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What attributes make some individuals more likely to win a fight than others? A range of morphological and physiological traits have been studied intensely but far less focus has been placed on the actual agonistic behaviours used. Current studies of agonistic behaviour focus on contest duration and the vigour of fighting. It also seems obvious that individuals that fight more skilfully should have a greater chance of winning a fight. Here, we discuss the meaning of skill in animal fights. As the activities of each opponent can be disrupted by the behaviour of their rival, we differentiate among ability, technique and skill itself. In addition to efficient, accurate and sometimes precise movement, skilful fighting also requires rapid decision-making, so that appropriate tactics and strategies are selected. We consider how these different components of skill could be acquired, through genes, experiences of play-fighting and of real fights. Skilful fighting can enhance resource holding potential (RHP) by allowing for sustained vigour, by inflicting greater costs on opponents and by minimizing the chance of damage. Therefore, we argue that skill is a neglected but important component of RHP that could be readily studied to provide new insights into the evolution of agonistic behaviour.

Intraspecific aggression, or agonism, is a widespread intrasexual selective behavior important to understanding animal behavioral ecology and reproductive systems. Such behavior can be studied either by direct observation or inferred from wound/scar frequency in extant species but is difficult to document in extinct taxa, limiting understanding of its evolution. Among extant archosaurs, crocodylians display extensive intrasexual aggression, whereas birds show extreme visual/vocal intersexual display. The evolutionary origin of this behavioral divergence, and pattern in non-avian dinosaurs, is unknown. Here we document the morphology, frequency, and ontogeny of intraspecific facial bite lesions (324 lesions) in a large sample of tyrannosaurids (202 specimens, 528 elements) to infer patterns of intraspecific aggression in non-avian theropods. Facial scars are consistent in position and orientation across tyrannosaurid species, suggesting bites were inflicted due to repeated/postured behavior. Facial scars are absent in young tyrannosaurids, first appear in immature animals (∼50% adult skull length), are present in ∼60% of the adult-sized specimens, and show aggressor:victim size isometry. The ontogenetic distribution of bite scars suggests agonistic behavior is associated with the onset of sexual maturity, and scar presence in approximately half the specimens may relate to a sexual pattern. Considered in a phylogenetic context, intraspecific bite marks are consistent and widely distributed in fossil and extant crocodyliforms and non-maniraptoriform theropods, suggesting a potential plesiomorphic behavior in archosaurs. Their absence in maniraptoriform theropods, including birds, may reflect a transition from boney cranial ornamentation and crocodylian-like intrasexual aggression to avian-like intersexual display with the evolution of pennaceous feathers.

Historically, infectious diseases have been the leading cause of human psychosomatic strain and death tolls. This research investigated the recent threat of COVID-19 contagion, especially its impact among frontline paramedics treating patients with COVID-19, and their perception of self-infection, which ultimately increases their agonistic behaviour. Based on the stressor–strain–outcome paradigm, a research model was proposed and investigated using survey-based data through a structured questionnaire. The results found that the perceived threat of COVID-19 contagion (emotional and cognitive threat) was positively correlated with physiological anxiety, depression, and emotional exhaustion, which led toward agonistic behaviour. Further, perceived social support was a key moderator that negatively affected the relationships between agonistic behaviour and physiological anxiety, depression, and emotional exhaustion. These findings significantly contributed to the current literature concerning COVID-19 and pandemic-related effects on human behaviour. This study also theorized the concept of human agonistic behaviour, which has key implications for future researchers.

Anemonefish are one of the most popular and frequently encountered fish groups by divers, and it is necessary to know how the approaches of humans affect them to maintain a balance between utilization and conservation in coral reefs. Agonistic behaviors toward divers were analyzed for 130 individuals of 4 species of anemonefish (Amphiprion ocellaris, A. clarkii, A. perideraion, and A. frenatus) on the west coast of Okinawa Island, Japan. Divers’ approaches differently affected each species of anemonefish, even though the fish inhabited the same area. The duration of agonistic behavior in female A. frenatus was observed to be longest of the 4 species. Sexual differences in agonistic behavior were prominent in A. perideraion and A. frenatus. When human observers stayed at a distance of 2.0 m from host anemones, no responses were observed in any of the species. Agonistic behavior increased when the distance of observers decreased to 1.0 m in females of A. frenatus and A. clarkii, and to 0.3 m in A. perideraion. During observation periods of 3 min, anemonefish behavior did not return completely to pre-observation behavior. We hypothesize that frequent human approaches could affect behavior and stress levels of some species of anemonefish. Thus, the distance and frequency of human approaches around anemonefish may need to be considered in order to protect anemonefish, as they are popular and commonly observed in diving tourism.

Agonistic behavior is a common behavior among agonistic Chinese mitten crabs (Eriocheir sinensis). Such behavior often leads to limb loss or physical impairment, and significantly affects the survival, growth, and quality of the crabs, and even the yield and economic value for E. sinensis. Agonistic behavior often occurs in agonistic crabs, which is closely related to personality traits and interactive behavior of animals. E. sinensis has personality traits such as boldness, aggression, and exploration as evidenced by the partition-crossing experiment, mirror experiment, and shelter experiment. Agonistic crabs were identified as individuals with boldness, high aggression, and high exploration. The interactive behavior spectrum of E. sinensis was first obtained, consisting of 15 behaviors. This spectrum described and summarized all interactive behaviors of E. sinensis during fights. The interactive behavior characteristics of agonistic crabs were identified as darting, intimidating, grabbing, pushing, stretching, and visitation. These results lay a theoretical basis for in-depth behavioral research on E. sinensis in the future. The technique of identifying agonistic crabs by personality traits and interactive behaviors not only allows for the elimination of agonistic crabs from the aquaculture process and the reduction in negative impacts caused by aggressive crabs, but also allows for the breeding of non-agonistic crabs and the further reduction in the economic losses caused by fighting behaviors.

Dusky damselfish (Stegastes fuscus) behaviour was investigated under natural and controlled conditions to evaluate how territory and familiarity affect aggressive behaviour. In the natural environment, fish occupies territories of 2.74 ± 1.3 m2 and the most frequent behaviours exhibited were monitoring swimming, feeding, shelter occupation and agonistic interactions. Larger-territory individuals spend more time in monitoring swimming than smaller-territory ones, which results in a reduction of food intake. Agonistic interactions were more frequent with heterospecifics than conspecifics. Whenever agonistic interaction occurred, confrontations were not frequent. Territorial behaviour in the lab was evaluated considering two variables: prior residence and familiarity between conspecific opponents. Resident fish invested more against intruders irrespective of the intruder’s identity (familiar or unfamiliar). When no previous territory was established, S. fuscus showed lower aggressive behaviour, and it was even lower when a familiar fish was the opponent. Data from the field and the lab suggest that S. fuscus territoriality and aggression are related to the size of the defended area and the competitor’s identity. Thus, reduced reef areas may result in increased interindividual aggression, while the intruders’ recognition may be a key trait controlling agonistic behaviour in the reef community where S. fuscus is inserted.

This study investigated the welfare of laying hens in different non-caged housing systems, namely a deep-litter barn system (BS), a free-range system (FRS) and an organic system (OS). The study was conducted on 270 hens of a native breed Green-legged Partridge (Z-11) and 270 Hy-Line Brown hybrids. Visual scans were performed to record behaviour of hens. Hens were housed in groups of 30 and observed over the course of one day at 20, 36 and 56 weeks of age. Dustbathing, scratching, wing stretching, wing flapping and preening were recorded as comfort behaviours. Pecking, fighting, threatening and chasing were recorded as agonistic behaviours. The percentage of run use was higher in native hens than in commercial hens (p < 0.05). The proportion of hens exhibiting comfort behaviours housed in the FRS and OS was similar but over twice as high as in the BS (p < 0.05). In the FRS and OS, the percentage of hens displaying comfort behaviours increased with age (p < 0.05). In all the production systems, the percentage of birds displaying comfort behaviours was higher in native breed hens than in commercial breeds (p < 0.05). In the BS, the higher proportion of hens displaying an agonistic behaviour was seen more in commercial breed than in the native breed hens (p < 0.05). The percentage of birds displaying an agonistic behaviour declined with hen age, both in commercial and native breed hens.

There are indications that companion dogs of multi-dog households form a hierarchy, maintained by formal and agonistic dominance. Although it was found that the behaviour of dogs depends on their rank in several contexts, so far, the assessment of their rank itself has been based on owner-completed questionnaires. With this research we endeavoured to find associations between rank scores from the Dog Rank Assessment Questionnaire (DRA-Q) and cohabiting dogs’ behaviour in a competitive test (Toy Possession test—32 dog pairs) and a non-competitive, citizen science scenario (Greeting test—20 dog pairs). Based on the grabbing the toy first and keeping the toy at the end variables, the dogs’ rank score provided a reliable indication of the dominant and subordinate dogs’ behaviour in the Toy Possession test. Similarly, the occurrence of dominant and submissive behaviours in the Greeting Test showed a good match with the agonistic and leadership subscores of the composite rank score from the DRA-Q. Our results provide a pioneering case for validating a questionnaire-based rank scoring method with biologically meaningful behavioural tests in the case of companion dogs. The finer analysis of the results highlighted that in the case of a multi-question scoring system, some components might provide more effective prediction of the dogs’ rank-related behaviour in some situations, while other components are more relevant in others, with traits related to agonistic dominance having relevance across contexts.

Abstract The large size variation of Macrobrachium amazonicum reflects a complex population structure that consists of four morphotypes, called TC (Translucent Claw), CC (Cinnamon Claw), GC1 (Green Claw 1), and GC2 (Green Claw 2). The effect of the largest morphotype (GC2) claws on development and behaviour of the smallest male morphotype (TC) was analysed through manipulations of the large prawn’s second pair of claws. TC males were paired for 75 days in aquaria with (a) an intact GC2, (b) a GC2 with immobilized dactyls, and (c) a GC2 without chelipeds. Isolated TC males served as a control. The maintenance activities of TC males and social interactions with the GC2 morphotype were monitored. Survival and growth of TC males was lower in relation to the control when they were paired with intact GC2 males. Aggressive interactions were carried out almost exclusively by GC2 and strongly affected the behaviour of the small prawns. The absence of chelipeds and immobilization of dactyls in GC2 prawns reduced the negative effect on the development of TC males and agonistic behaviour. The social interactions between GC2 and TC prawns reflect a stable dominance hierarchy. The large claw of the GC2 morphotype plays a major role in the social interaction.

Yamato et al present the first documentation of conspecific aggression in dugongs (Dugong dugon) in Thailand. Conspecific aggression, which involves attempts to injure or monopolize resources, has been observed in various marine mammal species. Agonistic behavior is also present in sirenians, such as dugongs and manatees. Male-male aggression in dugongs is driven by competition for resources and mates. They used drones to observe and analyze the aggressive behavior of dugongs in two events. The events included approaching, pursuing, agonistic collision, rushing, mounting, and separating behaviors. The initiators of the aggression were presumed to be males, based on their behavior. The events were distinguishable from mating behavior and were characterized by brief and violent contacts. The study provides insights into the behavioral categories and indicators of dugong aggression and highlights the advantages of using drones for aerial observations. Further research is needed to understand the benefits and functions of aggression in dugongs.