Maternal aggression in mice and rats towards male and female conspecifics

Although postpartum aggression is primarily studied in laboratory mice and rats, it is unclear how the two species compare in terms of the factors associated with peak levels of aggressive behavior. Using the same experimental protocol, we assessed the relative effect of intruder sex and time since parturition on the frequency of maternal aggression in Long-Evans rats and CFW mice. Females were studied for 2 consecutive cycles of pregnancy and lactation. During the first lactation, aggression was tested 2 times per week for 3 weeks in order to select animals that attacked at least once. During the second lactation, both pup care and aggressive behavior were assessed in detail. Testing occurred twice in each lactation week, with postpartum days 1–7, 8–14, and 15–21 considered weeks 1, 2, and 3, respectively. Maternal behavior towards 3 pups was observed for 5 minutes, followed by a confrontation with an intruder. Lactating females encountered female intruders once per week, and male intruders in the alternate weekly test. The same behaviors were measured in the 2 species, except for the tail rattle exhibited by mice and the aggressive posture shown by rats. Lactating rats and mice show similar decreases in pup care behavior as lactation progresses in time; yet the factors associated with peak levels of aggression differ between species. In Long-Evans rats, female intruders receive more attacks, threats, and aggressive postures than males. Frequency of attack bite and sideways threat declines in each passing week of lactation. Lactating mice are more aggressive toward male intruders throughout the lactation period. Mice still attack and threaten during the third week of lactation, but less often in comparison to the first week. Therefore, peak levels of aggression vary in mice and rats both as a function of intruder sex and lactation week.     

Play fighting and the development of agonistic behavior in male and female rats

Two longitudinal studies were conducted to quantify the social behaviors exhibited by both male and female Long-Evans rats from the immediate postweaning period until young adulthood. In Experiment 1, male sibling pairs engaged in a high level of play fighting during the early juvenile period but such activity declined to a level significantly lower than that of female and mixed-sex pairs after 54 days of age. In Experiment 2, social exchanges during maturation were examined during the presence and absence of the piloerection response in an effort to distinguish play fighting from agonistic interactions. In male pairs, piloerection was rarely seen before 55–75 days of age but thereafter occurred with increasing frequency especially among dominant males. Furthermore, subordinate males retreated from their dominant partners and remained in an escape chamber for a significant amount of time only during encounters involving the exhibition of piloerection. This finding suggests that piloerection can be useful in identifying play and aggressive interactions. In female and heterosexual pairs, piloerection was observed infrequently during social encounters occurring throughout maturation. In addition, when given the opportunity to escape, females were less likely to retreat from play activity if their partner was another female than a male.     

Relationships between testosterone metabolism in the brain,other endocrine variables and intermale aggression in mice

Relationships between some endocrine variables (plasma testosterone and estradiol; in vitro gonadal biosynthesis from pregnenolone precursor and adrenocortical biosynthesis from progesterone precursor; in vitro activity of 17β-hydroxysteroid de-hydrogenase (17β-HSDH) and of aromatizing enzymes in the subcellular fractions of the brain) and isolation-induced inter-male aggressiveness were studied. A significant positive correlation was found between fighting behavior, measured by the number of wins in a series of paired encounters, and the activity of brain 17β-HSDH. A significant inverse correlation was found between fighting behavior and the activity of aromatizing enzymes in the nuclear fraction of the brain. No significant correlations were found between fighting and the other endocrine variables investigated. These results may suggest that the conversions testosterone → androstenedione and testosterone → estradiol in the brain play a role in the control of inter-male fighting in the mouse. These results may also account for the effect of repeated wins and defeats on brain steroidogenesis.     

Influence of timing of post-weaning isolation on play fighting and serious aggression in the male golden hamster (Mesocricetus auratus)

Effects of timing of social isolation on play fighting and serious fighting were studied at different ages in male golden hamsters. Litters were isolated at 21, 35, and 65 days of age, and tested in a resident-intruder paradigm. Behaviors were compared within grous and with a fourth group of socially reared conspecifics. The earlier the pups were isolated, the more they engaged in play activities. Later, in adulthood, the aggression level of the same animals was retested using the same paradigm. The three isolated groups showed a high level of aggression, with significant differences among them. When compared with socially reared subjects, a reliable difference in the level of aggression was also found. These results support the view that early social experience is important, suggesting that isolation during early critical periods of socialization has a significant impact on play fighting, whereas short periods of isolation may be enough to trigger adult agonistic behavior. © 1994 Wiley-Liss, Inc.     

Agonistic behavior,plasma testosterone,and hypothalamic estradiol binding in male rabbits

The purpose of this study was to establish a relation between agonistic behavior, gonadal hormones, and their receptorial capacity at the central level. Male rabbits were observed in seminatural conditions and three components of their agonistic behavior were recorded: follow, attack, and chase. The three behaviors were mutually correlated and clearly differed among the four members of each group. Within the social group, one rabbit was agonistically more active than the others and his supremacy was associated with an increased level of peripheral testosterone and higher estradiol binding in the hypothalamus. On the whole, the values of the hypothalamic estradiol binding were positively correlated with the behaviors. The results show that, in the male rabbit, agonistic activity is associated with changes in testosterone concentration and in the binding at the central level of its aromatized metabolite estradiol. Aggr. Behav. 23:33–40, 1997. © 1997 Wiley-Liss, Inc.     

Diversity in agonistic behavior of croaking gouramis (Trichopsis vittata,T. schalleri,and T. pumila; Anabantoidei) and the paradise fish (Macropodus opercularis; Anabantoidei)

Agonistic encounters of all three species of the vocalizing genus Trichopsis were observed in order to compare species-specific fighting strategies and the specific investment in acoustics. Additionally, these encounters were compared to agonistic encounters of Macropodus opercularis which was considered to be mute. The aim of this comparison was to investigate if mute fishes stress visual or tactile displays. Within the genus Trichopsis, significant differences among the three species were found in qualitative and quantitative analysis of displays. Frontal display occurred only in Trichopsis vittata, whereas a strong tail-beating while vocalizing was only observed in Trichopsis pumila. Fight duration and the number of sounds and circlings were highest in Trichopsis schalleri. The largest relative distances between circling opponents occurred in T. pumila, the smallest species. Also, the number of attacks was lowest in T. pumila. Fighting assessment seemed to be different in each species. For the first time, sound production has been reported for Macropodus opercularis (infrequently and with extreme low sound pressure levels), but much more investment in visual and tactile displays has been demonstrated. Lowering the branchiostegal membrane and spreading the opercula occurred only in M. opercularis and was never observed in any of the Trichopsis species. The number of attacks was higher in Macropodus than in any Trichopsis species. The relative distance between Macropodus opponents while circling was closest compared to the three Trichopsis species. Visual and contact displays are reduced in extensively vocalizing fish species, like Trichopsis sp., compared to mute or seldom vocalizing species, like Macropodus. © 1996 Wiley-Liss, Inc.     

Dominance and aggression in various sized groups of red deer stags

The influence of group size on agonistic behaviour of “white” red deer stags (Cervus elophus L.) of different ranks in the hierarchy was examined during artificial feeding. Size of the social group was dependent on the season in the year and on age and general rank within the whole bachelor group inhabiting the enclosure of the stags. Group size differentially affected the behaviour of the stags according to the rank of the individual in the particular groups. Increased group size resulted in increased agonistic activity in top-ranking stags. The number of attacks directed towards bottom-ranking stags by other group members was also elevated. Stags of intermediate rank position showed a decrease in the number of interactions involved and a suppression of agonistic activity.     

The effects of two response-elimination procedures on reinforced and induced aggression.

Pecks against a stuffed pigeon were reinforced according to a fixed-interval schedule for one group of pigeons and a variable-interval schedule for a second group. Red and green stimulus lights were alternately illuminated. Subsequently, food deliveries no longer occurred during one color (extinction). In the presence of the other color, food was presented only when no attack occurred for 30 sec. When attack produced food, all pigeons generally exhibited characteristic fixed-interval or variable-interval response patterns. Two birds in each group frequently exhibited postreinforcement schedule-induced aggression. Attack was reduced to low levels at approximately the same rate by extinction and differential reinforcement of other behavior. For birds that had previously exhibited schedule-induced aggression the initial reduction of attack during the second experimental phase was followed by induced attack immediately after food delivery in the differential-reinforcement-of-other-behavior component and upon onset of the extinction component, Either extinction or differential reinforcement of other behavior may eliminate reinforced aggression but may be relatively ineffective for reducing induced attack.     

Effects of serotonin receptor agonists and antagonists on offensive aggression in mice

The effects of serotonin receptor agonists 5-methoxytryptamine and quipazine, and antagonist mianserin on resident-intruder offensive aggression were investigated. Both agonists reduced aggression. The fact that 5-methoxytryptamine preferentially binds to 5-HT-1 receptors strongly suggest that the decreased aggression with S-methoxytryptamine was related to stimulation of an inhibitory 5-HT-1 receptor. It is also suggested that the reduction in aggression with quipazine was related to quipazine's preferential binding to the 5-HT-1 receptor. The 5-HT-2 receptor antagonist mianserin reduced aggression suggesting that 5-HT-2 receptor blockade is inhibitory for aggression. Thus, two serotonin classes of receptors may be differentially involved in offensive aggression.     

Inter-male aggression in mice: Influence of gonadectomy and prior fighting experience

Groups of adult male mice of the Rockland-Swiss strain were paired 0, 2, 7, or 15 times with adult male stimulus animals rendered non-aggressive by extirpation of olfactory bulbs. All animals were castrated and tested until fighting ceased, following which each was given testosterone replacement and tested until fighting was reinstated. More than 50% of mice with no pre-castration fighting experience fought following gonadectomy. Castrated animals permitted 15 pre-castration pairings fought significantly longer than did animals of any of the other treatment groups. Finally, there was no difference among the groups with regard to the latency to resume fighting following the commencement of testosterone replacement. It is concluded that fighting experience enhances the persistence of the behavior following castration.     

Anger,aggression, and humor in newfoundland floor hockey: An evolutionary analysis

This paper examines patterns of anger, aggression, and humor during 95 floor hockey games in a small fishing village in Newfoundland. The observed behaviors meet the prediction, based on evolutionary theory, that anger and aggression will be more frequent among males at the age when mate competition is most intense. Aggression was also found to be combined with humor most frequently in interactions among players attempting to form social relationships. This last finding is consistent with the hypothesis that combining humor (smiling and laughing) with what would otherwise be interpreted as aggressive behavior is a means of establishing trusting relationships between individuals. The potential contribution of an evolutionary approach to studies of anger and aggression is discussed. ©1993 Wiley-Liss, Inc.     

Home correlates of aggression in preschool

Is aggressive behaviour in preschool more closely related to individual characteristics of the child as assessed at home, to aspects of mother-child interaction, or to the motherchild relationship? The issue was studied in three replications. Aggression in preschool was related to temperamental characteristics in girls but not boys, and to Self-esteem. There were very few significant correlations between aspects of mother-child interaction and hostility in preschool, but hostility with peers was related to the absence of positive or presence of mildly negative interactions with the sibling. Aggression in preschool was related to an aspect of the mother-child relationship; least aggression was shown by those childred whose mothers used warmth and control more or less “in balance” (authortative Mothers). Such children also differed in other aspects of the mother-child relationship, and these provided some explanation of those children who appeared to be exceptions to the “balance” hypethesis. © 1993 Wiley-Liss, Inc.     

Agonistic behavior and social reactivity of LG/J mice in both an arena and a seminatural setting

In order to determine the relatively long-term effects of having been primed for agonistic behaviors in an arena setting, 28 male LG/J mice were observed for these behaviors in a seminatural environment for a period of 5 days following a 20 min arena test. The mice were first placed in an arena in which they were allowed either immediate physical contact with another strain (control condition) or were briefly separated from another strain by a transparent partition before being allowed physical access to them (priming condition). Subjects, recorded as either having fought or not fought in the arena, were then placed in a 101 cm square seminatural setting. Seven trials, using 8 LGs each (4 arenaexperienced males and 4 naive females), were made, and agonistic behaviors were recorded for the priming and control condition subjects. The results showed that the control condition fighters (CF) like the priming condition fighters (PF) fought in the arena situation, but different agonistic patterns in the seminatural setting were noted. While in the seminatural environment, both CF and PF mice were attacked frequently and submitted frequently, but PF mice attacked opponents more frequently than did CF subjects (p < 0.025) and elicited significantly more submissions from opponent mice than did CF mice (p < 0.025). It is concluded that: (1) there are more and different agonistic behavior patterns available in the more natural environment than in the arena setting, and more specifically (2) there is a greater effect on agonistic behaviors in a seminatural environment for mice that fought when exposed to the arena priming procedure as compared with mice having fought in the arena control condition.     

Parent–child interactions and relational aggression in peer relationships

The major aim of this review is to propose new ways of thinking about the role of parents in the development and course of children’s relationally aggressive behavior. An important theoretical framework from which to start thinking about linkages between parenting and relational aggression is provided by attachment theory. Attachment theory proposes that early family experiences are an important basis for the development of later peer relationships. Recent studies are only beginning to suggest possible linkages between children’s parental attachment and relational aggression. One possible reason for the scant research is that theoreticians studying these constructs have not yet developed a conceptual framework combining the two, but rather have focused on different characteristics of different interpersonal contexts. Based on the premise that both relational aggression and attachment are relational constructs and given the already established correlations between insecure attachment and physical aggression, this paper will attempt to devise a heuristic model that may serve as an aid to discover links between parent–child interactions, attachment, and relational aggression. Finally, implications for future studies of relational aggression are discussed.     

Illuminating the nomological network of digital aggression: Results from two studies

We examined the nomological network surrounding digital aggression (DA), in regards to other forms of aggression/antisocial behavior and individual difference variables commonly associated with other forms of aggression/antisocial behavior. Two large samples of university students (N = 713 and 633, respectively) completed a series of questionnaires and in some cases, an additional experience sampling study. Results revealed that, in emerging adulthood, DA appears to have a unique demographic profile relative to the other forms of aggression and antisocial behavior. Results further suggested that, when examined simultaneously, only social aggression and non‐aggressive rule‐breaking evidenced independent associations with DA. These associations persisted even in the absence of social media use. Unique associations with most individual difference variables dissipated once we controlled for social aggression and rule‐breaking, although DA was independently associated with extraversion and alcohol use problems. Such findings begin to embed DA in its broader nomological network and suggest clear functional links with both social aggression and non‐aggressive rule‐breaking.

     

Defensive aggression in terns: Effect of species,density, and isolation

Defensive aggression was examined in seven species of terns during the hatching period when young are most vulnerable and adults most responsive. Aggression toward an unfamiliar person varied with respect to species, flush distance, approach distance, number of birds overhead and diving, and number of dives per 2 min for all birds and the nest owner. Defensive aggression involved birds circling over and diving at the experimenter. Generally, flush distance was negatively correlated with nest density, while the number of birds diving was positively correlated with the nest density. The number of birds diving was positively related to the number of dives, dives by the owner, and the number overhead.     

Social isolation,aggression, and dominance in attacks in juvenile angelfish,Pterophyllum scalare

The effects of social isolation on aggressive behavior and rank order have been investigated in small groups of juvenile angelfish, Pterophyllum scalare. An experimental protocol including a “double transfer” of the subjects was used, in which fish were transferred to new aquaria in groups, before subsequent isolation and regrouping. A significant decrease in aggression was observed in the first recording session following both isolation and group transfer, after which the level returned to that recorded in the home tanks. The social hierarchy was also perturbed, but changes generally involed the two highest ranking fish in two out of the three groups, and were found not to be statistically significant. The behavior patterns are interpreted as adaptive responses to environmental change. © 1993 Wiley-Liss, Inc.