Trait aggressiveness does not predict social dominance of rats in the Visible Burrow System

Social conflict: Illuminating the great resignation

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.

Manifestations of domination: Assessments of social dominance in rodents

Social hierarchies are ubiquitous features of virtually all animal groups. The varying social ranks of members within these groups have profound effects on both physical and emotional health, with lower-ranked individuals typically being the most adversely affected by their respective ranks. Thus, reliable measures of social dominance in preclinical rodent models are necessary to better understand the effects of an individual's social rank on other behaviors and physiological processes. In this review, we outline the primary methodologies used to assess social dominance in various rodent species: those that are based on analyses of agonistic behaviors, and those that are based on resource competition. In synthesizing this review, we conclude that assays based on resource competition may be better suited to characterize social dominance in a wider variety of rodent species and strains, and in both males and females. Lastly, albeit expectedly, we demonstrate that similarly to many other areas of preclinical research, studies incorporating female subjects are lacking in comparison to those using males. These findings emphasize the need for an increased number of studies assessing social dominance in females to form a more comprehensive understanding of this behavioral phenomenon.

Spatial working memory is disparately interrelated with social status through different developmental stages in rats

Social life necessitates cognitive competence to meet the dynamic demands of social development. The formation of dominance hierarchy is a general phenomenon in social groups. As an essential element of executive and cognitive function, working memory could influence and be influenced by social status in a dominance hierarchy. However, the direction and degree of the association between them through different developmental stages remain unclear. To address this issue and clarify the "cause or consequence" problem, we investigated the spatial working memory performance in a Y-maze and Morris water maze in home-caged sibling Wistar rats (N = 26 cages, three rats/cage) through three stages of their life: before (week 7), during (week 10), and after (week 20) assumed timings of the social dominance hierarchy formation (SDHF). We used the social dominance tube test during the assumed time of hierarchy formation (weeks 9-11) to measure the relative dominance status in each cage. Here, we found that higher working memory index before SDHF could be predictive of later acquisition of higher social status. Working memory performance declined for all animals during SDHF, in which agonistic conflicts are increased. However, living within an established hierarchical social network for several weeks deteriorated the working memory performance of dominant and middle-ranked animals, while the performance of subordinates improved and got significantly better than higher-ranked animals. In conclusion, while working memory and social status were correlated positively before dominance hierarchy formation, there was a trade-off between them after the formation of it. In contrast to the common view, these results highlight the adverse effect of higher social status on cognitive behavior.

Multidimensional nature of dominant behavior: Insights from behavioral neuroscience

Social interactions for many species of animals are critical for survival, wellbeing, and reproduction. Optimal navigation of a social system increases chances for survival and reproduction, therefore there is strong incentive to fit into social structures. Social animals rely heavily on dominant-submissive behaviors in establishment of stable social hierarchies. There is a link between extreme manifestation of dominance/submissiveness and behavioral deviations. To understand neural substrates affiliated with a specific hierarchical rank, there is a real need for reliable animal behavioral models. Different paradigms have been consolidated over time to study the neurobiology of social rank behavior in a standardized manner using rodent models to unravel the neural pathways and substrates involved in normal and abnormal intraspecific social interactions. This review summarizes and discusses the commonly used behavioral tests and new directions for the assessment of dominance in rodents. We discuss the hierarchy inheritable nature and other critical issues regarding hierarchical rank manifestation which may help in designing social-rank-related studies that serve as promising pre-clinical tools in behavioral psychiatry.

Let's get wild: A review of free-ranging rat assays as context-enriched supplements to traditional laboratory models

More than 24,000 rodent studies are published annually, with the vast majority of these studies focused on genetically undiverse animals in highly-controlled laboratory settings. However, findings from the laboratory have become increasingly unreliable for predicting outcomes in field and clinical settings, leading to a perceived crisis in translational research. One cause of this disparity might be that most human societies, in contrast to laboratory rodents, are genetically diverse and live in super-enriched environments. Methods for importing wild rats into the laboratory, and also exporting laboratory-style chambers into natural environments are not well-known outside their respective disciplines. Therefore, we have reviewed the current status of supplements to the laboratory rodent assay. We progress logically from highly-controlled experiments with natural breeding colonies to purely naturalistic approaches with free-ranging rats. We then highlight a number of approaches that allow genetically-diverse wild rats to be utilized in context-enriched paradigms. While considering the benefits and shortcomings of each available approach, we detail protocols for random sampling, remote-sensing, and deployment of laboratory chambers in the field. As supplements to standardized laboratory trials, some of these assays could offer key insights to help unify outcomes between laboratory and field studies. However, we note several outstanding questions that must be addressed such as: the trade-off between control and context, possible reductions in sample size, ramifications for the 'standardization fallacy', and ethical dilemmas of working with wild animals. Given these challenges, further innovation will be required before supplemental assays can be made broadly-accessible and thus, transferrable across disciplines.

The bullies are the leaders of the next generation: Inherited aminergic neurotransmitter system changes in socially dominant zebrafish, Danio rerio

We studied the social hierarchy in zebrafish and assessed differences in neurotransmitters and behavior in the F1 generation offspring of dominant and subordinate zebrafish (Danio rerio). We used behavioral assays to study locomotion, ability to complete cognitive tasks, social interaction and aggression. To study the neurochemical changes, we applied quantitative polymerase chain reaction, high pressure liquid chromatography and immunohistochemistry. Social hierarchies were formed both by males and females when animals were kept in same sex pairs in the dyadic dominant-subordinate hierarchy test. The offspring of dominant animals were the leaders in social interactions, however aggression in the mirror-test was not altered in any group. Serotonin and noradrenaline levels were lower in the F1 generation subordinate animals when compared with dominant animals, but not compared with animals that were naïve to social hierarchy. The mRNA level of the rate-limiting enzyme in histamine synthesis, histidine decarboxylase, was significantly lower in dominant and subordinate larval zebrafish when compared with control animals. In the dominant adult zebrafish tyrosine hydroxylase 1 mRNA level was lower compared with control animals, whereas tyrosine hydroxylase 2 mRNA was not different. The result was verified with immunohistochemistry. There were gender specific differences between the dominant and subordinate animals, where the dominant females performed better in cognitive tasks such as the T-maze than subordinate females. This was not observed in males, as the behavior of the dominant and subordinate males did not differ. These results add to the understanding of the plastic nature of the central nervous system and show that neurochemical features in aminergic neurotransmitter systems are associated with social leadership and dominance.

Stress in groups: Lessons from non-traditional rodent species and housing models

A major feature of life in groups is that individuals experience social stressors of varying intensity and type. Social stress can have profound effects on health, social behavior, and ongoing relationships. Relationships can also buffer the experience of exogenous stressors. Social stress has most commonly been investigated in dyadic contexts in mice and rats that produce intense stress. Here we review findings from studies of diverse rodents and non-traditional group housing paradigms, focusing on laboratory studies of mice and rats housed in visible burrow systems, prairie and meadow voles, and mole-rats. We argue that the use of methods informed by the natural ecology of rodent species provides novel insights into the relationship between social stress, behavior and physiology. In particular, we describe how this ethologically inspired approach reveals how individuals vary in their experience of and response to social stress, and how ecological and social contexts impact the effects of stress. Social stress induces adaptive changes, as well as long-term disruptive effects on behavior and physiology.

Morphological Correlates of Personality in Female Asian Particolored Bats (Vespertilio sinensis)

Simple Summary

Personality emerges because of individual differences in repeatable state variables, such as metabolic rate, age, sex, or body size. Personality and its correlation with body size, however, have been relatively unexplored in bats. Our study showed that the exploration of female Asian particolored bats was significantly repeatable, but we did not find significant correlations among exploration, activity, and aggression. This finding suggested that female Asian particolored bats may not have a behavioral syndrome. Additionally, the body mass of female Asian particolored bats was correlated with aggression and activity, suggesting that body mass may have an impact on the behavioral characteristics of bats. Our findings not only added to the literature concerning personality in bats but are also helpful for understanding the maintenance of an animal’s personality.

Abstract

Personality traits represent a leading edge in the evolutionary process, as natural selection acts directly on variations in individual phenotypes within populations. Recent theoretical models have focused on the concept of adaptive state-dependent behavior, proposing that repeatable differences in behavior emerge because of individual differences in repeatable state variables, such as metabolic rate, age, sex, or body size. Personality and its correlation with body size, however, have been relatively unexplored in bats. We used female Asian particolored bats (Vespertilio sinensis) to investigate three personality characteristics (exploration, activity, and aggression) using the classic hole-board test and examined their relationships with body size using an information-theoretical approach. Our results showed that the exploration of female Asian particolored bats was significantly repeatable, but we did not find significant correlations among the three personality traits. This finding suggested that the female Asian particolored bat may not have a behavioral syndrome. In addition, the body mass of female Asian particolored bats was positively correlated with aggression but was negatively correlated with activity, suggesting that body mass was an important physiological basis affecting the behavioral characteristics of female Asian particolored bats.

Inter-individual and inter-strain differences in cognitive and social abilities of Dark Agouti and Wistar Han rats

Healthy animals displaying extreme behaviours that resemble human psychiatric symptoms are relevant models to study the natural psychobiological processes of maladapted behaviours. Using a Rat Gambling Task, healthy individuals spontaneously making poor decisions (PDMs) were found to co-express a combination of other cognitive and reward-based characteristics similar to symptoms observed in human patients with impulse-control disorders. The main goals of this study were to 1) confirm the existence of PDMs and their unique behavioural phenotypes in Dark Agouti (DA) and Wistar Han (WH) rats, 2) to extend the behavioural profile of the PDMs to probability-based decision-making and social behaviours and 3) to extract key discriminative traits between DA and WH strains, relevant for biomedical research. We have compared cognitive abilities, natural behaviours and physiological responses in DA and WH rats at the strain and at the individual level. Here we found that the naturally occurring PDM's profile was consistent between both rat lines. Then, although the PDM individuals did not take more risks in probability discounting task, they seemed to be of higher social ranks. Finally and despite their similarities in performance, WH and DA lines differed in degree of reward sensitivity, impulsivity, locomotor activity and open space-occupation. The reproducibility and conservation of the complex phenotypes of PDMs and GDMs (good decision makers) in these two genetically different strains support their translational potential. Both strains, present large phenotypic variation in behaviours pertinent for the study of the underlying mechanisms of poor decision making and associated disorders.

The role of personality, cognition, and affective state in same-sex contests in the red junglefowl

Abstract

Intra-species contests are common in the animal kingdom and can have fitness consequences. Most research on what predicts contest outcome focuses on morphology, although differences in personality and cognition may also be involved. Supporting this, more proactive individuals often have dominant status, although the causality of this relationship is rarely investigated. Contest initiators often win; thus, individuals that are more proactive in their personality (e.g., more aggressive, risk-taking) or cognition (e.g., more optimistic, impulsive) may initiate contests more often. To investigate this, we assayed the behavior and cognition of sexually mature male and female red junglefowl (Gallus gallus), a species in which both sexes contest over social status, before staging intra-sexual contests. We confirm that contest initiators were more likely to win. In males, individuals that behaved more boldly in a novel arena test were more likely to initiate and win contests. Female initiators tended to be less active in novel object test, more aggressive in a restrained opponent test, and respond less optimistically in a cognitive judgement bias test, whereas the main predictor of whether a female would win a contest was whether she initiated it. These results suggest that behaviors attributed to proactive and reactive personalities, and—at least for female red junglefowl—optimism, can affect contest initiation and outcome. Therefore, within species, and depending on sex, different aspects of behavior and cognition may independently affect contest initiation and outcome. The generality of these findings, and their fitness consequences, requires further investigation.

Significance statement

In red junglefowl, we explored how behavior previously shown to describe personality, cognition, and affective state affected initiation and outcome of intra-sexual contests, by staging contests between sexually mature individuals previously assayed in behavioral and cognitive tests. In both sexes, contest initiators usually won. Bolder males were more likely to initiate and win contests. Female contests initiators were less active, more aggressive, and less optimistic. Our results suggest that personality and cognition could affect the initiation and outcome of contests and that how this occurs may differ between sexes.

Perinatal fluoxetine exposure changes social and stress-coping behavior in adult rats housed in a seminatural environment

The use of selective serotonin reuptake inhibitors (SSRI) during pregnancy has increased tremendously, but the consequences for the offspring remain largely unclear. Several studies have described potential effects of perinatal SSRI-exposure on neurobehavioral outcomes using simplified rodent test set-ups, however these set-ups only assess a small fraction of the behavior. For translational purposes it is important to take the environmental influences into account which children are exposed to in real life. By using a seminatural environmental set-up, this study is the first to assess behavioral outcomes in offspring exposed to perinatal SSRI exposure under seminatural circumstances. Mothers received daily the SSRI fluoxetine (FLX, 10 mg/kg p.o.) or vehicle (CTR) from gestational day 1 until postnatal day 21. To assess the effect of FLX exposure during early development, female and male offspring were behaviorally tested in the seminatural environment at adulthood. Baseline behavior was measured in addition to responses during and after stressful white-noise events. Behavior was observed on two days, day 4 on which females were sexually non-receptive, and day 7, on which females were sexual receptive. Perinatal FLX exposure reduced general activity in females and increased behavior related to a social context in both males and females. After a stressful white-noise event some behaviors switched. Whereas FLX-females switch from resting socially to resting more solitarily, FLX-males show an increase in self-grooming behavior after the stressor and showed more freezing behavior in the open area. We conclude that perinatal FLX exposure leads to alterations in social and stress-coping behaviors in adulthood, when observed in a seminatural environment. Whether these adaptations in behavior are advantageous or disadvantageous remains to be established.

Aggression, Social Stress, and the Immune System in Humans and Animal Models

Social stress can lead to the development of psychological problems ranging from exaggerated anxiety and depression to antisocial and violence-related behaviors. Increasing evidence suggests that the immune system is involved in responses to social stress in adulthood. For example, human studies show that individuals with high aggression traits display heightened inflammatory cytokine levels and dysregulated immune responses such as slower wound healing. Similar findings have been observed in patients with depression, and comorbidity of depression and aggression was correlated with stronger immune dysregulation. Therefore, dysregulation of the immune system may be one of the mediators of social stress that produces aggression and/or depression. Similar to humans, aggressive animals also show increased levels of several proinflammatory cytokines, however, unlike humans these animals are more protected from infectious organisms and have faster wound healing than animals with low aggression. On the other hand, subordinate animals that receive repeated social defeat stress have been shown to develop escalated and dysregulated immune responses such as glucocorticoid insensitivity in monocytes. In this review we synthesize the current evidence in humans, non-human primates, and rodents to show a role for the immune system in responses to social stress leading to psychiatric problems such as aggression or depression. We argue that while depression and aggression represent two fundamentally different behavioral and physiological responses to social stress, it is possible that some overlapped, as well as distinct, pattern of immune signaling may underlie both of them. We also argue the necessity of studying animal models of maladaptive aggression induced by social stress (i.e., social isolation) for understanding neuro-immune mechanism of aggression, which may be relevant to human aggression.

Major urinary protein levels are associated with social status and context in mouse social hierarchies

We have previously shown that male mice living in groups of 12 males establish and maintain stable linear social hierarchies with each individual having a defined social rank. However, it is not clear which social cues mice use to signal and recognize their relative social status within their hierarchy. In this study, we investigate how individual social status both in pairs and in groups affects the levels of major urinary proteins (MUPs) and specifically MUP20 in urine. We housed groups of adult outbred CD1 male mice in a complex social environment for three weeks and collected urine samples from all individuals repeatedly. We found that dominant males produce more MUPs than subordinates when housed in pairs and that the production of MUPs and MUP20 is significantly higher in alpha males compared with all other individuals in a social hierarchy. Furthermore, we found that hepatic mRNA expression of Mup3 and Mup20 is significantly higher in alpha males than in subordinate males. We also show that alpha males have lower urinary creatinine levels consistent with these males urinating more than others living in hierarchies. These differences emerged within one week of animals being housed together in social hierarchies. This study demonstrates that as males transition to become alpha males, they undergo physiological changes that contribute to communication of their social status that may have implications for the energetic demands of maintaining dominance.