Biology subjects

Aonuma, H.

Publications and source records attributed to Aonuma, H..

12 recordsLinked to original sources

bioRxiv2026

Removing head ganglia in amphibious centipedes unveils descending contribution to versatile locomotor repertoire

Understanding how animals produce a versatile locomotor repertoire requires unraveling the interplay between higher centers, decentralized locomotor circuits, and sensory feedback. However, the principles governing their integration remain elusive. We investigated amphibious centipedes through stepwise neural lesions and neuromechanical modeling. Behavioral experiments revealed that while decentralized circuits autonomously generate coordination, the brain and subesophageal ganglion provide situational flexibility, such as modulating trunk undulation and initiating leg folding. Integrating these findings, our model demonstrated how higher centers selectively inhibit or release lower circuit dynamics. Simulations verified that varying only a few descending control parameters reproduces transitions between slow walking, fast walking, and swimming. This work may capture the essence of the locomotor circuitry that harnesses decentralized self-organization to coordinate the bodys large degrees of freedom.

neuroscience↗

bioRxiv2026

Self-organized Recovery of Coordinated Locomotion in Crickets Revealed by Prosthetic Limb Integration

Distributed sensorimotor interactions facilitate the coordination of multi-legged locomotion in insects without centralized control, yet the mechanisms that allow coordinated locomotion to re-emerge following limb loss remain poorly understood. Here, we systematically evaluate the effects of leg amputation and the integration of prosthetic legs on walking coordination in crickets Gryllus bimaculatus. Spherical treadmill experiments revealed that leg amputation disrupts inter-leg phase coupling, decreases locomotor speed, and alters spatial foot placement in a state-dependent manner, indicating impaired load-mediated coordination. Prosthetic legs did not merely restore intact kinematics; instead, they selectively reinstated coherent temporal coordination and axis-specific spatial organization. This structured recovery illustrates that re-introducing mechanically relevant sensory constraints is sufficient to re-engage distributed coordination networks, even in the absence of anatomical integrity. The selective recovery of temporal over spatial coordination, demonstrated here quantitatively for the first time, reveals the hierarchical architecture of distributed locomotion control and elucidates an embodied principle by which sensory-mechanical feedback facilitates the self-organization of resilient multi-legged locomotion following morphological intervention. Load-mediated sensory signals thus emerge as a key driver of distributed coordination in biohybrid systems, providing design principles for adaptive prosthetic engineering and sensorimotor rehabilitation.

neuroscience↗

bioRxiv2025

Opponent-flipping tactics in aggressive interactions of the cricket Gryllus bimaculatus

Male crickets engage in intense aggressive behavior, competing for resources. In this study, we focus on the quick movements during tactile combat in the cricket fight, to understand how they defeat the opponents. We performed kinematic analysis following high-speed cam recording of the fight. High-speed cam recordings showed that the attacker jumped to the head of the attacked cricket and thrusted it backwards. The attacked cricket was sometimes flipped over and tended to retreat. To understand how the attacker jumps effectively to flip over the opponent, we compared the attack-jump and escape-jump. The kinematics analysis demonstrated that the attack motion is different from the jump in the case of escaping from threats. The attacker cricket adjusted the direction of its body using its forelegs. The mandibles were used to hook onto the head of the attacked cricket. The attacked cricket moved its hindlegs with different kinematics to jump in the case of escape and exerted greater velocity. These findings advance our knowledge of how animals utilize their body depending on the situation.

animal behavior and cognition↗

bioRxiv2023

Photoreceptor genes in a trechine beetle, Trechiama kuznetsovi, living in the upper hypogean zone

To address how organisms adapt to a new environment, subterranean organisms whose ancestors colonized subterranean habitats from surface habitats have been studied. Photoreception abilities have been shown to have degenerated in organisms living in caves and calcrete aquifers. Meanwhile, the organisms living in a shallow subterranean environment, which are inferred to reflect an intermediate stage in an evolutionary pathway to colonization of a deeper subterranean environment, have not been studied well. In the present study, we examined the photoreception ability in a trechine beetle, Trechiama kuznetsovi, which inhabits the upper hypogean zone and has a vestigial compound eye. By de novo assembly of genome and transcript sequences, we were able to identify photoreceptor genes and phototransduction genes. Specifically, we focused on opsin genes, where one long wavelength opsin gene and one ultraviolet opsin gene were identified. The encoded amino acid sequences had neither a premature stop codon nor a frameshift mutation, and appeared to be subject to purifying selection. Subsequently, we examined the internal structure of the compound eye and nerve tissue in the adult head, and found potential photoreceptor cells in the compound eye and nerve bundle connected to the brain. The present findings suggest that T. kuznetsovi has retained the ability of photoreception. This species represents a transitional stage of vision, in which the compound eye regresses, but it may retains the ability of photoreception using the vestigial eye.

zoology↗

bioRxiv2022

Embodied Latch Mechanism of the Mandible to Power at an Ultrahigh Speed in the Trap-jaw Ants Odontomachus kuroiwae

Rapid movements of limbs and appendages, faster than those produced by simple muscle contraction alone, are generated through mechanical networks consisting of springs and latches. The latch plays a central role in these spring-loaded mechanisms, but the structural details of the latch are not always known. The mandibles of the trapjaw ant Odontomachus kuroiwae closes the mandible extremely quickly to capture prey or to perform mandible-powered defensive jumps to avoid potential threats. The jump is mediated by a mechanical spring and latch system embodied in the mandible. An ant can strike the tip of the mandible onto the surface of an obstacle (prey, predator, or ground) in order to bounce its body away from potential threats. The angular velocity of the closing mandible was 2.3x104 rad/s. Latching of the joint is a key mechanism to aid the storage of energy required to power the ballistic movements of the mandibles. We have identified the fine structure of two latch systems on the mandible forming a balljoint using an X-ray micro-computational tomography system (X-ray micro-CT) and X-ray live imaging with a synchrotron. Here we describe the surface of the inner section of the socket and a projection on the lip of the ball. The X-ray live imaging and movements of the 3D model show that the ball with a detent ridge slipped into a socket and over the socket ridge before snapping back at the groove edge. Our results give insight into the complex spring-latch systems that underpin ultra-fast movements in biological systems.

animal behavior and cognition↗

bioRxiv2020

Descending and ascending signals that maintain rhythmic walking pattern in the cricket

The cricket is one of the model animals used to investigate the neuronal mechanisms underlying adaptive locomotion. An intact cricket walks with a tripod gait, similar to other insects. The motor control center of the leg movements is located in the thoracic ganglia. In this study, we investigated the walking gait patterns of crickets whose ventral nerve cords were surgically cut to gain an understanding of how the descending signals from the head ganglia and ascending signals from the abdominal nervous system into the thoracic ganglia mediate the initiation and coordination of the walking gait pattern. Crickets whose paired connectives between the brain and subesophageal ganglion (SEG) were cut exhibited a tripod gait pattern. However, when one side of the connectives between the brain and SEG was cut, the crickets continued to turn in the opposite direction to the connective cut. Crickets whose paired connectives between the SEG and prothoracic ganglion were cut did not walk, whereas the crickets exhibited an ordinal tripod gait pattern when one side of the connectives was intact. Crickets whose paired connectives between the metathoracic ganglion and abdominal ganglia were cut initiated walking, although the gait was not a coordinated tripod pattern, whereas the crickets exhibited a tripod gait when one side of the connectives was intact. These results suggest that the brain plays an inhibitory role in initiating leg movements, and that both the descending signals from the head ganglia and the ascending signals from the abdominal nervous system are both important in initiating and coordinating insect walking gait patterns.

animal behavior and cognition↗

bioRxiv2020

Serotonergic control in initiating defensive response to unexpected tactile stimulus in the trap-jaw ant Odontomachus kuroiwae

A decision to express a defensive response or an escape response to a potential threat is crucial for insects to survive. This study investigated an aminergic mechanism underlying defensive responses to unexpected touch in an ant that has powerful mandibles, the so-called trap-jaw. The mandibles close extremely quickly and are used as a weapon during hunting. Tactile stimulation to the abdomen elicited quick forward movements in a "dart escape" in 90% of the ants in a colony. Less than 10% of the ants responded with a quick "defensive turn" towards the source of stimulation. To reveal the neuronal control mechanisms underlying this defensive behavior, the effects of brain biogenic amines on the responses to tactile stimulus were investigated. The levels of octopamine (OA), dopamine (DA) and serotonin (5HT) in the brain were significantly elevated in ants that responded with a defensive turn to the unexpected stimulus compared to ants that responded with a dart escape. Oral administration of DA and 5HT demonstrated that both amines contributed to the initiation of a defensive response to the stimulus. Oral administration of L-DOPA weakly affected the initiation of the defensive turn, while 5HTP strongly affected the initiation of defensive behavior. Oral administration of an antagonist of 5HT, ketanserin, abolished the effect of 5HTP. These results indicate that endogenous 5HT in the brain has a key role to play in modulating the initiation of defensive behavior in the trap-jaw ant.

animal behavior and cognition↗

bioRxiv2019

Arm swapping autograft shows functional equivalency of five arms in sea stars

Extant echinoderms show five-part radial symmetry in typical shape. However, we can find some asymmetry in their details, represented by the madreporite position not at the center, different skeletal arrangement in two of the five rays of sea urchins, and a circular cavity formed by two-end closure. We suspect the existence of any difference in hidden information between the five. In our hypothesis, deep equivalency makes no issue in function even after exchanging the position of rays; otherwise, this autograft causes some trouble in behavior or tissue formation. For this attempt, we firstly developed a method to transplant an arm tip to the counterpart of another arm in the sea star Patiria pectinifera. As a result, seven arms were completely implanted--four into the original positions for a control and three into different positions--with underwater surgery where we sutured with nylon thread and physically prevented nearby tube feet extending. Based on our external and internal observation, each grafted arm (i) gradually recovered movement coordination with the proximal body, (ii) regenerated its lost half as in usual distal regeneration, and (iii) formed no irregular intercalation filling any positional gap at the suture, no matter whether two cut arms were swapped. We here suggest a deep symmetry among the five rays of sea stars not only in morphology but also in physiology, representing an evolutionary strategy that has given equal priority to all the radial directions. Moreover, our methodological notes for grafting a mass of body in sea stars would help echinoderm research involving positional information as well as immunology.

developmental biology↗

bioRxiv2019

Three-dimensional morphological analysis of the dynamic digestive system in the green brittle star

Brittle stars (Echinodermata: Ophiuroidea) digest a great diversity of food in their stomach, which widely lies in the central disk. As for a possible digestive activity, the green brittle star Ophiarachna incrassata (Lamarck, 1816) is known to show a dynamic movement at the disk. This phenomenon would deeply involve the morphological structure of the stomach. However, past anatomical studies have shown the digestive system in two dimensions after wide incision of the body wall anchoring the stomach. This methodology restrains us from understanding how the stomach actually shapes inside a brittle star. We aim to visualize the morphology of brittle stars digestive system in a non-destructive and three-dimensional way, with a comparison between a relaxed specimen and a specimen fixed at the very moment of the disks movement. Employing X-ray micro-computed tomography (micro-CT) and introducing an instant freezing method with cryogenic ethanol, we found the stomach wholly transformed during the movement. We here brought transparency to the in vivo position of gut contents to hint the mechanism and digestive function of the movement. Our outcome spotlights a dynamic digestive process in echinoderms and a widely applicable method for probing into its relation with body structure.

physiology↗

bioRxiv2019

Generalized locomotion of brittle stars with an arbitrary number of arms

Typical brittle stars have five radially symmetrical arms, which coordinate to move their body in a certain direction. However, some species of them show individual difference in the number of arms. We found this trait unique since intact legged animals each own a fixed number of limbs in general. How does a single species manage such different numbers of motile organs to realize adaptive locomotion? We here described four-, five-, six-, and seven-armed locomotion with the aim to generalize a common rule which is flexible with arm numbers in brittle stars. We mechanically stimulated an arm in Ophiactis brachyaspis to analyze escape direction and arm movements. Gathering quantitative indices and employing Bayesian statistical modeling, we figured out an average locomotion: regardless of the total number of arms, a front position emerges at one of the second neighboring arms to a mechanically stimulated arm, while side arms adjacent to the front synchronously work as left and right rowers. We suggest a model where some afferent signal runs either clockwise or anticlockwise along the nerve ring while linearly counting how many arms it passes. This idea would explain how left and right emerges in a radially symmetrical body via a decentralized system.

animal behavior and cognition↗

bioRxiv2018

Excretion initiates walking in the cricket Gryllus bimaculatus

Feces contain information about the donor and potentially attracts both conspecifics and predators and parasites. The excretory system must be coordinated with other behaviors in insects. We found that crickets start walking forward following excretion of feces. Most intact crickets walked around the experimental arena, stopped at a particular site and raised up their body with a slight backward drift to excrete feces. After the feces dropped on the floor, the animal started walking with a random gait pattern away from the feces, and then changed the gait pattern to a tripod gait. Headless cricket also showed walking following excretion. In more than half of excretion events, headless crickets walked backward before excretion. The posture adopted during excretion was similar to that of intact crickets, and post-excretory forward walking was also observed. The occurrence rate of post-excretory walking was more than that of intact crickets. The gait pattern during forward walking was random and never transitioned to a tripod gait in the headless crickets. In animals whose abdominal nerve cords were cut, in any position, pre- or post-excretion walking was not shown in both intact and headless crickets, although they excreted feces. These results indicate that ascending signals from the terminal abdominal ganglion initiate leg movement through the neuronal circuits within thoracic ganglia, and that descending signals from the brain must regulate leg the motor circuit to express the appropriate walking gait.

animal behavior and cognition↗

bioRxiv2018

Five- and Six-armed Brittle Stars Make Different Currents in the Disk

AbstractPhysiological experiments and mathematical models have supported that neuronal activity is crucial for coordinating rhythmic movements of animals. On the other hand, robotics studies have suggested the importance of physical properties made by body structure. However, it remains unclear how morphology affects movement coordination in animals independent of neuronal activity. To begin to understand this issue, this study reports a rhythmic movement in the green brittle star. We found this animal moved five radially symmetric parts in a well-ordered unsynchronized pattern. We explained the coordinated pattern without considering neuronal activity, by building a phenomenological model where internal fluid flows between the body parts. Changing the number of body parts from five to six simulated a synchronized pattern, which is also demonstrated by a rare individual with six symmetric parts. This model suggests the different number in morphology changes the symmetry of the fluid flow, leading to the different synchronization patterns.

physiology↗