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The Challenge Hypothesis is an influential framework for understanding how androgens are involved in the promotion of competitive behavior during mating-related challenges and has been tested extensively in studies across scientific disciplines. Mixed support in psychological research led scholars to develop the Dual Hormone Hypothesis as a potential path forward, which argues that glucocorticoids moderate the relationship between androgens and status-striving. In the current study, we examine the Challenge Hypothesis and the Dual Hormone Hypothesis in wild male mountain gorillas, representing the first time the latter hypothesis has been tested in a non-human primate. In a sample of 30 adult males comprising over 600 days of observation, we find some limited support for the Challenge Hypothesis. Greater daily rates of targeted aggression toward other adult males corresponded to higher fecal androgen metabolites 1-2 days following observations, though this pattern did not fully generalize to dominance rank or other competitive behaviors examined. However, we find no support for the Dual Hormone Hypothesis: neither dominance rank nor any category of competitive behavior was predicted by the interaction between androgens and glucocorticoids. We close by discussing how this initial investigation might be leveraged toward the development of an expanded Dual Hormone Hypothesis that draws on the large evidence base in primate behavioral ecology., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Although aggression is associated with several psychiatric disorders, there is no effective treatment nor a rigorous definition for "pathological aggression". Mice make a valuable model for studying aggression. They have a dynamic social structure that depends on the habitat and includes reciprocal interactions between the mice's aggression levels, social dominance hierarchy (SDH), and resource allocation. Nevertheless, the classical behavioral tests for territorial aggression and SDH in mice are reductive and have limited ethological and translational relevance. Recent work has explored the use of semi-natural environments to simultaneously study dominance-related behaviors, resource allocation, and aggressive behavior. Semi-natural setups allow experimental control of the environment combined with manipulations of neural activity. We argue that these setups can help bridge the translational gap in aggression research toward discovering neuronal mechanisms underlying maladaptive aggression., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Social hierarchy is a crucial element for survival, reproduction, fitness, and the maintenance of a stable social group in social animals. This study aimed to investigate the physiological indicators, nociception, unfamiliar female mice preference, spatial learning memory, and contextual fear memory of male mice with different social status in the same cage. Our findings revealed significant differences in the trunk temperature and contextual fear memory between winner and loser mice. However, there were no major discrepancies in body weight, random and fasting blood glucose levels, whisker number, frontal and perianal temperature, spleen size, mechanical and thermal pain thresholds, preference for unfamiliar female mice, and spatial memory. In conclusion, social status can affect mice in multiple ways, and, therefore, its influence should be considered when conducting studies using these animals., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Dominance hierarchies often form between species, especially at common feeding locations. Yet, relative to work focused on the factors that maintain stable dominance hierarchies within species, large-scale analyses of interspecific dominance hierarchies have been comparatively rare. Given that interspecific behavioral interference mediates access to resources, these dominance hierarchies likely play an important and understudied role in community assembly and behavioral evolution. To test alternative hypotheses about the formation and maintenance of interspecific dominance hierarchies, we employ an large, participatory science generated dataset of displacements observed at feeders in North America in the non-breeding season. Consistent with the hypothesis that agonistic interference can be an adaptive response to exploitative competition, we find that species with similar niches are more likely to engage in costly aggression over resources. Among interacting species, we find broad support for the hypothesis that familiarity (measured as fine-scale habitat overlap) predicts adherence to the structure of the dominance hierarchy and reduces aggression between species. Our findings suggest that the previously documented agonistic hierarchy in North American birds emerges from species-level adaptations and learned behaviors that result in the avoidance of costly aggression., (© 2024. The Author(s).)

Dominance rank is a vital descriptor of social dynamics in animal societies and regularly used in studies to explain observed interaction patterns. However, researchers can choose between different indices and standardizations, and can specify dyadic rank relations differently when studying interaction distributions. These researcher degrees of freedom potentially introduce biases into studies and reduce replicability. Here, I demonstrate the impact of researcher choices by comparing the performance of different combinations of rank index, standardization, and model specification when explaining dyadic interaction patterns in sooty mangabeys (Cercocebus atys atys). I show that while no combination consistently performed best across interaction types (aggression, grooming, proximity, supplants), model specifications allowing for nonlinear patterns performed better than other models on average. Choices made in pre-processing and model building impacted model performance and subsequent interpretation of results. Researchers could end up describing social systems differently based on the same data. These results highlight the impact of researcher choices in the processing of behavioural data and potential limitations when using indirect species comparisons in animal behaviour research. To increase repeatability, researchers could make the impact of their processing choices more transparent and report results using a variety of indices and model specifications., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Alexander Mielke. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Social conflict between conspecifics results in the establishment of a hierarchy composed of a winner and loser. A recent study elucidates the molecular mechanism that may underlie the behavioral switch between winner and loser states., Competing Interests: Declaration of interests The author declares no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Dominance hierarchy is a fundamental social phenomenon in a wide range of mammalian species, critically affecting fitness and health. Here, we investigate the role of pheromone signals in the control of social hierarchies and individual personalities within groups of wild mice. For this purpose, we combine high-throughput behavioral phenotyping with computational tools in freely interacting groups of wild house mice, males and females, in an automated, semi-natural system. We show that wild mice form dominance hierarchies in both sexes but use sex-specific strategies, displaying distinct male-typical and female-typical behavioral personalities that were also associated with social ranking. Genetic disabling of VNO-mediated pheromone detection generated opposite behavioral effects within groups, enhancing social interactions in males and reducing them in females. Behavioral personalities in the mutated mice displayed mixtures of male-typical and female-typical behaviors, thus blurring sex differences. In addition, rank-associated personalities were abolished despite the fact that both sexes of mutant mice formed stable hierarchies. These findings suggest that group organization is governed by pheromone-mediated sex-specific neural circuits and pave the way to investigate the mechanisms underlying sexual dimorphism in dominance hierarchies under naturalistic settings., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Dominance-based social hierarchies are common among teleost fishes. The rank of an animal greatly affects its behaviour, physiology and development. The outcome of fights for social dominance is affected by heritable factors and previous social experience. Divergent stress-coping styles have been demonstrated in a large number of teleosts, and fish displaying a proactive coping style have an advantage in fights for social dominance. Coping style has heritable components, but it appears to be largely determined by environmental factors, especially social experience. Agonistic behaviour is controlled by the brain's social decision-making network, and its monoaminergic systems play important roles in modifying the activity of this neuronal network. In this Review, we discuss the development of dominance hierarchies, how social rank is signalled through visual and chemical cues, and the neurobiological mechanisms controlling or correlating with agonistic behaviour. We also consider the effects of social interactions on the welfare of fish reared in captivity., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2022. Published by The Company of Biologists Ltd.)

A century ago, foundational work by Thorleif Schjelderup-Ebbe described a 'pecking order' in chicken societies, where individuals could be ordered according to their ability to exert their influence over their group-mates. Now known as dominance hierarchies, these structures have been shown to influence a plethora of individual characteristics and outcomes, situating dominance research as a pillar of the study of modern social ecology and evolution. Here, we first review some of the major questions that have been answered about dominance hierarchies in the last 100 years. Next, we introduce the contributions to this theme issue and summarize how they provide ongoing insight in the epistemology, physiology and neurobiology, hierarchical structure, and dynamics of dominance. These contributions employ the full range of research approaches available to modern biologists. Cross-cutting themes emerging from these contributions include a focus on cognitive underpinnings of dominance, the application of network-analytical approaches, and the utility of experimental rank manipulations for revealing causal relationships. Reflection on the last 100 years of dominance research reveals how Schjelderup-Ebbe's early ideas and the subsequent research helped drive a shift from an essentialist view of species characteristics to the modern recognition of rich inter-individual variation in social, behavioural and physiological phenotypes. This article is part of the theme issue 'The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies'.

Dominance is important for access to resources. As dominance interactions are costly, individuals should be strategic in whom they interact with. One hypothesis is that individuals should direct costly interactions towards those closest in rank, as they have most to gain-in terms of attaining or maintaining dominance-from winning such interactions. Here, we show that male vulturine guineafowl ( Acryllium vulturinum ), a gregarious species with steep dominance hierarchies, strategically express higher-cost aggressive interactions towards males occupying ranks immediately below themselves in their group's hierarchy. By contrast, lower-cost aggressive interactions are expressed towards group members further down the hierarchy. By directly evaluating differences in the strategic use of higher- and lower-cost aggressive interactions towards competitors, we show that individuals disproportionately use highest-cost interactions-such as chases-towards males found one to three ranks below themselves. Our results support the hypothesis that the costs associated with different interaction types can determine their expression in social groups with steep dominance hierarchies. This article is part of the theme issue 'The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies'.

Thorlief Schjelderup-Ebbe's seminal paper on the 'pecking' order of chickens inspired numerous ethologists to research and debate the phenomenon of dominance. The expansion of dominance to the broader concept of power facilitated disentangling aggression, strength, rank and power. Aggression is only one means of coercing other individuals, and can sometimes highlight a lack of power. The fitness advantages of aggression may only outweigh the costs during periods of uncertainty. Effective instruments of power also include incentives and refusals to act. Moreover, the stability of the power relationship might vary with the instruments used if different means of power vary in the number and types of outcomes achieved, as well as the speed of accomplishing those outcomes. In well-established relationships, actions or physiological responses in the subordinate individual may even be the only indicator of a power differential. A focus on strength, aggression and fighting provides an incomplete understanding of the power landscape that individuals actually experience. Multiple methods for constructing hierarchies exist but greater attention to the implications of the types of data used in these constructions is needed. Many shifts in our understanding of power were foreshadowed in Schjelderup-Ebbe's discussion about deviations from the linear hierarchy in chickens. This article is part of the theme issue 'The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies'.

Objectives: Chimpanzees (Pan troglodytes) are notable for exhibiting high levels of male-to-female aggression. Much of this aggression from adult males serves sexually coercive functions. Despite being smaller and lower-ranking than adult males, adolescent males also engage in regular aggression against adult females. Here, we test whether the primary function of this aggression is sexual coercion, as in adult males, or, alternatively, whether adolescent males use aggression to establish social dominance over females., Materials and Methods: We analyzed 1771 copulations and 1812 instances of male-initiated aggression between adolescent males (aged nine through 14 years) and adult females across 21 years of observation of the Kanyawara chimpanzee community in Kibale National Park, Uganda., Results: Our test of the sexual coercion hypothesis revealed that adolescent males did not selectively target cycling females for aggression, nor did aggression against cycling females predict rates of copulation with those females. Our test of the social dominance hypothesis showed that males succeeded in dominating all adult females before, or soon after, dominating their first adult male. Additionally, we found that adolescent males dominated females approximately in the order of the females' own ranks, from the bottom to the top of the female hierarchy., Discussion: Our data illustrate that the establishment of social dominance was more important than sexual coercion in explaining patterns of adolescent male aggression toward females. In comparison, evidence for sexual coercion was clear and compelling in adult males. These findings highlight that the primary function of male-to-female aggression differs between adolescent and adult males., (© 2021 Wiley Periodicals LLC.)

Context: Dama wallaby (Notamacropus eugenii) and Bennett's wallaby (N. rufogriseus) are invasive pests on the New Zealand mainland and consequently are subject to ongoing control measures that include deployment of toxic baits in feeding stations. Aim: We investigated whether behavioural interactions between wallabies and introduced brushtail possums (Trichosurus vulpecula) at bait feeders are likely to reduce the efficacy of this method for wallaby control. Methods: Wallaby and possum visits and encounters at cereal bait feeders were monitored with trail cameras for several months in dama wallaby habitat near Rotorua, and in Bennett's wallaby habitat in South Canterbury. The response of Bennett's wallabies to possum carcases placed at feeders was also assessed. Key results: The diurnal activity of wallabies and possums at the feeders overlapped extensively, although Bennett's wallabies exhibited more daytime activity than the other two species. Thousands of visits by wallabies and possums were recorded but close encounters between the species at feeders were infrequent (N = 251). When encounters did occur, the wallaby was usually excluded from the feeder (72% of 229 encounters at Titoki Estate, near Rotorua, and 95% of 22 encounters at Blue Cliffs, South Canterbury) regardless of which species arrived at the feeder first. Zero instances of a wallaby excluding a possum from a feeder were recorded. When possum carcases were placed beside feeders, visitations by Bennett's wallabies reduced significantly, by 86% during the first week when a possum carcase was present. This effect was short lived, however, because the carcase soon decayed or was scavenged by other wildlife. Conclusions: Despite their smaller body size, possums are strongly behaviourally dominant over both wallaby species. Consequently, possums may empty feeders of bait before visiting wallabies have an opportunity to feed. Furthermore, interruption and exclusion of feeding wallabies by possums will increase the risk of sublethal toxic dosing and consequent bait shyness. Implications: Since possums are common throughout most wallaby habitat in New Zealand, their dominance behaviour is likely to reduce the efficacy of bait feeder control of wallabies at many sites. Possum population suppression is, therefore, likely to increase the effectiveness of wallaby bait feeder programs but will be costly to achieve. Feeding stations deploying toxic bait are being developed to control invasive dama and Bennett's wallabies on the New Zealand mainland. This field study investigated whether brushtail possums' behaviour affects wallabies' use of such feeders. Despite their smaller size, possums dominated wallabies and often excluded them from feeders. Possum population suppression is likely to improve the success of wallaby bait feeder programs. Photograph by Tim Day. [ABSTRACT FROM AUTHOR]

The article proposes a radical distinction in understanding human aggression and violence. It will seek to comprehend aggression as an inextricable and also valuable part of life. At the same time, it must be shown that human violence has nothing to do with a vital necessity but is a policy based on the assumption and imposition of a hierarchical conception of existence, from which domination and delegitimization relationships are built, devaluing the "subalterns". This perspective will be imposed by force to later be rationalized, normalized, and legitimized to the extent that in many situations violence ceases to be consciously perceived as such. Those who hold power arrogate to themselves the right to define what is to be considered violent and what will not be, imposing on the victims a double submission through the pedagogy of cruelty. [ABSTRACT FROM AUTHOR]

Simple Summary: Animals often inflict bite wounds in laboratory housing, compromising animal welfare and, potentially, experimental results. For example, 1.5–14% of male laboratory mice (Mus musculus) obtain bite wounds over the course of a year. Recently, spiny mice (Acomys cahirinus) have become more popular in laboratory research for their regenerative healing and menstrual cycling, but we noticed frequent severe wounding in males and females in our colony—likely related to their relatively weak skin. Thus, we recorded the frequency and severity of bite wounding in our colony for one year and found that 46% of spiny mice had at least one bite wound, regardless of sex. The bite wounds in females were less severe, with single wounds on the rump, while males more often had multiple wounds on their anterior and rump. In a separate study, both sexes established stable dominance structures, with most of the fights occurring at the start of the active/dark cycle. Aged animals greater than 22 months old were never observed fighting, and the study on bite wounding suggested they also do not inflict bite wounds. These results have implications for both spiny mouse welfare and experimental results using spiny mice since repeated physical trauma can affect healing and menstrual cycling in mice and humans. Bite wounds due to aggression in male laboratory mice (Mus musculus) are a major welfare concern, often leading to attrition, chronic activation of the innate immune system, and significant impacts on the experimental results derived from the use of these animals as models. Bite wounding within the home-cage of spiny mice (Acomys cahirinus)—a valuable research model for wound healing and menstruation—is poorly characterized. While we have anecdotally observed frequent bite wounding in Acomys, the frequency of aggression within the home-cage, the severity of the bite wounds, and the types of dominance structures remain unstudied. Here, we report that 46% of Acomys cages in our colony had at least one bite wound over the course of a year and that same-sex pairs fought in the home-cage 10% of the time during their dark/active phase. Both sexes inflicted wounds and frequently engaged in agonistic behaviors, even with stable dominance structures. We found that females inflicted less severe bite wounds in same-sex housing. Also, aged females in same-sex pairs were never observed fighting, and no bite wounds were observed in aged Acomys. These results suggest that we should consider whether bite wounding negatively impacts our experimental results since physical trauma is known to alter menstrual cycling and healing. [ABSTRACT FROM AUTHOR]

The current study explored a form of femmephobia (specifically, negative attitudes toward femininity in men) as a predictor of anti-gay behaviors among a sample of heterosexual men (N = 417). Additional predictor variables included hierarchical worldviews (i.e., social dominance orientation, right-wing authoritarianism, narcissism) and prejudicial attitudes (i.e., old-fashioned and modern homonegativity). Femmephobia emerged as a robust predictor, accounting for 23% of the variance in anti-gay behavior, surpassing the explanatory power (15%) of all other considered variables combined. Moreover, social dominance only predicted anti-gay behavior when femmephobia levels were high. Future research on discrimination and violence related to sexual identity and gender expression should incorporate femmephobia as a key predictive factor. [ABSTRACT FROM AUTHOR]

Forming groups of captive rhesus macaques (Macaca mulatta) is a common management practice. New formations of unfamiliar macaques can be costly, with high levels of trauma, particularly as intense aggression is used to establish a dominance hierarchy. Combining previous subgroups into one new group may be beneficial, as some individuals already have established dominance relationships. We tested this hypothesis by forming a new mixed-sex group of rhesus macaques that combined an established group of females with an established group of males. Prior to the mixed-sex group formation, both the female and male hierarchies had been stable for 3 y; after mixed-sex group formation these hierarchies were maintained by the females and were initially maintained by the males for 3 wks. However, the temporary hospitalization (due to a laceration caused by aggression) of the alpha male destabilized the male hierarchy. Age and weight then predicted male rank. Temporary hospitalizations resulted in rank changes for the males, evidenced by reversals in subordination signals. This study indicates that using established groups of familiar individuals may maintain female hierarchical stability in a mixedsex group formation, but further research is needed to understand how to maintain and predict male hierarchical stability to reduce trauma. Improved knowledge of hierarchical stability would be invaluable to managers of large rhesus macaque groups and would help improve the welfare of captive rhesus macaques.

The current study investigated the relationship between social dominance orientation (SDO), aggression, sense of superiority, external value and meaning in life (MIL) in a sample of 291 college students. Results showed that SDO and aggression positively correlated with sense of superiority and external value. Mediating effect analysis revealed that SDO could satisfied an individual's external value through the mediating role of sense of superiority or the chain mediating role of aggression and sense of superiority, thus enabling people to experience MIL. These results play an important role in understanding MIL. External value may be the most important source of an individual's MIL. All behaviors that help individuals obtain external values can enable them to acquire MIL, even if some of these behaviors violate the moral rules that society upholds. [ABSTRACT FROM AUTHOR]

Within social dominance hierarchies, rank has a major impact on health and fitness. Dominance hierarchies are rarely stable as individuals may change rank due to changes in the social environment. Here we describe general group-level social network properties and changes in social ties and behavior during rank transitions in 16 communities of the cichlid Astatotilapia burtoni. Social networks based on chases were dense with dominant males frequently chasing subordinate males and females. This intense territoriality of dominant males was also reflected by a high degree of 'power' inequality. Compared to chase-based networks, display-based networks were characterized by a high degree of reciprocity due to display behaviors mostly occurring bidirectionally among a few highly ranked males. Territory ownership is tightly linked to social dominance and territory loss (i.e., social descent) was, as expected, associated with a sharp reduction in aggression level and an increase in chases received. However, although territory acquisition (i.e., social ascent) was an abrupt process, ascending males displayed elevated aggression prior to ascent, in sharp contrast to previous studies carried out in less complex settings. Together, our results provide novel insights into dynamic changes in behavior in cichlid dominance hierarchies. [ABSTRACT FROM AUTHOR]

Dominance relationships between males and their associated traits are usually heritable and have implications for sexual selection in animals. In particular, social dominance and its related male pheromones are heritable in inbred mice; thus, we wondered whether epigenetic changes due to altered levels of DNA methylation determine inheritance. Here, we used C57BL/6 male mice to establish a social dominance–subordination relationship through chronic dyadic encounters, and this relationship and pheromone covariation occurred in their offspring, indicative of heritability. Through transcriptome sequencing and whole-genome DNA methylation profiling of the sperm of both generations, we found that differential methylation of many genes was induced by social dominance–subordination in sires and could be passed on to the offspring. These methylated genes were mainly related to growth and development processes, neurodevelopment, and cellular transportation. The expression of the genes with similar functions in whole-genome methylation/bisulfite sequencing was also differentiated by social dominance–subordination, as revealed by RNA-seq. In particular, the gene Dennd1a, which regulates neural signaling, was differentially methylated and expressed in the sperm and medial prefrontal cortex in paired males before and after dominance–subordination establishment, suggesting the potential epigenetic control and inheritance of social dominance-related aggression. We suggest that social dominance might be passed on to male offspring through sperm DNA methylation and that the differences could potentially affect male competition in offspring by affecting the development of the nervous system. [ABSTRACT FROM AUTHOR]

Interspecific dominance interactions have consequences for behavior, ecology, and the stability of species coexistence. Determinants of the outcomes of these interspecific interactions are therefore of great interest. However, few large-scale comparative works have demarcated the potential behavioral and morphological traits that explain dominance between species. To delineate which traits may influence species dominance, we rely on a newly established dominance ranking of bird species in North America. We pair these dominance rankings with phylogenetic analysis and incorporate social, morphological, and natural history variables to determine how morphological and social traits contribute. Like previous studies, we find that body mass is a positive predictor of dominance, but we also find that after controlling for body mass, bill length positively predicts a species' rank in the hierarchy. In addition to morphological traits, we find that species that engage in proportionally more intraspecific fights tend to be less interspecifically dominant. Consequently, both morphological and social variables influence the interspecific dominance rank of a species. Such effects may have downstream consequences for the acquisition of foraging resources and the evolution of a species. [ABSTRACT FROM AUTHOR]

Simple Summary: When male mice are kept in groups at animal facilities, aggressive interactions between cage mates are not uncommon. Systematically reviewing previous studies that explored the cause of male mice aggression, we found that studies were disparate, using several different strains, a diverse set of environmental enrichments and different ways of grouping and housing mice, as well as different ways to observe aggression. Understanding the cause of male mice aggression is difficult when researchers use different methods and study designs. Nevertheless, our results suggest that home cage aggression is best studied in home cage environments and not by introducing unfamiliar mice to each other in a novel environment. In addition, while we were able to provide recommendations on how to minimize aggression, our assessment was that there is no universal solution that could be used by all animal facilities. Instead, it is important to realize that aggression is complex and that animal facilities might have to try different possible solutions to find what works best under their specific conditions. Aggression among group-housed male mice is a major animal welfare concern often observed at animal facilities. Studies designed to understand the causes of male mice aggression have used different methodological approaches and have been heterogeneous, using different strains, environmental enrichments, housing conditions, group formations and durations. By conducting a systematic literature review based on 198 observed conclusions from 90 articles, we showed that the methodological approach used to study aggression was relevant for the outcome and suggested that home cage observations were better when studying home cage aggression than tests provoking aggression outside the home cage. The study further revealed that aggression is a complex problem; one solution will not be appropriate for all animal facilities and all research projects. Recommendations were provided on promising tools to minimize aggression, based on the results, which included what type of environmental enrichments could be appropriate and which strains of male mice were less likely to be aggressive. [ABSTRACT FROM AUTHOR]

Bite wounds due to aggression in male laboratory mice (Mus musculus) are a major welfare concern, often leading to attrition, chronic activation of the innate immune system, and significant impacts on the experimental results derived from the use of these animals as models. Bite wounding within the home-cage of spiny mice (Acomys cahirinus)—a valuable research model for wound healing and menstruation—is poorly characterized. While we have anecdotally observed frequent bite wounding in Acomys, the frequency of aggression within the home-cage, the severity of the bite wounds, and the types of dominance structures remain unstudied. Here, we report that 46% of Acomys cages in our colony had at least one bite wound over the course of a year and that same-sex pairs fought in the home-cage 10% of the time during their dark/active phase. Both sexes inflicted wounds and frequently engaged in agonistic behaviors, even with stable dominance structures. We found that females inflicted less severe bite wounds in same-sex housing. Also, aged females in same-sex pairs were never observed fighting, and no bite wounds were observed in aged Acomys. These results suggest that we should consider whether bite wounding negatively impacts our experimental results since physical trauma is known to alter menstrual cycling and healing.

Social stress is a negative emotional experience that can increase fear and anxiety. Dominance status can alter the way individuals react to and cope with stressful events. The underlying neurobiology of how social dominance produces stress resistance remains elusive, although experience-dependent changes in androgen receptor (AR) expression is thought to play an essential role. Using a Syrian hamster (Mesocricetus auratus) model, we investigated whether dominant individuals activate more AR-expressing neurons in the posterior dorsal and posterior ventral regions of the medial amygdala (MePD, MePV), and display less social anxiety-like behavior following social defeat stress compared to subordinate counterparts. We allowed male hamsters to form and maintain a dyadic dominance relationship for 12 days, exposed them to social defeat stress, and then tested their approach-avoidance behavior using a social avoidance test. During social defeat stress, dominant subjects showed a longer latency to submit and greater c-Fos expression in AR+ cells in the MePD/MePV compared to subordinates. We found that social defeat exposure reduced the amount of time animals spent interacting with a novel conspecific 24 h later, although there was no effect of dominance status. The amount of social vigilance shown by dominants during social avoidance testing was positively correlated with c-Fos expression in AR+ cells in the MePV. These findings indicate that dominant hamsters show greater neural activity in AR+ cells in the MePV during social defeat compared to their subordinate counterparts, and this pattern of neural activity correlates with their proactive coping response. Consistent with the central role of androgens in experience-dependent changes in aggression, activation of AR+ cells in the MePD/MePV contributes to experience-dependent changes in stress-related behavior. • Social dominance increases stress-induced cFos expression in AR+ MePD/MePV neurons. • Proactive coping is associated with greater neural activity in AR+ MePV neurons. • Subordinates show reduced activity in MePD/MePV cells during avoidance testing. • c-Fos expression in AR+ MePV neurons predicts social vigilance. • AR+ cells in MePD/MePV modulate experience-dependent changes in stress behavior. [ABSTRACT FROM AUTHOR]

Antisocial behavior in childhood and adolescence is associated with poor family and peer relationships, and a higher risk of mental and physical health problems in adulthood, as well as criminality. Emotions play a central role in children’s moral development, but most research has focused on negative emotions (e.g., shame and guilt), in relation to childhood antisocial behavior. Research in adult populations indicates that positive emotions experienced in anticipation of, during, and after antisocial acts may play an important role in the development and maintenance of antisocial behavior. Consequently, this systematic review aimed to investigate the relationship between positive emotion and antisocial behavior in children and adolescents. A systematic search in five databases was conducted, yielding 52 studies that used different methodological approaches, samples, designs and methods to examine this association. Results provide support for a positive relationship between positive emotion and antisocial behavior across community, forensic and clinical samples. This link appeared to be stronger for younger children, boys, and for children high in social dominance, callous-unemotional or sensation-seeking traits. Results suggested that positive affect may act in concert with negative emotion, cognitive, personality and motivational processes, as well as peer influences to determine the initiation and maintenance of antisocial behavior. This review presents directions for future research and discusses the implications of findings for prevention and intervention programs for youth with antisocial behavior. [ABSTRACT FROM AUTHOR]

Masculine facial morphology (e.g., larger jaw, prominent cheekbones) have been linked to a suite of social outcomes—including greater wealth, career progress, romantic desirability, and even greater political success. A leading explanation for these links is that dominant facial structures represent honest cues of physical dominance and fighting ability. Třebický et al. (2013) published the first study to demonstrate that masculine facial cues (e.g., large nose, deep-set eyes) similarly predict both dominance judgments and real-world fighting success, but no studies have replicated these popular findings that a large and specific assortment of masculine facial structures are implicated in both fighting ability and dominance perception. Thus, we conducted a pre-registered direct replication and extension of Třebický et al. (2013). Two separate samples of United States MTurk participants rated 516 UFC fighters' facial photographs on perceived aggressiveness (N = 500) and fighting ability (N = 500). Results showed that perceived aggressiveness was associated with masculine facial morphology (e.g., large nose, deep-set eyes) independent of bodily size. There was also some evidence that perceived fighting ability was associated with masculine facial morphology, which disappeared after controlling for bodily size. There was no support for the relation between facial structure and fighting success, and there were often negative relations between perceived aggressiveness and fighting ability on fighting success (i.e., more successful fighters were perceived as less successful and aggressive). We argue that our evolved psychology differentially processes the distinct avenues to victory that constitute overall fighting success (e.g., knockout versus submission wins). [ABSTRACT FROM AUTHOR]

Since the Kremlin made arguments from the historical past the main justification for aggression against Ukraine, it is important to study the connection between historical policy and the security policy of the Russian Federation. The purpose of the article. Recreate the image of an independent Ukraine in the Russian political vision, highlight the process of interaction of the historical policy of the Russian Federation with security policy through the dominance of military themes and show the use of history as a component of the anti-Ukrainian policy of the Kremlin and an argument for the legitimization of aggression against Ukraine. It was concluded that with the emergence of independent Ukraine as a result of the collapse of the USSR, Russia did not perceive it as a «real state». With the coming to power of V. Putin, a course was taken to restore the geopolitical dominance of Russia, in which Ukraine occupied a key place. In Putin’s Russia, history and historical memory are given great political importance. Great-power political practices were legitimized by historical arguments, and historical politics became an important part of Russia’s security policy. It was securitized and militarized and turned into an element of the Kremlin’s manipulative activity and justification of Russian aggression against Ukraine. [ABSTRACT FROM AUTHOR]

Group-living primates exhibit variable reactions to intergroup encounters (or IGEs), reflecting species-specific strategies and individual motivations. In chimpanzees (Pan troglodytes), dominating in IGEs provides fitness benefits. Less is known about responses to IGEs in bonobos (Pan paniscus) despite their equal relevance for understanding the origins of human intergroup relations. We observed the Bompusa West (WBp) bonobo community at LuiKotale during a 2-month shift in ranging resulting in frequent IGEs with the smaller Bompusa East (EBp) community. We tested whether incursions provided ecological benefits, and whether responses to IGEs were consistent with inter-community dominance or tolerance. We measured fruit availability and collected activity scans from 26 mature WBp community members when in their core ranging area, during incursions into the EBp ranging area, and during IGEs. We collected data on sexual interactions and aggression with in-group and out-group members during 19 independent IGEs. During their shift in ranging, fruit availability was greater in the EBp ranging area, and WBp bonobos consumed more fruit during incursions than when in their core ranging area. Coalitionary intergroup aggression occurred during nine IGEs, and outcomes were consistent with imbalances in fighting power, in that larger WBp parties supplanted smaller EBp parties from the immediate area. However, communities reformed associations following 70% of coalitionary conflicts, and prolonged IGEs facilitated out-group sexual interactions and female transfers. The WBp community shift in ranging was likely motivated by ecological factors and responses to increased IGEs reflected a mixture of competitive and tolerant strategies. [ABSTRACT FROM AUTHOR]

Social hierarchies are often found in group‐living animals and can be formed through pairwise aggressive interactions. The dominance rank can influence reproductive success (RS) with a skew towards high‐ranking individuals.Using game theory, we investigate how the opportunity for differently ranked individuals to achieve RS influences the costs of hierarchy formation and the strength of winner and loser effects.In our model, individuals adjust their aggressive and submissive behaviour towards others through reinforcement learning. The learning is based on rewards and penalties, which depend on relative fighting ability. From individual‐based simulations, we determine evolutionary equilibria of traits such as learning rates. We examine situations that differ in the extent of monopolisation of contested RS by dominants and in the proportion of total RS that is contested.The model implements two kinds of fighting costs: a decrease in effective fighting ability from damage (loss of condition) and a risk of mortality that increases with the total accumulated damage. Either of these costs can limit the amount of fighting.We find that individuals form stable dominance hierarchies, with a positive correlation between dominance position and fighting ability. The accumulated costs differ between dominance positions, with the highest costs paid by low or intermediately ranked individuals. Costs tend to be higher in high‐skew situations.We identify a 'stay‐in, opt‐out' syndrome, comprising a range from weaker (stay‐in) to stronger (opt‐out) winner–loser effects. We interpret the opt‐out phenotype to be favoured by selection on lower ranked individuals to opt out of contests over social dominance, because it is more pronounced when more of the total RS is uncontested.We discuss our results in relation to field and experimental observations and argue that there is a need for empirical investigation of the behaviour and reproductive success of lower ranked individuals. [ABSTRACT FROM AUTHOR]

Methamphetamine (METH) abuse is associated with a spectrum of behavioral consequences, among which heightened aggression presents a significant challenge. However, the causal role of METH's impact in aggression and its target circuit mechanisms remains largely unknown. We established an acute METH exposure-aggression mouse model to investigate the role of ventral tegmental area (VTA) dopaminergic neurons and ventral medial hypothalamus VMH glutamatergic neuron. Our findings revealed that METH-induced VTA dopamine excitability activates the ventromedial hypothalamus (VMH) glutamatergic neurons, contributing to pathological aggression. Notably, we uncovered a dopaminergic transmission within the VTA-VMH circuit that exclusively functioned under METH influence. This dopaminergic pathway emerged as a potential key player in enabling dopamine-related pathological aggression, with heightened dopaminergic excitability implicated in various psychiatric symptoms. Also, the modulatory function of this pathway opens new possibilities for targeted therapeutic strategies for intervention to improve treatment in METH abuse and may have broader implications for addressing pathological aggression syndromes. • Elevated VTA dopaminergic excitability emerges as a key contributor to METH-induced aggression. • Dopamine presence in the VMH is exclusive to METH influence. • The VTA-VMH circuit is engaged, playing a dual role in both the development and modulation of METH-induced aggression. [ABSTRACT FROM AUTHOR]

Strong, stable social bonds in primates are characterized by high levels of social affiliation, low levels of aggression, minimal stress, and affiliative reciprocity within the dyad. In relatively well‐studied catarrhine monkeys, these bonds tend to form most frequently between kin, animals close in age, and animals close in rank. This results in patterns of affiliation in which kin, similarly aged animals, and like‐ranked animals tend to affiliate and patterns of aggression and submission where animals tend to aggress more toward nonkin and closely ranked animals, and submit more toward distantly ranked animals. However, literature on how affiliative and agonistic relationships are organized in platyrrhine primate species like brown capuchin monkeys is limited and conflicting. In this study, we used social network analyses to characterize how age, sex, maternal kinship, and dominance rank relate to the patterns of submissive, aggressive, contact, and grooming interactions in a group of captive brown capuchin monkeys. Like catarrhine monkeys, brown capuchin monkeys showed a steep linear dominance hierarchy, tended to affiliate with kin, similarly aged animals, and like‐ranked animals, and tended to aggress more toward nonkin. However, our monkeys showed a pattern of affiliation and grooming down the hierarchy that is inconsistent with grooming up the hierarchy patterns often seen in catarrhine monkey groups, suggesting that brown capuchins do not compete for access to higher ranking social partners. Higher ranking monkeys were most central to the aggression network, and lower ranking monkeys were most central to the submission network. Mid‐ranking monkeys were the most central to the contact network, suggesting that they may play an important role in the affiliative cohesion of the group. These results inform our understanding of brown capuchin social behavior specifically, and of how demographic factors relate to social organization in platyrrhine primates generally. Highlights: Captive brown capuchins show a steep linear dominance hierarchy.Rank differentially predicts who is the most central across networks: High‐rankers for aggression, low‐rankers for submission, & mid‐rankers for contact.They affiliate with kin, similarly aged and like‐ranked animals, & aggress to nonkin. [ABSTRACT FROM AUTHOR]

Why some people, and not others, exhibit aggression remains unknown. Research points to certain personality traits being linked to either proactive or reactive aggression, or both. The current study attempts to address these gaps from the perspective of revised Reinforcement Sensitivity Theory (rRST). Using 146 participants, results revealed Behavioral Approach System (BAS)-Impulsivity and the Behavioral Inhibition System (BIS) predicted proactive and reactive aggression. Defensive Fight predicted reactive aggression. BAS-Impulsivity predicted proactive aggression partially mediated by Social Dominance Orientation. These findings suggest proactive and reactive aggression are motivated by a combination of anxiety and rapid, approach-motivational personality traits. This study provides further understanding of the specific relations between rRST and aggression, is integrated into the general aggression model, and has implications for treatment of aggressive individuals. [ABSTRACT FROM AUTHOR]

Dominance behaviours have been collected for many groups of animals since 1922 and serve as a foundation for research on social behaviour and social structure. Despite a wealth of data from the last century of research on dominance hierarchies, these data are only rarely used for comparative insight. Here, we aim to facilitate comparative studies of the structure and function of dominance hierarchies by compiling published dominance interaction datasets from the last 100 years of work. This compiled archive includes 436 datasets from 190 studies of 367 unique groups (mean group size 13.8, s.d. = 13.4) of 135 different species, totalling over 243 000 interactions. These data are presented in an R package alongside relevant metadata and a tool for subsetting the archive based on biological or methodological criteria. In this paper, we explain how to use the archive, discuss potential limitations of the data, and reflect on best practices in publishing dominance data based on our experience in assembling this dataset. This archive will serve as an important resource for future comparative studies and will promote the development of general unifying theories of dominance in behavioural ecology that can be grounded in testing with empirical data. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’. [ABSTRACT FROM AUTHOR]

Animal groups are often organized hierarchically, with dominant individuals gaining priority access to resources and reproduction over subordinate individuals. Initial dominance hierarchy formation may be influenced by multiple interacting factors, including an animal’s individual attributes, conventions and self-organizing social dynamics. After establishment, hierarchies are typically maintained over the long-term because individuals save time, energy and reduce the risk of injury by recognizing and abiding by established dominance relationships. A separate set of behaviours are used to maintain dominance relationships within groups, including behaviours that stabilize ranks (punishment, threats, behavioural asymmetry), as well as signals that provide information about dominance rank (individual identity signals, signals of dominance). In this review, we describe the behaviours used to establish and maintain dominance hierarchies across different taxa and types of societies. We also review opportunities for future research including: testing how self-organizing behavioural dynamics interact with other factors to mediate dominance hierarchy formation, measuring the long-term stability of social hierarchies and the factors that disrupt hierarchy stability, incorporating phenotypic plasticity into our understanding of the behavioural dynamics of hierarchies and considering how cognition coevolves with the behaviours used to establish and maintain hierarchies. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’. [ABSTRACT FROM AUTHOR]

A major challenge in the study of animal communication is distinguishing whether signals convey honest or dishonest information. Biologists infer the honesty of a signal from its correlation with the information being signalled (e.g. fecundity or fighting ability)—the better the correlation, the more honest the signal.However, this view of signalling potentially conflates unreliable indicators with dishonest signals. Just because a trait conveys unreliable information does not mean that the structure serves as a dishonest signal; developmental noise, genetic drift and environmental constraints can reduce the covariation between a putative signal and an organism's quality. Moreover, a trait must influence the behaviour of other organisms to qualify as a signal.We studied how a putative signal, claw size, affects physical performance and social dominance in three species of stream‐dwelling crayfish, which fight routinely over resources. For comparison, we measured the relationship between claw size and claw strength in three species of burrowing crayfish, which do not fight.In all species, crayfish with larger claws were not necessarily stronger, indicating that claw size poorly indicates claw strength. However, claw size is unlikely to function as a dishonest signal of fighting ability in these species for two reasons. First, claw size unreliably indicates claw strength in both the stream‐dwelling species and the burrowing species. Second, relative claw size poorly predicted whether stream‐dwelling crayfish would escalate aggression, questioning whether claw size serves as a signal. Instead, stream‐dwelling crayfish escalated aggression based on their relative body size.Our results highlight the importance of observing behaviour when determining the honesty of a signal. As such, future studies must distinguish between phenotypes that are unreliable indicators (or reliable indicators) from phenotypes that have been selected for dishonest (or honest) signalling. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Invasive species are one of the greatest threats to freshwater ecosystems globally. However, the causal mechanisms that drive negative impacts of many invasive species are poorly understood. In Tanzania, non-native Nile tilapia (Oreochromis niloticus) exists in sympatry with a diverse range of native species, many of which are congenerics with strong niche overlap. It has been suggested that O. niloticus can displace native species from preferred habitat through dominance during interference competition, yet interference competition between O. niloticus and a native tilapia species has never been directly tested under experimental conditions. In this study juvenile O. niloticus and Manyara tilapia (Oreochromis amphimelas), a functionally similar but endangered Tanzanian cichlid, were size matched in conspecific and heterospecific pairs. We presented pairs with limited shelter and recorded competitive interactions. We found that O. niloticus were more aggressive and faster to initiate agonistic interactions than O. amphimelas. Furthermore, O. niloticus showed a strong competitive dominance in their interactions with O. amphimelas. One-sided dominance hierarchies can drive fundamental changes in resource use by subordinate individuals, potentially resulting in habitat displacement over the long term. Based on this experimental evidence, we conclude that O. niloticus may threaten native tilapia species through dominance in interference competition. [ABSTRACT FROM AUTHOR]

• Hamsters show sex differences in the formation of dominance relationships. • Dominance relationships are less stable in female compared to male hamsters. • Dominance status creates sex differences in status-dependent neural plasticity. Dominance relationships are identified by changes in agonistic behavior toward specific individuals. While there are considerable individual and species differences in dominance relationships, sex differences are poorly understood in rodent models because aggression among female rodents is rare. The aim of this study was to characterize sex differences in the formation and maintenance of dominance relationships in same-sex pairs of male and female Syrian hamsters. We pooled data from multiple projects in our lab to evaluate dominance interactions in 68 male dyads and 88 female dyads. In each project, animals were matched with a partner similar in age, sex, and estrous cycle and we exposed animals to daily social encounters for two weeks in a resident-intruder format. We found that female hamsters were quicker to attack and attacked at higher rates compared to males regardless of dominance status. In addition, resident female hamsters were quicker to attack and attacked at higher rates than intruder females, but aggression in males did not depend on residency status. Female subordinates were quicker to submit and fled at higher rates from their dominant counterparts compared to male subordinates. Intruder subordinate females were quicker to submit and fled at higher rates than resident subordinate females. Females were also more resistant than males to becoming subordinate in that they fought back more consistently and were more likely to reverse their dominance status. These findings indicate that dominance relationships are less stable in females compared to males and that residency status has a larger impact on agonistic behavior in females than males. Overall, differences in how males and females display territorial aggression can lead to sex differences in the establishment and maintenance of dominance relationships. [ABSTRACT FROM AUTHOR]

This narrative review article summarizes the current state of knowledge regarding the relationship between the endocannabinoid system (ECS) and aggression across multiple vertebrate species. Experimental evidence indicates that acute administration of phytocannabinoids, synthetic cannabinoids, and the pharmacological enhancement of endocannabinoid signaling decreases aggressive behavior in several animal models. However, research on the chronic effects of cannabinoids on animal aggression has yielded inconsistent findings, indicating a need for further investigation. Cannabinoid receptors, particularly cannabinoid receptor type 1, appear to be an important part of the endogenous mechanism involved in the dampening of aggressive behavior. Overall, this review underscores the importance of the ECS in regulating aggressive behavior and provides a foundation for future research in this area. • Endocannabinoid system plays a role in aggression as demonstrated by pharmacological and genetic manipulations. • Acute activation of cannabinoid receptors reduces aggression in multiple vertebrate species. • Chronic treatment with cannabinoids on animal aggression has yielded inconsistent findings. • Evidence suggests that CB1 receptors play a role in brain process responsible for dampening aggressive behavior. [ABSTRACT FROM AUTHOR]