Behavioral correlates of learned aggression in male mice

The aims of this paper are to study the aggressive behavior in male mice with consecutive experience of victories in 2, 10, and 20 days (T2, T10, and T20 winners) of daily agonistic confrontations under the sensory contact model and to determine the most probable behavioral domains that should be used as animal models for learned aggression in humans. It has been shown that the structure of winners' behavior changes from test to test: the attacking behavior prevailed (81% of the total time) in the behavior of T2 winners. Attacks and diggings (herein: digging up and scattering the litter on the partner' territory) prevailed in the behavior of T10 winners (each approximately 40%). T20 winners demonstrated aggressive grooming half of the testing time and digging behavior 25% of the time. Correlational analysis revealed that the number of significant correlations between the behavioral domains (attacking, digging, aggressive grooming, self‐grooming, threats, rotations) and between different behavioral parameters (latency, number, total and average time) of one behavioral domain are growing from the second test to twentieth test, and the relationships between the behavioral domains change qualitatively. The following may be regarded as elements of learned aggression in male mice: (1) appearance of aggressive grooming instead of the intensive attacking behavior and (2) involvement of the digging behavior in the hostile behavior together with the threats and attacking behavior. Negative correlations between parameters of the behavioral domains may testify to the replacement of one behavioral pattern by another and reflect learned behavior. Positive correlations between certain behavioral domains may reflect the formation of a common motivational background for the winners' behavior. Aggr. Behav. 26:386–400, 2000. © 2000 Wiley‐Liss, Inc.     

An experimental approach to the study of learned aggression

The sensory contact technique increases aggressiveness in male mice and allows aggressive types of behavior to be formed as a result of the repeated experience of victories in daily agonistic confrontations. Some behavioral domains confirm the development of learned aggression in males similar to those in humans. The features are repeated experience of aggression reinforced by victories; elements of learned behavior after periods of confrontation; intent, measured by increase of the aggressive motivation prior to agonistic confrontation; and decreased emotionality, estimated by parameters of open‐field behavior. Relevant situation provokes increases in aggression (boundary aggression). This review summarizes data on the influence of positive fighting experience in daily intermale confrontations on the behavior, neurochemistry, and physiology of aggressive mice (winners). This sort of experience changes many characteristics in individual and social behaviors, these having been estimated in different tests and in varied situations. Some physiological parameters are also changed in the winners. Neurochemical data confirm the activation of brain dopaminergic systems and functional inhibition of serotonergic system in winners under the influence of the repeated experience of aggression. The expression of the neurochemical and behavioral changes observed in winners has been found to depend on the mouse strain and on the duration of their agonistic confrontations. Aggr. Behav. 26:241–256, 2000. © 2000 Wiley‐Liss, Inc.     

Effects of isolation during development on reactivity and home-cage agonistic behavior in rats

This experiment was designed to determine whether isolation during two developmental periods would contribute to differences in home-cage agonistic behavior and whether altered reactivity was a mediating variable. While early isolation (16–41 days) was shown to have a significant and sustained impact on agonistic behavior, isolation during a later developmental period (41–68 days) did not result in altered occurrences of agonistic behavior. While isolation did result in increased reactivity to both footshock and dorsal tactile stimuli, the pattern of these data suggested that hyperreactivity to tactile stimulation was not a satisfactory account of the increased agonistic behavior of rats raised in isolation.     

Motivational systems of social behavior in male rats and monkeys: Are they homologous?

A comparison is presented between the behaviors of male rats and male stumptail macaques that occur when two unfamiliar males are paired for 10 min. Results which have been presented in detail in separate papers elsewhere are compared and discussed here in terms of the hypothetical organization of motivational systems. The following motivational mechanisms appear to be homologous in the rat and monkey: offense, defense, submission, male sex, self grooming, and allogrooming. Two motivational mechanisms are analogous but not homologous: patrol/marking in the rat and display in the monkey. There is a shift in sensory modality of motivating stimuli from olfaction in the rat to complex visual and auditory stimuli in the monkey. There is also a shift in the modalities of motor patterns from predominant use of the mouth by the rat to use of the hands by the monkey. Both shifts affect most or all motivational systems of social behavior. It is hypothesized that the outer parts of motivational systems, their sensory and motor interfaces with the environment, change more rapidly and incrementally during the course of mammalian evolution than does the inner part, the integrational portion that consists of the motivational mechanisms.     

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.     

Social dominance and priority of access to drinking in Lemur macaco

Social dominance was analyzed in a group of Lemur macaco over a one-year period. A gonistic dominance was assessed by computing a dominance index for each individual in baseline conditions and in a competitive drinking situation, where success was measured as the amount of time in possession of the resource (a hottle of fruit juice). Dominance indexes during drinking competition were significantly correlated with baseline dominance indexes but were not correlated with individual drinking success. Adult females were agonistically do, omsmy over all other individuals, but were frequently challenged by juveniles of both sexes for access to the drinking bottle. In males, there was a significant negative correlation between age and dominance indexes during competition tests, and between age and drinking success. Results are analysed in the ligh of recent theories concerning the emergence of female social dominance. © 1993 Wiley-Liss, Inc.     

Aggression: Functions and control in social systems

This paper summarizes major research achievements concerning the understanding and control of aggression and destructive violence, seen in the contexts of evolution (both biological and cultural) and systems theory. Agonistic behavior, defined as behavior functional in situations of conflict between species mates, most probably evolved out of the function of defensive behavior but has since acquired a variety of other adaptive functions as well as the potential for destructive dysfunction. Recent research demonstrates the importance of culture in regulating human agonistic behavior, directing it toward either useful functions or destructive violence. Among advanced industrial nations, the United States has the most severe problems with violence as measured by homicide and murder rates. Similar but more extreme variation can be found among tribal societies. It is through cultural change that the available scientific information concerning improved methods for directing agonistic behavior into positive and beneficial channels must be achieved. Therefore, major emphasis should be placed on research dealing with human cultural evolution. The science of bringing about desirable social change is still in its infancy.     

Stigma Consciousness in Intergroup Contexts: The Power of Conviction

People vary in the extent to which they expect to be stereotyped, and these differences in “stigma consciousness” have cognitive and behavioral consequences that contribute to people's experience of stereotyping, prejudice, and discrimination (20). Here it is argued that high levels of stigma consciousness also have significant interpersonal consequences. Consistent with this claim, female participants who were high in stigma consciousness acted critically toward male participants whom they believed to be sexist. Moreover, these critical behaviors elicited unfavorable responses from the male participants, responses which then provided fodder for the women's belief that they would not like the men. The results are discussed in light of previous work on the target's perspective on stereotyping and call into question the wisdom of adopting a vigilant stance when interacting with out-group members.     

Behaviour of Young Growing Pigs in a Resident‐Intruder Test Designed to Measure Aggressiveness

A total of 125 growing pigs (47 days old) were tested for aggressive responses on two occasions using a resident‐intruder (R‐I) design. Our aims were twofold: (1) to attempt to replicate earlier work on pigs showing that resident aggression is a consistent individual characteristic, unaffected by weight or sex of the resident or intruder and (2) to develop behavioural measures to characterise the wide range of aggressive responses in the test. Resident pigs, housed since birth with littermates, were placed individually in a divided‐off portion of their home pen, and a smaller, unfamiliar intruder (approximately 66% of the resident's weight) was introduced. The test ended 5 min after the first investigation of the intruder by the resident or when one of the pigs began to attack the other (by delivering a sudden, rapid series of bites). On days 1 and 2, 33.6% and 43.2% of tests, respectively, ended in an attack by a resident. Intruder attacks were rare. Pigs were consistent in whether they attacked or not over the two tests, although attack latencies for pigs attacking in both tests were not correlated. Females were more likely to attack and attacked more quickly than males on the first test day but not in the second test or overall. Intruder sex had some effect on the test outcome (males were attacked more rapidly in the second test only). Resident and intruder weight had no effect. Aggressive pigs (meaning pigs that attacked vs. pigs that did not and fast‐attacking pigs vs. slow‐attacking pigs) showed a number of differences in behaviour during the R‐I test: (1) they took longer to make initial contact with the intruder in their first test; (2) they showed a higher frequency of aggressive acts (single head knocks, bites, and shoves); (3) they spent a greater proportion of the test engaging in social contact with the intruder rather than non‐social behaviours; (4) their social behaviour involved more postures directed toward the head as opposed to flank‐ or rear‐directed postures or re‐establishing social contact; and (5) they showed closer physical contact with intruders during social encounters, as characterised by their lower head positions. Some of these behavioural measures could be used to improve the measuring power of the test in the future. Improved behavioural measures would enable aggressiveness scoring among pigs that did not attack instead of classifying them all together as “non‐attacking.” Aggr. Behav. 28:401–415, 2002. © 2002 Wiley‐Liss, Inc.     

Pheromone‐mediated intrasexual aggression in male lizards,Podarcis hispanicus

Sex recognition is based on color signals in many species of lizards. However, olfactory stimuli are also clearly involved, and many species might rely primarily on chemoreception. We aimed to examine whether color pattern or odors, or a combination of both factors, induce the aggressive response of males of the lizard P. hispanicus. We experimentally manipulated the coloration and odor of male P. hispanicus, thereby creating groups with all combinations between coloration and odor of males or females. Using data from staged encounters, we compared the responses of resident males to the experimental groups of manipulated males and their response to unmanipulated individuals (males and females). Responding males reacted significantly more aggressively to intruders with male odors independent of their coloration, whereas intruders with female odors did not elicit aggressive responses but were preferentially courted, irrespective of their actual sex and body coloration. In addition, intruders with female odors elicited a higher number of tongue‐flick explorations than male odor ones. Comparisons with unmanipulated male and female intruders agreed with these expectations. Therefore, at least at close range, odoriferous cues seem to be more important than color patterns in sex recognition and intrasexual aggression by male P. hispanicus. We suggest that this might be a pattern commoner than expected in many species of reptiles.Aggr. Behav. 28:154–163, 2002. © 2002 Wiley‐Liss, Inc.