Effect of initial body orientation on escape probability of prey fish escaping from predators

Automated escape system: identifying prey's kinematic and behavioral features critical for predator evasion

Identifying the kinematic and behavioral variables of prey that influence evasion from predator attacks remains challenging. To address this challenge, we have developed an automated escape system that responds quickly to an approaching predator and pulls the prey away from the predator rapidly, similar to real prey. Reaction distance, response latency, escape speed and other variables can be adjusted in the system. By repeatedly measuring the response latency and escape speed of the system, we demonstrated the system's ability to exhibit fast and rapid responses while maintaining consistency across successive trials. Using the live predatory fish species Coreoperca kawamebari, we show that escape speed and reaction distance significantly affect the outcome of predator-prey interactions. These findings indicate that the developed escape system is useful for identifying kinematic and behavioral features of prey that are critical for predator evasion, as well as for measuring the performance of predators.

Effects of caudal fin stiffness on optimized forward swimming and turning maneuver in a robotic swimmer

In animal and robot swimmers of body and caudal fin (BCF) form, hydrodynamic thrust is mainly produced by their caudal fins, the stiffness of which has profound effects on both thrust and efficiency of swimming. Caudal fin stiffness also affects the motor control and resulting swimming gaits that correspond to optimal swimming performance; however, their relationship remains scarcely explored. Here using magnetic, modular, undulatory robots (μBots), we tested the effects of caudal fin stiffness on both forward swimming and turning maneuver. We developed six caudal fins with stiffness of more than three orders of difference. For aμBot equipped with each caudal fin (andμBot absent of caudal fin), we applied reinforcement learning in experiments to optimize the motor control for maximizing forward swimming speed or final heading change. The motor control ofμBot was generated by a central pattern generator for forward swimming or by a series of parameterized square waves for turning maneuver. In forward swimming, the variations in caudal fin stiffness gave rise to three modes of optimized motor frequencies and swimming gaits including no caudal fin (4.6 Hz), stiffness <10-4Pa m4(∼10.6 Hz) and stiffness >10-4Pa m4(∼8.4 Hz). Swimming speed, however, varied independently with the modes of swimming gaits, and reached maximal at stiffness of 0.23 × 10-4Pa m4, with theμBot without caudal fin achieving the lowest speed. In turning maneuver, caudal fin stiffness had considerable effects on the amplitudes of both initial head steering and subsequent recoil, as well as the final heading change. It had relatively minor effect on the turning motor program except for theμBots without caudal fin. Optimized forward swimming and turning maneuver shared an identical caudal fin stiffness and similar patterns of peduncle and caudal fin motion, suggesting simplicity in the form and function relationship inμBot swimming.

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.

Behavioural and neural responses of crabs show evidence for selective attention in predator avoidance

Selective attention, the ability to focus on a specific stimulus and suppress distractions, plays a fundamental role for animals in many contexts, such as mating, feeding, and predation. Within natural environments, animals are often confronted with multiple stimuli of potential importance. Such a situation significantly complicates the decision-making process and imposes conflicting information on neural systems. In the context of predation, selectively attending to one of multiple threats is one possible solution. However, how animals make such escape decisions is rarely studied. A previous field study on the fiddler crab, Gelasimus dampieri, provided evidence of selective attention in the context of escape decisions. To identify the underlying mechanisms that guide their escape decisions, we measured the crabs' behavioural and neural responses to either a single, or two simultaneously approaching looming stimuli. The two stimuli were either identical or differed in contrast to represent different levels of threat certainty. Although our behavioural data provides some evidence that crabs perceive signals from both stimuli, we show that both the crabs and their looming-sensitive neurons almost exclusively respond to only one of two simultaneous threats. The crabs' body orientation played an important role in their decision about which stimulus to run away from. When faced with two stimuli of differing contrasts, both neurons and crabs were much more likely to respond to the stimulus with the higher contrast. Our data provides evidence that the crabs' looming-sensitive neurons play an important part in the mechanism that drives their selective attention in the context of predation. Our results support previous suggestions that the crabs' escape direction is calculated downstream of their looming-sensitive neurons by means of a population vector of the looming sensitive neuronal ensemble.

Escaping from multiple visual threats: Modulation of escape responses in Pacific staghorn sculpin (Leptocottus armatus)

Fish perform rapid escape responses to avoid sudden predatory attacks. During escape responses, fish bend their bodies into a C-shape and quickly turn away from the predator and accelerate. The escape trajectory is determined by the initial turn (Stage 1) and a contralateral bend (Stage 2). Previous studies have used a single threat or model predator as a stimulus. In nature, however, multiple predators may attack from different directions simultaneously or in close succession. It is unknown whether fish are able to change the course of their escape response when startled by multiple stimuli at various time intervals. Pacific staghorn sculpin (Leptocottus armatus) were startled with a left and right visual stimulus in close succession. By varying the timing of the second stimulus, we were able to determine when and how a second stimulus could affect the escape response direction. Four treatments were used: a single visual stimulus (control); or two stimuli coming from opposite sides separated by a 0 ms (simultaneous treatment); a 33 ms; or a 83 ms time interval. The 33 ms and 83 ms time intervals were chosen to occur shortly before and after a predicted 60 ms visual escape latency (i.e. during Stage 1). The 0 ms and 33 ms treatments influenced both the escape trajectory and the Stage 1 turning angle, compared to a single stimulation, whereas the 83 ms treatment had no effect on the escape trajectory. We conclude that Pacific staghorn sculpin can modulate their escape trajectory only between stimulation and the onset of the response, but that escape trajectory cannot be modulated after the body motion has started.

Intersection of motor volumes predicts the outcome of ambush predation of larval zebrafish

Escape maneuvers are key determinants of animal survival and are under intense selection pressure. A number of escape maneuver parameters contribute to survival, including response latency, escape speed and direction. However, the relative importance of these parameters is context dependent, suggesting that interactions between parameters and predatory context determine the likelihood of escape success. To better understand how escape maneuver parameters interact and contribute to survival, we analyzed the responses of larval zebrafish (Danio rerio) to the attacks of dragonfly nymphs (Sympetrum vicinum). We found that no single parameter explains the outcome. Instead, the relative intersection of the swept volume of the nymph's grasping organs with the volume containing all possible escape trajectories of the fish is the strongest predictor of escape success. In cases where the prey's motor volume exceeds that of the predator, the prey survives. By analyzing the intersection of these volumes, we compute the survival benefit of recruiting the Mauthner cell, a neuron in anamniotes devoted to producing escapes. We discuss how the intersection of motor volume approach provides a framework that unifies the influence of many escape maneuver parameters on the likelihood of survival.

Functional effect of vaterite - the presence of an alternative crystalline structure in otoliths alters escape kinematics of the brown trout

The fast-start escape response is the main locomotor behaviour observed in fish to evade predatory attacks and thereby increase their probability of survival. Thus far, this high-speed sensory motor control has been extensively studied in relation to extrinsic factors. In contrast, there has been surprisingly little consideration of intrinsic individual factors that can mediate sensorial perception, such as inter-individual variability in mechanosensory systems. The inner ear of teleost fishes is composed of otoliths that play an important role in hearing and balance functions. While sagittal otoliths are normally composed of aragonite in many fish species, the inclusion of vaterite (an abnormal crystalline structure) has been reported in a number of individuals from different environments. There is currently strong theoretical and empirical evidence that vaterite deposition has a negative impact on auditory sensitivity in fishes. While the functional/behavioural implications of this defect on otolith-related hearing function has been hypothesised, it has remained largely untested experimentally. Here, using juvenile (0+ years) Salmo trutta originating from the wild in experimental conditions, we report for the first time that the deposition of calcium carbonate in its crystalline vateritic polymorph has significant pervasive effects on the escape kinematics of fish. The presence of an alternative crystalline structure in otoliths is likely to alter fish behaviour in ways that decrease survival. We also report that altered behaviour in individuals with vateritic otoliths is partially compensated for by the presence of a functional lateral line. Such functional compensation suggests more slight consequences, if any, in the wild.

Escape responses of fish: a review of the diversity in motor control, kinematics and behaviour

The study of fish escape responses has provided important insights into the accelerative motions and fast response times of these animals. In addition, the accessibility of the underlying neural circuits has made the escape response a fundamental model in neurobiology. Fish escape responses were originally viewed as highly stereotypic all-or-none behaviours. However, research on a wide variety of species has shown considerable taxon-specific and context-dependent variability in the kinematics and neural control of escape. In addition, escape-like motions have been reported: these resemble escape responses kinematically, but occur in situations that do not involve a response to a threatening stimulus. This Review focuses on the diversity of escape responses in fish by discussing recent work on: (1) the types of escape responses as defined by kinematic analysis (these include C- and S-starts, and single- versus double-bend responses); (2) the diversity of neuromuscular control; (3) the variability of escape responses in terms of behaviour and kinematics within the context of predator−prey interactions; and (4) the main escape-like motions observed in various species. Here, we aim to integrate recent knowledge on escape responses and highlight rich areas for research. Rapidly developing approaches for studying the kinematics of swimming motion both in the lab and within the natural environment provide new avenues for research on these critical and common behaviours.