exhibit this light response. Our study demonstrates that photosymbiotic Aiptasia polyps display negative phototactic behaviour in response to blue light, and that they also can perceive its direction, despite lacking specialized eye structures. We postulate that Aiptasia uses blue light, which penetrates seawater efficiently, as a general proxy for sunlight exposure to protect its symbionts from photodamage. [ABSTRACT FROM AUTHOR]

Channelrhodopsins stand out among other retinal proteins because of their capacity to generate passive ionic currents following photoactivation. Owing to that, channelrhodopsins are widely used in neuroscience and cardiology as instruments for optogenetic manipulation of the activity of excitable cells. Photocurrents generated by channelrhodopsins were first discovered in the cells of green algae in the 1970s. In this review we describe this discovery and discuss the current state of research in the field. [ABSTRACT FROM AUTHOR]

The cell membrane of Halobacterium salinarum contains a retinal‐binding photoreceptor, sensory rhodopsin II (HsSRII), coupled with its cognate transducer (HsHtrII), allowing repellent phototaxis behavior for shorter wavelength light. Previous studies on SRII from Natronomonas pharaonis (NpSRII) pointed out the importance of the hydrogen bonding interaction between Thr204NpSRII and Tyr174NpSRII in signal transfer from SRII to HtrII. Here, we investigated the effect on phototactic function by replacing residues in HsSRII corresponding to Thr204NpSRII and Tyr174NpSRII. Whereas replacement of either residue altered the photocycle kinetics, introduction of any mutations at Ser201HsSRII and Tyr171HsSRII did not eliminate negative phototaxis function. These observations imply the possibility of the presence of an unidentified molecular mechanism for photophobic signal transduction differing from NpSRII–NpHtrII. [ABSTRACT FROM AUTHOR]

Oriented movement (phototaxis) is an efficient way to optimize light‐driven processes and to avoid photodamage for motile algae. In Chlamydomonas the receptors for phototaxis are the channelrhodopsins ChR1 and ChR2. Both are directly light‐gated, plasma membrane‐localized cation channels. To optimally adjust its overall light‐dependent responses, Chlamydomonas must tightly control the ChRs cellular abundance and integrate their activities into its general photoprotective network. How this is achieved is largely unknown. Here we show that the ChR1 protein level decreases upon illumination in a light‐intensity and quality‐dependent manner, whereas it is stable in prolonged darkness. Analysis of knockout strains of six major photoreceptors absorbing in the blue–violet range, which is most effective in evoking ChR1 degradation, revealed that only phototropin (PHOT) is involved. Notably, ChR2 degradation was normal in a ΔPHOT strain. Further, our results indicate that a COP1‐SPA1 E3 ubiquitin ligase, the transcription factor Hy5 as well as changes in the cellular redox poise and cyclic nucleotide levels are additional components involved in this light acclimation response of Chlamydomonas. Our data highlight the presence of an adaptive framework connecting phototaxis with general photoprotective mechanisms via the use of overlapping signaling components already at the level of the primary photoreceptor. Summary Statement: How Chlamydomonas controls the level of ChR1, the main photoreceptor for its movement responses, is largely unknown. Here we show that regulatory elements involved in photoprotective gene expression are parts of this cascade(s), supporting an integrating link between phototaxis and photoprotection. [ABSTRACT FROM AUTHOR]

The first exploratory study was conducted on the compound eye morphology and spectral characteristics of Agasicles hygrophila (Selman & Vogt, 1971) to clarify its eye structure and its spectral sensitivity. Scanning electron microscopy, paraffin sectioning, and transmission electron microscopy revealed that A. hygrophila has apposition compound eyes with both eucones and open rhabdom. The micro-computed tomography (CT) results after 3D reconstruction demonstrated the precise position of the compound eyes in the insect’s head and suggested that the visual range was mainly concentrated in the front and on both sides of the head. The electroretinogram (ERG) experiment showed that red, yellow, green, blue, and ultraviolet light could stimulate the compound eyes of A. hygrophila to produce electrical signals. The behavioural experiment results showed that both males and females had the strongest phototaxis to yellow light and positive phototaxis to red, green, and blue light but negative phototaxis to UV light. This study of the compound eyes of A. hygrophila will be helpful for decoding its visual mechanism in future studies. [ABSTRACT FROM AUTHOR]

Light has a substantial effect on the behaviour and physiology of nocturnal moths. Ectropis grisescens is a major nocturnal tea pest in China, and light traps are commonly used to control geometrid moths because of their positive phototaxis. However, some moths gather around light traps and enter the light adaptation state, which decreases the efficacy of light traps in controlling this pest. We identified opsin genes and the spectral sensitivities of the photoreceptors of E. grisescens moths. We also determined the effects of several monochromatic lights on opsin gene expression and light adaptation. We detected three types of opsin genes and six spectral sensitive peaks (at 370, 390, 480, 530, 550, and 580 nm). We also observed significant changes in the diurnal rhythm of opsin gene expression under different light conditions. When active males were suddenly exposed to different monochromatic lights, they quickly entered the light adaptation state, and the adaptation time was negatively correlated with the light intensity. Males were most sensitive to 390 nm wavelengths, followed by 544 nm, 457 nm, and 593 nm. Red light (627 nm) did not affect the activity of E. grisescens males but had detectable physiological effects. [ABSTRACT FROM AUTHOR]

In insects and other terrestrial arthropods, foraging is guided in part by visual cues making use of optical radiation, which includes ultraviolet (UV) radiation. Manipulating UV exposure with lamps and photo‐selective materials can help protect crops by disrupting related wavelength‐dependent behaviours in various pests, but little is known on how this could also affect the behaviour of their natural enemies.To investigate the effects of UV‐A radiation on parasitoid wasp foraging behaviours, we conducted laboratory and semi‐field experiments on female Telenomus podisi and Trissolcus utahensis (Hymenoptera: Scelionidae) that parasitize stink bug egg masses.In small laboratory arenas, both species of egg parasitoid displayed a positive UV phototaxis, but UV exposure also reduced their daily spontaneous locomotor activity regardless of the time of day.In large field cages, parasitism (i.e., host discovery and exploitation) rates were mostly unaffected by UV‐attenuated conditions created by UV‐absorbing filters (macrohabitat level) and/or by the plant canopy (microhabitat level).This study indicates that UV radiation can be involved in egg parasitoid foraging behaviours without UV attenuation negatively affecting parasitism, reflecting the heterogeneity and potentially hazardous nature of this abiotic factor.We highlight the importance of examining the role of UV radiation as an environmental cue in beneficial insects, especially with the prospect of combining physical and biological pest management strategies. [ABSTRACT FROM AUTHOR]

Deciphering the behavioural ecology of adult (sessile) sponges is challenging. However, their motile larval stages afford opportunities to investigate how behaviour contributes to dispersal and selection of habitat. Light is a fundamental cue contributing to larval sponge dispersal where photoreceptive cells contribute to this process. But how universal is light as a cue to sponge larval dispersal and settlement? Behavioural choice experiments were used to test the effect of light on dispersal and settlement behaviours. Larvae of the tropical sponge species Coscinoderma mathewsi, Luffariella variabilis, Ircinia microconnulosa, and Haliclona sp., from deep (12–15 m) and shallower-water habitats (2–5 m), were used in experiments. Dispersal experiments provided a light-gradient-choice where light represented light attenuation with depth. Light treatments included white light and the spectral components of red and blue light. Settlement experiments comprised a choice between illuminated and shaded treatments. Fluorescence microscopy was used to establish the presence of fluorescent proteins associated with posterior locomotory cilia. Deeper-water species, C. mathewsi and I. microconnulosa discriminate light spectral signatures. Both species changed dispersal behaviour to light spectra as larvae aged. For C. mathewsi positive phototaxis to blue light changed to photophobic responses (all light treatments) after six hours and behaviours in I. microconnulosa changed from positive to negative phototaxis (white light) after six hours. L. variabilis, also a deeper-water species, was negatively phototactic to all light treatments. Larvae from the shallow-water species, Haliclona sp., moved towards all light wavelengths tested. There was no effect of light on settlement of the shallow-water Haliclona sp., but larvae in all three deeper-water species showed significantly higher settlement in shaded treatments. Fluorescence microscopy showed discrete fluorescent bands contiguous to posterior tufted cilia in all four species. These fluorescent bands may play a contributory role in larval photobehaviour. [ABSTRACT FROM AUTHOR]

Artificial light at night (ALAN) has been implicated in the global decline of insect populations. Causal mechanisms contributing to declines remain unclear, however. Here we examine causal factors which could link some declining terrestrial insect populations with ALAN. To do so, we defined the closest and furthest halves of individual bushes according to the nearest source of artificial light. We sampled leaves and invertebrates from both sides to determine herbivory and abundance. First, we observed that, within bushes, leaves were significantly more likely to display herbivory at closer distances to established streetlighting. This may be due to the phenomenon of positive phototaxis in insects (flight to light). Further, insects within bushes were significantly more abundant on the side closest to streetlighting at midnight, but not at midday, when lights are unilluminated. Consequently, we argue that ALAN creates bottom‐up trophic effects, driven by insect light attraction behaviours even at the scale of single plants. [ABSTRACT FROM AUTHOR]

This paper introduces a new metaheuristic algorithm called bacteria phototaxis optimizer (BPO). It is designed to solving optimization issues. Inspired by the bacteria phototaxis under the control of photosensory proteins in nature, and based on the basic law of bacterial colony growth and evolution, we have designed the photosensory protein concentration, phototaxis motion and growth operators. These three operators exhibit a highly adaptive and information interaction mechanism. The goal is to simulate the phototaxis process of bacteria and form a complete model of BPO. At the same time, BPO is compared with eight most representative as well as newly generated metaheuristics. Its performance is verified by using 23 well-known benchmark functions with three different types. Additionally, we have conducted several evaluation processes, such as qualitative and quantitative analysis as well as parametric and nonparametric tests. Finally, five classical engineering design problems are used to further test the effectiveness of the algorithm in solving constrained problems. The aforementioned experimental results show that compared with other algorithms, BPO has better accuracy, convergence, and robustness and shows strong competitiveness and optimization performance. [ABSTRACT FROM AUTHOR]

The parasitoid wasp Bathyplectes anurus (Hymenoptera: Ichneumonidae: Campopleginae) is a successful biocontrol agent against the alfalfa weevil, Hypera postica. This weevil is a serious pest of beneficial fabaceous plants such as alfalfa and Chinese milk vetch. One of the possible reasons for the success of this wasp in hot climates may be the ability of its cocooned larvae to repeatedly jump and roll until they relocate themselves away from detrimental sunlight and heat. It is not yet known which wavelengths of light trigger this avoidance behavior or the microstructure of the cocoon shell that might allow light transmission. Here, the response of the cocooned larvae to different wavelengths, and the microstructure, hardness, and elemental components of the cocoon shell were studied. A population of cocooned larvae were introduced on the boundary line between illuminated and shaded areas with blue, green, red, or near-infrared light-emitting diodes. The cocoons moved away from the blue and green light. The distance from the boundary to the cocoons in the shaded area was longer under these long wavelengths, followed by the red light and shortest under the near-infrared light and nil under darkness. No difference was found in mortality between different wavelengths after three days of illumination. Scanning electron microscope observations of the surface of the cocoon shell revealed that the belt-like central ridge was porous, which likely allows ventilation and light transmission. The surface of the cocoon shell showed a uniform distribution of sulfur, potentially aiding in the capture of green wavelengths. The ridge had twice the thickness of the main body and was 1.9 times harder than the main body. These results may be applied to better understand the individual responses of this biological control agent to modifications to their environment, including light pollution. [ABSTRACT FROM AUTHOR]

Filamentous cyanobacteria exhibit some of the greatest developmental complexity observed in the prokaryotic domain. This includes the ability to differentiate nitrogen-fixing cells known as heterocysts, spore-like akinetes, and hormogonia, which are specialized motile filaments capable of gliding on solid surfaces. Hormogonia and motility play critical roles in several aspects of the biology of filamentous cyanobacteria, including dispersal, phototaxis, the formation of supracellular structures, and the establishment of nitrogen-fixing symbioses with plants. While heterocyst development has been investigated extensively at the molecular level, much less is known about akinete or hormogonium development and motility. This is due, in part, to the loss of developmental complexity during prolonged laboratory culture in commonly employed model filamentous cyanobacteria. In this review, recent progress in understanding the molecular level regulation of hormogonium development and motility in filamentous cyanobacteria is discussed, with a focus on experiments performed using the genetically tractable model filamentous cyanobacterium Nostoc punctiforme, which retains the developmental complexity of field isolates. [ABSTRACT FROM AUTHOR]

In this work, we find analytical solutions to the Chavy-Waddy–Kolokolnikov equation, a continuum approximation for modeling aggregate formation in bacteria moving toward the light, also known as phototaxis. We used three methods to obtain the solutions, the generalized Kudryashov method, the e − R (ξ) -expansion, and exponential function methods, all of them being very efficient for finding traveling wave-like solutions. Findings can be classified into the case where the nonlinear term can be considered a small perturbation of the linear case and the regime of instability and pattern formation. Standing waves and traveling fronts were also found among the physically interesting cases, in addition to recovering stationary spike-like solutions. [ABSTRACT FROM AUTHOR]

Merobenthic octopods like Octopus vulgaris undergo a transitional period between the planktonic and benthic phases, known as settlement stage. In this work, three sub-stages ("pre-settlement", "settlement" and "post-settlement") have been defined based on morphological, anatomical, and behavioural changes. At the end of the planktonic phase advanced paralarvae are transparent with 65–80 chromatophores, iridophores covering eyes and digestive system, Kölliker organs, circular pupils, ~ 20 suckers per arm (spa), and mantle length (ML) bigger than total length (TL; ML/TL > 60%). The "pre-settlement" sub-stage (ML/TL from 65 to 55%, ~ 20–25 spa) is marked by the onset of clinging reflexes, where the pre-settlers touch the walls and bottom of the tank and start crawling clumsily. Morphologically, they are transparent with increased chromatophores along the arms and iridophores around the eyes and head. During the "settlement" sub-stage (~ 55–48% ML/TL, ~ 25–35 spa) there is an exponential increase of chromatophores in the dorsal area of head and mantle, and the settlers show strong negative phototaxis, crawling for shelter when disturbed. The skin is still transparent but new chromatic cells (leucophores) develop and Kölliker organs are almost lost. During the "post-settlement" sub-stage (~ 48–40% ML/TL, > 35 spa) the post-settlers display very fast and coordinated movements, have horizontal pupils, and develop the "eye-bar". The chromatic cells keep increasing exponentially, giving a pale appearance to the skin. The beginning of the benthic phase in O. vulgaris juveniles is marked by the presence of skin sculptural components (papillae) and a complex display of chromatic, postural, and cryptic patterns. [ABSTRACT FROM AUTHOR]

Self-propelled chemical micro/nanomotors (MNMs) have demonstrated considerable potential in targeted drug delivery, (bio)sensing, and environmental remediation due to their autonomous nature and possible intelligent self-targeting behaviors (e.g., chemotaxis and phototaxis). However, these MNMs are commonly limited by their primary propulsion mechanisms of self-electrophoresis and electrolyte self-diffusiophoresis, making them prone to quenching in high electrolyte environments. Thus, the swarming behaviors of chemical MNMs in high-electrolyte media remain underexplored, despite their potential to enable the execution of complex tasks in high-electrolyte biological media or natural waters. In this study, we develop ultrasmall tubular nanomotors that exhibit ion-tolerant propulsions and collective behaviors. Upon vertical upward UV irradiation, the ultrasmall Fe2O3 tubular nanomotors (Fe2O3 TNMs) demonstrate positive superdiffusive photogravitaxis and can further self-organize into nanoclusters near the substrate in a reversible manner. After self-organization, the Fe2O3 TNMs exhibit a pronounced emergent behavior, allowing them to switch from random superdiffusions to ballistic motions near the substrate. Even at a high electrolyte concentration (Ce), the ultrasmall Fe2O3 TNMs retain a relatively thick electrical double layer (EDL) compared to their size, and the electroosmotic slip flow in their EDL is strong enough to propel them and induce phoretic interactions among them. As a result, the nanomotors can rapidly concentrate near the substrate and then gather into motile nanoclusters in high-electrolyte environments. This work opens a gate for designing swarming ion-tolerant chemical nanomotors and may expedite their applications in biomedicine and environmental remediation. [ABSTRACT FROM AUTHOR]

Phototaxis is a well-studied insect behaviour described as rigid and stereotyped. Larval response to light can be assessed by a fast and highly repetitive assay like a half-dark/half-illuminated plate. Drosophila melanogaster Meigen (Diptera: Drosophilidae) mutants can be used to study the response of larvae to sensory stimuli. Adults of the ebony mutant show behavioural deficits such as abnormal circadian rhythms and severe defects in vision, whereas the tan mutants show a slight deficiency in vision. We analysed the response of D. melanogaster mutant larvae for N-ß-alanyl derivatives metabolism (ebony and tan) to determine whether they also show abnormal phototactic behaviour. Our results showed that ebony larvae exhibited a random response to light, whereas tan larvae showed a similar response to wild-type larvae. To assess if N-ß-alanyl derivatives metabolism might be involved in the response of larvae to light, we fed them with N-ß-alanyldopamine (NBAD), N-ß-alanylhistamine (carcinine) or dopamine. NBAD restored the wt response in ebony larvae, whereas carcinine and DA produced no effect. These results suggest, for the first time, that NBAD might act as a neuroactive compound involved in the phototactic response of the D. melanogaster larvae. [ABSTRACT FROM AUTHOR]