Role of female behavior in controlling population growth in mice

Sex ratio does not appear to be a factor in generating the characteristic population growth curve. Freely growing populations of house mice, consisting of all females and one male, stopped their growth at approximately the same densities as normal sexratio populations used as references. The mechanism(s) of female control of population dynamics may be related to female aggressive behavior. As the all-female/one-male populations approached their maximum size, the females began to show wounding patterns and social hierarchies in much the same manner as males in populations with normal sex ratios. The male in each of the populations was severely wounded in the posterior region, and each lost its tail as a result of injuries which could have been inflicted only by the females. The female social hierarchy can be seen only when there has been reproduction and population growth. Assembled populations of all females rarely exhibit aggressive behavior. Female aggression becomes apparent only when the population approaches its maximum size and thereafter. These data are consistent with the hypothesis that males are competitive among themselves for territory and social rank, and ultimately to mate with the females. Other investigators have indicated that females respond to population size, which may reflect increased competition between the females with the establishment of territories. Thus female agression may control population growth, a role previously ascribed to male aggression.     

Effects of alpha and beta adrenergic antagonists on aggressive behavior in male mice

The effects of a variety of alpha and beta adrenergic antagonists were examined on the social encounters of isolated male mice with anosmic male partners. A range of alpha antagonists, including phentolamine, prazosin, and yohimbine, all suppressed social aggression. A range of beta antagonists, including propranolol, atenolol, metaprolol, and ICI 118, 551, also reduced this type of attack. Ethological assessment of the lowest effective dose of these adrenergic antagonists revealed a marked inhibitor action on offensive, social, and nonsocial behavior, while defensive responses and immobility were enhanced. It is concluded that the noradrenergic system has a significant non-specific role in mediating intermale aggression via both alpha and beta adrenergic receptor subtypes. © 1993 Wiley-Liss, Inc.     

Gender-specific social experiences and the development of aggressive and sexual behavior in male mice

This study examined influences of gender-specific social experiences on the development of aggressive and sexual behavior in male mice. To determine the effects of gender-specific social experience three different types of groups were constituted after the animals had been weaned. The subjects were randomly assigned to different treatments. Female groups were composed of one experimental male and three female cohabitants. Male groups were composed of five experimental males each, and the mixed-sex groups were composed of two experimental males and of two females. The experimental subjects stayed in these groups until the age of approximately three months, when the testing for sexual and aggressive behavior commenced. For the sexuality tests, a receptive female was placed in the home cage of the experimental male for ten minutes. A nonaggressive male was placed in the home cage of the experimental male for seven minutes for the aggression tests. The experimental males were administered both sexuality and aggression tests, the sequence of testing sexual and aggressive behavior was systematically varied in order to control the influence of the two different types of behavioral tests. The results showed that males with only male social experiences showed fewer responses and were less active in both the aggression and sexuality tests than the males from the two other types of groups. Significant positive correlations between activity during aggression and sexual tests were obtained for all three groups. © 1994 Wiley-Liss, Inc.     

Effects of neonatal cyproterone acetate administration on isolation-induced fighting behavior and mounting behavior in male and female TO strain albino mice

The effects of a single dose (1 mg) of cyproterone acetate administered on either day 1 or day 20 of life on the adult behaviors of male and female TO strain albino mice were studied. The mice were tested both in a “standard opponent”-type situation and in a similar test using a hormonally primed receptive female, after being gonadectomized and maintained with testosterone propionate as adults. Neonatal treatment with this compound had little effect on subsequent fighting behavior in either sex, but clear evidence was produced that this treatment masculinized the sexual behavioral potentialities of the females, an effect which was apparent in animals which had been injected on either day 1 or day 20 of life. Indications were obtained that females treated neonatally with cyproterone acetate were capable of differentiating between the male and female “opponents” in a manner similar to the male. The effects of this treatment on fighting behavior consequently appear to be dissimilar to the effects of neonatal castration in this species. However, the effects on mounting behavior in the females, evidenced in adulthood, seem Likely to be a consequence of the weak androgenic properties of the antiandrogen. The administration of cyproterone acetate neonatally appears to have a more dramatic effect on the adult weights of endocrine organs in females than in mates.     

Comparison of agonistic behavior in individually-housed male mice with those cohabiting with females

Videotape recordings of male mice group-housed, individually-housed and cohabiting with females, were rated for their agonistic behavior in a “standard opponent” test. Previously mated male mice showed more fighting than isolated or grouped males. Marked differences in other social and non-social behaviors, which could not be accounted for in terms of increased fighting, were not evident. These results suggest that agonistic behavior may be usefully studied by examining male mice that have cohabited with females. One obvious advantage is that such mice cannot be dismissed as being “socially deprived,” as is sometimes claimed for individually-housed mice. Other advantages are that aggressiveness is induced quickly, at high levels, and the mice appear very sensitive to hormone manipulation following castration.     

Relationship between sexual activity and intraspecific fighting in male mice

Significantly more male mice having cohabited and mated with intact females subsequently displayed intraspecific fighting behavior after castration than males having cohabited with noncycling (ovariectomized) females. Also, intact males that failed to achieve a criterion for aggression during three screening tests subsequently showed a marked increase in fighting after having had copulatory experience relative to males that lived with ovariectomized females. Lastly, spontaneously aggressive males copulated more frequently than nonfighters.     

Differences between two strains of mice,selectively bred for high and low aggressiveness,in the capacity of male odors to affect aggressive behavior

The connection between a genetic disposition for aggressive behavior and the odor signal system in male mice was studied. The males belonged to two strains of mice which have been developed by selective breeding for high- (TA) and low aggressiveness (TNA). Urine from the high aggressive strain (TA), when applied to castrates, stimulated the aggressiveness of NMRI males while TA-soiled bedding suppressed their aggressiveness. In response to male odors from the low aggressive strain (TNA), the NMRI males showed quite contrasting reactions. The results provide evidences of a correlation between the hereditarily determined disposition for aggressive behavior and the odor signal system in TA- and TNA males.     

Effects of early exposure to mating on adult sexual behavior in male mice varying in their genetic disposition for aggressive behavior

This study examined whether the sexual behavior of adult male mice is influenced by exposure in early postnatal life to brief episodes of mating. Another focus of interest was the interplay between a genetic disposition for aggressive behavior and the early exposure experiences. The subjects used in the study were male mice of the fiftysixth generation of selection for high (Turku aggressive, TA) and low (Turku non-aggressive, TNA) levels of aggressiveness. Moderately aggressive males of the parental strain (normal, N) were also used. Subjects of each strain were exposed from 21 to 32 days of age to mating mice behind a wire mesh screen. Control subjects were placed in a comparable enclosure, but were exposed to nothing. The results showed that male mice exposed to mating early in life showed a higher rate of activities in the sexuality tests, including aggressive responses. A genetic potential for aggressive behavior was related to a higher degree of sexual activity, and the early exposures optimized the hereditary attributes. The relation between sexual and aggressive behavior is discussed. © 1994 Wiley-Liss, Inc.     

Aversive odors of male mice: Experiential and castration effects,and the predictability of the outcomes of agonistic encounters

The relationship between the aversive urine odors of adult male mice and their agonistic interactions was examined. The urine of 28 isolated intact donors was tested for its aversiveness before the donors had won or lost an agonistic encounter, by spotting a portion of an open field with their urine. Group-housed males (n = 28), each tested with the urine of an ultimate winner and loser, as well as a castrate, avoided both intact types. The urine of castrates was not aversive. Another group of subjects (n = 28), tested with urine collected following the encounter between donors, provided identical results. A second experiment examined the aversiveness of urine from 24 isolate mice, and their responsiveness to urine of other isolates, prior to their encounter. The urine was not highly aversive to the isolates However, winners and losers differed in their responsiveness, as ultimate winners exhibited greater aversion. The results are discussed with regard to territorial maintenance via odors, and how differential responsiveness to odors may influence the outcomes of agonistic encounters.     

Some characteristics of the aggressive behavior of mice after prolonged Isolation: Intraspecific and interspecific aspects

Experiments on mice have demonstrated changes in the relationships, interdependence and sequence of behavioral items following prolonged isolation. It was found that aggression in isolates was stereotyped and hardly amenable to the control not only by intraspecific but also by interspecific factors. Isolated mice, in contrast to the group-reared animals, spontaneously attacked adult rats. This finding was interpreted as being due to a disruption of behavioral plasticity under circumstances of prolonged isolation from conspecifics.     

Effects of early exposure to intermale aggression on the aggressiveness of adult male mice varying in their genetic disposition for aggressive behavior

This study examined whether adult male aggression is influenced by either visual or olfactory exposure in early postnatal life to brief episodes of aggression. Another focus of interest was the interplay between a genetic disposition for aggressive behavior and early exposure experiences. The subjects used in the study were male mice of the 49th generation of selection for high (Turku Aggressive, TA) and low (Turku Non-Aggressive, TNA) levels of aggressiveness. Moderately aggressive males of the parental strain (Normal, N) were also used. Subjects of each strain were exposed from 21 to 32 days of age to fighting males either behind a wire mesh or glass screen. Control subjects were isolated during the entire experimental period. At 90–100 days of age, each subjects was tested three times for its aggressiveness. Exposure to fighting males behind a wire mesh screen enhanced later aggressiveness of juvenile male mice. Juveniles exposed solely to visual cues were comparable to isolates, both groups showing less adult aggression. Early experience and the genetic disposition for aggression were correlated; TA males showing the greatest increase in aggressive behavior. The role of early olfactory learning is discussed. © 1993 Wiley-Liss, Inc.     

Habituation of aggressive behavior in mice: A parametric study

The decline of aggression as a result of repeated episodes of fighting may represent a habituation phenomenon. The frequency of biting and sideways threat by male mice toward conspecific intruders declined over ten 5-min confrontations. Aggression returned to about 50% of original levels when a new intruder was introduced. Variations in length or frequency of confrontation indicated that the rate of decline of attack bites and sideways threats depended on these confrontation parameters. The condition that provided the fewest opportunities to fight provided the least decline in the frequency of attack and threat. The frequency of attack bites and sideways threats elicited by the presentation of a new intruder after repeated confrontations was greater than the frequency of attack bite and sideways threat in the last confrontation with the original intruder, when the resident and intruder were relatively inexperienced. Spontaneous recovery of attack and threat occurred but rate of recovery did not depend on confrontation parameters. The results indicate that the decrement of aggression in mice in repeated confrontations may be the result of habituation but fatigue is an important cofactor.     

Intermale fighting and predatory behavior in house mice: An analysis of behavioral content

Two forms of aggression, intermale and predatory, wwere compared on the basis of behavioral content. Male wild mice were presented with opponents of two types, nonaggressive male mice and crickets, and the amounts of time spent in each of 18 behaviors were recorded. Results from analyses of variance and principal components analyses indicated that the structure of behavioral content differs greatly for intermale fighting and predatory behavior. It was, therefore, concluded that the integrated patterns of beahvior were controlled by separate mechanisms for predatory versus intermale aggression.     

Infanticide and maternal aggression: Synchrony of male and female reproductive strategies in mice

Thirty-six percent of male mice from three strains attacked newborn pups sired by another male. No male attacked its own offspring. Females did not show differential aggression toward males likely (strangers) or unlikely (sires) to attack their pups. Both forms of aggression were unaffected by housing in rooms which did or did not contain the aggression targets. The three strains differed in strength of maternal aggression but not in the incidence of infanticide. Females showed more aggression when mated with males of the same, rather than a different, strain but no differences with intruders of the same or a different strain. Infanticide by males is best viewed as a postcopulatory, intermale-competition strategy, and maternal aggression as a counter strategy.     

Anogenital distance and dominance status in male house mice (Mus domesticus)

Factors influencing the tendency to be aggressive were investigated in male house mice using a series of paired encounters. Body size, body lenght, body temperature, age, and anogenital distance were measured on all males. Paired encounters were conducted using a standard mouse cage as an arena. Across 64 males involved in 224 encounters, the tendency to be dominant and win encounters was significantly correlated only with anogenital distance (r = 0.383). These findings suggest that there are significant behavioral effects in male mice that could parallel the intrauterine position and related prental hormone effects that have been elucidated in female house mice and other rodents. © 1995 Wiley-Liss, Inc.     

The development of territorial-induced intermale agonistic behavior in albino laboratory mice

Male mice of the CF-1 strain (Mus musculus) were allowed to take up lone residence in a small territory consisting of a 60-cm enclosure attached by a tubular runway to a standard mouse cage with food, water, and bedding. A group of ten mice, each of which resided in its own separate enclosure for 24 hours, were more aggressive toward intruders than other groups of ten mice following six-hour residence periods, or no such residence. Aggression toward intruders increased in repeated weekly tests of the six-hour residents, but after four weeks of testing did not reach the maximum stable level displayed by the 24-hour residents over four weeks of testing. In another experiment, the 24-hour residence period of groups of 20 CF-1 male mice was disturbed by briefly removing the mouse from the enclosure, before introducing the intruder, at various intervals prior to testing. Removal of the resident five minutes before testing resulted in a marked decrease in aggression toward intruders. Although lesser decreases in aggression followed intervals of 30, 45, and 60 minutes, a 180 minute interval resulted in no appreciable effects compared to undisturbed controls. It is concluded that exposure to the stimuli provided by the enclosure results in an aggressive readiness in the resident mouse which reaches a high level within a 24-hour period.     

Quantitative chromatographic profiling of odours associated with dominance in male laboratory mice

Triads of male NMRI mice were housed together and dominance hierarchies allowed to form. At age 19 weeks the mice were ranked on the basis of wins in spontaneous aggressive encounters, and whole-body volatiles were sampled by the dynamic solvent effect and quantitatively analysed by capillary gas chromatography. At age 26 weeks the mice were again ranked on the basis of wins in aggressive encounters, number of aggressive encounters initiated, and scent marking patterns, and whole-body volatiles were sampled and analysed. Chromatographic odour profile ranks agreed perfectly with aggressive initiator ranks and poorly with encounter winner ranks. Eight components of the whole-body odour were identified by gas chromatography-mass spectrometry; two of these are known semiochemicals. The results demonstrate that murine semiochemicals are accessible to quantitative analysis at the level of the individual.     

Fighting experiences and natural killer cell activity in male laboratory mice

There is currently much interest in the potential impact of psychological factors on immune responses. An attempt was made to assess the effects of dominant/subordinate polarity in male mice on the cytotoxic activities of their natural-killer (NK) cells. On the basis of repeated agonistic encounters, categories of subordinate and dominat animals were selected. These animals were compared with manipulated controls (introduced to a novel test cage without an opponent on each occasion) and undisturbed controls (who remained in isolation without manipulation). In terms of NK activity, immunosuppression was observed in both dominant and subordinate categories when compared to undisturbed controls. There were, however, no differences between the fighting exposed subjects and the manipulated controls, suggesting that stress accounts for any changes. © 1994 Wiley-Liss, Inc.     

Predatory aggression in lines of wild mice selected for interfemale aggression

Mice descending from lines previously selected for high and low levels of interfemale aggression and from a nonselected control line were exposed to live crickets on two consecutive test days. Latencies both to attack and to eat the cricket were recorded. No line or sex differences in attacking were found, although latency to attack decreased over test days. Control line mice were more likely to engage in the eating of the cricket than either the high or low selected lines, suggesting that the selection procedure may have dissociated attacking and eating components of predatory behavior.     

An empirically derived scoring system for intermale aggression in mice

Scoring systems used to assess intermale aggression have been characterized by arbitrary scales and wide variability in the behaviors selected for measurement. The use of such different systems severely limits the ability of investigators to make meaningful comparisons among studies and indicates that there is a need for a common, statistically derived evaluative system for intermale aggression. We measured the frequency and duration of five major components of agonistic behavior exhibited by intact males toward olfactory bulbectomized stimulus males and then analyzed the data using a number of univariate and multivariate procedures. The results were used to generate two statistically based scoring systems, one a short-form index and the other a composite index for more detailed studies of aggression. It is hoped that these statistically derived systems will be adopted by other investigators to increase methodological congruence in the field.