Many aspects of reproductive physiology are subject to regulation by social interactions. These include changes in neural and physiological substrates of reproduction. How can social behavior produce such changes? In experiments reported here, we manipulated the social settings of teleost fish and measured the effect (1) on stress response as reflected in cortisol production, (2) on reproductive potential as measured in production of the signaling peptide, gonadotropin-releasing hormone, and (3) on reproductive function measured in gonad size. Our results reveal that the level of the stress hormone cortisol depends critically on both the social and reproductive status of an individual fish and on the stability of its social situation. Moreover, the reproductive capacity of an individual fish depends on these same variables. These results show that social encounters within particular social contexts have a profound effect on the stress levels as well as on reproductive competence. Social behavior may lead to changes in reproductive state through integration of cortisol changes in time. Thus, information available from the stress pathway may provide socially relevant signals to produce neural change.

The purpose of this study was to investigate the role of skin conductance level reactivity (SCLR) and respiratory sinus arrhythmia reactivity (RSAR) in preschoolers' social dominance, as well as potential gender differences in these associations. Reactivity was assessed in response to viewing videos of social exclusion and a post-aggression discussion. In a community sample of 94 preschool children followed over one calendar year, reactivity to the post-aggression discussion, but not exclusion, video was related to social dominance. Specifically, increased RSAR to the post-aggression discussion video was positively associated with concurrent social dominance for both boys and girls. Longitudinally, for boys only, coactivation (i.e., increases in SCLR accompanied by increases in RSAR) to the post-aggression discussion video, which may reflect dysregulated, emotionally labile reactions to stress, was associated with relatively low levels of social dominance across the course of the year. Overall, findings contribute to a growing literature documenting the role of autonomic reactivity in preschoolers' social adjustment and extend this work to their capacity to achieve and maintain socially dominant positions with peers.

Rodents establish dominance hierarchy as a social ranking system in which one subject acts as dominant over all the other subordinate individuals. Dominance hierarchy regulates food access and mating opportunities, but little is known about its significance in other social behaviors, for instance during collective navigation for foraging or migration. Here, we implemented a simplified goal-directed spatial task in mice, in which animals navigated individually or collectively with their littermates foraging for food. We compared between conditions and found that the social condition exerts significant influence on individual displacement patterns, even when efficient navigation rules leading to reward had been previously learned. Thus, movement patterns and consequent task performance were strongly dependent on contingent social interactions arising during collective displacement, yet their influence on individual behavior was determined by dominance hierarchy. Dominant animals did not behave as leaders during collective displacement; conversely, they were most sensitive to the social environment adjusting their performance accordingly. Social ranking in turn was associated with specific spontaneous neural activity patterns in the prefrontal cortex and hippocampus, with dominant mice showing higher firing rates, larger ripple oscillations, and stronger neuronal entrainment by ripples than subordinate animals. Moreover, dominant animals selectively increased their cortical spiking activity during collective movement, while subordinate mice did not modify their firing rates, consistent with dominant animals being more sensitive to the social context. These results suggest that dominance hierarchy influences behavioral performance during contingent social interactions, likely supported by the coordinated activity in the hippocampal-prefrontal circuit.

Individuals in social species commonly form dominance relationships, where dominant individuals enjoy greater access to resources compared to subordinates. A range of factors such as sex, age, body size and prior experiences has to varying degrees been observed to affect the social status an individual obtains. Recent work on animal personality (i.e. consistent variation in behavioural responses of individuals) demonstrates that personality can co-vary with social status, suggesting that also behavioural variation can play an important role in establishment of status. We investigated whether personality could predict the outcome of duels between pairs of morphologically matched male domestic fowl (Gallus gallus domesticus), a species where individuals readily form social hierarchies. We found that males that more quickly explored a novel arena, or remained vigilant for a longer period following the playback of a warning call were more likely to obtain a dominant position. These traits were uncorrelated to each other and were also uncorrelated to aggression during the initial part of the dominance-determining duel. Our results indicate that several behavioural traits independently play a role in the establishment of social status, which in turn can have implications for the reproductive success of different personality types.

When group-living animals develop individualized social relationships, they often regulate cooperation and conflict through a dominance hierarchy. Female common vampire bats have been an experimental system for studying cooperative relationships, yet surprisingly little is known about female conflict. Here, we recorded the outcomes of 1023 competitive interactions over food provided ad libitum in a captive colony of 33 vampire bats (24 adult females and their young). We found a weakly linear dominance hierarchy using three common metrics (Landau's h' measure of linearity, triangle transitivity and directional consistency). However, patterns of female dominance were less structured than in many other group-living mammals. Female social rank was not clearly predicted by body size, age, nor reproductive status, and competitive interactions were not correlated with kinship, grooming nor food sharing. We therefore found no evidence that females groomed or shared food up a hierarchy or that differences in rank explained asymmetries in grooming or food sharing. A possible explanation for such apparently egalitarian relationships among female vampire bats is the scale of competition. Female vampire bats that are frequent roostmates might not often directly compete for food in the wild.

Social dominance versus social submissiveness is a basic behavioral trait of social animals such as human beings and laboratory mice. The brain regions associated with this behavior have been intensely investigated, and early neuroimaging research on human subjects implies that the nucleus accumbens (NAc) might be involved in encoding social dominance. However, the underlying circuitry and synaptic mechanism are largely unknown. In this study, by introducing lesions to both NAc subregions, the shell and core, a causal relationship is established between social dominance and both NAc subregions. A further electrophysiology investigation on the circuitry of these two subregions revealed that the postsynaptic strength of excitatory synapses onto the medium spiny neurons that express the D1 dopamine receptors in the shell is negatively correlated, and the postsynaptic strength of excitatory synapses onto the medium spiny neurons that express the D2 dopamine receptors in the core is positively correlated, with social dominance. Correspondingly, a DREADD investigation revealed that the activities of these respective medium spiny neurons suppress and promote social dominance. These findings identify a neural substrate for social dominance, implying the potential for a therapeutic strategy for treating related psychiatric disorders.

Acquiring information about stimuli that predict danger, through either direct experience or inference from a social context, is crucial for individuals' ability to generate appropriate behaviors in response to threats. Utilizing a modified demonstrator-observer paradigm (fear conditioning by proxy) that allows for free interaction between subjects, we show that social dominance hierarchy, and the interactive social behaviors of caged rats, is predictive of social fear transmission, with subordinate rats displaying increased fear responses after interacting with a fear-conditioned dominant rat during fear retrieval. Fear conditioning by proxy conserves some of the pathways necessary for direct fear learning (e.g., lateral amygdala) but is unique in that it requires regions necessary for emotional regulation (e.g., anterior cingulate cortex), making this paradigm an important tool for evaluating learning and behavior in the laboratory setting.

Modelling complex social behavior in the laboratory is challenging and requires analyses of dyadic interactions occurring over time in a physically and socially complex environment. In the current study, we approached the analyses of complex social interactions in group-housed male CD1 mice living in a large vivarium. Intensive observations of social interactions during a 3-week period indicated that male mice form a highly linear and steep dominance hierarchy that is maintained by fighting and chasing behaviors. Individual animals were classified as dominant, sub-dominant or subordinate according to their David's Scores and I& SI ranking. Using a novel dynamic temporal Glicko rating method, we ascertained that the dominance hierarchy was stable across time. Using social network analyses, we characterized the behavior of individuals within 66 unique relationships in the social group. We identified two individual network metrics, Kleinberg's Hub Centrality and Bonacich's Power Centrality, as accurate predictors of individual dominance and power. Comparing across behaviors, we establish that agonistic, grooming and sniffing social networks possess their own distinctive characteristics in terms of density, average path length, reciprocity out-degree centralization and out-closeness centralization. Though grooming ties between individuals were largely independent of other social networks, sniffing relationships were highly predictive of the directionality of agonistic relationships. Individual variation in dominance status was associated with brain gene expression, with more dominant individuals having higher levels of corticotropin releasing factor mRNA in the medial and central nuclei of the amygdala and the medial preoptic area of the hypothalamus, as well as higher levels of hippocampal glucocorticoid receptor and brain-derived neurotrophic factor mRNA. This study demonstrates the potential and significance of combining complex social housing and intensive behavioral characterization of group-living animals with the utilization of novel statistical methods to further our understanding of the neurobiological basis of social behavior at the individual, relationship and group levels.

Dominance status has extensive effects on physical and mental health, and an individual's relative position can be shaped by experiential factors. A variety of considerations suggest that the experience of behavioral control over stressors should produce winning in dominance tests and that winning should blunt the impact of later stressors, as does prior control. To investigate the interplay between competitive success and stressor control, we first examined the impact of stressor controllability on subsequent performance in a warm spot competition test modified for rats. Prior experience of controllable, but not physically identical uncontrollable, stress increased later effortful behavior and occupation of the warm spot. Controllable stress subjects consistently ranked higher than did uncontrollable stress subjects. Pharmacological inactivation of the prelimbic (PL) cortex during behavioral control prevented later facilitation of dominance. Next, we explored whether repeated winning experiences produced later resistance against the typical sequelae of uncontrollable stress. To establish dominance status, triads of rats were given five sessions of warm spot competition. Reversible inactivation of the PL or NMDA receptor blockade in the dorsomedial striatum led to a long-term reduction in social rank. Stable dominance blunted the later stress-induced increase in dorsal raphe nucleus serotonergic activity, as well as prevented stress-induced social avoidance. In contrast, endocrine and neuroimmune responses to uncontrollable stress were unaffected, indicating a selective impact of prior dominance. Together, these data demonstrate that instrumental control over stress promotes later dominance, but also reveal that winning experiences buffer against the neural and behavioral outcomes of future adversity.

Social hierarchies are ubiquitous in all human relations since birth, but little is known about how they emerge during infancy. Previous studies have shown that infants can represent hierarchical relationships when they arise from the physical superiority of one agent over the other, but humans have the capacity to allocate social status in others through cues that not necessary entail agents' physical formidability. Here we investigate infants' capacity to recognize the social status of different agents when there are no observable cues of physical dominance. Our results evidence that a first presentation of the agents' social power when obtaining resources is enough to allow infants predict the outputs of their future. Nevertheless, this capacity arises later (at 18 month-olds but not at 15 month-olds) than showed in previous studies, probably due the increased complexity of the inferences needed to make the predictions.

Different aspects of sociality bear considerable weight on the individual- and group-level welfare of captive nonhuman primates. Social Network Analysis (SNA) is a useful tool for gaining a holistic understanding of the dynamic social relationships of captive primate groups. Gaining a greater understanding of captive chimpanzees through investigations of centrality, preferred and avoided relationships, dominance hierarchy, and social network diagrams can be useful in advising current management practices in sanctuaries and other captive settings. In this study, we investigated the dyadic social relationships, group-level social networks, and dominance hierarchy of seven chimpanzees (Pan troglodytes) at Chimpanzee Sanctuary Northwest. We used focal-animal and instantaneous scan sampling to collect 106.75 total hours of associative, affiliative, and agonistic data from June to September 2016. We analyzed our data using SOCPROG to derive dominance hierarchies and network statistics, and we diagrammed the group's social networks in NetDraw. Three individuals were most central in the grooming network, while two others had little connection. Through agonistic networks, we found that group members reciprocally exhibited agonism, and the group's dominance hierarchy was statistically non-linear. One chimpanzee emerged as the most dominant through agonism but was least connected to other group members across affiliative networks. Our results indicate that the conventional methods used to calculate individuals' dominance rank may be inadequate to wholly depict a group's social relationships in captive sanctuary populations. Our results have an applied component that can aid sanctuary staff in a variety of ways to best ensure the improvement of group welfare.

Dominance status has extensive effects on physical and mental health, and an individual's relative position can be shaped by experiential factors. A variety of considerations suggest that the experience of behavioral control over stressors should produce winning in dominance tests and that winning should blunt the impact of later stressors, as does prior control. To investigate the interplay between competitive success and stressor control, we first examined the impact of stressor controllability on subsequent performance in a warm spot competition test modified for rats. Prior experience of controllable, but not physically identical uncontrollable, stress increased later effortful behavior and occupation of the warm spot. Controllable stress subjects consistently ranked higher than did uncontrollable stress subjects. Pharmacological inactivation of the prelimbic (PL) cortex during behavioral control prevented later facilitation of dominance. Next, we explored whether repeated winning experiences produced later resistance against the typical sequelae of uncontrollable stress. To establish dominance status, triads of rats were given five sessions of warm spot competition. The development of stable dominance was prevented by reversible inactivation of the PL or NMDA receptor blockade in the dorsomedial striatum. Stable winning blunted the later stress-induced increase in dorsal raphe nucleus serotonergic activity, as well as prevented uncontrollable stress-induced social avoidance. In contrast, endocrine and neuroimmune responses to uncontrollable stress were unaffected, indicating a selective impact of prior dominance. Together, these data demonstrate that instrumental control over stress promotes later dominance, but also reveal that winning experiences buffer against the neural and behavioral outcomes of future adversity.

Social competence - the ability of animals to dynamically adjust their social behavior dependent on the current social context - is fundamental to the successful establishment and maintenance of social relationships in group-living species. The social opportunity paradigm, where animals rapidly ascend a social hierarchy following the removal of more dominant individuals, is a well-established approach for studying the neural and neuroendocrine mechanisms underlying socially competent behavior. In the current study, we demonstrate that this paradigm can be successfully adapted for studying socially competent behavior in laboratory mice. Replicating our previous reports, we show that male laboratory mice housed in a semi-natural environment form stable linear social hierarchies. Novel to the current study, we find that subdominant male mice immediately respond to the removal of the alpha male from a hierarchy by initiating a dramatic increase in aggressive behavior towards more subordinate individuals. Consequently, subdominants assume the role of the alpha male. Analysis of brain gene expression in individuals 1h following social ascent indicates elevated gonadotropin-releasing hormone (GnRH) mRNA levels in the medial preoptic area (mPOA) of the hypothalamus compared to individuals that do not experience a social opportunity. Moreover, hormonal analyses indicate that subdominant individuals have increased circulating plasma testosterone levels compared to subordinate individuals. Our findings demonstrate that male mice are able to dynamically and rapidly adjust both behavior and neuroendocrine function in response to changes in social context. Further, we establish the social opportunity paradigm as an ethologically relevant approach for studying social competence and behavioral plasticity in mammals.

Loss-of-function mutations in progranulin (GRN) are a major autosomal dominant cause of frontotemporal dementia (FTD), a neurodegenerative disorder in which social behavior is disrupted. Progranulin-insufficient mice, both Grn(+/-) and Grn(-/-) , are used as models of FTD due to GRN mutations, with Grn(+/-) mice mimicking the progranulin haploinsufficiency of FTD patients with GRN mutations. Grn(+/-) mice have increased social dominance in the tube test at 6 months of age, although this phenotype has not been reported in Grn(-/-) mice. In this study, we investigated how the tube test phenotype of progranulin-insufficient mice changes with age, determined its robustness under several testing conditions, and explored the associated cellular mechanisms. We observed biphasic social dominance abnormalities in Grn(+/-) mice: at 6-8 months, Grn(+/-) mice were more dominant than wild-type littermates, while after 9 months of age, Grn(+/-) mice were less dominant. In contrast, Grn(-/-) mice did not exhibit abnormal social dominance, suggesting that progranulin haploinsufficiency has distinct effects from complete progranulin deficiency. The biphasic tube test phenotype of Grn(+/-) mice was associated with abnormal cellular signaling and neuronal morphology in the amygdala and prefrontal cortex. At 6-9 months, Grn(+/-) mice exhibited increased mTORC2/Akt signaling in the amygdala and enhanced dendritic arbors in the basomedial amygdala, and at 9-16 months Grn(+/-) mice exhibited diminished basal dendritic arbors in the prelimbic cortex. These data show a progressive change in tube test dominance in Grn(+/-) mice and highlight potential underlying mechanisms by which progranulin insufficiency may disrupt social behavior.

Ubiquitous in the animal kingdom, dominance hierarchies emerge through social competition and underlie the control of resources. Confronting the disruptive influence of socioeconomic inequalities, human populations tend to split into groups who legitimize existing dominance hierarchies and groups who condemn them. Here, we hypothesized that variations in the neural sensitivity to dominance ranks partly underpins this ideological split, as measured by the social dominance orientation scale (SDO). Following a competitive task used to induce dominance representations about three opponents (superior, equal and inferior), subjects were passively presented the faces of these opponents while undergoing fMRI. Analyses demonstrated that two key brain regions, the superior temporal sulcus (STS) and anterior dorsolateral prefrontal cortex (aDLPFC) were sensitive to social ranks. Confirming our hypothesis, the sensitivity of the right aDLPFC to social ranks correlated positively with the SDO scale, which is known to predict behaviors and political attitudes associated with the legitimization of dominance hierarchies. This study opens new perspectives for the neurosciences of political orientation and social dominance.

The associations between social status and endogenous testosterone and corticosterone have been well-studied across taxa, including rodents. Dominant social status is typically associated with higher levels of circulating testosterone and lower levels of circulating corticosterone but findings are mixed and depend upon numerous contextual factors. Here, we determine that the social environment is a key modulator of these relationships in Mus musculus. In groups of outbred CD-1 mice living in stable dominance hierarchies, we found no evidence of simple linear associations between social rank and corticosterone or testosterone plasma levels. However, in social hierarchies with highly despotic alpha males that socially suppress other group members, testosterone levels in subordinate males were significantly lower than in alpha males. In less despotic hierarchies, where all animals engage in high rates of competitive interactions, subordinate males had significantly elevated testosterone compared to agonistically inhibited subordinates from despotic hierarchies. Subordinate males from highly despotic hierarchies also had elevated levels of corticosterone compared to alpha males. In pair-housed animals, the relationship was the opposite, with alpha males exhibiting elevated levels of corticosterone compared to subordinate males. Notably, subordinate males living in social hierarchies had significantly higher levels of plasma corticosterone than pair-housed subordinate males, suggesting that living in a large group is a more socially stressful experience for less dominant individuals. Our findings demonstrate the importance of considering social context when analyzing physiological data related to social behavior and using ethologically relevant behavioral paradigms to study the complex relationship between hormones and social behavior.

Dominance hierarchies of social animal groups are very sensitive to stress. Stress experienced prior to social interactions between conspecifics may be a determinant of their future social dynamics. Additionally, long-term occupancy of a specific hierarchical rank can have psychophysiological effects which increase vulnerability to future stressors.

Higher social status is expected to result in fitness benefits as it secures access to potential mates. In promiscuous species, male reproductive success is also determined by an individual's ability to compete for fertilization after mating by producing high-quality ejaculates. However, the complex relationship between a male's investment in social status and ejaculates remains unclear. Here, we examine how male social status influences ejaculate quality under a range of social contexts in the pygmy halfbeak Dermogenys collettei, a small, group-living, internally fertilizing freshwater fish. We show that male social status influences ejaculate traits, both in the presence and absence of females. Dominant males produced faster swimming and more viable sperm, two key determinants of ejaculate quality, but only under conditions with frequent male-male behavioral interactions. When male-male interactions were experimentally reduced through the addition of a refuge, differences in ejaculate traits of dominant and subordinate males disappeared. Furthermore, dominant males were in a better condition, growing faster, and possessing larger livers, highlighting a possible condition dependence of competitive traits. Contrary to expectations, female presence or absence did not affect sperm swimming speed or testes mass. Together, these results suggest a positive relationship between social status and ejaculate quality in halfbeaks and highlight that the strength of behavioral interactions between males is a key driver of social-status-dependent differences in ejaculate traits.

In this study, we investigated the effect of social environment on circadian patterns in activity by group housing either six male or six female mice together in a cage, under regular light-dark cycles. Based on the interactions among the animals, the social dominance rank of individual mice was quantitatively established by calculating Elo ratings. Our results indicated that, during our experiment, the social dominance hierarchy was rapidly established, stable yet complex, often showing more than one dominant mouse and several subordinate mice. Moreover, we found that especially dominant male mice, but not female mice, displayed a significantly higher fraction of their activity during daytime. This resulted in reduced rhythm amplitude in dominant males. After division into separate cages, male mice showed an enhancement of their 24 h rhythm, due to lower daytime activity. Recordings of several physiological parameters showed no evidence for reduced health as a potential consequence of reduced rhythm amplitude. For female mice, transfer to individual housing did not affect their daily activity pattern. We conclude that 24 h rhythms under light-dark cycles are influenced by the social environment in males but not in females, and lead to a decrement in behavioural rhythm amplitude that is larger in dominant mice.

Dominance hierarchies are ubiquitous in invertebrates and vertebrates, but little is known on how genes influence dominance rank. Our gaps in knowledge are specifically significant concerning female hierarchies, particularly in insects. To start filling these gaps, we studied the social bumble bee Bombus terrestris, in which social hierarchies among females are common and functionally significant. Dominance rank in this bee is influenced by multiple factors, including juvenile hormone (JH) that is a major gonadotropin in this species. We tested the hypothesis that the JH responsive transcription factor Krüppel homologue 1 (Kr-h1) mediates hormonal influences on dominance behavior. We first developed and validated a perfluorocarbon nanoparticles-based RNA interference protocol for knocking down Kr-h1 expression. We then used this procedure to show that Kr-h1 mediates the influence of JH, not only on oogenesis and wax production, but also on aggression and dominance rank. To the best of our knowledge, this is the first study causally linking a gene to dominance rank in social insects, and one of only a few such studies on insects or on female hierarchies. These findings are important for determining whether there are general molecular principles governing dominance rank across gender and taxa.