Establishment Of Dominance Relationships Research Articles

Gonadal steroid hormone receptors in the medial amygdala contribute to experience-dependent changes in stress vulnerability

Social experience can generate neural plasticity that changes how individuals respond to stress. Winning aggressive encounters alters how animals respond to future challenges and leads to increased plasma testosterone concentrations and androgen receptor (AR) expression in the social behavior neural network. In this project, our aim was to identify neuroendocrine mechanisms that account for changes in stress-related behavior following the establishment of dominance relationships over a two-week period. We used a Syrian hamster model in which acute social defeat stress increases anxiety-like responses in a conditioned defeat test in males and in a social avoidance test in females. First, we administered flutamide, an AR antagonist, via intraperitoneal injections daily during the establishment of dominance relationships in male hamsters. We found that pharmacological blockade of AR prevented a reduction in conditioned defeat in dominant males and blocked an upregulation of AR in the posterior dorsal medial amygdala (MePD) and posterior ventral medial amygdala (MePV), but not in the ventral lateral septum. Next, we administered flutamide into the posterior aspects of the medial amygdala (MeP) prior to acute social defeat stress or prior to conditioned defeat testing in males. We found that pharmacological blockade of AR in the MeP prior to social defeat, but not prior to testing, increased the conditioned defeat response in dominant males and did not alter behavior in subordinates. Finally, we developed a procedure to establish dominance relationships in female hamsters and investigated status-dependent changes in plasma steroid hormone concentrations, estrogen receptor alpha (ERα) immunoreactivity, and defeat-induced social avoidance. We found that dominant female hamsters showed reduced social avoidance regardless of social defeat exposure as well as increased ERα expression in the MePD, but no status-dependent changes in the concentration of plasma steroid hormones. Overall, these findings suggest that achieving and maintaining stable social dominance leads to sex-specific neural plasticity in the MeP that underlies status-dependent changes in stress vulnerability.

Shades of gray mouse lemurs: Ontogeny of female dominance and dominance-related behaviors in a nocturnal primate.

The ontogeny and establishment of dominance relationships in young individuals have been investigated in various group-living, diurnal primates but respective information is almost entirely lacking for nocturnal, non-gregarious species. As in many other mammals male primates often represent the dominant sex, but the opposite phenomenon (female dominance) is particularly frequent in lemurs, although almost nothing is known about its development. Therefore, we investigated the development of intersexual dominance in parallel to age-related changes in other relevant behaviors in the gray mouse lemur, a solitary forager with female dominance. In particular, the temporal trajectories of social play, marking behavior, social tolerance, and agonistic behaviors were characterized in captive dyads of three different age categories (ACs), among juveniles (ACI: 4-5 months, N = 6), adolescents (ACII: 8-9 months, N = 8) and young adults (ACIII: 12-13 months, N = 8). Data were collected during a series of three encounter experiments between one male and one female per dyad and age category (total observation time: 49.5 hr). Play behavior was observed in all age classes, although the number of playing dyads decreased with increasing age. A significant age-dependent increase in marking behavior was found in females, especially in substrate rubbing and urine washing, but not in males. Although conflict rates did not differ significantly between ACs, females started to win more conflicts from ACII onwards, and social tolerance decreased partly with increasing age. Clear dominance relationships were not observed in ACI and first indications of dominant females were found in ACII with an increasing number in ACIII. This study provides first information about the ontogeny of female dominance in a nocturnal primate and shows that this behavior develops relatively late during ontogeny. In conclusion, this study provides evidence for significant changes in the social lives of maturing mouse lemurs and a rather late social maturation in this species.

Social status and day-to-day behaviour of male serotonin transporter knockout mice

Humans differing in the amount of serotonin transporter (5-HTT) are known to be differentially prone to neuropsychiatric disorders. Genetically modified mice eliciting abrogated transporter function display a number of corresponding phenotypic changes in behavioural tests. However, a characterisation of the effects of serotonergic malfunction on the day-to-day life is still missing. Yet, this is precisely what an animal model is needed for in order to be meaningful for translation into human anxiety disorders. Homozygous 5-HTT knockout mice, heterozygous 5-HTT mice, and wild-type controls were housed in groups of males of the same genotype in spacious and richly structured cages. This enriched environment allowed the animals to show a wide variety of spontaneous behavioural patterns quantified by a trained experimenter. Additionally the mice could emigrate from the cages through a tunnel and a water basin. The results revealed unaltered daily behaviour in heterozygous mice. In knockouts, however, reduced locomotion, increased socio-positive behaviour, and reduced aggressive behaviour were observed. Nevertheless, all groups showed a significant amount of aggressive behaviour and there were no differences regarding the establishment of dominance relationships, emigration, and the number of animals remaining in their groups. In a second step, pairs of heterozygous and wild-type males and pairs of knockout and wild-type males were brought together in order to assess their ability to obtain a dominant social position in a direct encounter. Heterozygous mice did not differ from wild-type mice but knockout mice were significantly inferior in obtaining the dominant position. In addition to confirming multiple effects of abolished 5-HTT function in a real life situation, this study supports the central role of the 5-HTT in the control of social interactions.

Establishment of dominance relationships in gilthead sea bream Sparus aurata juveniles during feeding: effects on feeding behaviour, feed utilization and fish health

In gilthead sea bream Sparus aurata held in groups of two, five or 10 fish, social hierarchies were observed. Subordinate S. aurata were characterized by elevation of basal levels of plasma cortisol, together with a reduced immunological potential. Subordinate fish also showed lower feed intake, feed utilization and lower growth. Fatty acid composition was also affected by social status, with a lower content of saturated acids, oleic and eicosapentaenoic, in muscle and liver of fish considered as subordinate. Results show that social hierarchy acts as a stressor in S.aurata.

Social rank and winter forage quality affect aggressiveness in white-tailed deer fawns

Achieving a high social rank may be advantageous for individuals at high population densities, because dominance status may determine the priority of access to limited resources and reduce individual loss of body mass. The establishment of dominance relationships between individuals involves variable levels of aggressiveness that can be influenced by resource availability. The relationship between social rank and aggressiveness and the impacts of resource abundance on aggressiveness are, however, poorly understood, but may be relevant to understand the mechanisms determining dominance relationships between individuals. We experimentally simulated, in seminatural enclosures, a deterioration of winter forage quality induced by a high-density deer population and examined the effects of (1) social dominance and (2) diet quality on aggressiveness, forage intake and body mass loss of white-tailed deer, Odocoileus virginianus, fawns during two winters. Within diet-quality treatments, fawns were consistently organized into linear hierarchies and showed clear dominance relationships. Dominants initiated more interactions and showed higher aggressiveness than subordinates, but subordinates had higher forage intake than dominants throughout winter. Social rank did not influence cumulative body mass loss of fawns. During both winters, fawns fed the control diet maintained their aggressiveness level, whereas fawns fed the poor-quality diet decreased it. Our experimental approach revealed that white-tailed deer responded to a reduction in winter forage quality by modifying their aggressiveness, indicating that ungulates may show plasticity not only in their foraging behaviour in response to decreased resources but also in their social behaviour.

Individual coping characteristics, aggressiveness and fighting strategies in pigs

Individual pigs, Sus scrofa, differ considerably in how aggressive they are during encounters with unfamiliar conspecifics. We examined whether individual coping characteristics of pigs were predictive of aggression during social encounters and the resulting social status. Piglets were subjected to the Backtest during the suckling period, as their behavioural response in this test seems to be predictive of their coping style. Each piglet was restrained in a supine position for 1 min and the resistance (i.e. number of escape attempts) was scored. After weaning, 30 ‘high-resisting’ (HR) and 30 ‘low-resisting’ (LR) pigs were regrouped with unfamiliar pigs of similar weight and we recorded their aggressive behaviour for 180 min. In addition, we assessed the social rank of each pig. HR pigs showed more aggressive behaviour than LR pigs: they initiated more fights, started fighting earlier and spent more time fighting during the observation period. HR and LR pigs did not differ, however, in achieved social rank. Level of self-initiated fighting was positively correlated with social rank in LR pigs, but this relation was not found in HR pigs. In conclusion, the coping style of pigs is related to their aggressive behaviour and the establishment of dominance relationships after mixing. Our results indicate that LR pigs are flexible in using aggression, whereas the high level of aggression of HR pigs regardless of their success in encounters suggests that these animals are more rigid in their aggressive behaviour.

Establishment of dominance in domestic Norway rats: Effects of the degree of captivity and social experience

The effect of the level of captivity and prior social experience on the establishment of dominance was examined in 16 colonies of albino rats. Males were assigned to one of four treatment groups: aggressive experience, defeat experience, exposure to electric shock, and controls. Following treatment, colonies of four males were established for 12 days in one of three different captive setings: a large outdoor pen, an indoor pen, or laboratory group cages. Effects of treatment were minimal; however, the degree of captivity significantly affected the display of aggression and the establishment of dominance relationships. In the two pen settings, attacks were more frequent and dominance relationships were established in six of eight colonies. Attacks in the laboratory cages occurred almost exclusively during the first 2 days, and no dominance relationships were established in any of eight laboratory cage colonies.

Aggressive behaviors of the japanese brown bear

Film analysis and direct observation suggest that 2 very different types of intra-specific fights occur among Japanese brown bears maintained in large stable colonies. Disputes arising over food are short, and involve such activities as threatening, muzzling, chasing, and flight. Weapon use during feeding fights primarily involves slashing blows to the back or head areas of the opponent. In contrast, “spontaneous” fights are longer, and consist almost exclusively of wrestling, with bites and forepaw blows directed at the opponent's ruff area. These spontaneous fights occur primarily among the larger and higher-ranked male bears, especially among animals with closely adjacent rankings. It is suggested that such fights facilitate the establishment of dominance relationships by providing an opportunity for mutual assessment of strength and stamina without serious risk of injury.

The establishment of dominance relationships in the jewel fish, Hemichromis bimaculatus (Gill), as related to prior exposure to and configuration of visual cues

To investigate the interaction between prior exposure to and configurational aspects of visual cues on dominance behavior in jewel fish, subjects were individually maintained for 2 days in aquaria containing either four plants clumped in the center (C condition) or one plant in each corner of the aquarium (D condition). Pairs of fish met in a dominance encounter in a test aquarium similar to one pair member's “home” aquarium. C condition fish dominated D condition “intruders”, but D condition fish did not dominate C condition intruders. Also, more dominance fighting occurred in the C test aquarium than the D test aquarium. Results are related to the differential biological relevance of these visual cues to territorial establishment and defense.

The Establishment of Dominance Relationships in the Blue Gourami, Trichogaster Trichopter Us (Pallas)

Abstract I. Hierarchical relationships in the blue gourami, T. trichopterus, are characterized by two distinct temporal phases — an ephemeral period of dominance establishment and a period of hierarchical maintenance. Variable behavior patterns are shown in the mutual fighting during dominance establishment between pairs of fish, but the initial outcome is always a discrete event, i.e., one fish dominates the other. The influence of several parameters on this period of dominance establishment has heen investigated in this study, and the probable relationships between these parameters and patterns of behavior characteristic of ultimate winners and losers has been discussed. 2. Prior residency per se does not increase the "dominance potential" of this species. Residency was not found to act as a positive input for increased aggressiveness; rather it was concluded that the "fright" component due to moving a fish into unfamiliar surroundings acts to inhibit the "normal" expression of aggressive behavior. The residency factor interacts both with prior dominance experience and with time since that experience. 3. Prior experience as a dominant increases the probability that a fish will win a subsequent encounter, while fish previously dominated within the last 24 hr seldom win subsequent encounters. Forty-three behavior measures recorded during these subsequent encounters did not indicate an arousal phenomenon due to dominating a partner for 24 hr, but a highly significant inhibitory effect on all agonistic behaviors was observed for those fish which had been dominated for 24 hr. These inhibitory effects wane during the next 24 hr, provided the dominating partner is removed. It is conceivable that short-term arousal input due to winning per se may temporarily lower aggressive thresholds, but whether these lowered levels would be "transferred" into a new fighting context is questionable. 4. The inhibitory effects of "non-residency" are in part dependent upon the "dominance state" of a fish. Dominant-experienced fish are only slightly inhibited by non-residency, while subordinate-experienced fish are strongly inhibited by this factor. A s the prior experience effect wanes, the fright due to unfamiliarity with surroundings is less inhibiting. 5. Initially, the decrement in responses due to prior experience is greater than the decrement due to non-residency. 6. Two measures of intra-individual sequence uncertainty (entropy) were calculated. The first included the uncertainty associated with all the elements defined for the system, i.e., [L, O, BS, F,, S, and P], while the second entropy values were based on only the agonistic set [L, O, BS, and F]. The prior experience factor influenced both entropy values more strongly than it did any other single variable. 7. The relative sizes of opponents seem paramount in deciding bout outcome when standard length differences (Δ S.L.) are beyond the range tested here, i.e., where Δ S.L. > 5 mm. As the time since the last dominance experience increases, the influence of Δ S.L. also increases. The length of time that two fish fight was shown to depend upon Δ S.L., while the only behavior correlated with relative size was BS rate. Smaller fish bit more frequently than did their counterparts. Finally, entropy measures were found to be functions of Δ S.L. Since entropy values increase as Δ S.L. approaches zero, entropy may contribute more to the "dominance vector" when fish are of nearly equal size. Other variables, such as biting intensity, may be more important as "dominance vector" components when one fish is considerably larger than its partner. 8. A "dominance vector" was defined in this study as that complex of variables which contribute to the defeat of one fish by another. Such a complex, highly integrated variable remains hypothetical. Some possible components of this vector indicated by this study include: variables associated with fin tugging rate or duration, biting intensity, unpredictability, and redundancy of certain inter-individual or intra-individual dyads such as [B1-Bw] or [LW-B1] where their conditional probabilities may be important. 9. A simple descriptive model relating environmental, experiential, size, temporal or other parameters to the dominance vector was presented. A mechanism describing how such a vector might operate in determining bout outcome was also postulated.