Immediate-Early Promoter-Driven Transgenic Reporter System for Neuroethological Research in a Hemimetabolous Insect

Motor state changes escape behavior of crickets

Animals change their behavior depending on external circumstances, internal factors, and their interactions. Locomotion state is a crucial internal factor that profoundly affects sensory perception and behavior. However, studying the behavioral impacts of locomotion state in free-moving animals has been challenging due to difficulty in reproducing quantitatively identical stimuli in freely moving animals. We utilized a closed-loop controlled servosphere treadmill system, enabling unrestricted confinement and orientation of small animals, and investigated wind-induced escape behavior in freely moving crickets. When stimulated during locomotion, the crickets quickly stopped before initiating escape behavior. Moving crickets exhibited a higher probability of escape response compared to stationary crickets. The threshold for pausing response in moving crickets was also much lower than the escape response threshold. Moving crickets had delayed reaction times for escape and greater variance in movement direction compared to stationary crickets. The locomotion-related response delay may be compensated by an elevated sensitivity to airflow.

Octopamine neurons mediate reward signals in social learning in an insect

Social learning is found in many animals, but its mechanisms are not understood. We previously showed that a cricket that was trained to observe a conspecific staying at a drinking apparatus exhibited an increased preference for the odor of that drinking apparatus. Here we investigated a hypothesis that this learning is achieved by second-order conditioning (SOC), i.e., by associating conspecifics at a drinking bottle with water reward during group drinking in the rearing stage and then associating an odor with a conspecific in training. Injection of an octopamine receptor antagonist before training or testing impaired the learning or response to the learned odor, as we reported for SOC, thereby supporting the hypothesis. Notably, the SOC hypothesis predicts that octopamine neurons that respond to water in the group-rearing stage also respond to a conspecific in training, without the learner itself drinking water, and such mirror-like activities mediate social learning. This awaits future investigation.

Persistence of auditory modulation of wind-induced escape behavior in crickets

Animals, including insects, change their innate escape behavior triggered by a specific threat stimulus depending on the environmental context to survive adaptively the predators' attack. This indicates that additional inputs from sensory organs of different modalities indicating surrounding conditions could affect the neuronal circuit responsible for the escape behavior. Field crickets, Gryllus bimaculatus, exhibit an oriented running or jumping escape in response to short air puff detected by the abdominal mechanosensory organ called cerci. Crickets also receive a high-frequency acoustic stimulus by their tympanal organs on their frontal legs, which suggests approaching bats as a predator. We have reported that the crickets modulate their wind-elicited escape running in the moving direction when they are exposed to an acoustic stimulus preceded by the air puff. However, it remains unclear how long the effects of auditory inputs indicating surrounding contexts last after the sound is terminated. In this study, we applied a short pulse (200 ms) of 15-kHz pure tone to the crickets in various intervals before the air-puff stimulus. The sound given 200 or 1000 ms before the air puff biased the wind-elicited escape running backward, like the previous studies using the longer and overlapped sound. But the sounds that started 2000 ms before and simultaneously with the air puff had little effect. In addition, the jumping probability was higher only when the delay of air puff to the sound was 1000 ms. These results suggest that the cricket could retain the auditory memory for at least one second and alter the motion choice and direction of the wind-elicited escape behavior.

Silencing the odorant receptor co-receptor impairs olfactory reception in a sensillum-specific manner in the cockroach

Insects detect odors via a large variety of odorant receptors (ORs) expressed in olfactory sensory neurons (OSNs). The insect OR is a heteromeric complex composed of a ligand-specific receptor and the co-receptor (ORco). In this study, we identified the ORco gene of the cockroach, Periplaneta americana (PameORco), and performed RNAi-based functional analysis of PameORco. All OSNs in the basiconic sensilla expressed PameORco and received a large variety of odors including sex pheromones. In trichoid sensilla, a PameORco-positive OSN was consistently paired with a PameORco-negative OSN tuned to acids. In adult cockroaches injected with PameORco dsRNA at the nymphal stage, the expression of PameORco, odor receptions via ORs, and its central processing were strongly suppressed. These results provide new insights into the molecular basis of olfactory reception in the cockroach. The long-lasting and irreversible effects of PameORco RNAi would be an effective method for controlling the household pest.

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Whole sequence of ORco in the American cockroach (PameORco) was characterized

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PameORco expressed in olfactory sensory neurons in a sensillar type-specific manner

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RNAi chronically and irreversibly suppressed the PameORco expression beyond molts

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PameORco was essential for receptions of sex pheromones and general odors

Roles of neural communication between the brain and thoracic ganglia in the selection and regulation of the cricket escape behavior

To survive a predator's attack, prey animals must exhibit escape responses that are appropriately regulated in terms of their moving speed, distance, and direction. Insect locomotion is considered to be controlled by an interaction between the brain, which is involved in behavioral decision-making, and the thoracic ganglia (TG), which are primary motor centers. However, it remains unknown which descending and ascending signals between these neural centers are involved in the regulation of the escape behavior. We addressed the distinct roles of the brain and TG in the wind-elicited escape behavior of crickets by assessing the effects of partial ablation of the intersegmental communications on escape responses. We unilaterally cut the ventral nerve cord (VNC) at different locations, between the brain and TG, or between the TG and terminal abdominal ganglion (TAG), a primary sensory center of the cercal system. The partial ablation of ascending signals to the brain greatly reduced the jumping response rather than running, indicating that sensory information processing in the brain is essential for the choice of escape responses. The ablation of descending signals from the brain to the TG impaired locomotor performance and directional control of the escape responses, suggesting that locomotion in the escape behavior largely depends on the descending signals from the brain. Finally, the extracellular recording from the cervical VNC indicated a difference in the descending activities preceding the escape responses between running and jumping. Our results demonstrated that the brain sends the descending signals encoding the behavioral choice and locomotor regulation to the TG, while the TG seem to have other specific roles, such as in the preparation of escape movement.

Cis-regulatory elements of the cholinergic gene locus in the silkworm Bombyx mori

Genes of choline acetyltransferase (ChAT) and vesicular acetylcholine transporter are encoded in the same gene locus, called the cholinergic gene locus. They are essential in cholinergic neurons to maintain their functional phenotype. The genomic structure of the cholinergic gene locus is conserved among invertebrates to mammals. However, the cholinergic gene expression in a specific subset of neurons is unknown in insects except for Drosophila melanogaster. In this study, we analysed the upstream sequence of cholinergic gene locus in the silkworm Bombyx mori to identify specific cis-regulatory regions. We found multiple enhancer regions that are localized within 1 kb upstream of the cholinergic gene locus. The combination of promoter assays using small deletions and bioinformatic analysis among insect species illuminates two conserved sequences in the cis-regulatory region: TGACGTA and CCAAT, which are known as the cAMP response element and CAAT box, respectively. We found that dibutyryl-cAMP, an analogue of cAMP, influences the expression of ChAT in B. mori. Tissue-specific expression analysis of transcriptional factors identified potential candidates that control the cholinergic gene locus expression. Our investigation provides new insight into the regulation mechanism of cholinergic neuron-specific gene machinery in this lepidopteran insect.

Spatial perception mediated by insect antennal mechanosensory system

Animals perceive their surroundings by using various modalities of sensory inputs to guide their locomotion. Nocturnal insects such as crickets use mechanosensory inputs mediated by their antennae to orient in darkness. Spatial information is acquired via voluntary antennal contacts with surrounding objects, but it remains unclear whether the insects modulate behaviors mediated by other sensory organs based on that information. Crickets exhibit escape behavior in response to a short air-puff, which is detected by the abdominal mechanosensory organs called cerci and is perceived as a “predator approach” signal. We placed objects of different shapes at different locations with which the cricket actively made contact using its antenna. We then examined the effects on wind-elicited escape behavior. The crickets changed their movement trajectory in response to nearby objects like walls so that they could avoid collision with these obstacles even during the cercal-mediated behavior. For instance, when a wall was placed in front of the crickets so that it was detected by one antenna, the escape trajectory in response to a stimulus from behind was significantly biased toward the side opposite the wall. Even when the antenna on the free side without the wall was ablated, this collision avoidance was also observed, suggesting that the mechanosensory inputs from one antenna detecting an object edge would be sufficient to perceive the location of obstacle in front. This study demonstrated that crickets were able to use the spatial information acquired with their antennal system to modify their behavior mediated by other sensory organs.

Action selection based on multiple-stimulus aspects in wind-elicited escape behavior of crickets

Escape behavior is essential for animals to avoid attacks by predators. In some species, multiple escape responses could be employed. However, it remains unknown what aspects of threat stimuli affect the choice of an escape response. We focused on two distinct escape responses (running and jumping) to short airflow in crickets and examined the effects of multiple stimulus aspects including the angle, velocity, and duration on the choice between these responses. The faster and longer the airflow, the more frequently the crickets jumped. This meant that the choice of an escape response depends on both the velocity and duration of the stimulus and suggests that the neural basis for choosing an escape response includes the integration process of multiple stimulus parameters. In addition, the moving speed and distance changed depending on the stimulus velocity and duration for running but not for jumping. Running away would be more adaptive escape behavior.

Design of Structural Parameters of Cutters for Tea Harvest Based on Biomimetic Methodology

Owing to their sharp teeth, crickets can eat through new shoots of the stalks of tea plants. Inspired by the special geometrical structure of the teeth of crickets, this study designed a biomimetic cutter to reduce the force and energy required to cut the stalks of tea plants. Therefore, four biomimetic cutters were considered: a, b, c, and d. Cutter a was a traditional cutter used for comparison with the other three cutters, which were biomimetic. The cutters were manufactured using 3D printing technology and assessed by a texture tester at different loading speeds (5, 10, and 15 mm/s, respectively). The results show that cutter c delivered better performance compared to cutter a at loading speeds of 5, 10, and 15 mm/s, respectively. However, at 15 mm/s loading speed, the maximum cutting forces required for cutters b and c were 9.43% and 6.04% lower, respectively, than that for cutter a (9.021 N). Similarly, the energies consumed by cutters b and c were 13.8% and 4.24% lower than that consumed by cutter a (1.225 J). In addition, cutter c delivered the best results compared to others. Based on the study results, it was concluded that the biomimetic cutters can thus help to optimize the tea harvest.

The Compound Eye Possesses a Self-Sustaining Circadian Oscillator in the Cricket Gryllus bimaculatus

Many insects show daily and circadian changes in morphology and physiology in their compound eye. In this study, we investigated whether the compound eye had an intrinsic circadian rhythm in the cricket Gryllus bimaculatus. We found that clock genes period (per), timeless (tim), cryptochrome 2 (cry2), and cycle (cyc) were rhythmically expressed in the compound eye under 12-h light/12-h dark cycles (LD 12:12) and constant darkness (DD) at a constant temperature. After the optic nerves were severed (ONX), a weak but significant rhythmic expression persisted for per and tim under LD 12:12, while under DD, tim and cyc showed rhythmic expression. We also found that more than half of the ONX compound eyes exhibited weak but significant circadian electroretinographic rhythms. These results clearly demonstrate that the cricket compound eye possesses an intrinsic circadian oscillator which can drive the circadian light sensitivity rhythm in the eye, and that the circadian clock in the optic lobe exerts its influence on the oscillator in the eye.

Report on the First Symposium on Invertebrate Neuroscience held on 13-17th August 2019 at the Balaton Limnological Institute, MTA Centre for Ecological Research, Tihany, Hungary

This meeting report provides an overview of the oral and poster presentations at the first international symposium for invertebrate neuroscience. The contents reflect the contributions of invertebrate neuroscience in addressing fundamental and fascinating challenges in understanding the neural substrates of animal behaviour.

Immediate early gene kakusei potentially plays a role in the daily foraging of honey bees

kakusei is a non-coding RNA that is overexpressed in foraging bee brain. This study describes a possible role of the IEG kakusei during the daily foraging of honey bees. kakusei was found to be transiently upregulated within two hours during rewarded foraging. Interestingly, during unrewarded foraging the gene was also found to be up-regulated, but immediately lowered when food was not rewarded. Moreover, the kakusei overexpression was diminished within a very short time when the time schedule of feeding was changed. This indicates the potential role of kakusei on the motivation of learned reward foraging. These results provide evidence for a dynamic role of kakusei during for aging of bees, and eventually its possible involvement in learning and memory. Thus the kakusei gene could be used as search tool in finding distinct molecular pathways that mediate diverse behavioral components of foraging.

Evolution of the neural sex-determination system in insects: does fruitless homologue regulate neural sexual dimorphism in basal insects?

In the brain of holometabolous insects such as the fruit fly Drosophila melanogaster, the fruitless gene produces sex-specific gene products under the control of the sex-specific splicing cascade and contributes to the formation of the sexually dimorphic circuits. Similar sex-specific gene products of fruitless homologues have been identified in other holometabolous insects such as mosquitoes and a parasitic wasp, suggesting the fruitless-dependent neural sex-determination system is widely conserved amongst holometabolous insects. However, it remains obscure whether the fruitless-dependent neural sex-determination system is present in basal hemimetabolous insects. To address this issue, identification, characterization, and expression analyses of the fruitless homologue were conducted in the two-spotted cricket, Gryllus bimaculatus, as a model hemimetabolous insect. The Gryllus fruitless gene encodes multiple isoforms with a unique zinc finger domain, and does not encode a sex-specific gene product. The Gryllus Fruitless protein is broadly expressed in the neurones and glial cells in the brain, and there was no prominent sex-related difference in the expression levels of Gryllus fruitless isoforms. The results suggest that the Gryllus fruitless gene is not involved in the neural sex-determination in the cricket brain.

The fight to understand fighting: neurogenetic approaches to the study of aggression in insects

Aggression is an evolutionarily conserved behavior that evolved in the framework of defending or obtaining resources. When expressed out of context, unchecked aggression can have destructive consequences. Model systems that allow examination of distinct neuronal networks at the molecular, cellular, and circuit levels are adding immensely to our understanding of the biological basis of this behavior and should be relatable to other species up to and including man. Investigators have made particular use of insect models to both describe this quantifiable and stereotyped behavior and to manipulate genes and neuron function via numerous genetic and pharmacological tools. This review discusses recent advances in techniques that improve our ability to identify, manipulate, visualize, and compare the genes, neurons, and circuits that are required for the output of this complex and clinically relevant social behavior.