Subordinate Females Research Articles

Relationship between cognitive performance and social rank in male and female cynomolgus macaques: Implications for the role of cognition in vulnerability to cocaine use disorder

Cocaine use disorder (CUD) currently has no FDA-approved pharmacological treatment. One of the most promising behavioral interventions is cognitive behavioral therapy. Still, there is a continuing need to understanding what makes an individual susceptible to CUD. A major goal of this study is to determine if cognitive performance can serve as a behavioral biomarker related to vulnerability to cocaine abuse. Previous studies have shown sex differences in vulnerability to cocaine based on social rank (Morgan et al., 2002; Nader et al., 2012). The goal of the present study is to evaluate cognitive performance as a potential biomarker for vulnerability to cocaine abuse, in socially housed cocaine-naïve female and male monkeys. In an earlier study involving newly formed social groups of female monkeys, performance on one cognitive domain, working memory using a delayed-match-to-sample task, showed social rank differences only during establishment of the social hierarchy; once the hierarchies were stable, there were no differences in working memory across social ranks (Kromrey et al., 2016). The present study differs from our earlier work by studying several cognitive domains in well-established, same-sex, male and female social groups (N=8/sex). Monkeys were trained to complete a battery of cognitive tasks which evaluated learning and memory (stimulus discrimination; SD and compound discrimination; CD), executive function (reversal learning; SDR) and behavioral flexibility (interdimensional shifting; ID, extradimensional shifting; and reversal, ED, EDR). The test battery consisted of monkeys performing all tasks (SD/SDR, CD, ID, ED/EDR) in 1-3 sessions; criteria for moving to the next task was 12/15 trials correct. All studies were performed in accordance with the FASEB Statement of Principles for the Use of Vertebrate Animals in Research and Education and Wake Forest's IACUC. We hypothesized that because earlier work had shown subordinate males and dominant females were more vulnerable to cocaine reinforcement, that they would show poorer cognitive performance relative to dominant males and subordinate females. In preliminary findings, dominant male and female monkeys made fewer total errors and required less trials to complete the battery compared with subordinate animals, in contrast to our hypothesis. Next, acquisition of cocaine reinforcement will be examined in an effort to replicate earlier findings and then the test battery will be repeated at various timepoints in order to evaluate the effects of cocaine on cognitive performance as a function of sex and social rank.

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.

Limited sexual segregation in a dimorphic avian scavenger, the Andean condor.

Sexual segregation is widely reported among sexually dimorphic species and generally attributed to intraspecific competition. Prey diversity and human activities can reinforce niche segregation by increasing resource heterogeneity. Here, we explored trophic and spatial sexual segregation in the only avian scavenger that exhibits pronounced sexual size dimorphism (up to 50% difference in body mass) and a highly despotic social system, the Andean condor (Vultur gryphus). We predicted that larger and dominant males would exclude smaller and subordinate females from high-quality resources, leading to sexual segregation particularly in human-dominated landscapes showing increased prey diversity. We compared resource use between females and males across six sites in Argentina featuring a range of prey diversity via stable isotopes analysis of molted feathers (n = 141 individuals). We then focused on two sites featuring contrasting levels of prey diversity and quantified assimilated diet via stable isotopes and space use via GPS monitoring (n = 23 and 12 tagged individuals). We found no clear differences in isotopic niche space, individual variation in isotopic signature, or assimilated diet between females and males. However, there were differences in foraging locations between sexes, with females apparently using areas of fewer food resources more frequently than males. Local conditions defined the dynamics of fine-scale sexual differences in foraging sites; yet, unpredictable and ephemeral carrion resources likely prevent segregation by sexes at the landscape scale. Our study highlights complex dynamics of sexual segregation in vultures and the relevancy of analyses under multiple spatial-temporal scales to explore segregation in social species.

Female helpers signal their contribution to chick provisioning in a cooperatively breeding bird

Behaviours whose primary function is not signalling can convey information that other individuals can use to make relevant decisions. In cooperatively breeding vertebrates, feeding young that are not own offspring typically provides indirect fitness payoffs, but group members may also benefit directly by advertising their contribution to their social mates, to either increase their ‘social prestige’ or obtain a share of territory commodities (‘pay to stay’). Evidence of such a signalling component of brood provisioning, however, remains controversial. In the cooperative society of carrion crows, Corvus corone , male subordinates have little chance of independent reproduction and do the best of a bad job by helping to raise the current brood. The value of future reproduction is instead higher for subordinate females, which, because they have better prospects of finding a breeding vacancy, generally invest less than males in helping at the nest. Under these circumstances, dominants are expected to be more vigilant over the contribution to brood provisioning by female subordinates, which in turn, might need to show their helpfulness to retain group membership. In accordance with this idea, we found that female retained offspring increased the ‘visibility’ of their contribution by provisioning in front of the dominant breeders significantly more than any other category of group members. In addition, retention of group membership for female offspring was associated with their perceived effort in chick feeding. Our results are consistent with the hypothesis of ‘pay to stay’ and suggest that a signalling component of helping can arise in a ‘typical’ kin-based cooperative society. • In carrion crows, retained offspring and immigrants help at the nests. • Female helpers often provision the brood in front of the dominant breeders. • Their perceived effort correlates with the probability of remaining in the group. • By advertising their work, they show that they are paying a rent for staying. • For female helpers, brood provisioning may therefore have a signalling component.

Sex-dependent effects of social status on the regulation of arginine-vasopressin (AVP) V1a, oxytocin (OT), and serotonin (5-HT) 1A receptor binding and aggression in Syrian hamsters (Mesocricetus auratus)

Dominance status in hamsters is driven by interactions between arginine-vasopressin V1a, oxytocin (OT), and serotonin 1A (5-HT1A) receptors. Activation of V1a and OT receptors in the anterior hypothalamus (AH) increases aggression in males, while decreasing aggression in females. In contrast, activation of 5-HT1A receptors in the AH decreases aggression in males and increases aggression in females. The mechanism underlying these differences is not known. The purpose of this study was to determine if dominance status and sex interact to regulate V1a, OT, and 5-HT1A receptor binding. Same-sex hamsters (N = 47) were paired 12 times across six days in five min sessions. Brains from paired and unpaired (non-social control) hamsters were collected immediately after the last interaction and processed for receptor binding using autoradiography. Differences in V1a, OT, and 5-HT1A receptor binding densities were observed in several brain regions as a function of social status and sex. For example, in the AH, there was an interaction between sex and social status, such that V1a binding in subordinate males was lower than in subordinate females and V1a receptor density in dominant males was higher than in dominant females. There was also an interaction in 5-HT1A receptor binding, such that social pairing increased 5-HT1A binding in the AH of males but decreased 5-HT1A binding in females compared with unpaired controls. These results indicate that dominance status and sex play important roles in shaping the binding profiles of key receptor subtypes across the neural circuitry that regulates social behavior.

Germ cell nests in adult ovaries and an unusually large ovarian reserve in the naked mole-rat.

The naked mole-rat (NMR, Heterocephalus glaber) is renowned for its eusociality and exceptionally long lifespan (> 30 y) relative to its small body size (35-40 g). A NMR phenomenon that has received far less attention is that females show no decline in fertility or fecundity into their third decade of life. The age of onset of reproductive decline in many mammalian species is closely associated with the number of germ cells remaining at the age of sexual maturity. We quantified ovarian reserve size in NMRs at the youngest age (6 months) when subordinate females can begin to ovulate after removal from the queen's suppression. We then compared the NMR ovarian reserve size to values for 19 other mammalian species that were previously reported. The NMR ovarian reserve at 6 months of age is exceptionally large at 108,588 ± 69,890 primordial follicles, which is more than 10-fold larger than in mammals of a comparable size. We also observed germ cell nests in ovaries from 6-month-old NMRs, which is highly unusual since breakdown of germ cell nests and the formation of primordial follicles is generally complete by early postnatal life in other mammals. Additionally, we found germ cell nests in young adult NMRs between 1.25 and 3.75 years of age, in both reproductively activated and suppressed females. The unusually large NMR ovarian reserve provides one mechanism to account for this species' protracted fertility. Whether germ cell nests in adult ovaries contribute to the NMR's long reproductive lifespan remains to be determined.

Drosophila melanogaster and worker honeybees (Apis mellifera) do not require olfaction to be susceptible to honeybee queen mandibular pheromone

Eusociality is characterised by the reproductive division of labour; a dominant female (queen) or females are responsible for the majority of reproduction, and subordinate females are reproductively constrained. Reproductive constraint can be due to behavioural aggression and/or chemical cues, so-called queen pheromones, produced by the dominant females. In the honeybee, Apis mellifera, this repressive queen pheromone is queen mandibular pheromone (QMP). The mechanism by which honeybee workers are susceptible to QMP is not yet completely understood, however it is thought to be through olfaction via the antennae and/or gustation via trophallaxis.We have investigated whether olfaction is key to sensing of QMP, using both Drosophila melanogaster- a tractable non-eusocial insect which is also reproductively repressed by QMP- and the target species, A. mellifera worker honeybees. D. melanogaster are still capable of sensing and responding to QMP without their antenna and maxillary palps, and therefore without olfactory receptors. When worker honeybees were exposed to QMP but unable to physically interact with it, therefore required to use olfaction, they were similarly not reproductively repressed. Combined, these findings support either a non-olfactory based mechanism for the repression of reproduction via QMP, or redundancy via non-olfactory mechanisms in both D. melanogaster and A. mellifera. This study furthers our understanding of how species are susceptible to QMP, and provides insight into the mechanisms governing QMP responsiveness in these diverse species.

Reproductive physiology corresponds to adult nutrition and task performance in a Neotropical paper wasp: a test of dominance-nutrition hypothesis predictions

The dominance-nutrition hypothesis predicts that nutritional intake and energetic costs in adulthood interact to drive behavioral and physiological differences between females in primitively eusocial insects, and thereby affect reproductive caste. We tested predictions of this hypothesis in independent-founding Mischocyttarus pallidipectus paper wasps. We measured stable isotope tissue composition to compare nutritional status before adult emergence and among adult females. Adult tissue δ15N content (an indicator of feeding at a higher trophic level because it is enriched in animal prey relative to plant-based foods) was significantly higher in adults than at the end of pupal development, suggesting adult nutrition affects δ15N content after the end of pupal development. We then asked if behavior and nutritional status predicted ovary development. We measured ovary development, nitrogen and carbon stable isotope ratios, dominance behavior, and task performance (foraging, as indicated by time spent on the nest) for adult female wasps. We used social network analysis to quantify differences in social status between females with developed and undeveloped (filamentous) ovaries. Dominant females spent more time on the nest and were significantly more enriched in δ15N than subordinate females. These data support the dominance-nutrition hypothesis: adult behavior and energy expenditure, and access to animal-based diets, correspond to female reproductive physiology, and may play a role in adult-stage caste determination. Within animal social groups, differential access to resources can affect differences in reproductive success. This may affect caste determination in eusocial colonies, where reproductive tasks are divided between female castes, with a queen (or multiple queens) capable of egg-laying and helped by sterile workers. Female sterile workers and reproductives of some social Hymenoptera are morphologically similar at adult emergence, suggesting that adult experience may impact caste status. We asked whether patterns of nutritional physiology in Mischocyttarus pallidipectus paper wasps matched adult-stage caste determination by testing predictions of the dominance-nutrition hypothesis, which states that adult nutrition and energetic costs of tasks shape reproductive female development through behavioral and physiological changes.

Contextual complexity of chemical signals in callitrichids.

In nearly four decades our research and that of others on chemical signaling in callitrichid primates suggest a high degree of contextual complexity in both the use of signals and the response to these signals. We describe our research including observational field studies, behavioral bioassays ("playbacks"), functional imaging, and conditioning studies. Scent marking in both captivity and the wild is used for more than just territorial marking. Social contextual effects are seen in responses by subordinate females responding with ovulatory inhibition only to chemical signals from familiar dominant reproductive females. Males detect ovulation through changes in scent marks. Males responded behaviorally and hormonally to chemical signals of novel ovulating females as a function of their reproductive status (fathers, males paired with a female but not fathers, and single males). Multiple brain areas are activated in males by female chemical signals of ovulation including areas relating to memory, evaluation, and motivation. Furthermore, males can be conditioned to respond sexually to a nonsexual odor demonstrating that learning plays an important role in response to chemical signals. Male androgen and estrone levels changed significantly in response to infant chemical signals as a function of whether the males were fathers or not, whether the odors were from their own versus other infants, as well as the infant's stage of development. Chemical signals in callitrichids are providing a rich source of understanding the context and function of the chemical sensory system and its stimulation of neural, behavioral, and hormonal actions in the recipients.

Cues of dominance hierarchy, fertility and nestmate recognition in the primitively eusocial wasp Mischocyttarus parallelogrammus (Vespidae: Polistinae: Mischocyttarini)

Chemical communication is pivotal for social insects to ensure proper functioning of their colonies. Cuticular hydrocarbons (CHCs) are the most well-known class of compounds used to regulate different types of behavioural interaction within a social context. Queens of highly eusocial insects rely on the use of chemical communication to keep their reproductive monopoly, whereas queens of primitively eusocial insects often exert physical control to maintain reproductive dominance. However, in the past years, ample evidence has demonstrated that primitively eusocial insects also use chemical compounds to communicate. Based on this evidence, we aimed to elucidate whether CHCs carry some information regarding female hierarchical position, ovary activation and nestmate recognition in the primitively eusocial wasp Mischocyttarus parallelogrammus. Additionally, females were classified by their ovary activation. Finally, the cuticular profiles of females originating from different nests were compared to check whether CHCs convey information about their nest of origin. Our results confirmed that the chemical composition of alpha and subordinate females differed significantly in post-worker emergence nests, but that alpha and beta females surprisingly were not chemically different from each other in either of the colony phases. Furthermore, females with activated ovaries expressed a chemical profile distinct from that of females with non-activated ovaries. Lastly, we showed that CHCs might convey information about nest origin, since females hailing from different nests showed distinct chemical profiles. Based on our results, we conclude that CHCs might play a critical role in the nest-functioning of M. parallelogrammus, since they mirror social status.

Assessment of Stress on Serum Estradiol and Cortisol Levels in Female Subordinate Naked Mole Rats Following Isolation from Natal Colony

This study investigated the effects of isolation of subordinate naked mole rats from natal colonies on their reproductive success. Naked mole rat is one of the known mammals that exhibit eusociality. It has been noted that naked mole rats have their reproduction restricted to one queen and less than three males; the rest of the animals within the colony remain sterile. The study aimed at establishing whether the reproductive suppression in subordinate naked mole rats is the outcome of social stress exerted by breeding female in the colony or other unknown environmental factors within the colony set-up. Experimental period was 20 weeks and it involved two stages, acclimatization and isolation. Before acclimation, 2 female subordinate naked mole rats were sacrificed. Blood samples were collected and appropriately preserved for later analysis. On the 2nd, 4th and 6th weeks of acclimatization, 2 female mole rats were sacrificed at each stage and blood samples were harvested for analysis. On week 7, eighteen subordinate females were isolated and randomly assigned into two groups of 9 animals each in two separate cages for 14 weeks. One week 8, 2 subordinate females from each group were randomly selected, sacrificed and blood samples collected for analysis. The same procedure was repeated on week 12 and 20 of study. Hormonal analysis was done using ELISA technique. The Statistical analysis done using student t-test at 95% confidence level and significance level was set at P < 0.05. Results showed increase in cortisol levels only in singly isolated females which were the greatest on week 8 (from 35.5 ng/ml to 123.4 ng/ml). Mean estradiol in singly isolated females was 18 ± 2.52 pg/ml while females paired with males had 19.0 ± 3.0 pg/ml hence no significant difference (paired t = -1.73, P = 0.23). Conclusively, the observed reproductive suppression among subordinate naked mole rats in natal colonies is probably due to presence of queen or other reproductive aspects that may not be directly related to stress.

Ultrasound monitoring of the uterus and ovaries of dominant and subordinate females of yellow-breasted capuchin (Sapajus xanthosternos) and robust tufted capuchin (Sapajus robustus) in captive colonies during the ovarian cycle and anestrus periods

ABSTRACT: The yellow-breasted capuchin (Sapajus xanthosternos) and robust tufted capuchin (Sapajus robustus) are endangered species due to destruction of their natural habitat and predatory chase. However, it is still necessary to elucidate some details of their reproductive physiology in order to obtain better indices in the assisted reproduction of these species. This study aimed to evaluate the ovarian cycle of 13 dominant and subordinate females of S. xanthosternos (n=8) and S. robustus (n=5) using sagittal and transversally scanned ultrasound of their uterus and ovaries. Sonograms were performed every seven days for two months. The ovarian cycle phase and anestrous condition were confirmed by colpocytology. Our results showed different uterine parameters (craniocaudal diameter, dorso-ventral diameter, and transverse diameter) (P&lt;0.05) between anestrous subordinate females and other ovarian cycle phases and social classes. The mean of uterine volume was higher in dominant females than subordinate females in all cycle phases (P&lt;0.05), except in follicular phase. During anestrus, endometrial width was smaller in subordinate females than in dominant females (P&lt;0.05). Subordinate females showed differences in endometrial measures (P&lt;0.05) between anestrous period and follicular and luteal periods. Ovarian measures in dominant females were higher than in subordinate females only during anestrus (P&lt;0.05). In the subordinate females, ovarian parameters were different (P&lt;0.05) between anestrus and follicular and luteal phases. Dominant females showed higher volume of right ovary compared to volume of the left ovary during anestrus and follicular phase (P&lt;0.05). Follicles and corpus luteum were distinguished by ultrasonography in most exams (86.11%). During anestrus, measurable ovarian structures were not observed in both ovaries in dominant and subordinate females. In conclusion, the methodology used in this study allowed to evaluate the ovarian cycle in S. xanthosternos e S. robustus females and that cycle phase/anestrus and social class of the female influenced the size of the uterus and ovaries.

Perceived dominance status affects chemical signalling in the neriid fly Telostylinus angusticollis

Chemical communication mediates many social interactions in insects but is still less well understood than other forms of communication. In particular, chemical signalling of social dominance is believed to play an important role in competitive interactions in both sexes, but much of the evidence is correlational. Here we manipulated social dominance and examined its effect on CHC profiles in Telostylinus angusticollis, a fly with a resource defence polygyny mating system. Focal individuals' perception of their own dominance status was manipulated by placing them in an arena with larger or smaller competitors to render them ‘subordinate’ or ‘dominant.’ We found that social dominance treatment affected males' and females' social status (quantified as proximity to the larval medium/oviposition dish), as well as their CHC profiles. Dominant individuals tended to have CHC profiles less similar to those of the opposite sex. Moreover, dominant females exhibited an overall elevation of all CHC expression, relative to subordinate females, whereas males that perceived themselves as subordinate exhibited a near-significant downregulation of male-limited CHCs. Our findings suggest that T. angusticollis males and females alter their CHC profiles in response to their self-perceived social dominance status. These chemical signals could play a role in social interactions both within and between the sexes.

Experimental evidence that intruder and group member attributes affect outgroup defence and associated within-group interactions in a social fish.

In many social species, individuals communally defend resources from conspecific outsiders. Participation in defence and in associated within-group interactions, both during and after contests with outgroup rivals, is expected to vary between group members because the threat presented by different outsiders is not the same to each individual. However, experimental tests examining both the contributions to, and the consequences of, outgroup conflict for all group members are lacking. Using groups of the cichlid Neolamprologus pulcher, we simulated territorial intrusions by different-sized female rivals and altered the potential contribution of subordinate females to defence. Dominant females and subordinate females defended significantly more against size- and rank-matched intruders, while males displayed lower and less variable levels of defence. Large and small, but not intermediate-sized, intruders induced increased levels of within-group aggression during intrusions, which was targeted at the subordinate females. Preventing subordinate females from helping in territorial defence led to significant decreases in post-contest within-group and female-specific submissive and affiliative displays. Together, these results show that the defensive contributions of group members vary greatly depending both on their own traits and on intruder identity, and this variation has significant consequences for within-group social dynamics both during and in the aftermath of outgroup contests.

Aggressiveness, Mating Behaviour and Lifespan of Group Housed Rabbit Does.

Simple SummaryAggressiveness is a well-known trait in different animal species, including the European wild and domesticated rabbit. It is one of the main problems in group housing of rabbit does. The aim of the experiment was to investigate the frequency of aggressiveness and mating behaviour as well as the lifespan of does depending on their rank order. Dominance hierarchy developed during aggressive behaviour, i.e., fighting. In most cases the primary position in the rank order was clear. Mating activity was very high after assembling the groups. In addition to male–female mating, some female-female and female-male mounting was also observed, which could lead to pseudo-pregnancy. A second small peak of sexual activity was observed at the end of the hypothetical pseudo-pregnancy. Based on the results it can be concluded that aggressive behaviour is frequent in group housing systems which is contrary to animal welfare. Natural mating is not effective in group-housing systems.Aggressiveness is one of the main problems in group housing of rabbit does. The aim of the experiment was to investigate the frequency of aggressiveness and mating behaviour as well as the lifespan of does depending on group composition. The female and male rabbits were housed in one of the 7.7 m2 pens (four females and one male per pen). Based on the ages of female rabbits two homogenous groups (HOM) were formed containing four 17-week-old females and two heterogeneous groups (HET) containing three 17-week-old and one 1-year-old female. Twenty-four-hour video recordings were taken during the first month after assembling the groups, and the aggressive actions (fights) and matings were counted. The lifespan was examined over a 200-day experimental period. On the day after assembling the groups the number of fights among does was high in HET group. The same aggressive behaviour only started a week later in HOM group, and some fights between females and the male were also observed. The daily peaks of aggressiveness were in the morning (after the light on) and in the evening (before and after the lights off). The primary position of females in the hierarchy was clear but sometimes no differences were detected among the subordinate females. The mortality of does was connected with their rank order. The number of matings was very high on the day of assembling the groups and a second small peak was observed at the end of the hypothetical pseudo-pregnancy. In addition to mating between male and females, female–female and female–male mounting was also observed. Despite of the small sample size it seems that aggressive behaviour is frequent in group housing systems, which is contrary to animal welfare. Natural mating is not effective in group-housing system.

Do Primitively Eusocial Wasps Use Queen Pheromones to Regulate Reproduction? A Case Study of the Paper Wasp Polistes satan

In several highly eusocial insect species with morphologically distinct castes, queen-characteristic cuticular hydrocarbons (CHCs) have been shown to act as queen signals that suppress the reproduction of nestmate workers. However, it is not known whether such queen pheromones might also play a role in regulating reproductive division of labour in primitively eusocial insects that lack morphologically defined castes. Here, we experimentally tested whether a blend of CHCs which occurred in higher concentrations in the dominant breeding female act as a queen pheromone, and inhibit reproduction by subordinate females in the primitively eusocial paper wasp Polistes satan. In contrast to earlier findings with highly eusocial species, our results show that although specific compounds were enhanced in dominant, reproductively active females, a blend of five of these compounds did not inhibit development of the ovaries of female nestmates. Instead, the dominant female had to be physically present to prevent subordinate females from reproducing. Our results are in line with earlier evidence suggesting that fertility-linked compounds in primitively eusocial wasps act only as cues and help to regulate reproduction when used in conjunction with aggressive dominance behaviour, meaning the physical presence of the dominant female. Alternatively, our results support the hypothesis that queen pheromones in highly eusocial insects were co-opted from fertility cues that were already present in primitively eusocial ancestors, even when initially, such compounds were merely produced as by-products of ovarian activation, without actually serving to signal reproductive status.

Socio-ecological conditions and female infidelity in the Seychelles warbler.

Within socially monogamous breeding systems, levels of extra-pair paternity can vary not only between species, populations, and individuals, but also across time. Uncovering how different extrinsic conditions (ecological, demographic, and social) influence this behavior will help shed light on the factors driving its evolution. Here, we simultaneously address multiple socio-ecological conditions potentially influencing female infidelity in a natural population of the cooperatively breeding Seychelles warbler, Acrocephalus sechellensis. Our contained study population has been monitored for more than 25 years, enabling us to capture variation in socio-ecological conditions between individuals and across time and to accurately assign parentage. We test hypotheses predicting the influence of territory quality, breeding density and synchrony, group size and composition (number and sex of subordinates), and inbreeding avoidance on female infidelity. We find that a larger group size promotes the likelihood of extra-pair paternity in offspring from both dominant and subordinate females, but this paternity is almost always gained by dominant males from outside the group (not by subordinate males within the group). Higher relatedness between a mother and the dominant male in her group also results in more extra-pair paternity—but only for subordinate females—and this does not prevent inbreeding occurring in this population. Our findings highlight the role of social conditions favoring infidelity and contribute toward understanding the evolution of this enigmatic behavior.

Social hierarchy position in female mice is associated with plasma corticosterone levels and hypothalamic gene expression

Social hierarchies emerge when animals compete for access to resources such as food, mates or physical space. Wild and laboratory male mice have been shown to develop linear hierarchies, however, less is known regarding whether female mice have sufficient intrasexual competition to establish significant social dominance relationships. In this study, we examined whether groups of outbred CD-1 virgin female mice housed in a large vivaria formed social hierarchies. We show that females use fighting, chasing and mounting behaviors to rapidly establish highly directionally consistent social relationships. Notably, these female hierarchies are less linear, steep and despotic compared to male hierarchies. Female estrus state was not found to have a significant effect on aggressive behavior, though dominant females had elongated estrus cycles (due to increased time in estrus) compared to subordinate females. Plasma estradiol levels were equivalent between dominant and subordinate females. Subordinate females had significantly higher levels of basal corticosterone compared to dominant females. Analyses of gene expression in the ventromedial hypothalamus indicated that subordinate females have elevated ERα, ERβ and OTR mRNA compared to dominant females. This study provides a methodological framework for the study of the neuroendocrine basis of female social aggression and dominance in laboratory mice.

The effects of fluoxetine on socioemotional behavior in female rhesus monkeys is influenced by social status

BackgroundChronic adverse social experience is a major environmental variable linked to multiple psychiatric disorders. The use of social subordination in nonhuman primates represents a translational model of chronic psychosocial stress. While social dominance is associated with a resistance to a range of stressors and social subordination produces stress‐susceptible phenotypes, the neural mechanisms that underlie status‐induced differences in susceptibility remain unclear. The current study assessed the effects of increasing serotonin (5HT) activity by administering fluoxetine on rates of socioemotional behavior (including agonistic, affiliative, and anxiety‐like behaviors) in female rhesus monkeys. We hypothesized that fluoxetine would increase rates of aggression in dominant but not subordinate animals.MethodsSubjects were gonadally intact adult female rhesus monkeys (n=14) housed in small social groups of four to six females each (6 dominant and 8 subordinate females). Using a counterbalanced design, subjects received both a 14‐day treatment with fluoxetine (SC dose of 2.8 mg/kg/day) and vehicle (50% polyethylene glycol in sterile saline) separated by a three‐week washout period. Behavioral observations were collected every two days using a standard monkey ethogram during each treatment, and CSF samples were collected at the end of each treatment for assessment of central 5‐hydroxyindoleacetic (5HIAA).ResultsThe amount of aggression directed at group mates was influenced by a status by treatment interaction (p=0.05, η2=0.27), with fluoxetine enhancing aggression in dominant females and decreasing aggression in subordinate females. As expected, subordinate females emitted significantly higher rates of submission behavior than did dominant females and this was unaffected by treatment (p=0.001). Affiliation emitted towards others was influenced by a status by treatment interaction (p=0.05, η2=0.27), as fluoxetine treatment decreased affiliation emitted in dominant females and increased it in subordinates. Anxiety‐like behavior was also influenced by a status by treatment interaction (p=0.011), as anxiety‐like behaviors were reduced only in subordinate females by fluoxetine treatment (p=0.012). CSF 5HIAA concentrations were reduced by fluoxetine (p&lt;0.001) regardless of social status.ConclusionThe data show that increased 5HT activity following fluoxetine treatment in female monkeys alters socioemotional behavior in a status‐dependent manner. Notably, subordinate females are less aggressive and more affiliative during fluoxetine treatment. Future studies include determining whether these effects of fluoxetine are sex dependent and whether subordinate males respond similarly to subordinate females.Support or Funding InformationThis research was supported by an NIMH grant MH110212.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Male immigration triggers increased growth in subordinate female meerkats.

There is increasing evidence that some vertebrates can adjust their growth rate in relation to changes in the social context that affect their probability of breeding. Here, we show that, in meerkats (Suricata suricatta), which are singular cooperative breeders, subordinate females increase in body mass after their father is replaced as the dominant male in their natal group by an immigrant male, giving them regular access to an unfamiliar and unrelated mating partner, while their brothers showed no similar increase nor did subordinate females living in other stable groups (where male immigration did not occur did) in this time period. Moreover, subordinate females showed a greater increase in growth rate when their father was succeeded by an unfamiliar immigrant male than when he was replaced by a familiar male who was already resident. These results suggest that female meerkats can adjust their rate of growth to changes in the kinship composition of their groups that provide them with increased access to unrelated breeding partners, which may occur in other mammals as well when breeding opportunities change.