Studying emotion in invertebrates: what has been done, what can be measured and what they can provide

Efficacy of anesthetics in an echinoderm based on multifaceted stress biomarkers

Animal care committees remain ambiguous on the need for anesthetics during experimental procedures on invertebrate taxa due to long-standing questioning of their sentience and pain perception. When used, anesthetizing procedures for invertebrates have commonly been adapted from those developed for vertebrates, under the largely unverified assumption that they afford the same benefits. The present study formally tested the efficacy of four common anesthetics of aquatic invertebrates (ethanol, MgCl2, clove oil, MS-222) using behavioural (reaction to physical contact and presence of a predator), physiological (respiration rate), cellular (coelomocytes), and hormonal (cortisol) biomarkers in the holothuroid Cucumaria frondosa (Echinodermata). While subjects recovered from exposures to all anesthetics tested, their responses differed markedly. Ethanol did not immobilize the individuals and concurrently increased their respiration rate, and cellular and hormonal stress markers. MgCl2 and clove oil reduced the behavioural and physiological responses, and decreased the cellular markers, but increased the cortisol levels. Only MS-222 fully immobilized the treated individuals and decreased their respiration rate, both during exposure and throughout ulterior interactions with a predator, while keeping coelomocyte counts and cortisol concentrations at baseline levels. MS-222 thus appears to induce the loss of sensation, representing a promising anesthetic and sedative in soft-bodied aquatic invertebrates.

Physically stressed bees expect less reward in an active choice judgement bias test

Emotion-like states in animals are commonly assessed using judgment bias tests that measure judgements of ambiguous cues. Some studies have used these tests to argue for emotion-like states in insects. However, most of these results could have other explanations, including changes in motivation and attention. To control for these explanations, we developed a novel judgment bias test, requiring bumblebees to make an active choice indicating their interpretation of ambiguous stimuli. Bumblebees were trained to associate high or low rewards, in two different reward chambers, with distinct colours. We subsequently presented bees with ambiguous colours between the two learnt colours. In response, physically stressed bees were less likely than control bees to enter the reward chamber associated with high reward. Signal detection and drift diffusion models showed that stressed bees were more likely to choose low reward locations in response to ambiguous cues. The signal detection model further showed that the behaviour of stressed bees was explained by a reduction in the estimated probability of high rewards. We thus provide strong evidence for judgement biases in bees and suggest that their stress-induced behaviour is explained by reduced expectation of higher rewards, as expected for a pessimistic judgement bias.

Near and Dear? If animal welfare concepts do not apply to species at a great phylogenetic distance from humans, what concepts might serve as alternatives?

A wide range of animal taxa, including vertebrates and invertebrates, are controlled or kept by humans. They may be used as pets, for recreation, sport and hobbies, as working animals, as producers of animal-derived (food) products or as biomedical models in research. There is a need for clear guidance on the treatment of animals, regardless of their phylogenetic distance from humans. Current animal welfare concepts, which emphasise animal sentience and the ability of animals to experience negative or positive mental states, are limited in scope to a small proportion of the animal kingdom, as the vast majority of species are (currently) thought to lack sentience. We discuss four options for addressing the question of which basic concept(s) could be used to derive guidelines for the treatment of animal species, sentient or non-sentient: (1) alternative concepts tailored to specific groups of species; (2) 'welfare' concepts not presupposing sentience; (3) the precautionary principle; or (4) the concept of animal integrity. Since questions regarding the appropriate treatment of animals, including species with a large phylogenetic distance from humans, have an ethical/moral dimension, we also address who counts morally and how much, and how animals should be treated given their moral status. We suggest that the concept of animal integrity, possibly complemented and extended by the concept of habitat/ecosystem integrity, is suitable for application to all species. However, a current concept of animal welfare should serve as the primary basis for guidance on how to treat species that are sentient and capable of experiencing emotions.

Behavioral indicators of heterogeneous subjective experience in animals across the phylogenetic spectrum: Implications for comparative animal phenomenology

This behavioral study was undertaken to provide empirical evidence in favor of or opposed to the notion that animals across a wide breadth of the animal kingdom have subjective (personal) experience that varies with their lifestyles, ecological constraints, or phylogeny. Twelve species representing two invertebrate phyla and six vertebrate classes were observed unobtrusively in 15-min episodes, during which three modes of behavior (volitional, interactive, and egocentric) were quantified according to the frequency, variety, and dynamism of each mode. Volitional behavior was the most prevalent and dynamic mode for nearly all species, largely without regard to phylogenetic position. Interactive behavior likewise varied inconsistently across the entire evolutionary spectrum. Egocentric behavior was concentrated among the avian and mammalian species, but evidence of it were observed in the invertebrate species as well. Diagrams of the matrix constructed from the three qualitative modes and three quantitative attributes for each mode provide a metaphorical representation of the unique experiential profile of each species. To the extent that these behavioral measures correlate with the nature of the animal's subjective experience, they support the growing view that phenomenology is heterogeneous, multimodal, and non-linear in extent across the animal kingdom.

A Model for Consumer Acceptance of Insect-Based Dog Foods among Adult UK Dog Owners

The use of alternative proteins is becoming more common in pet feed, and insect-based dog foods (IBDFs) are becoming more widely available. However, little research has been conducted to date in respect of the drivers for consumers' acceptance of IBDF. This study aimed to investigate the acceptance of IBDF among adult UK dog owners and the factors influencing the decision to try and buy such products. A theoretical model was developed following a review of the existing literature. An online survey of 280 participants was carried out and the results were analysed using structural equation modelling (SEM) to test the theoretical model. The following constructs all had a significant impact on attitudes towards IBDF and/or intentions to try and buy IBDF: food preferences for animal welfare, health and environment; attitudes towards uses of animals; beliefs about insect sentience; disgust; perceptions of benefits and risks; and social norms. Social norms had the strongest influence of any single construct. Consumer acceptance of IBDF is multi-faceted including social, cultural and ethical components, and it is likely that the better availability of information and opportunities for consumers to familiarise themselves with IBDF would help to drive consumer acceptance. In order to allow dog owners to make informed decisions in line with their ethical preferences, further research is needed to establish the overall health and welfare implications of IBDF on the animals involved in production, as well as the companion animals, who are the ultimate consumers.

Capturing wild animal welfare: a physiological perspective

Affective states, such as emotions, are presumably widespread across the animal kingdom because of the adaptive advantages they are supposed to confer. However, the study of the affective states of animals has thus far been largely restricted to enhancing the welfare of animals managed by humans in non-natural contexts. Given the diversity of wild animals and the variable conditions they can experience, extending studies on animal affective states to the natural conditions that most animals experience will allow us to broaden and deepen our general understanding of animal welfare. Yet, this same diversity makes examining animal welfare in the wild highly challenging. There is therefore a need for unifying theoretical frameworks and methodological approaches that can guide researchers keen to engage in this promising research area. The aim of this article is to help advance this important research area by highlighting the central relationship between physiology and animal welfare and rectify its apparent oversight, as revealed by the current scientific literature on wild animals. Moreover, this article emphasises the advantages of including physiological markers to assess animal welfare in the wild (e.g. objectivity, comparability, condition range, temporality), as well as their concomitant limitations (e.g. only access to peripheral physiological markers with complex relationships with affective states). Best-practice recommendations (e.g. replication and multifactorial approaches) are also provided to allow physiological markers to be used most effectively and appropriately when assessing the welfare of animals in their natural habitat. This review seeks to provide the foundation for a new and distinct research area with a vast theoretical and applied potential: wild animal welfare physiology.

Trait sensitivity to stress and cognitive bias processes in fish: A brief overview

Like other animals, fish have unique personalities that can affect their cognition and responses to environmental stressors. These individual personality differences are often referred to as "behavioural syndromes" or "stress coping styles" and can include personality traits such as boldness, shyness, aggression, exploration, locomotor activity, and sociability. For example, bolder or proactive fish may be more likely to take risks and present lower hypothalamo-pituitary-adrenal/interrenal axis reactivity as compared to shy or reactive individuals. Likewise, learning and memory differ between fish personalities. Reactive or shy individuals tend to have faster learning and better association recall with aversive stimuli, while proactive or bold individuals tend to learn more quickly when presented with appetitive incentives. However, the influence of personality on cognitive processes other than cognitive achievement in fish has been scarcely explored. Cognitive bias tests have been employed to investigate the interplay between emotion and cognition in both humans and animals. Fish present cognitive bias processes (CBP) in which fish's interpretation of stimuli could be influenced by its current emotional state and open to environmental modulation. However, no study in fish has explored whether CBP, like in other species, can be interpreted as long-lasting traits and whether other individual characteristics may explain its variation. We hold the perspective that CBP could serve as a vulnerability factor for the onset, persistence, and recurrence of stress-related disorders. Therefore, studying fish's CBP as a state or trait and its interactions with individual variations may be valuable in future efforts to enhance our understanding of anxiety and stress neurobiology in animal models and humans.

Tricks of the puppet masters: morphological adaptations to the interaction with nervous system underlying host manipulation by rhizocephalan barnacle Polyascus polygeneus

Background

Rhizocephalan interaction with their decapod hosts is a superb example of host manipulation. These parasites are able to alter the host's physiology and behavior. Host-parasite interaction is performed, presumably, via special modified rootlets invading the ventral ganglions.

Methods

In this study, we focus on the morphology and ultrastructure of these special rootlets in Polyascus polygeneus (Lützen & Takahashi, 1997), family Polyascidae, invading the neuropil of the host's nervous tissue. The ventral ganglionic mass of the infected crabs were fixed, and the observed sites of the host-parasite interplay were studied using transmission electron microscopy, immunolabeling and confocal microscopy.

Results

The goblet-shaped organs present in the basal families of parasitic barnacles were presumably lost in a common ancestor of Polyascidae and crown "Akentrogonida", but the observed invasive rootlets appear to perform similar functions, including the synthesis of various substances which are transferred to the host's nervous tissue. Invasive rootlets significantly differ from trophic ones in cell layer composition and cuticle thickness. Numerous multilamellar bodies are present in the rootlets indicating the intrinsic cell rearrangement. The invasive rootlets of P. polygeneus are enlaced by the thin projections of glial cells. Thus, glial cells can be both the first hosts' respondents to the nervous tissue damage and the mediator of the rhizocephalan interaction with the nervous cells. One of the potential molecules engaged in the relationships of P. polygeneus and its host is serotonin, a neurotransmitter which is found exclusively in the invasive rootlets but not in trophic ones. Serotonin participates in different biological pathways in metazoans including the regulation of aggression in crustaceans, which is reduced in infected crabs. We conclude that rootlets associated with the host's nervous tissue are crucial for the regulation of host-parasite interplay and for evolution of the Rhizocephala.

Electric shock causes a fleeing-like persistent behavioral response in the nematode Caenorhabditis elegans

Behavioral persistency reflects internal brain states, which are the foundations of multiple brain functions. However, experimental paradigms enabling genetic analyses of behavioral persistency and its associated brain functions have been limited. Here, we report novel persistent behavioral responses caused by electric stimuli in the nematode Caenorhabditis elegans. When the animals on bacterial food are stimulated by alternating current, their movement speed suddenly increases 2- to 3-fold, persisting for more than 1 minute even after a 5-second stimulation. Genetic analyses reveal that voltage-gated channels in the neurons are required for the response, possibly as the sensors, and neuropeptide signaling regulates the duration of the persistent response. Additional behavioral analyses implicate that the animal's response to electric shock is scalable and has a negative valence. These properties, along with persistence, have been recently regarded as essential features of emotion, suggesting that C. elegans response to electric shock may reflect a form of emotion, akin to fear.

Disgusted snails, oxytocin, and the avoidance of infection threat

Disgust is considered to be a fundamental affective state associated with triggering the behavioral avoidance of infection and parasite/pathogen threat. In humans, and other vertebrates, disgust affects how individuals interact with, and respond to, parasites, pathogens and potentially infected conspecifics and their sensory cues. Here we show that the land snail, Cepaea nemoralis, displays a similar "disgust-like" state eliciting behavioral avoidance responses to the mucus associated cues of infected and potentially infected snails. Brief exposure to the mucus of snails treated with the Gram-negative bacterial endotoxin, lipopolysaccharide (LPS), elicited dose-related behavioral avoidance, including acute antinociceptive responses, similar to those expressed by mammals. In addition, exposure to the mucus cues of LPS treated snails led to a subsequent avoidance of unfamiliar individuals, paralleling the recognition of and avoidance responses exhibited by vertebrates exposed to potential pathogen risk. Further, the avoidance of, and antinociceptive responses to, the mucus of LPS treated snails were attenuated in a dose-related manner by the oxytocin (OT) receptor antagonist, L-368,899. This supports the involvement of OT and OT receptor homologs in the expression of infection avoidance, and consistent with the roles of OT in the modulation of responses to salient social and infection threats by rodents and other vertebrates. These findings with land snails are indicative of evolutionarily conserved disgust-like states associated with OT/OT receptor homolog modulated behavioral avoidance responses to infection and pathogen threat.

It Is Not Only Data-Freshwater Invertebrates Misused in Biological Monitoring

The article presents and discusses the issues of the use of free-living invertebrates to assess the ecological status of freshwater environments with different methods of biological monitoring. Invertebrates are excluded from ethical consideration in the procedures of environmental protection, which results in the killing of many more individuals during sampling than necessary. Biomonitoring is used as a routine method for environmental protection that results in the cruel death of even millions of aquatic animals annually. In many cases, the mortality of animals used in such types of activities has been shown as excessive, e.g., because the vast majority die due to unnecessary subsampling procedures. Improperly planned and conducted procedures which result in excessive mortality have or may have a negative impact on the environment and biodiversity. Their existence as sensitive beings is reduced to an information function; they become only data useful for biomonitoring purposes. The main problem when trying to determine the mortality of invertebrates due to biomonitoring activities and its impact on natural populations seems to be the lack of access to raw data presenting how many animals were killed during sampling.

Handling and Training of Wild Animals: Evidence and Ethics-Based Approaches and Best Practices in the Modern Zoo

There is an ethical responsibility to provide all animals living in human care with optimal and positive well-being. As animals living in zoos and aquariums frequently interact with their human caregivers as part of their daily care routines, it is both relevant and essential to consider the impact of these interactions on animal well-being. Allowing animals to have choice and control in multiple areas of their lives, such as by providing opportunities for them to voluntarily participate in their own care through, for example, positive reinforcement training, is an essential component of good animal well-being programs. This review aims to describe evidence-based approaches, ethics, and best practices in the handling and training of the many taxa held in zoos and aquariums worldwide, drawing from work in related animal care fields such as laboratories, farms, rescue, and sanctuaries. The importance of ongoing animal well-being assessments is discussed, with a particular focus on the need for continued review and refinement of processes and procedures pertaining to animal training and handling specifically. Review, enquiry, assessment, evaluation, and refinement will aim to dynamically support positive well-being for all animals.

When Do We Start Caring About Insect Welfare?

The world is facing an incoming global protein shortage due to existing malnutrition and further rapid increases in population size. It will however be difficult to greatly expand traditional methods of protein production such as cattle, chicken and pig farming, due to space limitations and environmental costs such as deforestation. As a result, alternative sources of protein that require less space and fewer resources, such as insects and other invertebrates, are being sought. The Neotropics are a key area of focus given the widespread prevalence of entomophagy and developing animal welfare regulations. Unlike vertebrate livestock however, insect "minilivestock" are typically not protected by existing animal welfare regulations. This is despite the fact that the evidence is mounting that insects possess "personalities", may experience affective states analogous to emotions and feel something like pain. In this forum article, we highlight this discrepancy, outline some of the emerging research on the topic and identify areas for future research. There are various empirical and ethical questions that must be addressed urgently while insect farming is ramped up around the globe. Finally, we describe the benefits and also potential costs of regulation for insect welfare.

Infection with an acanthocephalan helminth reduces anxiety-like behaviour in crustacean host

Trophically transmitted heteroxenous parasites of diverse clades can decrease or reverse antipredator behaviours in their intermediate hosts, thereby increasing their chances of reaching their final hosts. Such behavioural alterations could result from compromised cognitive abilities affecting fear- or more generally stress-related neurophysiological pathways. We tested this hypothesis in a key model system in the study of parasitic manipulation, the fish acanthocephalan parasite Pomphorhynchus tereticollis and its intermediate crustacean host Gammarus fossarum, using the 'threat of electric shock' paradigm. We exposed uninfected and infected G. fossarum to chronic and/or acute electric shock programs at two different intensities (voltage), and then quantified their sheltering behaviour as a proxy for anxiety-like state. Infected gammarids did not express anxiety-like response to electric shocks, while uninfected gammarids hid more when exposed to acute treatments, and when exposed to the high intensity chronic treatment. Interestingly, the lack of response in infected gammarids depended on parasite developmental stage. Our results support the hypothesis that this acanthocephalan parasite impacts the general anxiety-like circuitry of their intermediate host. Further studies are needed to investigate whether it involves inappropriate processing of information, impaired integration, or altered activation of downstream pathways initiating behavioural action.

Contextual memory reactivation modulates Ca2+-activity network state in a mushroom body-like center of the crab N. granulata

High-order brain centers play key roles in sensory integration and cognition. In arthropods, much is known about the insect high-order centers that support associative memory processes, the mushroom bodies. The hypothesis that crustaceans possess structures equivalent to the mushroom bodies -traditionally called hemiellipsoid body- has been receiving neuroanatomical endorsement. The recent functional support is limited to the short term: in a structure of the true crab Neohelice granulata that has many insect-like mushroom bodies traits, the plastic learning changes express the context attribute of an associative memory trace. Here, we used in vivo calcium imaging to test whether neuronal activity in this structure is associated with memory reactivation in the long-term (i.e., 24 h after training). Long-term training effects were tested by presenting the training-context alone, a reminder known to trigger memory reconsolidation. We found similar spontaneous activity between trained and naïve animals. However, after training-context presentation, trained animals showed increased calcium events rate, suggesting that memory reactivation induced a change in the underlying physiological state of this center. Reflecting the change in the escape response observed in the paradigm, animals trained with a visual danger stimulus showed significantly lower calcium-evoked transients in the insect-like mushroom body. Protein synthesis inhibitor cycloheximide administered during consolidation prevented calcium mediated changes. Moreover, we found the presence of distinct calcium activity spatial patterns. Results suggest that intrinsic neurons of this crustacean mushroom body-like center are involved in contextual associative long-term memory processes.

Domestic pig sound classification based on TransformerCNN

Excellent performance has been demonstrated in implementing challenging agricultural production processes using modern information technology, especially in the use of artificial intelligence methods to improve modern production environments. However, most of the existing work uses visual methods to train models that extract image features of organisms to analyze their behavior, and it may not be truly intelligent. Because vocal animals transmit information through grunts, the information obtained directly from the grunts of pigs is more useful to understand their behavior and emotional state, which is important for monitoring and predicting the health conditions and abnormal behavior of pigs. We propose a sound classification model called TransformerCNN, which combines the advantages of CNN spatial feature representation and the Transformer sequence coding to form a powerful global feature perception and local feature extraction capability. Through detailed qualitative and quantitative evaluations and by comparing state-of-the-art traditional animal sound recognition methods with deep learning methods, we demonstrate the advantages of our approach for classifying domestic pig sounds. The scores for domestic pig sound recognition accuracy, AUC and recall were 96.05%, 98.37% and 90.52%, respectively, all higher than the comparison model. In addition, it has good robustness and generalization capability with low variation in performance for different input features.

Approaches to studying injury-induced sensitization and the potential role of an endocannabinoid transmitter

Endocannabinoids are traditionally thought to have an analgesic effect. However, it has been shown that while endocannabinoids can depress nociceptive signaling, they can also enhance non-nociceptive signaling. Therefore, endocannabinoids have the potential to contribute to non-nociceptive sensitization after an injury. Using Hirudo verbana (the medicinal leech), a model of injury-induced sensitization was developed in which a reproducible piercing injury was delivered to the posterior sucker of Hirudo. Injury-induced changes in the non-nociceptive threshold of Hirudo were determined through testing with Von Frey filaments and changes in the response to nociceptive stimuli were tested by measuring the latency to withdraw to a nociceptive thermal stimulus (Hargreaves apparatus). To test the potential role of endocannabinoids in mediating injury-induced sensitization, animals were injected with tetrahydrolipstatin (THL), which inhibits synthesis of the endocannabinoid transmitter 2-arachidonoylglycerol (2-AG). Following injury, a significant decrease in the non-nociceptive response threshold (consistent with non-nociceptive sensitization) and a significant decrease in the response latency to nociceptive stimulation (consistent with nociceptive sensitization) were observed. In animals injected with THL, a decrease in non-nociceptive sensitization in injured animals was observed, but no effect on nociceptive sensitization was observed.

The effect of unexpected rewards on decision making in cuttlefish

Despite numerous studies demonstrating the cognitive ability of cephalopods, there is currently no study showing an emotion-like behavior in this group of animals. To examine whether cuttlefish have different internal states, we developed a behavioral paradigm to assess if prior surprised events are able to alter the choice made by cuttlefish. By presenting unexpected food rewards to cuttlefish before the test, we investigated whether the reaction time of choosing between two shrimps, an intuitive response toward the prey without previous learning, at three different levels of discriminative tests (easy, difficult, and ambiguous), are different compared to the one without an unexpected reward. This behavioral paradigm serves to demonstrate whether cuttlefish are aware of ambiguous situations, and their choice outcome and reaction time are dependent of their internal states. The results show that the response latency was significantly shortened in the difficult and ambiguous tests when choosing from two shrimps that are either moderately different in size or similar sizes, respectively, when cuttlefish have received unexpected rewards before the test. These results were compared with tests during which the cuttlefish did not receive any reward in advance. Furthermore, this shortening of latency did not result in a difference in choice outcome during the difficult and ambiguous tests. Interestingly, even when cuttlefish have obtained the expected food rewards or simply made tentacular strike without prey capture each time before test, these prior experiences were sufficient to shorten the response latency in the difficult and ambiguous tests. However, different from the result of unexpected rewards, food consumption alone or prey capture failure did affect the choice outcome during the simple and difficult tests. Taken together, our findings suggest that pre-test treatments of unexpected and expected rewards or simply unsuccessful visual attack seem to induce cuttlefish to adopt different foraging behaviors. This context dependent decision making suggests that cuttlefish’s foraging strategies are influenced by the previously surprised event and their internal states. It also shows a speed-accuracy tradeoff in difficult and ambiguous situations when foraging for prey. This observation may lead to a future investigation of the presence of emotional state in cephalopods.

Emotions as Abstract Evaluation Criteria in Biological and Artificial Intelligences

Biological as well as advanced artificial intelligences (AIs) need to decide which goals to pursue. We review nature's solution to the time allocation problem, which is based on a continuously readjusted categorical weighting mechanism we experience introspectively as emotions. One observes phylogenetically that the available number of emotional states increases hand in hand with the cognitive capabilities of animals and that raising levels of intelligence entail ever larger sets of behavioral options. Our ability to experience a multitude of potentially conflicting feelings is in this view not a leftover of a more primitive heritage, but a generic mechanism for attributing values to behavioral options that can not be specified at birth. In this view, emotions are essential for understanding the mind. For concreteness, we propose and discuss a framework which mimics emotions on a functional level. Based on time allocation via emotional stationarity (TAES), emotions are implemented as abstract criteria, such as satisfaction, challenge and boredom, which serve to evaluate activities that have been carried out. The resulting timeline of experienced emotions is compared with the “character” of the agent, which is defined in terms of a preferred distribution of emotional states. The long-term goal of the agent, to align experience with character, is achieved by optimizing the frequency for selecting individual tasks. Upon optimization, the statistics of emotion experience becomes stationary.

From human wellbeing to animal welfare

What does it mean to be "well" and how might such a state be cultivated? When we speak of wellbeing, it is of ourselves and fellow humans. When it comes to nonhuman animals, consideration turns to welfare. My aim herein is to suggest that theoretical approaches to human wellbeing might be beneficially applied to consideration of animal welfare, and in so doing, introduce new lines of inquiry and practice. I will review current approaches to human wellbeing, adopting a triarchic structure that delineates hedonic wellbeing, eudaimonic wellbeing, and social wellbeing. For each, I present a conceptual definition and a review of how researchers have endeavored to measure the construct. Drawing these three domains of research together, I highlight how these traditionally anthropocentric lines of inquiry might be extended to the question of animal welfare - namely by considering hedonic welfare, eudaimonic welfare, and social welfare as potentially distinguishable and complementary components of the broader construct of animal welfare.

Patterns of heart rate and cardiac pausing in unrestrained resting decapod crustaceans

Measurement of heart rate (HR) has been used as an important physiological indicator in a broad range of taxa. In the present study HR patterns were measured in five species of unrestrained, resting decapod crustaceans. In addition to variation in HR among individuals, it was also very variable within an individual animal. While some of this variation was related to activity, there was also a non-locomotory component. Unstressed, resting crabs exhibited intermittent heart activity, whereas HR in stressed crabs was more stable, suggesting differential control of HR in resting crabs. Once the animals settled in the experimental apparatus they exhibited regular and extended cardiac pauses (acardia) of 15-300-s duration. As with HR, there was a significant variation in the frequency and length of acardic events, which were only observed in inactive crabs. Regaining of HR, following a period of acardia, was characterized by small adjustments in position and movement of the mouthparts. This rhythmic pattern, and the fact that entry into and out of acardia was not instantaneous, suggested that these events were related to release of neurohormones and their subsequent degradation in the system, rather than direct neural control of the heart. Because HR was variable and interrupted by regular periods of acardia, caution is recommended when calculating baseline levels of HR, or using HR alone as an indicator of physiological stress. Incorporating a coefficient of variation for HR and/or measuring the periods of acardia may be a more reliable indicator of physiological stress in decapod crustaceans.

Evidence of anticipatory immune and hormonal responses to predation risk in an echinoderm

Recent efforts have been devoted to the link between responses to non-physical stressors and immune states in animals, mostly using human and other vertebrate models. Despite evolutionary relevance, comparatively limited work on the appraisal of predation risk and aspects of cognitive ecology and ecoimmunology has been carried out in non-chordate animals. The present study explored the capacity of holothuroid echinoderms to display an immune response to both reactive and anticipatory predatory stressors. Experimental trials and a mix of behavioural, cellular and hormonal markers were used, with a focus on coelomocytes (analogues of mammalian leukocytes), which are the main components of the echinoderm innate immunity. Findings suggest that holothuroids can not only appraise threatening cues (i.e. scent of a predator or alarm signals from injured conspecifics) but prepare themselves immunologically, presumably to cope more efficiently with potential future injuries. The responses share features with recently defined central emotional states and wane after prolonged stress in a manner akin to habituation, which are traits that have rarely been shown in non-vertebrates, and never in echinoderms. Because echinoderms sit alongside chordates in the deuterostome clade, such findings offer unique insights into the adaptive value and evolution of stress responses in animals.

A thermal stressor, propranolol and long-term memory formation in freshly collected Lymnaea

A heat stressor (1 h at 30°C) in Lymnaea stagnalis before operant conditioning training of aerial respiration is sufficient to enhance long-term memory (LTM) formation in 'average' cognitive ability, laboratory-reared, inbred snails. However, in freshly collected outbred snails, the same heat stressor blocks LTM formation in 'smart' cognitive phenotype but not in average cognitive phenotype strains. Here, we hypothesize that (1) preventing the stress associated with the heat stressor before training allows LTM to form in the smart phenotype strains; and (2) alleviating the stress before a memory recall session allows a formed LTM to be recalled in the smart phenotype strains. We found that an injection of propranolol, which mitigates the stressor, before snails experience the heat stressor enabled two strains of the smart phenotype snails to form LTM, consistent with our first hypothesis. However, the injection of propranolol before a memory test session did not alleviate a memory recall block in the smart phenotype snails. Thus, our second hypothesis was not supported. Therefore, smart cognitive phenotype snails encountering a heat stressor have an inability to form LTM, but this inability can be overcome by the pre-injection of propranolol.

In the great pond snail (Lymnaea stagnalis), two stressors that individually enhance memory in combination block memory formation

Stress plays an important role in memory formation in the great pond snail (Lymnaea stagnalis (Linnaeus, 1758)). Individual stressors have been shown to enhance or to perturb long-term memory (LTM) formation. However, when snails perceive a combination of two stressors, it is unclear the outcome with regards to LTM formation. Here we first show that when L. stagnalis are exposed individually to either a predator stressor (crayfish effluent (CE), which is a kairomone) or a thermal stressor (30 °C), LTM formation is enhanced. In their natural environment, L. stagnalis may experience temperatures approaching 30 °C and they may encounter crayfish at the same time. How such a combination of stressors alters adaptive behaviour is unknown. Here we show that when these two stressors are combined, LTM formation is blocked. Since boiling CE inactivates the kairomone, we used previously boiled CE that we combined with the thermal stressor and found that LTM formation is again enhanced. These data show that (i) it cannot accurately be predicted how a combination of stressors when combined interact to alter LTM formation and (ii) there is a difference between hot CE and room temperature CE.

Wildlife-pet markets in a one-health context

Background and Aim: Wildlife markets are centers of trade involving live animals and their derivatives from wild-caught and captive-bred non-domesticated animals, including for the culinary, fashion, traditional medicine, curio, and pet sectors. These markets occur in Southeast Asia, India, North America, Latin America, Europe, Africa, and elsewhere. This study aims to address a diversity of related issues that have a one-health bearing while focusing on wildlife markets in relation to the pet trade. Across relevant regions and countries, all major animal classes are traded at wildlife-pet markets. Wildlife markets, in general, are considered distinct from so-called "wet markets" at which domesticated animals, fish, and other "seafood" are offered only for consumption. Several aspects of wildlife markets have attracted scientific and popular scrutiny, including animal welfare concerns, species conservation threats, legality, ecological alteration, introduction of invasive alien species, presence of undescribed species, and public and agricultural animal health issues. Materials and Methods: Onsite inspections were conducted for markets in the United States, Spain, Germany, The Netherlands, and the UK, as well as observational research of visual imagery of market conditions, and we compared these conditions with evidence-based standards for animal welfare and public health management. Results: Wildlife markets globally shared common similar structures and practices including the presence of sick, injured, or stressed animals; mixing of animals of uncertain origin and health state; and no specific or any hygiene protocols, with issues of animal welfare, public health and safety, agricultural animal health, and other one-health concerns being inherently involved. Conclusion: We conclude that wildlife markets are incompatible with responsible standards and practices, and we recommend that such events are banned globally to ameliorate inherent major problems.

Convergent evolution of complex cognition: Insights from the field of avian cognition into the study of self-awareness

Pioneering research on avian behaviour and cognitive neuroscience have highlighted that avian species, mainly corvids and parrots, have a cognitive tool kit comparable with apes and other large-brained mammals, despite conspicuous differences in their neuroarchitecture. This cognitive tool kit is driven by convergent evolution, and consists of complex processes such as casual reasoning, behavioural flexibility, imagination, and prospection. Here, we review experimental studies in corvids and parrots that tested complex cognitive processes within this tool kit. We then provide experimental examples for the potential involvement of metacognitive skills in the expression of the cognitive tool kit. We further expand the discussion of cognitive and metacognitive abilities in avian species, suggesting that an integrated assessment of these processes, together with revised and multiple tasks of mirror self-recognition, might shed light on one of the most highly debated topics in the literature-self-awareness in animals. Comparing the use of multiple assessments of self-awareness within species and across taxa will provide a more informative, richer picture of the level of consciousness in different organisms.

Valuing what happens: a biogenic approach to valence and (potentially) affect

Valence is half of the pair of properties that constitute core affect, the foundation of emotion. But what is valence, and where is it found in the natural world? Currently, this question cannot be answered. The idea that emotion is the body's way of driving the organism to secure its survival, thriving and reproduction runs like a leitmotif from the pathfinding work of Antonio Damasio through four book-length neuroscientific accounts of emotion recently published by the field's leading practitioners. Yet while Damasio concluded 20 years ago that the homeostasis-affect linkage is rooted in unicellular life, no agreement exists about whether even non-human animals with brains experience emotions. Simple neural animals-those less brainy than bees, fruit flies and other charismatic invertebrates-are not even on the radar of contemporary affective research, to say nothing of aneural organisms. This near-sightedness has effectively denied the most productive method available for getting a grip on highly complex biological processes to a scientific domain whose importance for understanding biological decision-making cannot be underestimated. Valence arguably is the fulcrum around which the dance of life revolves. Without the ability to discriminate advantage from harm, life very quickly comes to an end. In this paper, we review the concept of valence, where it came from, the work it does in current leading theories of emotion, and some of the odd features revealed via experiment. We present a biologically grounded framework for investigating valence in any organism and sketch a preliminary pathway to a computational model. This article is part of the theme issue 'Basal cognition: conceptual tools and the view from the single cell'.

Animal affect and decision-making

The scientific study of animal affect (emotion) is an area of growing interest. Whilst research on mechanism and causation has predominated, the study of function is less advanced. This is not due to a lack of hypotheses; in both humans and animals, affective states are frequently proposed to play a pivotal role in coordinating adaptive responses and decisions. However, exactly how they might do this (what processes might implement this function) is often left rather vague. Here we propose a framework for integrating animal affect and decision-making that is couched in modern decision theory and employs an operational definition that aligns with dimensional concepts of core affect and renders animal affect empirically tractable. We develop a model of how core affect, including short-term (emotion-like) and longer-term (mood-like) states, influence decision-making via processes that we label affective options, affective predictions, and affective outcomes and which correspond to similar concepts in schema of the links between human emotion and decision-making. Our framework is generalisable across species and generates questions for future research.

Shell damage leads to enhanced memory formation in Lymnaea

Ecologically relevant stressors alter the ability of the pond snail, Lymnaea stagnalis, to form long-term memory (LTM). Here, we show that an environmentally relevant stressor, shell damage, has a dramatic effect on the enhancement of LTM formation. Damage in the form of a shell clip 24 h before operant conditioning training resulted in long-term memory (LTM) formation following a single 0.5 h training session (TS). Typically, in these snails, two 0.5 h TSs with a 1 h interval between the sessions are required to cause LTM formation. We show here that even with a 72 h interval between shell clip and training, memory enhancement still occurred. The stress associated with shell clip could be mitigated by an ongoing high-Ca^{2 +} pond water environment, an injection of propranolol and a DNA methylation blocker. However, use of an anaesthetic (MgCl₂) during the clip or intermittent exposure to the high-Ca^{2 +} pond water environment did not mitigate the stress associated with the shell clip. Shell clip was also sufficient to cause juvenile snails, which neither learn nor form memory, to gain the capacity to form LTM. Together, the experiments demonstrate that shell clipping is an environmentally relevant stressor that can cause enhancement of LTM formation.

Welfare-aligned Sentience: Enhanced Capacities to Experience, Interact, Anticipate, Choose and Survive

The focus of this opinion is on the key features of sentience in animals which can experience different states of welfare, encapsulated by the new term 'welfare-aligned sentience'. This term is intended to exclude potential forms of sentience that do not enable animals in some taxa to have the subjective experiences which underlie different welfare states. As the scientific understanding of key features of sentience has increased markedly during the last 10 to 15 years, a major purpose here is to provide up-to-date information regarding those features. Eleven interconnected statements about sentience-associated body functions and behaviour are therefore presented and explained briefly. These statements are sequenced to provide progressively more information about key scientifically-supported attributes of welfare-aligned sentience, leading, in their entirety, to a more comprehensive understanding of those attributes. They are as follows: (1) Internal structure-function interactions and integration are the foundations of sentience; (2) animals posess a capacity to respond behaviourally to a range of sensory inputs; (3) the more sophisticated nervous systems can generate subjective experiences, that is, affects; (4) sentience means that animals perceive or experience different affects consciously; (5) within a species, the stage of neurobiological development is significant; (6) during development the onset of cortically-based consciousness is accompanied by cognitively-enhanced capacities to respond behaviourally to unpredictable postnatal environments; (7) sentience includes capacities to communicate with others and to interact with the environment; (8) sentience incorporates experiences of negative and positive affects; (9) negative and positive affective experiences 'matter' to animals for various reasons; (10) acknowledged obstacles inherent in anthropomorphism are largely circumvented by new scientific knowledge, but caution is still required; and (11) there is increasing evidence for sentience among a wider range of invertebrates. The science-based explanations of these statements provide the foundation for a brief definition of 'welfare-aligned sentience', which is offered for consideration. Finally, it is recommended that when assessing key features of sentience the same emphasis should be given to positive and negative affective experiences in the context of their roles in, or potential impacts on, animal welfare.

Negative emotional contagion and cognitive bias in common ravens (Corvus corax)

Emotional contagion is described as an emotional state matching between subjects, and has been suggested to facilitate communication and coordination in complex social groups. Empirical studies typically focus on the measurement of behavioral contagion and emotional arousal, yet, while highly important, such an approach often disregards an additional evaluation of the underlying emotional valence. Here, we studied emotional contagion in ravens by applying a judgment bias paradigm to assess emotional valence. We experimentally manipulated positive and negative affective states in demonstrator ravens, to which they responded with increased attention and interest in the positive condition, as well as increased redirected behavior and a left-eye lateralization in the negative condition. During this emotion manipulation, another raven observed the demonstrator's behavior, and we used a bias paradigm to assess the emotional valence of the observer to determine whether emotional contagion had occurred. Observers showed a pessimism bias toward the presented ambiguous stimuli after perceiving demonstrators in a negative state, indicating emotional state matching based on the demonstrators' behavioral cues and confirming our prediction of negative emotional contagion. We did not find any judgment bias in the positive condition. This result critically expands upon observational studies of contagious play in ravens, providing experimental evidence that emotional contagion is present not only in mammalian but also in avian species. Importantly, this finding also acts as a stepping stone toward understanding the evolution of empathy, as this essential social skill may have emerged across these taxa in response to similar socioecological challenges.

State-dependent judgement bias in Drosophila: evidence for evolutionarily primitive affective processes

Affective states influence decision-making under ambiguity in humans and other animals. Individuals in a negative state tend to interpret ambiguous cues more negatively than individuals in a positive state. We demonstrate that the fruit fly, Drosophila melanogaster, also exhibits state-dependent changes in cue interpretation. Drosophila were trained on a Go/Go task to approach a positive (P) odour associated with a sugar reward and actively avoid a negative (N) odour associated with shock. Trained flies were then either shaken to induce a purported negative state or left undisturbed (control), and given a choice between: air or P; air or N; air or ambiguous odour (1 : 1 blend of P : N). Shaken flies were significantly less likely to approach the ambiguous odour than control flies. This ‘judgement bias’ may be mediated by changes in neural activity that reflect evolutionarily primitive affective states. We cannot say whether such states are consciously experienced, but use of this model organism's versatile experimental tool kit may facilitate elucidation of their neural and genetic basis.

Examining affective structure in chickens: valence, intensity, persistence and generalization measured using a Conditioned Place Preference Test

When measuring animals' valenced behavioural responses to stimuli, the Conditioned Place Preference (CPP) test goes a step further than many approach-based and avoidance-based tests by establishing whether a learned preference for, or aversion to, the location in which the stimulus was encountered can be generated. We designed a novel, four-chambered CPP test to extend the capability of the usual CPP paradigm to provide information on four key features of animals' affective responses: valence, scale, persistence and generalization. Using this test, we investigated the affective responses of domestic chickens (Gallus gallus domesticus) to four potentially aversive stimuli: 1. Puffs of air; 2. Sight of (robotic) snake; 3. Sprays of water; 4. Sound of conspecific alarm calls. We found conditioned avoidance of locations associated with the air puffs and water sprays (Friedman's χ2 (3) = 13.323 p > .005; χ2 (3) = 14.235 p > .005), but not with the snake and alarm calls. The scale of the learned avoidance was similar for the air puff and water spray stimuli, but persistence and generalization differed. We conclude that the four chambered CPP test can have a valuable role to play in making multi-feature measurements of stimulus-generated affective responses, and we highlight the value of such measurements for improving our understanding of the structure of affect in chickens and other animals.

Looking on the Bright Side of Livestock Emotions-the Potential of Their Transmission to Promote Positive Welfare

Emotions can be defined as an individual's affective reaction to an external and/or internal event that, in turn, generates a simultaneous cascade of behavioral, physiological, and cognitive changes. Those changes that can be perceived by conspecifics have the potential to also affect other's emotional states, a process labeled as "emotional contagion." Especially in the case of gregarious species, such as livestock, emotional contagion can have an impact on the whole group by, for instance, improving group coordination and strengthening social bonds. We noticed that the current trend of research on emotions in livestock, i.e., investigating affective states as a tool to assess and improve animal welfare, appears to be unbalanced. A majority of studies focuses on the individual rather than the social component of emotions. In this paper, we highlight current limitations in the latter line of research and suggest a stronger emphasis on the mechanisms of how emotions in livestock are transmitted and shared, which could serve as a promising tool to synergistically enhance the welfare of all individuals within a group.