Referential gestures in fish collaborative hunting

Multimodal communication and audience directedness in the greeting behaviour of semi-captive African savannah elephants

Many species communicate by combining signals into multimodal combinations. Elephants live in multi-level societies where individuals regularly separate and reunite. Upon reunion, elephants often engage in elaborate greeting rituals, where they use vocalisations and body acts produced with different body parts and of various sensory modalities (e.g., audible, tactile). However, whether these body acts represent communicative gestures and whether elephants combine vocalisations and gestures during greeting is still unknown. Here we use separation-reunion events to explore the greeting behaviour of semi-captive elephants (Loxodonta africana). We investigate whether elephants use silent-visual, audible, and tactile gestures directing them at their audience based on their state of visual attention and how they combine these gestures with vocalisations during greeting. We show that elephants select gesture modality appropriately according to their audience's visual attention, suggesting evidence of first-order intentional communicative use. We further show that elephants integrate vocalisations and gestures into different combinations and orders. The most frequent combination consists of rumble vocalisations with ear-flapping gestures, used most often between females. By showing that a species evolutionarily distant to our own primate lineage shows sensitivity to their audience's visual attention in their gesturing and combines gestures with vocalisations, our study advances our understanding of the emergence of first-order intentionality and multimodal communication across taxa.

Collaborative hunting in artificial agents with deep reinforcement learning

Collaborative hunting, in which predators play different and complementary roles to capture prey, has been traditionally believed to be an advanced hunting strategy requiring large brains that involve high-level cognition. However, recent findings that collaborative hunting has also been documented in smaller-brained vertebrates have placed this previous belief under strain. Here, using computational multi-agent simulations based on deep reinforcement learning, we demonstrate that decisions underlying collaborative hunts do not necessarily rely on sophisticated cognitive processes. We found that apparently elaborate coordination can be achieved through a relatively simple decision process of mapping between states and actions related to distance-dependent internal representations formed by prior experience. Furthermore, we confirmed that this decision rule of predators is robust against unknown prey controlled by humans. Our computational ecological results emphasize that collaborative hunting can emerge in various intra- and inter-specific interactions in nature, and provide insights into the evolution of sociality.

Coexistence, resource partitioning, and fisheries management: A tale of two mesopredators in equatorial waters

Rock hind (Epinephelus adscensionis) and spotted moray (Gymnothorax moringa) are ubiquitous mesopredators that co-occur in the nearshore waters of Ascension Island in the South Atlantic Ocean, where they have significant cultural and subsistence value, but management of their non-commercial take is limited. This isolated volcanic system is home to high biomass and low species diversity, which poses two key questions: How can two mesopredators that perform similar ecological roles coexist? And if these two species are so ecologically similar, can they be managed using the same approach? Here, we combined acoustic telemetry, stomach content analysis, and stable isotope analysis to (i) explore space use and diet choices within and between these two species and (ii) to assess appropriate species-specific management options. Although rock hind had high residency and small calculated home ranges (0.0001-0.3114 km2), spotted moray exhibited shorter periods of residency (<3 months) before exiting the array. Vertical space use differed significantly across the 20-month tracking period, with individual differences in vertical space observed for both species. A hierarchical generalized additive model using 12-h averaged depth data identified that rock hind occurred lower in the water column than spotted moray, with both species occupying moderately deeper depths at night versus day (+1.6% relative depth). Spotted moray depth was also significantly predicted by lunar illumination. Aggregating samples by species and tissue type, Bayesian ecological niche modeling identified a 53.14%-54.15% and 78.02%-97.08% probability of niche overlap from fin clip and white muscle, respectively, whereas limited stomach content data indicated a preference for piscivorous prey. Variability in niche breadth between years suggests these species may exploit a range of prey items over time. These findings indicate that although these two species perform a similar ecological role by feeding on prey occupying the same trophic levels, subtle differences in movement behaviors between them suggest a one-rule-fits-all management approach is not likely the most effective option.

The 'after you' gesture in a bird

Gestures are ubiquitous in human communication, involving movements of body parts produced for a variety of purposes, such as pointing out objects (deictic gestures) or conveying messages (symbolic gestures)1. While displays of body parts have been described in many animals2, their functional similarity to human gestures has primarily been explored in great apes3,4, with little research attention given to other animal groups. To date, only a few studies have provided evidence for deictic gestures in birds and fish5,6,7, but it is unclear whether non-primate animals can employ symbolic gestures, such as waving to mean 'goodbye', which are, in humans, more cognitively demanding than deictic gestures1. Here, we report that the Japanese tit (Parus minor), a socially monogamous bird, uses wing-fluttering to prompt their mated partner to enter the nest first, and that wing-fluttering functions as a symbolic gesture conveying a specific message ('after you'). Our findings encourage further research on animal gestures, which may help in understanding the evolution of complex communication, including language.

GesturalOrigins: A bottom-up framework for establishing systematic gesture data across ape species

Current methodologies present significant hurdles to understanding patterns in the gestural communication of individuals, populations, and species. To address this issue, we present a bottom-up data collection framework for the study of gesture: GesturalOrigins. By "bottom-up", we mean that we minimise a priori structural choices, allowing researchers to define larger concepts (such as 'gesture types', 'response latencies', or 'gesture sequences') flexibly once coding is complete. Data can easily be re-organised to provide replication of, and comparison with, a wide range of datasets in published and planned analyses. We present packages, templates, and instructions for the complete data collection and coding process. We illustrate the flexibility that our methodological tool offers with worked examples of (great ape) gestural communication, demonstrating differences in the duration of action phases across distinct gesture action types and showing how species variation in the latency to respond to gestural requests may be revealed or masked by methodological choices. While GesturalOrigins is built from an ape-centred perspective, the basic framework can be adapted across a range of species and potentially to other communication systems. By making our gesture coding methods transparent and open access, we hope to enable a more direct comparison of findings across research groups, improve collaborations, and advance the field to tackle some of the long-standing questions in comparative gesture research.

A fish can change its stripes: investigating the role of body colour and pattern in the bluelined goatfish

Bluelined goatfish (Upeneichthys lineatus) rapidly change their body colour from a white horizontally banded pattern to a seemingly more conspicuous vertically banded red pattern, often when foraging. Given the apparent conspicuousness of the pattern to a range of observers, it seems unlikely that this colour change is used for camouflage and instead may be used for communication/signalling. Goatfish often drive multispecies associations, and it is possible that goatfish use this colour change as a foraging success signal to facilitate cooperation, increase food acquisition, and reduce predation risk through a 'safety in numbers' strategy. Using a novel approach, we deployed 3D model goatfish in different colour morphs-white without bands, white with black vertical bands, and white with red vertical bands-to determine whether the red colouration is an important component of the signal or if it is only the vertical banding pattern, regardless of colour, that fish respond to as an indicator of foraging success. Use of remote underwater video allowed us to obtain information without the influence of human observers on the communities and behaviours of other fish in response to these different colours exhibited by goatfish. We found that conspecifics were more abundant around the black- and red-banded model fish when compared with the white models. Conspecifics were also more likely to forage around the models than to pass or show attraction, but this was unaffected by model colour. No difference in the abundance and behaviour of associated heterospecifics around the different models was observed, perhaps due to the static nature of the models. Some species did, however, spend more time around the red- and black-banded fish, which suggests the change in colour may indicate benefits in addition to food resources. Overall, the results suggest that the body colour/pattern of U. lineatus is likely a signalling tool but further work is required to explore the benefits to both conspecifics and heterospecifics and to further determine the behavioural functions of rapid colour change in U. lineatus.

The Inner Lives of Cephalopods

The minds of cephalopods have captivated scientists for millennia, yet the extent that we can understand their subjective experiences remains contested. In this article, we consider the sum of our scientific progress towards understanding the inner lives of cephalopods. Here, we outline the behavioral responses to specific experimental paradigms that are helping us to reveal their subjective experiences. We consider evidence from three broad research categories, which help to illuminate whether soft-bodied cephalopods (octopus, cuttlefish, and squid) have an awareness of self, awareness of others, and an awareness of time. Where there are current gaps in the literature, we outline cephalopod behaviors that warrant experimental investigation. We argue that investigations, especially framed through the lens of comparative psychology, have the potential to extend our understanding of the inner lives of this extraordinary class of animals.

A multifaceted framework to establish the presence of meaning in non-human communication

Does non-human communication, like language, involve meaning? This question guides our focus through an interdisciplinary review of the theories and terminology used to study meaning across disciplines and species. Until now, it has been difficult to apply the concept of meaning to communication in non-humans. This is partly because of the varied approaches to the study of meaning. Additionally, while there is a scholarly acknowledgement of potential meaning in non-human cognition, there is also scepticism when the topic of communication arises. We organise some of the key literature into a coherent framework that can bridge disciplines and species, to ensure that aspects of meaning are accurately and fairly compared. We clarify the growing view in the literature that, rather than requiring multiple definitions or being split into different types, meaning is a multifaceted yet still unified concept. In so doing, we propose that meaning is an umbrella term. Meaning cannot be summed up with a short definition or list of features, but involves multiple complexities that are outlined in our framework. Specifically, three global facets are needed to describe meaning: a Signal Meaning Facet, an Interactant Meaning Facet, and a Resultant Meaning Facet. Most importantly, we show that such analyses are possible to apply as much to non-humans as to humans. We also emphasise that meaning nuances differ among non-human species, making a dichotomous approach to meaning questionable. Instead, we show that a multifaceted approach to meaning establishes how meaning appears within highly diverse examples of non-human communication, in ways consistent with the phenomenon's presence in human non-verbal communication and language(s). Therefore, without further recourse to 'functional' approaches that circumvent the critical question of whether any non-human meaning exists, we show that the concept of meaning is suitable for evolutionary biologists, behavioural ecologists, and others to study, to establish exactly which species exhibit meaning in their communication and in what ways.

Dynamic colour change as a signalling tool in bluelined goatfish (Upeneicthtys lineatus)

Many animal species can rapidly change their body colouration and patterning, but often the ecological drivers of such changes are unknown. Here, we explored dynamic colour change in the bluelined goatfish, Upeneichthys lineatus, a temperate marine teleost species. Upeneichthus lineatus can change in a matter of seconds, from a uniform white colour to display prominent, vertical, dark red stripes. Initial observations suggested that rapid colour change in U. lineatus was associated with feeding and may act as a signal to both conspecifics and heterospecifics that are frequently observed to follow feeding goatfish. Field observations of the colour and behaviour of individual U. lineatus were collected to (1) document the repertoire of behaviours that U. lineatus displays and categorise associated colour patterns; (2) quantify the speed of dynamic colour change; (3) establish the context in which U. lineatus changes colour and pattern; and (4) test whether the behaviour of follower fishes is influenced by colour patterning or specific behaviours of the focal goatfish. We found that U. lineatus changed colouration from white to the red banded pattern in less than 10 s. The key driver of rapid colour change in U. lineatus was feeding, particularly when the fish fed with its head buried in sediment. Conspecific followers were most likely to be white in colour and adopt searching behaviour, regardless of the focal fish colour or behaviour. Other species of follower fish spent significantly more time following U. lineatus that were displaying dark red stripes when searching or eating, implying the red stripes may be an interspecific signalling mechanism. Our findings indicate that rapid colour change in teleost fish may be used for social communication and may provide U. lineatus with increased protection from predation when feeding via a safety-in-numbers approach.

Stable isotopes and foraging behaviors support the role of antipredator benefits in driving the association between two marine fishes

Research from terrestrial communities shows that diminished predation risk is a principal driver of heterospecific grouping behavior, with foraging ecology predicting the roles that species play in groups, as more vulnerable foragers preferentially join more vigilant ones from whom they can benefit. Meanwhile, field studies examining the adaptive significance of heterospecific shoaling among marine fish have focused disproportionately on feeding advantages such as scrounging or prey-flushing. Juvenile bonefish (Albula vulpes) occur almost exclusively among mojarras (Eucinostomus spp.) and even elect to join them over conspecifics, suggesting they benefit from doing so. We evaluated the roles of risk-related and food-related factors in motivating this pattern of affiliation, estimating: (1) the relative levels of risk associated with each species' search and prey capture activities, via behavioral vulnerability traits discerned from in situ video of heterospecific shoals, and (2) resource use redundancy, using stable isotopes (δ¹³C, δ¹⁵N, and δ³⁴S) to quantify niche overlap. Across four distinct metrics, bonefish behaviors implied a markedly greater level of risk than those of mojarras, typified by higher activity levels and a reduced capacity for overt vigilance; consistent with expectations if their association conformed to patterns of joining observed in terrestrial habitats. Resource use overlap inferred from stable isotopes was low, indicating that the two species partitioned resources and making it unlikely that bonefish derived substantive food-related benefits. Collectively, these findings suggest that the attraction of juvenile bonefish to mojarras is motivated primarily by antipredator advantages, which may include the exploitation of risk-related social cues.

Towards a great ape dictionary: Inexperienced humans understand common nonhuman ape gestures

In the comparative study of human and nonhuman communication, ape gesturing provided the first demonstrations of flexible, intentional communication outside human language. Rich repertoires of these gestures have been described in all ape species, bar one: us. Given that the majority of great ape gestural signals are shared, and their form appears biologically inherited, this creates a conundrum: Where did the ape gestures go in human communication? Here, we test human recognition and understanding of 10 of the most frequently used ape gestures. We crowdsourced data from 5,656 participants through an online game, which required them to select the meaning of chimpanzee and bonobo gestures in 20 videos. We show that humans may retain an understanding of ape gestural communication (either directly inherited or part of more general cognition), across gesture types and gesture meanings, with information on communicative context providing only a marginal improvement in success. By assessing comprehension, rather than production, we accessed part of the great ape gestural repertoire for the first time in adult humans. Cognitive access to an ancestral system of gesture appears to have been retained after our divergence from other apes, drawing deep evolutionary continuity between their communication and our own.

Are ape gestures like words? Outstanding issues in detecting similarities and differences between human language and ape gesture

Opinion piece: ape gestures are made intentionally, inviting parallels with human language; but how similar are their gestures to words? Here we ask this in three ways, considering: flexibility and ambiguity, first- and second-order intentionality, and usage in interactive exchanges. Many gestures are used to achieve several, often very distinct, goals. Such apparent ambiguity in meaning is potentially disruptive for communication, but-as with human language-situational and interpersonal context may largely resolve the intended meaning. Our evidence for first-order intentional use of gesture is abundant, but how might we establish a case for the second-order intentional use critical to language? Finally, words are rarely used in tidy signal-response sequences but are exchanged in back-and-forth interaction. Do gestures share this property? In this paper, we examine these questions and set out ways in which they can be resolved, incorporating data from wild chimpanzees. This article is part of the theme issue 'Cognition, communication and social bonds in primates'.

Coordinating social action: a primer for the cross-species investigation of communicative repair

Human joint action is inherently cooperative, manifested in the collaborative efforts of participants to minimize communicative trouble through interactive repair. Although interactive repair requires sophisticated cognitive abilities, it can be dissected into basic building blocks shared with non-human animal species. A review of the primate literature shows that interactionally contingent signal sequences are at least common among species of non-human great apes, suggesting a gradual evolution of repair. To pioneer a cross-species assessment of repair this paper aims at (i) identifying necessary precursors of human interactive repair; (ii) proposing a coding framework for its comparative study in humans and non-human species; and (iii) using this framework to analyse examples of interactions of humans (adults/children) and non-human great apes. We hope this paper will serve as a primer for cross-species comparisons of communicative breakdowns and how they are repaired. This article is part of the theme issue 'Revisiting the human 'interaction engine': comparative approaches to social action coordination'.

Interaction and ostension: the myth of 4th-order intentionality

Research in comparative cognition on allegedly uniquely human capacities considers the identification of these human capacities in other species as one of their main points of inquiry. Capacities are applied in their theoretical descriptions to promising empirical data. The conclusion then often is that even though, on a behavioural level, the human and nonhuman cases appear related, on a cognitive level there is no relation whatsoever because the underlying cognitive states diverge in quality. This result seems dissatisfying for two reasons: (1) there is ample empirical evidence that suggests the presence of the capacities in other species, and (2) the claim that the underlying states diverge often hinges on the reference to the theoretical definitions of these capacities only. This opinion piece focuses on the capacity of ostensive intentional communication to demonstrate that the original theoretical analyses often are not befitting a comparative endeavour and should therefore not be used as pivotal reference within comparative research. An outlook will be provided on more promising approaches to identifying ostensive communication, namely an interactive approach that will allow for ostension to not be perceived as a one-turn signalling behaviour, but as interactive, with the possibility of being established in a trial-and-error manner. This article is part of the theme issue 'Revisiting the human 'interaction engine': comparative approaches to social action coordination'.

Vocal signals facilitate cooperative hunting in wild chimpanzees

Cooperation and communication likely coevolved in humans. However, the evolutionary roots of this interdependence remain unclear. We address this issue by investigating the role of vocal signals in facilitating a group cooperative behavior in an ape species: hunting in wild chimpanzees. First, we show that bark vocalizations produced before hunt initiation are reliable signals of behavioral motivation, with barkers being most likely to participate in the hunt. Next, we find that barks are associated with greater hunter recruitment and more effective hunting, with shorter latencies to hunting initiation and prey capture. Our results indicate that the coevolutionary relationship between vocal communication and group-level cooperation is not unique to humans in the ape lineage and is likely to have been present in our last common ancestor with chimpanzees.

Iconicity as Multimodal, Polysemiotic, and Plurifunctional

Investigations of iconicity in language, whereby interactants coordinate meaningful bodily actions to create resemblances, are prevalent across the human communication sciences. However, when it comes to analysing and comparing iconicity across different interactions (e.g., deaf, deafblind, hearing) and modes of communication (e.g., manual signs, speech, writing), it is not always clear we are looking at the same thing. For example, tokens of spoken ideophones and manual depicting actions may both be analysed as iconic forms. Yet spoken ideophones may signal depictive and descriptive qualities via speech, while manual actions may signal depictive, descriptive, and indexical qualities via the shape, movement, and placement of the hands in space. Furthermore, each may co-occur with other semiotics articulated with the face, hands, and body within composite utterances. The paradigm of iconicity as a single property is too broad and coarse for comparative semiotics, as important details necessary for understanding the range of human communicative potentialities may be masked. Here, we draw on semiotic approaches to language and communication, including the model of language as signalled via describing, indicating and/or depicting and the notion of non-referential indexicality, to illustrate the multidimensionality of iconicity in co-present interactions. This builds on our earlier proposal for analysing how different methods of semiotic signalling are combined in multimodal language use. We discuss some implications for the language and communication sciences and explain how this approach may inform a theory of biosemiotics.

Intergroup conflict: origins, dynamics and consequences across taxa

Although uniquely destructive and wasteful, intergroup conflict and warfare are not confined to humans. They are seen across a range of group-living species, from social insects, fishes and birds to mammals, including nonhuman primates. With its unique collection of theory, research and review contributions from biology, anthropology and economics, this theme issue provides novel insights into intergroup conflict across taxa. Here, we introduce and organize this theme issue on the origins and consequences of intergroup conflict. We provide a coherent framework by modelling intergroup conflicts as multi-level games of strategy in which individuals within groups cooperate to compete with (individuals in) other groups for scarce resources, such as territory, food, mating opportunities, power and influence. Within this framework, we identify cross-species mechanisms and consequences of (participating in) intergroup conflict. We conclude by highlighting crosscutting innovations in the study of intergroup conflict set forth by individual contributions. These include, among others, insights on how within-group heterogeneities and leadership relate to group conflict, how intergroup conflict shapes social organization and how climate change and environmental degradation transition intergroup relations from peaceful coexistence to violent conflict.

This article is part of the theme issue ‘Intergroup conflict across taxa’.

Male zebrafish (Danio rerio) do not preferentially associate with familiar over unfamiliar conspecifics

Members of several shoaling species have been shown to prefer to associate with familiar individuals, enhancing the benefits of aggregation. The authors used a series of social preference tasks in the laboratory to evaluate whether prior familiarity with potential partners influences preference of shoaling partner in male zebrafish (Danio rerio), a social species found in shallow, slow-moving waters. The authors found that though male zebrafish exhibited a strong preference for shoaling with a male conspecific as opposed to remaining alone, they exhibited no preference for familiar over unfamiliar conspecifics. This suggests that the benefits of familiarity for shoaling behaviour may not be as important for male zebrafish as has been shown in other social fish species.

Inferential Communication: Bridging the Gap Between Intentional and Ostensive Communication in Non-human Primates

Communication, when defined as an act intended to affect the psychological state of another individual, demands the use of inference. Either the signaler, the recipient, or both must make leaps of understanding which surpass the semantic information available and draw from pragmatic clues to fully imbue and interpret meaning. While research into human communication and the evolution of language has long been comfortable with mentalistic interpretations of communicative exchanges, including rich attributions of mental state, research into animal communication has balked at theoretical models which describe mentalized cognitive mechanisms. We submit a new theoretical perspective on animal communication: the model of inferential communication. For use when existing proximate models of animal communication are not sufficient to fully explain the complex, flexible, and intentional communication documented in certain species, specifically non-human primates, we present our model as a bridge between shallower, less cognitive descriptions of communicative behavior and the perhaps otherwise inaccessible mentalistic interpretations of communication found in theoretical considerations of human language. Inferential communication is a framework that builds on existing evidence of referentiality, intentionality, and social inference in primates. It allows that they might be capable of applying social inferences to a communicative setting, which could explain some of the cognitive processes that enable the complexity and flexibility of primate communication systems. While historical models of animal communication focus on the means-ends process of behavior and apparent cognitive outcomes, inferential communication invites consideration of the mentalistic processes that must underlie those outcomes. We propose a mentalized approach to questions, investigations, and interpretations of non-human primate communication. We include an overview of both ultimate and proximate models of animal communication, which contextualize the role and utility of our inferential communication model, and provide a detailed breakdown of the possible levels of cognitive complexity which could be investigated using this framework. Finally, we present some possible applications of inferential communication in the field of non-human primate communication and highlight the role it could play in advancing progress toward an increasingly precise understanding of the cognitive capabilities of our closest living relatives.

Cooperative herbivory between two important pests of rice

Normally, when different species of herbivorous arthropods feed on the same plant this leads to fitness-reducing competition. We found this to be different for two of Asia's most destructive rice pests, the brown planthopper and the rice striped stem borer. Both insects directly and indirectly benefit from jointly attacking the same host plant. Double infestation improved host plant quality, particularly for the stemborer because the planthopper fully suppresses caterpillar-induced production of proteinase inhibitors. It also reduced the risk of egg parasitism, due to diminished parasitoid attraction. Females of both pests have adapted their oviposition behaviour accordingly. Their strong preference for plants infested by the other species even overrides their avoidance of plants already attacked by conspecifics. This cooperation between herbivores is telling of adaptations resulting from the evolution of plant-insect interactions, and points out mechanistic vulnerabilities that can be targeted to control these major pests.

Comparative brain structure and visual processing in octopus from different habitats

Octopods are masters of camouflage and solve complex tasks, and their cognitive ability is said to approach that of some small mammals. Despite intense interest and some research progress, much of our knowledge of octopus neuroanatomy and its links to behavior and ecology comes from one coastal species, the European common octopus, Octopus vulgaris. Octopod species are found in habitats including complex coral reefs and the relatively featureless mid-water. There they encounter different selection pressures, may be nocturnal or diurnal, and are mostly solitary or partially social. How these different ecologies and behavioral differences influence the octopus central nervous system (CNS) remains largely unknown. Here we present a phylogenetically informed comparison between diurnal and nocturnal coastal and a deep-sea species using brain imaging techniques. This study shows that characteristic neuroanatomical changes are linked to their habits and habitats. Enlargement and division of the optic lobe as well as structural foldings and complexity in the underlying CNS are linked to behavioral adaptation (diurnal versus nocturnal; social versus solitary) and ecological niche (reef versus deep sea), but phylogeny may play a part also. The difference between solitary and social life is mirrored within the brain including the formation of multiple compartments (gyri) in the vertical lobe, which is likened to the vertebrate cortex. These findings continue the case for convergence between cephalopod and vertebrate brain structure and function. Notably, within the current push toward comparisons of cognitive abilities, often with unashamed anthropomorphism at their root, these findings provide a firm grounding from which to work.

Fish self-awareness: limits of current knowledge and theoretical expectations

Animal self-awareness is divided into three levels: bodily, social, and introspective self-awareness. Research has focused mainly on the introspection of so-called higher organisms such as mammals. Herein, we turn our attention to fish and provide opinions on their self-awareness based on a review of the scientific literature. Our specific aims are to discuss whether fish (A) could have a neural substrate supporting self-awareness and whether they display signs of (B) social and (C) introspective self-awareness. The present knowledge does not exclude the possibility that fish could have a simple neocortex or other structures that support certain higher cognitive processes, as the function of the primate cerebral cortex can be replaced by other neurological structures. Fish are known to display winner, loser, and audience effects, which could be interpreted as signs of social self-awareness. The audience effect may be explained not only by ethological cost and benefit theory but also by the concept of public self-awareness, which comes from human studies. The behavioural and neural manifestations of depression may be induced in fish under social subordination and may be viewed as certain awareness of a social status. The current findings on fish introspective self-awareness have been debated in the scientific community and, therefore, demand replication to provide more evidence. Further research is needed to verify the outlined ideas; however, the current knowledge indicates that fish are capable of certain higher cognitive processes, which raises questions and implications regarding ethics and welfare in fish-related research and husbandry.

Sensitivity to the communicative partner's attentional state: A developmental study on mother-infant dyads in wild chimpanzees (Pan troglodytes schweinfurthii)

Gestural communication permeates all domains of chimpanzees' social life and is intentional in use. However, we still have only limited information on how young apes develop the sociocognitive skills needed for intentional communication. In this cross-sectional study, we document the development of behavioral adjustment to the recipient's visual attention-considered a hallmark of intentional communication-in wild immature chimpanzees' gestural communication. We studied 11 immature chimpanzees (Pan troglodytes schweinfurthii): three infants, four juveniles, and four adolescents gesturing towards their mother. We quantified silent-visual, audible, and contact gestures indexed to maternal visual attention and inattention. We investigated unimodal adjustment, defined by the capacity of young chimpanzees to deploy fewer silent-visual signals when their mothers did not show full visual attention towards them as compared with when they did. We then examined cross-modal adjustment, defined as the capacity of chimpanzees to deploy more audible-or-contact gestures than silent-visual gestures in the condition where their mothers did not show full visual attention as compared to when they did. Our results show a gradual decline in the use of silent-visual gestures when the mother is not visually attentive with increasing age. The absence of silent-visual gesture production toward a visually inattentive recipient (complete unimodal adjustment) was not fully in place until adolescence. Immature chimpanzees used more audible-or-contact gestures than silent-visual ones when their mothers did not show visual attention and vice-versa when they did. This cross-modal adjustment was expressed in juveniles and adolescents but not in infants. Overall, this study shows that infant chimpanzees were limited in their sensitivity to maternal attention when gesturing, whereas adolescent chimpanzees adjusted their communication appropriately. Juveniles present an intermediate pattern with cross-modal adjustment preceding unimodal adjustment and with variability in the age of onset.

No evidence for conspecific recruitment for cooperative hunting in lionfish Pterois miles

Lionfish are common piscivores in the Indo-Pacific and invasive in the Caribbean. A fin flaring pattern, involving a rapid undulation of the caudal fin and sequential turning of both pectoral fins, was described in zebra lionfish as a signal to initiate cooperative hunting, and it was hypothesized that such hunting tactics may also exist in other lionfish species and contribute to their successful invasion in the Caribbean. Here, we investigated one of those invasive species, Pterois miles, in its natural range in the Red Sea. We did not observe evidence for cooperative hunting in the field. We complemented field observations with a laboratory experiment aimed at inducing subjects to recruit partners for cooperative hunts, exposing subjects to inaccessible prey in transparent housing as well as to a potential partner. We regularly observed the fin flaring pattern, but importantly, it was not directed at the partner. Thus, rather than being a signal, the fin flaring movement pattern seems to be a swimming mode in a confined environment. Furthermore, the two lionfish did not aggregate at the prey housing, reinforcing the field results that this species in the Red Sea does not depend on cooperation to hunt fish.

Assessing joint commitment as a process in great apes

Many social animals interact jointly, but only humans experience a specific sense of obligation toward their co-participants, a joint commitment. However, joint commitment is not only a mental state but also a process that reveals itself in the coordination efforts deployed during entry and exit phases of joint action. Here, we investigated the presence and duration of such phases in N = 1,242 natural play and grooming interactions of captive chimpanzees and bonobos. The apes frequently exchanged mutual gaze and communicative signals prior to and after engaging in joint activities with conspecifics, demonstrating entry and exit phases comparable to those of human joint activities. Although rank effects were less clear, phases in bonobos were more moderated by friendship compared to phases in chimpanzees, suggesting bonobos were more likely to reflect patterns analogous to human “face management”. This suggests that joint commitment as process was already present in our last common ancestor with Pan.

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Great apes exchange signals and gaze before entering and exiting joint actions

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Joint action structure of both ape species resembles that of humans

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Coordinated joint action phases indicate an underlying joint commitment

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Social bonds affect joint action structure more in bonobos than in chimpanzees

Nested information processing in the living world

Living organisms create, copy, and make use of information, the content depending on the level of organization. In cells, a network of signal chain proteins regulates gene expression and other cell functions. Incoming information is encoded through signal reception, processed by the network, and decoded by the synthesis of new gene products and other biological functions. Signaling proteins represent nodes, and signal transmission proceeds via allosteric binding, chemical and structural modifications, synthesis, sequestering, and degradation. The induction of the gene caudal type homeobox 2 (CDX2) in the mammalian preimplantation embryo is outlined as a demonstration of this concept. CDX2 is involved in the decision of cells to enter the trophoblast lineage. Two signal chains are coordinated into an information processing model with the help of logic gates. The model introduces a formal structure that incorporates experimental and morphological data. Above the cell level, information flow relates to tissue formation and functioning, and whole cells play the role of network nodes. This is described for the anatomical patterning of bone with implications for bone formation and homeostasis. The information usage in cells and tissues is set into a context of the nervous system and the interaction of human individuals in societies, both established scenes of information processing.

Prosocial and antisocial choices in a monogamous cichlid with biparental care

Human society is cooperative and characterized by spontaneous prosociality. Comparative studies on endotherm vertebrates suggest that social interdependence causes the evolution of proactive prosociality. To test the generality of this hypothesis, we modify a prosocial choice task for application to the convict cichlid, Amatitlania nigrofasciata, a monogamous fish with biparental care and a strong pair bond. We also affirm that male subjects learn to favor prosocial choices when their mates are the recipients in a neighboring tank. When the neighboring tank is empty, males choose randomly. Furthermore, in the absence of their mates, males behave prosocially toward a stranger female. However, if the mate of the subjects is also visible in the third tank, or if a male is a potential recipient, then subjects make antisocial choices. To conclude, fish may show both spontaneous prosocial and antisocial behaviors according to their social relationships with conspecifics and the overall social context.

Intentional communication: solving methodological issues to assigning first-order intentional signalling

Intentional signalling plays a fundamental role in human communication. Mapping the taxonomic distribution of comparable capacities may thus shed light on the selective pressures that enabled the evolution of human communication. Nonetheless, severe methodological issues undermine comparisons among studies, species and communicative modalities. Here, we discuss three main obstacles that hinder comparative research of 'first-order' intentional signalling (i.e. voluntary signalling in pursuit of a cognitively represented goal): (i) inconsistency in how behavioural hallmarks are defined and operationalised, (ii) testing of behavioural hallmarks without statistical comparison to control conditions, and (iii) bias against the publication of negative results. To address these obstacles, we present a four-step scheme with 20 statistical operational criteria to distinguish between non-intentional and first-order intentional signalling. Our unified scheme applies to visual and audible signals, thereby validating comparison across communicative modalities and species. This, in turn, promotes the generation and testing of hypotheses about the evolution of intentional communication.

Ravens parallel great apes in physical and social cognitive skills

Human children show unique cognitive skills for dealing with the social world but their cognitive performance is paralleled by great apes in many tasks dealing with the physical world. Recent studies suggested that members of a songbird family-corvids-also evolved complex cognitive skills but a detailed understanding of the full scope of their cognition was, until now, not existent. Furthermore, relatively little is known about their cognitive development. Here, we conducted the first systematic, quantitative large-scale assessment of physical and social cognitive performance of common ravens with a special focus on development. To do so, we fine-tuned one of the most comprehensive experimental test-batteries, the Primate Cognition Test Battery (PCTB), to raven features enabling also a direct, quantitative comparison with the cognitive performance of two great ape species. Full-blown cognitive skills were already present at the age of four months with subadult ravens' cognitive performance appearing very similar to that of adult apes in tasks of physical (quantities, and causality) and social cognition (social learning, communication, and theory of mind). These unprecedented findings strengthen recent assessments of ravens' general intelligence, and aid to the growing evidence that the lack of a specific cortical architecture does not hinder advanced cognitive skills. Difficulties in certain cognitive scales further emphasize the quest to develop comparative test batteries that tap into true species rather than human specific cognitive skills, and suggest that socialization of test individuals may play a crucial role. We conclude to pay more attention to the impact of personality on cognitive output, and a currently neglected topic in Animal Cognition-the linkage between ontogeny and cognitive performance.

Intentional partial beaching in a coral reef fish: a newly recorded hunting behaviour of titan triggerfish, Balistoides viridescens

Coral reef fishes use a multitude of diverse feeding behaviours to increase their ability to successfully capture a wide range of prey. Here, this study reports a novel hunting behaviour in a coral reef fish, the titan triggerfish, Balistoides viridescens, where an individual was seen partially beaching itself while attempting to catch a Red Sea ghost crab, Ocypode saratan. This is the first report of this behaviour in the order Tetraodontiformes and represents an astonishing capability of this species to exploit food resources outside their typical assumed ecological niche.

Old and New Approaches to Animal Cognition: There Is Not "One Cognition"

Using the comparative approach, researchers draw inferences about the evolution of cognition. Psychologists have postulated several hypotheses to explain why certain species are cognitively more flexible than others, and these hypotheses assume that certain cognitive skills are linked together to create a generally "smart" species. However, empirical findings suggest that several animal species are highly specialized, showing exceptional skills in single cognitive domains while performing poorly in others. Although some cognitive skills may indeed overlap, we cannot a priori assume that they do across species. We argue that the term "cognition" has often been used by applying an anthropocentric viewpoint rather than a biocentric one. As a result, researchers tend to overrate cognitive skills that are human-like and assume that certain skills cluster together in other animals as they do in our own species. In this paper, we emphasize that specific physical and social environments create selection pressures that lead to the evolution of certain cognitive adaptations. Skills such as following the pointing gesture, tool-use, perspective-taking, or the ability to cooperate evolve independently from each other as a concrete result of specific selection pressures, and thus have appeared in distantly related species. Thus, there is not "one cognition". Our argument is founded upon traditional Darwinian thinking, which-although always at the forefront of biology-has sometimes been neglected in animal cognition research. In accordance with the biocentric approach, we advocate a broader empirical perspective as we are convinced that to better understand animal minds, comparative researchers should focus much more on questions and experiments that are ecologically valid. We should investigate nonhuman cognition for its own sake, not only in comparison to the human model.

Marmoset prosociality is intentional

Marmoset monkeys show high levels of proactive prosociality, a trait shared with humans, presumably because both species rely on allomaternal care. However, it is not clear whether the proximate regulation of this convergent trait is also similar, in particular with regard to intentionality, which is a defining characteristic of prosocial behavior in the human literature. The aim of this paper was to investigate whether marmoset monkeys' prosociality fulfils the criteria of intentionality developed in primate communication research. The results show that marmoset prosocial behavior (i) has some degree of flexibility, since individuals can use multiple means to reach their goal and adjust them to specific conditions, (ii) depends on the presence of an audience, i.e. potential recipients (social use), and (iii) is goal-directed, because (a) it continues exactly until the putative goal is reached, and (b) individuals check back and look at/for their partner when their prosocial actions do not achieve the putative goal (i.e. if their actions don't lead to the expected outcome, this elicits distinct reactions in the actor). These results suggest that marmoset prosociality is under some degree of voluntary, intentional control. They are in line with other findings that marmosets perceive each other as intentional agents, and only learn socially from actions that are perceived as intentional. The most parsimonious conclusion is, therefore, that prosocial behavior is fundamentally under voluntary control in marmosets, just as it is in humans, even though our more sophisticated cognitive abilities allow for a far more complex integration of prosociality into a broader variety of contexts and of behavioral goals.

How animals collaborate: Underlying proximate mechanisms

Collaboration or social interactions in which two or more individuals coordinate their behavior to produce outcomes from which both individuals benefit are common in nature. Individuals from many species hunt together, defend their territory, and form coalitions in intragroup competition. However, we still know very little about the proximate mechanisms underlying these behaviors. Recent theories of human cognitive evolution have emphasized the role collaboration may have played in the selection of socio-cognitive skills. It has been argued that the capacity to form shared goals and joint intentions with others, is what allows humans to collaborate so flexibly and efficiently. Although there is no evidence that nonhuman animals are capable of shared intentionality, there is conceivably a wide range of proximate mechanisms that support forms of, potentially flexible, collaboration in other species. We review the experimental literature with the aim of evaluating what we know about how other species achieve collaboration; with a particular focus on chimpanzees. We structure the review with a new categorization of collaborative behavior that focuses on whether individuals intentionally coordinate actions with others. We conclude that for a wider comparative perspective we need more data from other species but the findings so far suggest that chimpanzees, and possibly other great apes, are capable of understanding the causal role of a partner in collaboration. This article is categorized under: Cognitive Biology > Evolutionary Roots of Cognition Psychology > Comparative Psychology.

Overcome Competitive Exclusion in Ecosystems

Explaining biodiversity in nature is a fundamental problem in ecology. An outstanding challenge is embodied in the so-called Competitive Exclusion Principle: two species competing for one limiting resource cannot coexist at constant population densities, or more generally, the number of consumer species in steady coexistence cannot exceed that of resources. The fact that competitive exclusion is rarely observed in natural ecosystems has not been fully understood. Here we show that, by forming chasing pairs and chasing triplets among the consumers and resources in the consumption process, the Competitive Exclusion Principle can be naturally violated. The modeling framework developed here is broadly applicable and can be used to explain the biodiversity of many consumer-resource ecosystems and hence deepens our understanding of biodiversity in nature.

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Foraging with only chasing pairs cannot break the Competitive Exclusion Principle (CEP)

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A population dynamics model involving both chasing pairs and triplets can break CEP

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Redundant foraging within the chasing triplets facilitates species coexistence

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The theoretical framework is testable in ecosystems involving pack hunting

Presence of CTXs in moray eels and dusky groupers in the marine environment of the Canary Islands

Local population frequently consumes moray eels and dusky groupers from the Canary Islands. These species are top predators and the interactions between them include predation but also, in some cases, collaborative hunting. These fish are well known to cause ciguatera (CFP) outbreaks in several marine areas such as Japan, Hawaii, French Polynesia and Caribe. Groupers have been involved in CFP events in the Canary Islands, however, moray eels have not yet been well studied in this regard. The present research seeks to describe the finding of a black moray in the stomach of a positive dusky grouper during its necropsy, and to clarify the implication of groupers and moray eels in the food webs, accumulating CTXs in the Canarian environment. The study also updates statistics on the presence of toxic groupers in this archipelago. For these purposes, 248 grouper samples from the CFP official control in the Canary Islands (2018-2019) were analysed and 36 moray eels (5 species) were collected under the EuroCigua project and one was obtained during a dusky grouper necropsy. All samples were analysed with the Neuro-2a cell-based assay (CBA) to evidence CTX-like toxicity. Regarding the necropsied grouper and the moray eel found in its stomach content, the LCMS/MS method allowed the identification and quantification of CCTX1 in both fish at similar levels while none of the P-CTXs for which standards were available were detected. Among groupers, 25.4 % displayed CTX-like toxicity with differences between islands. For moray eels 38.9 % showed toxicity, involving 4 species. Black moray exhibited a high proportion of positives (9/12) and a positive correlation was found between CTX-like toxicity quantification and the black moray weight. Regarding the grouper, and the moray eel found in its stomach, the LCMS/MS method allowed the identification and quantification of C-CTX1 in both fish at similar levels. This found suggests a trophic interaction between these species and their role in maintaining CTXs in the Canary waters where local population commonly demand those species for consumption. The island of El Hierro stands out above all the other Canary Islands with the concerning percentage of positive grouper samples and the high CTX toxicity levels obtained in moray eel specimens analysed in this marine area. This is the first report of CTX-like toxicity in flesh of moray eels fished in the Canary archipelago and the confirmation of the presence of C-CTX1 by LCMS/MS in a black moray from this marine area.

Bioluminescent backlighting illuminates the complex visual signals of a social squid in the deep sea

Visual signals rapidly relay information, facilitating behaviors and ecological interactions that shape ecosystems. However, most known signaling systems can be restricted by low light levels-a pervasive condition in the deep ocean, the largest inhabitable space on the planet. Resident visually cued animals have therefore been hypothesized to have simple signals with limited information-carrying capacity. We used cameras mounted on remotely operated vehicles to study the behavior of the Humboldt squid, Dosidicus gigas, in its natural deep-sea habitat. We show that specific pigmentation patterns from its diverse repertoire are selectively displayed during foraging and in social scenarios, and we investigate how these behaviors may be used syntactically for communication. We additionally identify the probable mechanism by which D. gigas, and related squids, illuminate these patterns to create visual signals that can be readily perceived in the deep, dark ocean. Numerous small subcutaneous (s.c.) photophores (bioluminescent organs) embedded throughout the muscle tissue make the entire body glow, thereby backlighting the pigmentation patterns. Equipped with a mechanism by which complex information can be rapidly relayed through a visual pathway under low-light conditions, our data suggest that the visual signals displayed by D. gigas could share design features with advanced forms of animal communication. Visual signaling by deep-living cephalopods will likely be critical in understanding how, and how much, information can be shared in one of the planet's most challenging environments for visual communication.

Octopus Arm-Inspired Tapered Soft Actuators with Suckers for Improved Grasping

Octopuses can employ their tapered arms to catch prey of all shapes and sizes due to their dexterity, flexibility, and gripping power. Intrigued by variability in arm taper angle between different octopus species, we explored the utility of designing soft actuators exhibiting a distinctive conical geometry, compared with more traditional cylindrical forms. We find that these octopus-inspired conical-shaped actuators exhibit a wide range of bending curvatures that can be tuned by simply altering their taper angle and they also demonstrate greater flexibility compared with their cylindrical counterparts. The taper angle and bending curvature are inversely related, whereas taper angle and applied bending force are directly related. To further expand the functionality of our soft actuators, we incorporated vacuum-actuated suckers into the actuators for the production of a fully integrated octopus arm-inspired gripper. Notably, our results reveal that because of their enhanced flexibility, these tapered actuators with suckers have better gripping power than their cylindrical-shaped counterparts and require significantly larger forces to be detached from both flat and curved surfaces. Finally, we show that by choosing appropriate taper angles, our tapered actuators with suckers can grip, move, and place a remarkably wide range of objects with flat, nonplanar, smooth, or rough surfaces, as well as retrieve objects through narrow openings. The results from this study not only provide new design insights into the creation of next-generation soft actuators for gripping a wide range of morphologically diverse objects but also contribute to our understanding of the functional significance of arm taper angle variability across octopus species.

Scratching beneath the surface: intentionality in great ape signal production

Despite important similarities having been found between human and animal communication systems, surprisingly little research effort has focussed on whether the cognitive mechanisms underpinning these behaviours are also similar. In particular, it is highly debated whether signal production is the result of reflexive processes, or can be characterized as intentional. Here, we critically evaluate the criteria that are used to identify signals produced with different degrees of intentionality, and discuss recent attempts to apply these criteria to the vocal, gestural and multimodal communicative signals of great apes and more distantly related species. Finally, we outline the necessary research tools, such as physiologically validated measures of arousal, and empirical evidence that we believe would propel this debate forward and help unravel the evolutionary origins of human intentional communication. This article is part of the theme issue 'What can animal communication teach us about human language?'