Neuroethology of releasing mechanisms: Prey-catching in toads

Pathways for Naturalistic Looking Behavior in Primate I: Behavioral Characteristics and Brainstem Circuits

Organisms control their visual worlds by moving their eyes, heads, and bodies. This control of "gaze" or "looking" is key to survival and intelligence, but our investigation of the underlying neural mechanisms in natural conditions is hindered by technical limitations. Recent advances have enabled measurement of both brain and behavior in freely moving animals in complex environments, expanding on historical head-fixed laboratory investigations. We juxtapose looking behavior as traditionally measured in the laboratory against looking behavior in naturalistic conditions, finding that behavior changes when animals are free to move or when stimuli have depth or sound. We specifically focus on the brainstem circuits driving gaze shifts and gaze stabilization. The overarching goal of this review is to reconcile historical understanding of the differential neural circuits for different "classes" of gaze shift with two inconvenient truths. (1) "classes" of gaze behavior are artificial. (2) The neural circuits historically identified to control each "class" of behavior do not operate in isolation during natural behavior. Instead, multiple pathways combine adaptively and non-linearly depending on individual experience. While the neural circuits for reflexive and voluntary gaze behaviors traverse somewhat independent brainstem and spinal cord circuits, both can be modulated by feedback, meaning that most gaze behaviors are learned rather than hardcoded. Despite this flexibility, there are broadly enumerable neural pathways commonly adopted among primate gaze systems. Parallel pathways which carry simultaneous evolutionary and homeostatic drives converge in superior colliculus, a layered midbrain structure which integrates and relays these volitional signals to brainstem gaze-control circuits.

In paired preference tests, domestic chicks innately choose the colour green over red, and the shape of a frog over a sphere when both stimuli are green

Many animals express unlearned colour preferences that depend on the context in which signals are encountered. These colour biases may have evolved in response to the signalling system to which they relate. For example, many aposematic animals advertise their unprofitability with red warning signals. Predators' innate biases against these warning colours have been suggested as one of the potential explanations for the initial evolution of aposematism. It is unclear, however, whether unlearned colour preferences reported in a number of species is truly an innate behaviour or whether it is based on prior experience. We tested the spontaneous colour and shape preferences of dark-hatched, unfed, and visually naive domestic chicks (Gallus gallus). In four experiments, we presented chicks with a choice between either red (a colour typically associated with warning patterns) or green (a colour associated with palatable cryptic prey), volume-matched spheres (representing a generalised fruit shape) or frogs (representing an aposematic animal's shape). Chicks innately preferred green stimuli and avoided red. Chicks also preferred the shape of a frog over a sphere when both stimuli were green. However, no preference for frogs over spheres was present when stimuli were red. Male chicks that experienced a bitter taste of quinine immediately before the preference test showed a higher preference for green frog-shaped stimuli. Our results suggest that newly hatched chicks innately integrate colour and shape cues during decision making, and that this can be augmented by other sensory experiences. Innate and experience-based behaviour could confer a fitness advantage to novel aposematic prey, and favour the initial evolution of conspicuous colouration.

Neurocircuitry of Predatory Hunting

Predatory hunting is an important type of innate behavior evolutionarily conserved across the animal kingdom. It is typically composed of a set of sequential actions, including prey search, pursuit, attack, and consumption. This behavior is subject to control by the nervous system. Early studies used toads as a model to probe the neuroethology of hunting, which led to the proposal of a sensory-triggered release mechanism for hunting actions. More recent studies have used genetically-trackable zebrafish and rodents and have made breakthrough discoveries in the neuroethology and neurocircuits underlying this behavior. Here, we review the sophisticated neurocircuitry involved in hunting and summarize the detailed mechanism for the circuitry to encode various aspects of hunting neuroethology, including sensory processing, sensorimotor transformation, motivation, and sequential encoding of hunting actions. We also discuss the overlapping brain circuits for hunting and feeding and point out the limitations of current studies. We propose that hunting is an ideal behavioral paradigm in which to study the neuroethology of motivated behaviors, which may shed new light on epidemic disorders, including binge-eating, obesity, and obsessive-compulsive disorders.

In search for consciousness in animals: Using working memory and voluntary attention as behavioral indicators

Whether animals have subjective experiences about the content of their sensory input, i.e., whether they are aware of stimuli, is a notoriously difficult question to answer. If consciousness is present in animals, it must share fundamental characteristics with human awareness. Working memory and voluntary/endogenous attention are suggested as diagnostic features of conscious awareness. Behavioral evidence shows clear signatures of both working memory and voluntary attention as minimal criterium for sensory consciousness in mammals and birds. In contrast, reptiles and amphibians show no sign of either working memory or volitional attention. Surprisingly, some species of teleost fishes exhibit elementary working memory and voluntary attention effects suggestive of possibly rudimentary forms of subjective experience. With the potential exception of honeybees, evidence for conscious processing is lacking in invertebrates. These findings suggest that consciousness is not ubiquitous in the animal kingdom but also not exclusive to humans. The phylogenetic gap between animal taxa argues that evolution does not rely on specific neural substrates to endow distantly related species with basic forms of consciousness.

Quantity as a Fish Views It: Behavior and Neurobiology

An ability to estimate quantities, such as the number of conspecifics or the size of a predator, has been reported in vertebrates. Fish, in particular zebrafish, may be instrumental in advancing the understanding of magnitude cognition. We review here the behavioral studies that have described the ecological relevance of quantity estimation in fish and the current status of the research aimed at investigating the neurobiological bases of these abilities. By combining behavioral methods with molecular genetics and calcium imaging, the involvement of the retina and the optic tectum has been documented for the estimation of continuous quantities in the larval and adult zebrafish brain, and the contributions of the thalamus and the dorsal-central pallium for discrete magnitude estimation in the adult zebrafish brain. Evidence for basic circuitry can now be complemented and extended to research that make use of transgenic lines to deepen our understanding of quantity cognition at genetic and molecular levels.

Directional Preference in Avian Midbrain Saliency Computing Nucleus Reflects a Well-Designed Receptive Field Structure

Simple Summary

Directional preference neurons has been found in many vertebrate sensory systems. The isthmi pars magnocellularis (Imc) in avian midbrain, playing a key role in visual selective attention, shows impressive motion directional preference, but little is known about the physiological basis of this phenomenon. Herein, artificial visual stimuli, statistical analyses, and a neural computational model were used to unravel this mystery. This study deepens the understanding of the relationship between the directional preference and special receptive field structure of pigeon’s (Columba livia) Imc neuron.

Abstract

Neurons responding sensitively to motions in several rather than all directions have been identified in many sensory systems. Although this directional preference has been demonstrated by previous studies to exist in the isthmi pars magnocellularis (Imc) of pigeon (Columba livia), which plays a key role in the midbrain saliency computing network, the dynamic response characteristics and the physiological basis underlying this phenomenon are unclear. Herein, dots moving in 16 directions and a biologically plausible computational model were used. We found that pigeon Imc’s significant responses for objects moving in preferred directions benefit the long response duration and high instantaneous firing rate. Furthermore, the receptive field structures predicted by a computational model, which captures the actual directional tuning curves, agree with the real data collected from population Imc units. These results suggested that directional preference in Imc may be internally prebuilt by elongating the vertical axis of the receptive field, making predators attack from the dorsal-ventral direction and conspecifics flying away in the ventral-dorsal direction, more salient for avians, which is of great ecological and physiological significance for survival.

Numerosities and Other Magnitudes in the Brains: A Comparative View

The ability to represent, discriminate, and perform arithmetic operations on discrete quantities (numerosities) has been documented in a variety of species of different taxonomic groups, both vertebrates and invertebrates. We do not know, however, to what extent similarity in behavioral data corresponds to basic similarity in underlying neural mechanisms. Here, we review evidence for magnitude representation, both discrete (countable) and continuous, following the sensory input path from primary sensory systems to associative pallial territories in the vertebrate brains. We also speculate on possible underlying mechanisms in invertebrate brains and on the role played by modeling with artificial neural networks. This may provide a general overview on the nervous system involvement in approximating quantity in different animal species, and a general theoretical framework to future comparative studies on the neurobiology of number cognition.

Visual stimulus-specific habituation of innate defensive behaviour in mice

Innate defensive responses such as freezing or escape are essential for animal survival. Mice show defensive behaviour to stimuli sweeping overhead, like a bird cruising the sky. Here, we tested this in young male mice and found that mice reduced their defensive freezing after sessions with a stimulus passing overhead repeatedly. This habituation is stimulus specific, as mice freeze again to a novel shape. Habituation occurs regardless of the visual field location of the repeated stimulus. The mice generalized over a range of sizes and shapes, but distinguished objects when they differed in both size and shape. Innate visual defensive responses are thus strongly influenced by previous experience as mice learn to ignore specific stimuli.

The integration of sensory feedback in the modulation of anuran landing preparation

Controlled landing requires preparation. Mammals and bipedal birds vary how they prepare for landing by predicting the timing and magnitude of impact from the integration of visual and non-visual information. Here, we explore how the cane toad Rhinella marina - an animal that moves primarily through hopping - integrates sensory information to modulate landing preparation. Earlier work suggests that toads may modulate landing preparation using predictions of impact timing and/or magnitude based on non-visual sensory feedback during takeoff rather than visual cues about the landing itself. We disentangled takeoff and landing conditions by hopping toads off platforms of different heights while measuring electromyographic (EMG) activity of an elbow extensor (m. anconeus) and capturing high-speed images to quantify whole body and forelimb kinematics. This enabled us to test how toads integrate visual and non-visual information in landing preparation. We asked two questions: (1) when they conflict, do toads correlate landing preparation with takeoff or landing conditions? And (2) for hops with the same takeoff conditions, does visual information alter the timing of landing preparation? We found that takeoff conditions are a better predictor of the onset of landing preparation than landing conditions, but that visual information is not ignored. When hopping off higher platforms, toads start to prepare for landing later when takeoff conditions are invariant. This suggests that, unlike mammals, toads prioritize non-visual sensory feedback about takeoff conditions to coordinate landing, but that they do integrate visual information to fine-tune landing preparation.

Reproductive State Modulates Retinal Sensitivity to Light in Female Túngara Frogs

Visual cues are often a vital part of animal communication and courtship. While a plethora of studies have focused on the role that hormones play in acoustic communication of anurans, relatively few have explored hormonal modulation of vision in these animals. Much of what we do know comes from behavioral studies, which show that a frog’s hormonal state can significantly affect both its visual behavior and mating decisions. However, to fully understand how frogs use visual cues to make these mating decisions, we must first understand how their visual system processes these cues, and how hormones affect these processes. To do this, we performed electroretinograms (ERGs) to measure retinal sensitivity of túngara frogs (Physalaemus pustulosus), a neotropical species whose mating behavior includes previously described visual cues. To determine the effect of hormonal state on visual sensitivity, ERGs were recorded under scotopic and photopic conditions in frogs that were either non-reproductive or hormone-treated with human chorionic gonadotropin (hCG) prior to testing. Additionally, measurements of optical anatomy determined how túngara frog eye and retina morphology related to physiological sensitivity. As expected, we found that both sexes display higher visual sensitivity under scotopic conditions compared to photopic conditions. However, hormone injections significantly increased retinal sensitivity of females under scotopic conditions. These results support the hypothesis that hormonal modulation of neural mechanisms, such as those mediating visually guided reproductive behavior in this species, include modulation of the receptor organ: the retina. Thus, our data serve as a starting point for elucidating the mechanism of hormonal modulation of visual sensitivity.

Elements of a stochastic 3D prediction engine in larval zebrafish prey capture

The computational principles underlying predictive capabilities in animals are poorly understood. Here, we wondered whether predictive models mediating prey capture could be reduced to a simple set of sensorimotor rules performed by a primitive organism. For this task, we chose the larval zebrafish, a tractable vertebrate that pursues and captures swimming microbes. Using a novel naturalistic 3D setup, we show that the zebrafish combines position and velocity perception to construct a future positional estimate of its prey, indicating an ability to project trajectories forward in time. Importantly, the stochasticity in the fish's sensorimotor transformations provides a considerable advantage over equivalent noise-free strategies. This surprising result coalesces with recent findings that illustrate the benefits of biological stochasticity to adaptive behavior. In sum, our study reveals that zebrafish are equipped with a recursive prey capture algorithm, built up from simple stochastic rules, that embodies an implicit predictive model of the world.

Dynamics of electroencephalogram oscillations underlie right-eye preferences in predatory behavior of the music frog

Visual lateralization is a typical characteristic of many vertebrates; however, its underlying dynamic neural mechanism is unclear. In this study, predatory responses and dynamic brain activities were evaluated in the Emei music frog (Nidirana daunchina) to assess the potential eye preferences and their underlying dynamic neural mechanism, using behavioral and electrophysiological experiments, respectively. To do this, when the prey stimulus (live cricket and leaf as control) was moved around the frogs in both clockwise and anticlockwise directions at constant velocity, the number of predatory responses were counted and electroencephalogram (EEG) absolute power spectra for each band were measured for the telencephalon, diencephalon and mesencephalon. The results showed that: (1) no significant differences in the number of predatory responses could be found for the control (leaf), but the number of predatory responses for the right visual field (RVF) was significantly greater than that for the left visual field (LVF) when the live cricket was moved into the RVF clockwise; (2) compared with no stimulus in the visual field and stimulus in the LVF, the power spectra of each EEG band were greater when the prey stimulus was moved into the RVF clockwise; and (3) the power spectra of the theta, alpha and beta bands in the left diencephalon were significantly greater than those of the right counterpart for the clockwise direction, but similar significant differences presented for the delta, theta and alpha bands in the anticlockwise direction. Together, the results suggested that right-eye preferences for predatory behaviors exist in music frogs, and that the dynamics of EEG oscillations might underlie this right eye/left hemisphere advantage.

Neural architecture of the vertebrate brain: implications for the interaction between emotion and cognition

Cognition is considered a hallmark of the primate brain that requires a high degree of signal integration, such as achieved in the prefrontal cortex. Moreover, it is often assumed that cognitive capabilities imply "superior" computational mechanisms compared to those involved in emotion or motivation. In contrast to these ideas, we review data on the neural architecture across vertebrates that support the concept that association and integration are basic features of the vertebrate brain, which are needed to successfully adapt to a changing world. This property is not restricted to a few isolated brain centers, but rather resides in neuronal networks working collectively in a context-dependent manner. In different vertebrates, we identify shared large-scale connectional systems involving the midbrain, hypothalamus, thalamus, basal ganglia, and amygdala. The high degree of crosstalk and association between these systems at different levels supports the notion that cognition, emotion, and motivation cannot be separated - all of them involve a high degree of signal integration.

Predatory behavior changes with satiety or increased insulin levels in the praying mantis (Tenodera sinensis)

At any given moment, behavior is controlled by a combination of external stimuli and an animal's internal state. As physiological conditions change, vastly different behaviors might result from the same stimuli. For example, the motivation to hunt and hunting strategy are influenced by satiety. Here, we describe how sensory responsiveness and motor activity of a praying mantis (Tenodera sinensis) change as the insect feeds, leading to an altered hunting strategy. We further show that these changes can be induced by injection of insulin, which likely functions as a metabotropic indicator. Praying mantises directed their attention toward real and simulated prey less often as they fed and became sated. The range of distance and azimuth at which prey was detected decreased as did pursuit of prey, while opportunistic close-range attacks persisted. Together, these sensorimotor changes are indicative of a behavioral paradigm shift from 'pursuit' to 'ambush'. A similar effect was induced in starved praying mantises injected with 0.05 ml of 200 μg ml^-1 bovine insulin. These experiments showed that insulin injection into the circulating hemolymph is sufficient to decrease prey orientation as well as in prey-directed locomotor behaviors (tracking and pursuit). The effects of prey consumption and insulin injection were similarly dose dependent. These results suggest that insulin is a signal of internal, physiological conditions that can modify responses to external stimuli. A change in hunting strategy thus results from coordinated effects of a neurohormone on a set of independent sensorimotor processes and the overall activity level of the animal.

Visually-naïve chicks prefer agents that move as if constrained by a bilateral body-plan

From the first hours of life, the prompt detection of animate agents allows identification of biologically relevant entities. The motion of most animate agents is constrained by their bilaterally-symmetrical body-plan, and consequently tends to be aligned with the main body-axis. Thus parallelism between the main axis of a moving object and its motion trajectory can signal the presence of animate agents. Here we demonstrated that visually-naïve newborn chicks (Gallus gallus domesticus) are attracted to objects displaying such parallelism, and thus show preference for the same type of motion patterns that elicit perception of animacy in humans. This is the first demonstration of a newborn non-human animal's social preference for a visual cue related to the constraints imposed on behaviour by bilaterian morphology. Chicks also showed preference for rotational movements - a potential manifestation of self-propulsion. Results are discussed in relation to the mechanisms of animacy and agency detection in newborn organisms.

Tectal CRFR1 receptors modulate food intake and feeding behavior in the South African clawed frog Xenopus laevis

The optic tectum and superior colliculus rapidly inhibit food intake when a visual threat is present. Previous work indicates that CRF, acting on CRFR1 receptors, may play a role in tectal inhibition of feeding behavior and food intake. Here we test the hypothesis that tectal CRFR1 receptors modulate food intake and feeding behavior in juvenile Xenopus laevis. We performed five experiments to test the following questions: 1) Does tectal CRF injection decrease food intake/feeding behavior? 2) Does a selective CRFR1 antagonist block CRF effects on feeding/feeding behavior? 3) Does a reactive stressor decrease food intake/feeding behavior? 4) Does a selective CRFR1 antagonist block reactive stress-induced decrease in feeding/feeding behavior? 5) Does food deprivation increase food intake/feeding behavior? Tectal CRF injections reduced food intake and influenced exploratory behavior, hindlimb kicks, and time in contact with food. These effects were blocked by the selective R1 antagonist NBI-27914. Exposure to a reactive stressor decreased food intake and this effect was blocked by NBI-27914. Neither food intake or feeding behavior changed following 1 wk of food deprivation. Overall, we conclude that activation of tectal CRFR1 inhibits food intake in juvenile X. laevis. Furthermore, tectal CRFR1 receptors appear to be involved in the reduction of food intake that occurs in response to a reactive stressor.

Emotion and the Interactive Brain: Insights From Comparative Neuroanatomy and Complex Systems

Although emotion is closely associated with motivation, and interacts with perception, cognition, and action, many conceptualizations still treat emotion as separate from these domains. Here, a comparative/evolutionary anatomy framework is presented to motivate the idea that long-range, distributed circuits involving the midbrain, thalamus, and forebrain are central to emotional processing. It is proposed that emotion can be understood in terms of large-scale network interactions spanning the neuroaxis that form "functionally integrated systems." At the broadest level, the argument is made that we need to move beyond a Newtonian view of causation to one involving complex systems where bidirectional influences and nonlinearities abound. Therefore, understanding interactions between subsystems and signal integration becomes central to unraveling the organization of the emotional brain.

Homeostatic and regenerative neurogenesis in salamanders

Large-scale regeneration in the adult central nervous system is a unique capacity of salamanders among tetrapods. Salamanders can replace neuronal populations, repair damaged nerve fibers and restore tissue architecture in retina, brain and spinal cord, leading to functional recovery. The underlying mechanisms have long been difficult to study due to the paucity of available genomic tools. Recent technological progress, such as genome sequencing, transgenesis and genome editing provide new momentum for systematic interrogation of regenerative processes in the salamander central nervous system. Understanding central nervous system regeneration also entails designing the appropriate molecular, cellular, and behavioral assays. Here we outline the organization of salamander brain structures. With special focus on ependymoglial cells, we integrate cellular and molecular processes of neurogenesis during developmental and adult homeostasis as well as in various injury models. Wherever possible, we correlate developmental and regenerative neurogenesis to the acquisition and recovery of behaviors. Throughout the review we place the findings into an evolutionary context for inter-species comparisons.

The promise and perils of causal circuit manipulations

The development of increasingly sophisticated methods for recording and manipulating neural activity is revolutionizing neuroscience. By probing how activity patterns in different types of neurons and circuits contribute to behavior, these tools can help inform mechanistic models of brain function and explain the roles of distinct circuit elements. However, in systems where functions are distributed over large networks, interpreting causality experiments can be challenging. Here we review common assumptions underlying circuit manipulations in behaving animals and discuss the strengths and limitations of different approaches.

Sensory feedback and coordinating asymmetrical landing in toads

Coordinated landing requires anticipating the timing and magnitude of impact, which in turn requires sensory input. To better understand how cane toads, well known for coordinated landing, prioritize visual versus vestibular feedback during hopping, we recorded forelimb joint angle patterns and electromyographic data from five animals hopping under two conditions that were designed to force animals to land with one forelimb well before the other. In one condition, landing asymmetry was due to mid-air rolling, created by an unstable takeoff surface. In this condition, visual, vestibular and proprioceptive information could be used to predict asymmetric landing. In the other, animals took off normally, but landed asymmetrically because of a sloped landing surface. In this condition, sensory feedback provided conflicting information, and only visual feedback could appropriately predict the asymmetrical landing. During the roll treatment, when all sensory feedback could be used to predict an asymmetrical landing, pre-landing forelimb muscle activity and movement began earlier in the limb that landed first. However, no such asymmetries in forelimb preparation were apparent during hops onto sloped landings when only visual information could be used to predict landing asymmetry. These data suggest that toads prioritize vestibular or proprioceptive information over visual feedback to coordinate landing.

Variation in brain anatomy in frogs and its possible bearing on their locomotor ecology

Despite the long-standing interest in the evolution of the brain, relatively little is known about variation in brain anatomy in frogs. Yet, frogs are ecologically diverse and, as such, variation in brain anatomy linked to differences in lifestyle or locomotor behavior can be expected. Here we present a comparative morphological study focusing on the macro- and micro-anatomy of the six regions of the brain and its choroid plexus: the olfactory bulbs, the telencephalon, the diencephalon, the mesencephalon, the rhombencephalon, and the cerebellum. We also report on the comparative anatomy of the plexus brachialis responsible for the innervation of the forelimbs. It is commonly thought that amphibians have a simplified brain organization, associated with their supposedly limited behavioral complexity and reduced motor skills. We compare frogs with different ecologies that also use their limbs in different contexts and for other functions. Our results show that brain morphology is more complex and more variable than typically assumed. Moreover, variation in brain morphology among species appears related to locomotor behavior as suggested by our quantitative analyses. Thus we propose that brain morphology may be related to the locomotor mode, at least in the frogs included in our analysis.

Simple lines and shapes are associated with, and communicate, distinct emotions

We investigated whether lines and shapes that present face-like features would be associated with emotions. In Experiment 1, participants associated concave, convex, or straight lines with the words happy or sad. Participants found it easiest to associate the concave line with happy and the convex line with sad. In Experiment 2, participants rated (valence, pleasantness, liking, and tension) and categorised (valence and emotion words) two convex and concave lines that were paired with six distinct pairs of eyes. The presence of eyes affected participants' valence ratings and response latencies; more congruent eye-mouth matches produced more consistent ratings and faster reaction times. In Experiment 3, we examined whether dots that resembled eyes would be associated with emotional words. Participants found it easier to match certain sets of dots with specific emotions. These results suggest that facial gestures that are associated with specific emotions can be captured using relatively simple shapes and lines.

Revisiting the concept of behavior patterns in animal behavior with an example from food-caching sequences in wolves (Canis lupus), coyotes (Canis latrans), and red foxes (Vulpes vulpes)

We discuss the history, conceptualization, and relevance of behavior patterns in modern ethology by explaining the evolution of the concepts of fixed action patterns and modal action patterns. We present the movement toward a more flexible concept of natural action sequences with significant degrees of (production and expressive) freedom. An example is presented with the food caching behavior of three Canidae species: red fox (Vulpes vulpes), coyote (Canis latrans) and gray wolf (Canis lupus). Evolutionary, ecological, and neuroecological/neuroethological arguments are presented to explain the difference in levels of complexity and stereotypy between Canis and Vulpes. This article is part of a Special Issue entitled: Canine Behavior.

Action anticipation in human infants reveals assumptions about anteroposterior body-structure and action

Animal actions are almost universally constrained by the bilateral body-plan. For example, the direction of travel tends to be constrained by the orientation of the animal's anteroposterior axis. Hence, an animal's behaviour can reliably guide the identification of its front and back, and its orientation can reliably guide action prediction. We examine the hypothesis that the evolutionarily ancient relation between anteroposterior body-structure and behaviour guides our cognitive processing of agents and their actions. In a series of studies, we demonstrate that, after limited exposure, human infants as young as six months of age spontaneously encode a novel agent as having a certain axial direction with respect to its actions and rely on it when anticipating the agent's further behaviour. We found that such encoding is restricted to objects exhibiting cues of agency and does not depend on generalization from features of familiar animals. Our research offers a new tool for investigating the perception of animate agency and supports the proposal that the underlying cognitive mechanisms have been shaped by basic biological adaptations in humans.

Discontinuous locomotion and prey sensing in the leech

The medicinal leech, Hirudo verbana, is an aquatic predator that utilizes water waves to locate its prey. However, to reach their prey, the leeches must move within the same water that they are using to sense prey. This requires that they either move ballistically towards a pre-determined prey location or that they account for their self-movement and continually track prey. We found that leeches do not localize prey ballistically. Instead, they require continual sensory information to track their prey. Indeed, in the event that the prey moves, leeches will approach the prey's new location. While leeches need to continually sense water disturbances to update their percept of prey location, their own behavior is discontinuous--prey involves switching between swimming, crawling and non-locomoting. Each of these behaviors may allow for different sensory capabilities and may require different sensory filters. Here, we examined the sensory capabilities of leeches during each of these behaviors. We found that while one could expect the non-locomoting phases to direct subsequent behaviors, crawling phases were more effective than non-locomotor phases for providing direction. During crawling bouts, leeches adjusted their heading so as to become more directed towards the stimulus. This was not observed during swimming. Furthermore, in the presence of prey-like stimuli, leeches crawled more often and for longer periods of time.

Predation of Ladybird Beetles (Coleoptera: Coccinellidae) by Amphibians

Studies of predation of ladybird beetles (Coccinellidae) have focused on a limited number of predator taxa, such as birds and ants, while other potential predators have received limited attention. I here consider amphibians as predators of ladybirds. Published amphibian gut analyses show that ladybirds are quite often eaten by frogs and toads (Anura), with recorded frequencies reaching up to 15% of dietary items. Salamanders (Caudata) eat ladybirds less frequently, probably as their habits less often bring them into contact with the beetles. Amphibians do not appear to be deleteriously affected by the potentially toxic alkaloids that ladybirds possess. Amphibians, especially frogs and toads, use primarily prey movement as a release cue to attack their food; it is thus likely that their ability to discriminate against ladybirds and other chemically defended prey is limited. Because of this poor discriminatory power, amphibians have apparently evolved non-specific resistance to prey defensive chemicals, including ladybird alkaloids. Although amphibian-related ladybird mortality is limited, in certain habitats it could outweigh mortality from more frequently studied predators, notably birds. The gut analyses from the herpetological literature used in this study, suggest that in studying predation of insects, entomologists should consider specialized literature on other animal groups.

Modularity of mind and the role of incentive motivation in representing novelty

Animal and human brains contain a myriad of mental representations that have to be successfully tracked within fractions of a second in a large number of situations. This retrieval process is hard to explain without postulating the massive modularity of cognition. Assuming that the mind is massively modular, it is then necessary to understand how cognitive modules can efficiently represent dynamic environments-in which some modules may have to deal with change-induced novelty and uncertainty. Novelty of a stimulus is a problem for a module when unknown, significant stimuli do not satisfy the module's processing criteria-or domain specificity-and cannot therefore be included in its database. It is suggested that the brain mechanisms of incentive motivation, recruited when faced with novelty and uncertainty, induce transient variations in the domain specificity of cognitive modules in order to allow them to process information they were not prepared to learn. It is hypothesised that the behavioural transitions leading from exploratory activity to habit formation are correlated with (and possibly caused by) the organism's ability to counter novelty-induced uncertainty.

An unprecedented role reversal: ground beetle larvae (Coleoptera: Carabidae) lure amphibians and prey upon them

Amphibians often feed on beetle larvae, including those of ground beetles (Carabidae). Preliminary reports have detailed an unusual trophic interaction in which, in contrast, larvae of the ground beetle Epomis prey upon juvenile and adult amphibians. While it is known that these larvae feed exclusively on amphibians, how the predator-prey encounter occurs to the advantage of the beetle larvae had been unknown to date. Using laboratory observations and controlled experiments, we recorded the feeding behavior of Epomis larvae, as well as the behavior of their amphibian prey. Here we reveal that larvae of two species of Epomis (E. circumscriptus and E. dejeani) lure their potential predator, taking advantage of the amphibian's predation behavior. The Epomis larva combines a sit-and-wait strategy with unique movements of its antennae and mandibles to draw the attention of the amphibian to the presence of a potential prey. The intensity of this enticement increases with decreasing distance between the larva and the amphibian. When the amphibian attacks, the larva almost always manages to avoid the predator's protracted tongue, exploiting the opportunity to attach itself to the amphibian's body and initiate feeding. Our findings suggest that the trophic interaction between Epomis larvae and amphibians is one of the only natural cases of obligatory predator-prey role reversal. Moreover, this interaction involves a small insect larva that successfully lures and preys on a larger vertebrate. Such role reversal is exceptional in the animal world, extending our perspective of co-evolution in the arms race between predator and prey, and suggesting that counterattack defense behavior has evolved into predator-prey role reversal.

From an animal's point of view: Motivation, fitness, and animal welfare

To study animal welfare empirically we need an objective basis for deciding when an animal is suffering. Suffering includes a wide range ofunpleasant emotional states such as fear, boredom, pain, and hunger. Suffering has evolved as a mechanism for avoiding sources ofdanger and threats to fitness. Captive animals often suffer in situations in which they are prevented from doing something that they are highly motivated to do. The “price” an animal is prepared to pay to attain or to escape a situation is an index ofhow the animal “feels” about that situation. Withholding conditions or commodities for which an animal shows “inelastic demand” (i.e., for which it continues to work despite increasing costs) is very likely to cause suffering. In designing environments for animals in zoos, farms, and laboratories, priority should be given to features for which animals show inelastic demand. The care ofanimals can thereby be based on an objective, animal-centered assessment of their needs.