Thanatosis

Tonic immobility and phenomenal consciousness in animals: a review

Tonic immobility (TI) is an innate, last-resort response to the presence of a predator, commonly referred to as feigning death or thanatosis. However, it is critical to distinguish death feigning from TI; the former encompasses a complex series of behaviors, with TI representing its final aspect. Given this complexity, death feigning is hypothesized to manifest a higher-order intentionality in animals. Considering that third-order and higher intentional states are correlated with some form of phenomenal consciousness, their presence in animals has significant implications for their conscious experiences. This hypothesis surrounding third-order and higher intentional states is subject to dispute, in part due to the lack of sufficient evidence indicating that the behaviors associated with death feigning, aside from TI, serve a protective function against predation. Evidence suggests that TI alone constitutes an effective mechanism for predator defense. It is posited that the cessation of TI by the prey organism signifies the presence of a first-order intentional state. Furthermore, it is proposed that behavioral indicators suggest that the termination of TI by the prey is linked to anoetic and potentially noetic consciousness. The relationship between TI and fear is also examined. It is contended that, within the framework of formulating hypotheses concerning the mechanisms of TI and developing experimental designs to test these hypotheses, fear should be characterized as an intervening variable. The conclusions derived from this analysis indicate that TI can occasionally function as an effective predator defense associated with primal sensory and anoetic consciousness. Its termination may imply the presence of noetic consciousness; however, self-reflective autonoetic consciousness appears to be absent. Finally, the hypothesis suggesting that TI serves as an evolutionary precursor to the theory of mind in humans is discussed, serving as a cautionary note in the interpretation of findings from animal research concerning the evolution of cognitive functions in humans.

Seeing life in the teeming world: animacy perception in arthropods

The term "animacy perception" describes the ability of animals to detect cues that indicate whether a particular object in the environment is alive or not. Such skill is crucial for survival, as it allows for the rapid identification of animated agents, being them potential social partners, or dangers to avoid. The literature on animacy perception is rich, and the ability has been found to be present in a wide variety of vertebrate taxa. Many studies suggest arthropods also possess this perceptual ability, however, the term "animacy" has not often been explicitly used in the research focused on these models. Here, we review the current literature providing evidence of animacy perception in arthropods, focusing especially on studies of prey categorization, predator avoidance, and social interactions. First, we present evidence for the detection of biological motion, which involves recognizing the spatio-temporal patterns characteristic of liveliness. We also consider the congruency between shape and motion that gives rise to animacy percept, like the maintenance of a motion direction aligned with the main body axis. Next, we discuss how some arthropods use static visual cues, such as facial markings, to detect and recognize individuals. We explore the mechanisms, development, and neural basis of this face detection system, focusing on the well-studied paper wasps. Finally, we discuss thanatosis-a behavior in which an animal feigns death to disrupt cues of liveliness-as evidence for the active manipulation of animacy perception in arthropods.

Physiological and gene expression responses of Protohermes xanthodes (Megaloptera: Corydalidae) larvae to imidacloprid

Megaloptera larvae are important bioindicator species and potential resource insects. To further cultivate their economic role, their living environment must be examined in more detail. In this study, we analyzed the physiological and biochemical effects of a sublethal dose of imidacloprid, a widely used neonicotinoid insecticide, on the larvae of Protohermes xanthodes. After treatment with imidacloprid, P. xanthodes larvae exhibited clear symptoms of poisoning, including the head curling up toward the ventral surface. Additionally, the activity of acetylcholinesterase was significantly inhibited following exposure. The activities of glutathione S-transferases initially continuously increased but showed a slight decrease after 8 days. Catalase activity initially increased and then decreased following imidacloprid treatment; superoxide dismutase activity fluctuated over time, and peroxidase activity continuously increased. The expression levels of HSP70s genes were evaluated using qRT-PCR. These results indicate that P. xanthodes larvae exhibit a toxic response to imidacloprid exposure, manifested as oxidative stress, as observed through behavioral and physiological indicators.

Seeking safety: Movement dynamics after post-contact immobility

Post-contact immobility (PCI) is a final attempt to avoid predation. Here, for the first time, we examine the pattern of movement and immobility when antlion larvae resume activity after PCI. To simulate contact with, and escape from, a predator we dropped the larvae onto three different substrates: Paper, Shallow sand (2.3mm-deep) and Deep sand (4.6mm-deep). The Paper lining a Petri dish represented a hard surface that antlion larvae could not penetrate to hide. The Shallow sand permitted the antlions to dig but not to submerge completely whereas the Deep sand allowed them both to dig and to submerge. We tracked their paths automatically and recorded alternating immobility and movement durations over 90min. On the impenetrable substrate, antlion larvae showed super-diffusive dispersal, their movement durations became longer, their immobility durations became shorter and their instantaneous speeds increased. This is consistent with the antlions needing to leave an area of hard substrate and quickly to find somewhere to hide. On Shallow sand, antlion larvae exhibited a modest increase in movement duration, a modest decrease in immobility duration and a concomitant diffusive dispersal. This is consistent with their use of a spiral search, presumably for a suitable depth of sand, to conceal themselves. On Deep sand, the movement and immobility durations of the antlion larvae did not change and their dispersal was sub-diffusive because they were able to bury themselves. On Paper, the distribution of immobility durations had a long tail, consistent with a log-normal distribution. On Shallow and Deep sand, most of the distribution was fitted better by a power law or a log-normal. Our results suggest that PCI in antlion larvae is a disruptive event and that post-PCI movement and immobility gradually return to the pattern typical of intermittent locomotion, depending on the scope for burying and hiding in the substrate.

Catatonia

Catatonia is a neuropsychiatric disorder characterized by motor, affective and cognitive-behavioural signs, which lasts from hours to days. Intensive research over the past two decades has led to catatonia being recognized as an independent diagnosis in the International Classification of Diseases, 11th Revision (ICD-11) since 2022. Catatonia is found in 5-18% of inpatients on psychiatric units and 3.3% of inpatients on medical units. However, in an unknown number of patients, catatonia remains unrecognized and these patients are at risk of life-threatening complications. Hence, recognizing the symptoms of catatonia early is crucial to initiate appropriate treatment to achieve a favourable outcome. Benzodiazepines such as lorazepam and diazepam, electroconvulsive therapy, and N-methyl-D-aspartate antagonists such as amantadine and memantine, are the cornerstones of catatonia therapy. In addition, dopamine-modulating second-generation antipsychotics (for example, clozapine and aripiprazole) are effective in some patient populations. Early and appropriate treatment combined with new screening assessments has the potential to reduce the high morbidity and mortality associated with catatonia in psychiatric and non-psychiatric settings.

Brain evolution and the meaning of catatonia - An update

Back in 2004, in a chapter titled "Brain Evolution and the Meaning of Catatonia", a case was made that the syndrome's core meaning is embedded in millions of years of vertebrate brain evolution. (Fricchione, 2004) In this update, advances over the last almost 20 years, in catatonia theory and research in particular, and pertinent neuropsychiatry in general, will be applied to this question of meaning. The approach will rely heavily on a number of thought leaders, including Nicos Tinbergen, Paul MacLean, John Bowlby, M. Marsel Mesulam, Bruce McEwen and Karl Friston. Their guidance will be supplemented with a selected survey of 21sty century neuropsychiatry, neurophysiology, molecular biology, neuroimaging and neurotherapeutics as applied to the catatonic syndrome. In an attempt to address the question of the meaning of the catatonic syndrome in human life, we will employ two conceptual networks representing the intersubjectivity of the quantitative conceptual network of physical terms and the subjectivity of the qualitative conceptual network of mental and spiritual terms. In the process, a common referent providing extensional identity may emerge (Goodman, 1991). The goal of this exercise is to enhance our attunement with the experience of patients suffering with catatonia. A deeper understanding of catatonia's origins in brain evolution and of the challenges of individual epigenetic development in the setting of environmental events coupled with appreciation of what has been described as the most painful mammalian condition, that of separation, has the potential to foster greater efforts on the part of clinicians to diagnose and treat patients who present with catatonia. In addition, in this ancient and extreme tactic, evolved to provide safety from extreme survival threat, one can speculate what is at the core of human fear and the challenge it presents to all of us. And when the biology, psychology and sociology of catatonia are examined, the nature of solutions to the challenge may emerge.

Outstanding issues in the study of antipredator defenses

Protective defense mechanisms are well documented across the animal kingdom, but there are still examples of antipredator defenses that do not fit easily into the current conceptualization. They either fall within the intersection of multiple mechanisms or fail to fall neatly into pre-existing categories. Here, using Endler's predatory sequence as a framework, we identify problematic examples of antipredator defenses, separating them into protective mechanisms that are difficult to classify and those which act sequentially depending on context. We then discuss three ways of improving underlying terminological and definitional problems: (1) issues with English and polysemy, (2) overlapping aspects of similar mechanisms, and (3) unclear definitions. By scrutinizing the literature, we disentangle several opaque areas in the study of protective defense mechanisms and highlight questions that require further research. An unclear conceptual framework for protective defense mechanisms can lead to misconceptions in understanding the costs and benefits of defenses displayed by animals, while interchangeable terminologies and ambiguous definitions can hinder communication in antipredator studies.

Observations on neurophysiological pattern and behavioural traits as death-feigning mechanism in Eucryptorrhynchus scrobiculatus (Coleoptera: Curculionidae)

In adaptation to surrounding environmental stimuli, most insects exhibit defense behaviour (death feigning) to improve survival rates in the wild. However, the underlying mechanism of death feigning remains largely unknown. Here, we tested the neurophysiological pattern and behavioural traits of the death-feigning mechanism in the forestry pest Eucryptorrhynchus scrobiculatus. Using neuroanatomy, LC-MS/MS target metabolomics detection technology and qRT-PCR, we investigated the effects of neurochemicals and metabolic pathways in experimental weevils. Excision and drug tests were conducted to verify the key regulatory body parts involved in regulating the central nervous system in death feigning. Our results reconstructed the death-feigning mechanism of E. scrobiculatus: when the effective stimuli point of arousal weevils received mechanical stimulation, the thoracoabdominal ganglion transmitted signals into the brain through the ventral nerve cord, and then the brain regulated dopamine (DA) and serotonin (5-HT) metabolic pathways, reducing the expression of dopamine (dar2) and octopamine (oar1, oab2) receptor genes, finally inducing death feigning. Our study suggests that the variation of neurotransmitters in the brain is an important indicator of the physiological response of death feigning, and the results provide ecological and theoretical information for future investigations to reveal key behaviour and target genes for pest control.

Drop dead! Female mate avoidance in an explosively breeding frog

Males' and females' reproductive strategies may differ, potentially leading to sexual conflict. Increased efforts by males (harassment, forced copulation, intimidation) to gain access to females could even negatively affect female survival and thus lead to reproductive failure for both individuals. In anurans, a higher mortality risk of mating females has been reported in explosive breeding species. During these mating events, several males cling to a female, which are mostly unable to get rid of the unwanted males. This can lead to the female's death. From the literature, it seems that females of explosive breeding frogs have no means to reject unwanted males. Here we describe female mate avoidance behaviours in the European common frog. We observed three female avoidance behaviours, namely 'rotation', 'release call(s)' and tonic immobility (death feigning). These behaviours were significantly associated with smaller female body size, and smaller females were more successful in escaping amplexus. Tonic immobility as a tactic to avoid mating or male harassment has only been observed in a handful of species and only in one other amphibian. Our observations show that females in explosive breeding frogs may not be as passive and helpless as previously thought.

Induced Coma, Death, and Organ Transplantation: A Physiologic, Genetic, and Theological Perspective

In the clinic, the death certificate is issued if brain electrical activity is no longer detectable. However, recent research has shown that in model organisms and humans, gene activity continues for at least 96 h postmortem. The discovery that many genes are still working up to 48 h after death questions our definition of death and has implications for organ transplants and forensics. If genes can be active up to 48 h after death, is the person technically still alive at that point? We discovered a very interesting parallel between genes that were upregulated in the brain after death and genes upregulated in the brains that were subjected to medically-induced coma, including transcripts involved in neurotransmission, proteasomal degradation, apoptosis, inflammation, and most interestingly, cancer. Since these genes are involved in cellular proliferation, their activation after death could represent the cellular reaction to escape mortality and raises the question of organ viability and genetics used for transplantation after death. One factor limiting the organ availability for transplantation is religious belief. However, more recently, organ donation for the benefit of humans in need has been seen as “posthumous giving of organs and tissues can be a manifestation of love spreading also to the other side of death”.

An exploratory study on differences in maternal care between two ecotypes of Nigerian indigenous chicken hens

The Yoruba (YRE) and Fulani (FLE) are the two notable indigenous chicken ecotypes in Nigeria. They exhibit broodiness and post-hatch care of their chicks. Studies on welfare, productivity, and maternal behaviors of these two ecotypes are scarce, hence the need for this study. Separate flocks of these ecotypes were housed intensively and hens that showed broodiness (ten YRE and five FLE) were monitored. Brooding behaviors were monitored for 3 days in the 1st and 2nd weeks of brooding and daily in the 3rd week of brooding for 6 h/day (07:00–09:00 h, 11:00–13:00 h, and 15:00–17:00 h). During brooding, surface body temperatures (eye, brood patch and under the wings), egg temperature and body weight of the hens were measured. Chicks hatched (44 chicks from the YRE and 24 chicks from the FLE) by these hens were subjected to tonic immobility tests on the 7th, 14th, and 21st days post-hatch and to a simulated predator test on the 8th, 15th, and 22nd days post-hatch to determine their level of fear. In each ecotype, brooding behaviors did not change over the three weeks, but the YRE hens spent longer time sitting on their eggs at the 2nd (U = 5.000, z = −2.454, P = 0.014) and 3rd (U = 9.000, z = −1.961, P = 0.050) week of brooding. The surface body temperatures of both ecotypes, egg temperature, and relative weekly weight loss were similar over the brooding period, but relative weekly weight loss was greater (P < 0.05) at the 3rd than 1st and 2nd week of brooding. The surface body temperatures were positively correlated (P < 0.01) with egg temperature. In both ecotypes, attempts to induce and duration of tonic immobility were similar over the test periods but on the 7th day post-hatch, the duration of tonic immobility was longer (U = 323.000, z = −2.632, P = 0.008) and on the 14th day post-hatch, the number of attempts to induce tonic immobility was less (U = 332.000, z = −2.630, P = 0.009) in the YRE chicks. In conclusion, YRE hens sat more on the eggs and their chicks were more fearful.

The evolutionary origin of near-death experiences: a systematic investigation

Near-death experiences are known from all parts of the world, various times and numerous cultural backgrounds. This universality suggests that near-death experiences may have a biological origin and purpose. Adhering to a preregistered protocol, we investigate the hypothesis that thanatosis, aka death-feigning, a last-resort defense mechanism in animals, is the evolutionary origin of near-death experiences. We first show that thanatosis is a highly preserved survival strategy occurring at all major nodes in a cladogram ranging from insects to humans. We then show that humans under attack by animal, human and ‘modern’ predators can experience both thanatosis and near-death experiences, and we further show that the phenomenology and the effects of the two overlap. In summary, we build a line of evidence suggesting that thanatosis is the evolutionary foundation of near-death experiences and that their shared biological purpose is the benefit of survival. We propose that the acquisition of language enabled humans to transform these events from relatively stereotyped death-feigning under predatory attacks into the rich perceptions that form near-death experiences and extend to non-predatory situations.

Tonic Immobility Is Influenced by Starvation, Life Stage, and Body Mass in Ixodid Ticks

The ability to escape predation modulates predator-prey interactions and represents a crucial aspect of organismal life history, influencing feeding, mating success, and survival. Thanatosis, also known as death feigning or tonic immobility (TI), is taxonomically widespread, but understudied in blood-feeding vectors. Hematophagous arthropods, such as ticks, are unique among animals as their predators (birds, mice, lizards, frogs, and other invertebrates) may also be their source of food. Therefore, the trade-off between predator avoidance and host-seeking may shift as the time since the last bloodmeal increases. Because ticks are slow-moving and unable to fly, or otherwise escape, we predicted that they may use TI to avoid predation, but that TI would be influenced by time since the last bloodmeal (starvation). We therefore aimed to quantify this relationship, examining the effect of starvation, body mass, and ontogeny on TI for two tick species: Dermacentor variabilis (Say) (Acari: Ixodidae) and Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae). As we predicted, the duration and use of TI decreased with time since feeding and emergence across species and life stages. Therefore, ticks may become more aggressive in their search for a bloodmeal as they continue to starve, opting to treat potential predators as hosts, rather than avoiding predation by feigning death. Antipredator behaviors such as TI may influence the intensity and amount of time ticks spend searching for hosts, driving patterns of tick-borne pathogen transmission. This identification and quantification of a novel antipredation strategy add a new component to our understanding of tick life history.

Proctodeal extrusion as a defensive behavioral response in blister beetles (Coleoptera: Meloidae)

Defensive mechanisms in blister beetles (Coleoptera: Meloidae) include a wide variety of behavioral responses, chemical defense, and conspicuous external colorations. Although some of these mechanisms have been previously described, proctodeal extrusion, a defensive behavior involving the extrusion of inner abdominal membranes from the proctodeal region which appear intensely red or orange colored when the hemolymph is seen through them, has not been reported to date. Here, we tested the ability to display proctodeal extrusion in response to threat stimuli in wild populations of three blister beetle species inhabiting Central Spain: Berberomeloe majalis (Linnaeus, 1758), Berberomeloe comunero Sánchez-Vialas, García-París, Ruiz & Recuero, 2020, and Physomeloe corallifer (Germar, 1818). In addition, we observed and recorded various other defensive behaviors such as immobility, antennal threat display, autohemorrhage (reflex bleeding), defecation, and thanatosis (death feigning). The frequency at which proctodeal extrusion was observed differed among species, as did the stress intensity needed for extrusion and the probability of proctodeal extrusion in response to a particular threatening stimulus. Our findings indicate that, although proctodeal extrusion might be a widespread potential defensive mechanism in Meloidae, the ability to elicit it is not generalized across lineages. Physomeloe and Berberomeloe are endemic to the semi-arid Mediterranean region, and species adapted to such a climate would have developed strategies that limit hydric stress such as proctodeal extrusion, which mirrors the effect of autohemorrhage but without the fluid loss.

Playing dead: lizards show tonic immobility without human handling

Tonic immobility, or the ability to play dead, is widespread among vertebrates. It is a last line of defence against a threat, and usually follows physical restraint. Here, I report two lizards exhibiting tonic immobility in the presence of humans, but remarkably, without any handling or physical contact. These two lizards belonged to an invasive population of the Italian Wall Lizard (Podarcis siculus), and both events took place in different years and situations, suggesting this behaviour may be more common than previously thought. There are rare documented cases of animals exhibiting this behaviour without handling; however, to my knowledge, this is the first description of a lizard displaying tonic immobility to humans, in the absence of handling. This is also the first incident of tonic immobility in the Italian Wall Lizard. I discuss these anecdotal events in the light of this invasive population inhabiting a highly urbanized location.

Hystero-epilepsy in the Tuesday Lessons and NMDA receptor function: A hypothesis for dissociative disorder

Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis patients demonstrate characteristic multistage progression and movement disorders, which are analogous to hystero-epilepsy in Jean-Martin Charcot's Tuesday Lessons. First, based on a review of the Tuesday Lessons recorded by Charcot's pupils, we hypothesized that there were patients with anti-NMDAR encephalitis among those diagnosed with hystero-epilepsy in the nineteenth century. We found acute-onset multiple neuropsychiatric manifestations resembling anti-NMDAR encephalitis among patients with hystero-epilepsy. Patients with drug withdrawal syndrome, dissociative and conversion disorders and patients under hypnosis from the modern point of view were also identified. These results suggested that hystero-epilepsy in the Tuesday Lessons could encompass dissociative and conversion disorders, hypnosis, drug withdrawal syndrome, and anti-NMDAR encephalitis-like manifestations. Based on Charcot's observations and current progress in molecular biology, such as the identification of glutamate/NMDAR system dysfunction in drug withdrawal syndrome, we then hypothesized that patients with dissociative and conversion disorders and those under hypnosis could also have hypofunction of the glutamatergic system. The NMDAR hypofunction hypothesis is emerging as a pathogenesis of schizophrenia. NMDAR antagonists are known to evoke symptoms similar to schizophrenia, anti-NMDAR encephalitis and near-death experiences. In current clinical reports, spectrum disorders such as dissociative disorder and conversion disorder have been observed in patients with anti-NMDAR encephalitis. Our hypothesis will offer an expansion of the NMDAR hypofunction hypothesis from psychosis to functional neurological disorders and normal specific situations, such as hypnosis, thanatosis, and near-death experiences.

Effect of Capture, Phenotype, and Physiological Status on Blood Glucose and Plasma Corticosterone Levels in Free-Ranging Dice Snakes

AbstractTheoretically, animals integrate intrinsic and extrinsic factors to respond appropriately to the wide range of stressors they encounter during their life span. We examined how stress response varies between sexes and among morphotypes in wild dice snakes (Natrix tessellata). We also considered reproductive and feeding status and antipredator behavior. We used two indicators of stress (glucose [GLUC] and corticosterone [CORT] levels) at eight sampling time intervals (immediately after capture, up to 17 h after) and a large sample size (N=113 snakes). Concentrations of both markers increased sharply after capture (an equivalent of predation). This acute phase occurred earlier for GLUC (30 min) compared to CORT (60 min). Then the values plateaued to very high levels without decline over time, indicating prolonged saturation of the hypothalamus-pituitary-adrenal axis. In contrast to our expectations, we found no effect of sex, morphotype, or reproductive status. Yet the CORT stress response of those individuals displaying death-feigning (DF) antipredator behavior was attenuated compared to those that did not. Low stress hormones levels may facilitate the expression of DF (high levels supporting fleeing behavior). The presence of partially digested material in the stomach was associated with higher blood GLUC during the plateau. Assaying blood GLUC requires very little blood but was as good as CORT at gauging acute stress response. The prolonged plateau suggests that captivity should be minimized during field studies.

Trade-off Investment between Tonic Immobility and Mate Search in the Sweetpotato Weevil, Cylas formicarius (Coleoptera: Brentidae)

Tonic immobility (TI) is a well-known anti-predator strategy adopted by diverse preys. Numerous studies on the cost-benefit involve in TI have been reported. Although, some studies have reported the effect of mating behavior on TI, few studies highlight the phases of mate search. In the present study, we investigated the relationship between mate search and TI behavior in the sweetpotato weevil (SPW), Cylas formicarius (Coleoptera: Brentidae). First, we found the most active mate search period of male SPW within 24 h. Then, we measured whether the duration of TI of virgin male and female were affected during the mate search. In the end, the Y-tube olfactometer was used to compare the duration of mate search and the proportion of orientation towards the females in two artificial selection groups of the male SPW with longer and shorter duration of TI. Our study confirmed that male mate searching increase after 3 h at night, and up to 73% at midnight, TI was affected by mate search in male, because the duration of TI of the male during mate search (Mean ± SE = 214.53 ± 22.74 s) was significantly shorter duration than the control (679.64 ± 69.77 s). However, mate search did not affect the strength of TI in the females tested. This study determined that mate search was affected by TI due to males from the group with shorter duration of TI who had 28% higher proportion of orientation towards the females than the males with longer duration of TI. Investment trade-off between TI and mate search was confirmed in the males of the SPW.

Pressure Algometry Validation and Determination of Efficacy of Articaine Hydrochloride Ring Block in Antler Removal in Red Deer (Cervus elaphus)

Simple Summary

Red deer (Cervus elaphus) are farmed in New Zealand for the production of velvet antler. Velvet is harvested as living antler tissue, and currently lignocaine is the only licensed local anaesthetic approved for deer antler removal in New Zealand. The use of lignocaine is not without consequences, including drug residues in harvested velvet antler tissue and its short acting analgesic effect. This study was designed to determine the effect of local anaesthetic, articaine hydrochloride as an alternative treatment and to establish the baseline measurements of mechanical nociceptive threshold in 40 male yearling red deer. Ten of the forty enrolled deer were selected for the articaine efficacy study. The mechanical nociceptive thresholds were measured using a handheld algometer applied at 4 points; the cranial, medial, caudal and lateral aspects of the base of each antler. The force applied, which resulted in a movement by the animal, was recorded in newtons (N). This study showed that nociceptive threshold response in deer could be reliably measured, and articaine proved to be a promising alternative for velveting the deer antlers.

Abstract

New Zealand deer farming centres on the production of meat and velvet antler. Velvet antler removal is a painful procedure and currently, New Zealand Animal Welfare regulations dictate surgical removal of velvet antlers under lignocaine anaesthesia. To improve our knowledge on the efficacy and duration of other local anaesthetics to mitigate pain after antler removal, it is important to accurately assess and quantify pain arising from antler removal. Therefore, the current study was designed to validate mechanical nociceptive threshold (MNT) testing using a Wagner hand-held algometer, and to apply this methodology to assess the efficacy and duration of action of articaine for antler removal in deer. Baseline force (N) required to elicit the nociceptive response was recorded in 40 yearling male red deer on three alternate days. Ten of the 40 animals were selected for antler removal after administration of 4% articaine hydrochloride as a ring block. The duration of analgesic efficacy of articaine was assessed by algometry across 5 time points. There was a significant difference in MNTs among the three days (day 3 versus day 1 (p < 0.0001), day 2 versus day 1 (p < 0.0001), and day 1 versus day 2 (p < 0.01)). Positive correlations were observed between weight, antler length and thresholds. The MNT values remained above 20N for 6 h after removal of velvet antlers under the articaine ring block. This study provides valuable information about the use of MNT in red deer. These findings lay a foundation for future studies in the topics of peri-operative and postoperative pain management in deer antler removal, and a possible alternative use for articaine.

What Does Neuroscience Tell Us About the Conversion Model of Functional Neurological Disorders?

A dualistic mind-body understanding of functional neurological disorders (FNDs), also known as conversion disorders, has led to the view that the cause of the symptom should be either psychological (psychogenic) or physical (neurogenic-"organic"). One of the most influential psychological approaches is the Freudian model of conversion, which suggests that FNDs arise from a defense process in which emotional stress is converted into physical symptoms. This conversion theory has been challenged in recent years, accompanied by a shift in emphasis toward neuropathophysiological models of FND and away from historical psychological concepts. In this review, the authors consider the contemporary relevance of the conversion model from the neuroscientific perspective to reconcile the role of both psychological and biological factors in FND. A narrative review of recent neuroscientific findings pertaining to the conversion model of FND, encompassing neuroimaging, cognitive psychology, biological markers, and epigenetic studies, was performed. Research on the role of psychological stressors is discussed. Neurobiological mechanisms of repression of traumatic memories and their translation into physical symptoms are then explored. Finally, the role of physical symptoms as a potential protective defense mechanism against social stressors is considered. The authors argue that the conversion concept is consistent with recent neuroscientific research findings, and the model allows psychological and neurobiological concepts to be reconciled within a single account of FND that begins to resolve the dualistic mind-body dichotomy.

Deep learning-assisted comparative analysis of animal trajectories with DeepHL

A comparative analysis of animal behavior (e.g., male vs. female groups) has been widely used to elucidate behavior specific to one group since pre-Darwinian times. However, big data generated by new sensing technologies, e.g., GPS, makes it difficult for them to contrast group differences manually. This study introduces DeepHL, a deep learning-assisted platform for the comparative analysis of animal movement data, i.e., trajectories. This software uses a deep neural network based on an attention mechanism to automatically detect segments in trajectories that are characteristic of one group. It then highlights these segments in visualized trajectories, enabling biologists to focus on these segments, and helps them reveal the underlying meaning of the highlighted segments to facilitate formulating new hypotheses. We tested the platform on a variety of trajectories of worms, insects, mice, bears, and seabirds across a scale from millimeters to hundreds of kilometers, revealing new movement features of these animals.

Death is common, so is understanding it: the concept of death in other species

Comparative thanatologists study the responses to the dead and the dying in nonhuman animals. Despite the wide variety of thanatological behaviours that have been documented in several different species, comparative thanatologists assume that the concept of death (CoD) is very difficult to acquire and will be a rare cognitive feat once we move past the human species. In this paper, we argue that this assumption is based on two forms of anthropocentrism: (1) an intellectual anthropocentrism, which leads to an over-intellectualisation of the CoD, and (2) an emotional anthropocentrism, which yields an excessive focus on grief as a reaction to death. Contrary to what these two forms of anthropocentrism suggest, we argue that the CoD requires relatively little cognitive complexity and that it can emerge independently from mourning behaviour. Moreover, if we turn towards the natural world, we can see that the minimal cognitive requirements for a CoD are in fact met by many nonhuman species and there are multiple learning pathways and opportunities for animals in the wild to develop a CoD. This allows us to conclude that the CoD will be relatively easy to acquire and, so, we can expect it to be fairly common in nature.

Death feigning as an adaptive anti-predator behaviour: Further evidence for its evolution from artificial selection and natural populations

Death feigning is considered to be an adaptive antipredator behaviour. Previous studies on Tribolium castaneum have shown that prey which death feign have a fitness advantage over those that do not when using a jumping spider as the predator. Whether these effects are repeatable across species or whether they can be seen in nature is, however, unknown. Therefore, the present study involved two experiments: (a) divergent artificial selection for the duration of death feigning using a related species T. freemani as prey and a predatory bug as predator, demonstrating that previous results are repeatable across both prey and predator species, and (b) comparison of the death-feigning duration of T. castaneum populations collected from field sites with and without predatory bugs. In the first experiment, T. freemani adults from established selection regimes with longer durations of death feigning had higher survival rates and longer latency to being preyed on when they were placed with predatory bugs than the adults from regimes selected for shorter durations of death feigning. As a result, the adaptive significance of death-feigning behaviour was demonstrated in another prey-predator system. In the second experiment, wild T. castaneum beetles from populations with predators feigned death longer than wild beetles from predator-free populations. Combining the results from these two experiments with those from previous studies provided strong evidence that predators drive the evolution of longer death feigning.

The Neurology of Death and the Dying Brain: A Pictorial Essay

As neurologists earn their living with the preservation and restoration of brain function, they are also well-positioned to address the science behind the transition from life to death. This essay in pictures highlights areas of neurological expertise needed for brain death determination; shows pitfalls to avoid during the clinical examination and interpretation of confirmatory laboratory tests in brain death protocols; illustrates the great variability of brain death legislations around the world; discusses arguments for the implementation of donation after circulatory death (DCD); points to unresolved questions related to DCD and the time between cardiac standstill and organ procurement (“hands-off period”); provides an overview of the epidemiology and semiology of near-death experiences, including their importance for religion, literature, and the visual arts; suggests biological mechanisms for near-death experiences such as dysfunction of temporoparietal cortex, N-methyl-D-aspartate receptor antagonism, migraine aura, and rapid eye movement sleep; hypothesizes that thanatosis (aka. death-feigning, a common behavioral trait in the animal kingdom) represents the evolutionary origin of near-death experiences; and speculates about the future implications of recent attempts of brain resuscitation in an animal model. The aim is to provide the reader with a thorough understanding that the boundaries within the neurology of death and the dying brain are being pushed just like everywhere else in the clinical neurosciences.

Post-contact immobility and half-lives that save lives

A wide variety of animals become completely immobile after initial contact with a potential predator. This behaviour is considered to be a last-ditch escape strategy. Here, we test the hypothesis that such immobility should have an extremely unpredictable duration. We find that it spans more than three orders of magnitude in antlion larvae. We also analyse the second period of immobility that follows the first bout of immobility, and consider the distributions of both first and second immobility periods within the context of the intermittence that characterizes the movement of most organisms. Both immobility durations were fitted best by exponential distributions. Therefore, both were characterized by high variability and hence, unpredictability. The immobility half-life, its mean duration and standard deviation were greater for the first than the second immobility. Furthermore, individual consistency was weak or absent in repeated measures of the first immobility and between the first and second immobilities. Our quantitative approach can be replicated across taxa and would help link an understanding of immobility after an initial predator contact in both vertebrates and invertebrates. To facilitate this, we contend that the terminology should be simplified, and we advocate the use of the term post-contact immobility (PCI).

Transcriptomic comparison between beetle strains selected for short and long durations of death feigning

The molecular basis of death feigning, an antipredator behavior that has received much attention recently, was analyzed. We compared the gene expression profiles of strains with different behaviors, i.e., different durations of death feigning, in the beetle Tribolium castaneum. Beetles artificially selected for short (S) and long (L) durations of death feigning for many generations were compared thoroughly by RNA sequencing. We identified 518 differentially expressed genes (DEGs) between the strains. The strains also showed divergence in unexpected gene expression regions. As expected from previous physiological studies, genes associated with the metabolic pathways of tyrosine, a precursor of dopamine, were differentially expressed between the S and L strains; these enzyme-encoding genes were expressed at higher levels in the L strain than in the S strain. We also found that several genes associated with insulin signaling were expressed at higher levels in the S strain than in the L strain. Quantitative real-time PCR analysis showed that the relative expression levels of Tchpd (encoding 4-hydroxyphenylpyruvate dioxygenase, Hpd) and Tcnat (encoding N-acetyltransferase, Nat) were significantly higher in the L strain than in the S strain, suggesting the influence of these enzymes on the supply of dopamine and duration of death feigning.

Sound repetition rate controls the duration of tonic immobility in chicks (Gallus gallus)

Tonic Immobility (TI) functions as anti-predator defense. Its duration depends on cues signaling predator proximity. One such cue includes alarm calls from conspecifics and non-conspecifics. This study aimed to determine the cue within alarm calls that controls TI duration. We induced TI in chicks (Gallus gallus) and found that their TI durations increased in the presence of adult conspecific alarm calls, non-conspecific alarm calls, and synthetic sounds made of white noise set to the repetition rate found in natural alarm calls. Moreover, chicks did not increase their TI durations when exposed to conspecific attraction calls, synthetic sounds made of white noise set to the repetition rate found in natural attraction calls, and derived sounds made of a natural alarm call lacking an internote interval. We then created: 1) sounds with white noise set to the internote interval found in natural alarm calls and the note duration found in natural attraction calls, and 2) sounds with white noise set to the internote interval found in natural attraction calls and the note duration found in natural alarm calls. Neither affected TI duration. We conclude that repetition rate acts as a salient cue that lengthens TI duration.

Arousal from Tonic Immobility by Vibration Stimulus

Tonic immobility (TI) is an effective anti-predator strategy. However, long immobility status on the ground increases the risk of being eaten by predators, and thus insects must rouse themselves when appropriate stimulation is provided. Here, the strength of vibration causing arousal from the state of TI was examined in strains artificially selected for longer duration of TI (L-strains: long sleeper) in a beetle. We provided different strengths of vibration stimuli to the long sleepers in Tribolium castaneum. Although immobilized beetles were never awakened by the stimuli from 0.01 to 0.12 mm in amplitude, almost of the beetles were aroused from immobilized status by the stimulus at 0.21 mm. There was a difference in sensitivity of individuals when the stimuli of 0.14 mm and 0.18 mm were provided. F2 individuals were also bred by crossing experiments of the strains selected for shorter and longer duration of TI. The arousal sensitivity to vibration was well separated in the F2 individuals. A positive relationship was observed between the duration of TI and the vibration amplitude, suggesting that immobilized beetles are difficult to arouse from a deep sleep, while light sleepers are easily aroused by even small vibrations. The results indicate a genetic basis for sensitivity to arousal from TI.

Avoiding death by feigning death

Thanatosis is a common phenomenon in which prey appear to feign death when attacked by predators. It was once widely believed that thanatosis exploited predators' tendencies to avoid dead prey. However, this hypothesis has never been tested, and its feasibility has been questioned to the point that it has been largely abandoned [1,2]. Here, I show that naive birds quickly learned that dead Indian stick insects Carausius morosus were unpalatable, and subsequently rejected live insects that displayed thanatosis, but not those that failed to show thanatosis. Thanatosis had no effect on the behavior of birds that had never experienced dead insects, or those that had experienced dead insects whose resemblance to thanatosic insects had been destroyed. Therefore, thanatosis clearly caused predators to avoid prey that they mistakenly perceived to be dead.

Parallel behavioral and morphological divergence in fence lizards on two college campuses

The spread of urban development has dramatically altered natural habitats, modifying community relationships, abiotic factors, and structural features. Animal populations living in these areas must perish, emigrate, or find ways to adjust to a suite of new selective pressures. Those that successfully inhabit the urban environment may make behavioral, physiological, and/or morphological adjustments that represent either evolutionary change and/or phenotypic plasticity. We tested for effects of urbanization on antipredator behavior and associated morphology across an urban-wild gradient in the western fence lizard (Sceloporus occidentalis) in two California counties, Santa Barbara and San Luis Obispo. We compared college campuses in both counties with adjacent rural habitats, conducting field trials that allowed us to characterize antipredator behavior in response to the acute stress of capture. We found notable divergence between campus and rural behavior, with campus lizards more frequently exhibiting diminished escape behavior, including tonic immobility, and lower sprint speeds. Furthermore, campus females had significantly shorter limbs, and while this did not explain variation in sprint speed, those with shorter limbs were more likely to show tonic immobility. We hypothesize that these parallel behavioral and morphological changes on both campuses reflect adjustment to a novel environment involving changes in predation and human presence.

Aphids Playing Possum - Defensive or Mutualistic Response?

Paper presents the phenomenon of thanatosis or death-feigning in selected aphids species. This specific reaction was predominantly analysed on the example of aphid subfamily Lachninae. Individuals of this group were used in experiments, during which a thanatotic response was induced with various results. The response differed from prolonged thanatosis, lasting for several minutes (Eulachnus rileyi), through shrinking behaviour (e. g. in Stomaphis graffii) to non-responsive species such as Cinara (Schizolachnus) pineti. The large interspecies variation of observed responses can be linked to other defensive mechanisms existing in the studied species, as well as to their mutualistic relationship with ants. The behaviour of shrinking is hypothesized to be the mutualistic response, developed from thanatosis, and being adapted to transportation by ant workers.

A review of thanatosis (death feigning) as an anti-predator behaviour

Abstract

Thanatosis—also known as death-feigning and, we argue more appropriately, tonic immobility (TI)—is an under-reported but fascinating anti-predator strategy adopted by diverse prey late on in the predation sequence, and frequently following physical contact by the predator. TI is thought to inhibit further attack by predators and reduce the perceived need of the predator to subdue prey further. The behaviour is probably present in more taxa than is currently described, but even within well-studied groups the precise taxonomic distribution is unclear for a number of practical and ethical reasons. Here we synthesise the key studies investigating the form, function, evolutionary and ecological costs and benefits of TI. This review also considers the potential evolutionary influence of certain predator types in the development of the strategy in prey, and the other non-defensive contexts in which TI has been suggested to occur. We believe that there is a need for TI to be better appreciated in the scientific literature and outline potentially profitable avenues for investigation. Future use of technology in the wild should yield useful developments for this field of study.

Significance statement

Anti-predatory defences are crucial to many aspects of behavioural ecology. Thanatosis (often called death-feigning) has long been an under-appreciated defence, despite being taxonomically and ecologically widespread. We begin by providing much-needed clarification on both terminology and definition. We demonstrate how apparently disparate observations in the recent literature can be synthesised through placing the behaviour within a cost-benefit framework in comparison to alternative behavioural choices, and how aspects of the ecology differentially affect costs and benefits. Extending this, we provide novel insights into why the evolution of thanatosis can be understood in terms of coevolution between predators and prey. We offer further novel hypotheses, and discuss how these can be tested, focussing on how emerging technologies can be of great use in developing our understanding of thanatosis in free-living animals.