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.     

A sensory contact model for the study of aggressive and submissive behavior in male mice

The technique for simultaneous development of aggressive and submissive behaviors as a result of successive experiences of defeats or victories in daily intermale confrontations in male mice permanently living under sensory contact conditions is offered for behavioral, pharmacological, and neurophysiological studies of mechanisms of agonistic social relations. Distant sensory contact is achieved by placing a pair of males into a common cage separated by a transparent partition with holes permitting visual contact and the individuals perceiving each other's odors but preventing any physical at contact all times except for 10-min daily tests. These conditions essentially elicit aggression in winner males and quickly result in submission by losers of the same strain of mice. The meaning of consecutive stages of the technique, the problem of controls, and applications of this model are discussed.     

Effects of ritanserin on offense and defense in male mice

Effects of ritanserin on agonistic behavior of isolated mice exhibiting aggressive or nonaggressive behavioral strategies were studied in pair-wise encounters with group-housed opponents. An ethological approach to behavioral scoring is adopted, which allows for examination of the profiles of individual subjects. Although the data generally support the view that ritanser in has little effect on offense or defense in male mice, the stimulation of pre-aggressive behavior (threats, alerts, tail rattles) was detected in some nonaggressive mice. © 1995 Wiley-Liss, Inc.     

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.     

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.     

Genetic basis for male aggression and survivorship in wild house mice (Mus domesticus)

Work on the genetic region of the house mice known as the t-complex has produced the hypothesis that mice heterozygous for t-haplotypes (+/t) may have a selective advantage over wild-type (+/+) males owing to the greater aggressiveness of +/t males. We tested this hypothesis by examining the behavior of +/+ and +/t mice placed in four large outdoor enclosures. We found that +/t males were dominant over +/+ males. Furthermore, in the outdoor enclosures +/t males had higher survivorship than +/+ males, both as adults and juveniles. However, males of the two genotypes did not differ in home range size. We suggest that t-haplotypes may be, in part, maintained in mouse populations because of a selective advantage in heterozygous males. © 1996 Wiley-Liss, Inc.     

No postnatal maternal effect on male aggressiveness in wild-derived strains of house mice

Male aggressiveness is a complex behavior influenced by a number of genetic and non-genetic factors. Traditionally, the contribution of each of these factors has been established from experiments using artificially selected strains for high/low aggressive phenotypes. However, little is known about the factors underlying aggressive behavior in natural populations. In this study, we assess the influence of genetic background vs. postnatal maternal environment using a set of cross-fostering experiments between two wild-derived inbred strains, displaying high (STRA, derived from Mus musculus domesticus) and low (BUSNA, derived from Mus musculus musculus) levels of aggressiveness. The role of maternal environment was tested in males with the same genetic background (i.e. strain origin) reared under three different conditions: unfostered (weaned by mother), infostered (weaned by an unfamiliar dam from the same strain), and cross-fostered (weaned by a dam from a different strain). All males were tested against non-aggressive opponents from the A/J inbred strain. Resource-holding potential was assessed through body weight gains and territory ownership. The STRA males were shown to be aggressive in both neutral cage and resident-intruder tests. On the contrary, the BUSNA males were less aggressive in all tests. We did not find a significant effect of postnatal maternal environment; however, we detected significant maternal effect on body weight with differences between the strains, fostering type and interactions between these factors. We conclude that the aggressiveness preserved in the two strains has significant genetic component whose genetic basis can be dissected by quantitative trait loci analysis.     

Exposure to ozone inhibits isolation-induced aggressive behavior of adult CD-1 male mice

Continuous exposure to ozone (O₃, 1.2 ppm) in adult CD-1 male mice for 20 consecutive days markedly influenced a number of items of aggressive behavior induced by 59 days of individual housing. The behavior of mice was videotaped on days 1, 3, and 5 of five consecutive daily encounters (10 min each; isolation days 55, 57, and 59). Ozone exposure caused an abatement of aggressive behavior and enhanced fear-associated displays shown by a significant decrease in the frequency of attacking and digging and an increase in freezing. Moreover, O₃ induced a decrease of time spent in attacking and exploration/activity. Nonexposed animals exhibited a day-dependent increase in self-grooming frequency which was not observed in O₃ mice; by contrast, freezing was higher in O₃ mice on day 5 of the test. Data suggest that O₃ exposure produces a remarkable reduction of mouse aggression, indirectly confirming previous findings on physical and neurobehavioral effects of O₃. © 1995 Wiley-Liss, Inc.     

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.     

An ephemeral sex pheromone in the urine of female house mice (Mus domesticus).

From previous research, the ultrasonic vocalizations of male mice (Mus domesticus) to female mouse urine were hypothesized to be learned as a result of classical conditioning during adult heterosexual encounters. According to this interpretation, a previously neutral conditioned stimulus in female urine comes to elicit vocalizations as a result of its association with some other unknown unconditioned stimulus associated with adult females. However, the research from which this hypothesis was derived utilized urine collected from females housed in metabolic cages. Three experiments further examined the classical conditioning hypothesis using two types of female urine: (i) metabolic-cage-collected urine and (ii) freshly voided urine. Experiment 1 demonstrated that, in contrast to vocalizations to metabolic-cage-collected urine, adult heterosexual experience was not necessary for males to vocalize to freshly voided female urine. In addition, unlike metabolic-cage-collected urine (Experiment 3), freshly voided urine remained a potent stimulus for eliciting vocalizations during repeated testing (Experiments 2 and 3). Finally, freshly voided urine appeared to cause a previously neutral stimulus (cotton swab) to acquire ultrasound eliciting properties (Experiment 2). We suggest from these findings that two chemosignals that elicit vocalizations from males may exist in female mouse urine: (i) a potent, but volatile or easily degraded, unconditioned stimulus to which males vocalize without sexual experience and (ii) a nonvolatile, chemically stable conditioned stimulus.     

Effect of anosmia on the behavior of standard non-aggressive male mice opponents during agonistic encounters

This study assessed whether the differences observed in a previous experiment [Martinez M, Salvador A, Simon VM (1994): Aggressive Behavior 20:441–451] in the behavior of isolated male mice over several agonistic encounters in which they confronted either an “anosmic” or an “intact” non-aggressive “standard opponent” were due to the differences in the behavior of the opponents themselves. Ethologically-inspired analysis was used to assess the behavior of the opponents during the first agonistic encounter. Anosmic opponents spent less time in social investigation and defense and more time in immobility than intact ones. These results suggest that the differences in the behavior of the opponents could be one of the causes of the differences observed in the behavior of the aggressive males confronting them. However, more research is needed to study if other variables, such as the production of odors, are also affected by the state (deprived or intact) of the olfactory sense. These findings provide additional support for the view that the type of opponent used in studies on intermale aggression is of paramount importance.Aggr. Behav. 23:179–181, 1997.© 1997 Wiley-Liss, Inc.     

Role reversal changes during the ontogeny of play fighting in male rats: Attack vs. defense

From weaning until sexual maturity, the rates at which young male rats hold each other supine during play fighting appear to become progressively asymmetrical. These changes have been previously thought to reflect an initial lack of dominance and a later development of dominance-subordinance relationships. In this paper it is shown that pairs of male rats exhibit asymmetries in playful attack and playful defense throughout development. The changes, resulting in greater asymmetry of pinning rates, are shown to result from age-dependent changes in defensive tactics; the relationship, therefore, remains constant while the form of the behavior changes. Furthermore, it is not the animals showing the highest rates of playful attack who become dominant in older ages.     

Noninvolvement of testosterone in aggressive defense behavior in the male blind mole rat Spalax ehrenbergi

Blind mole rats (Spalax ehrenbergi) are solitary and aggressive subterranean rodents. Aggressive defense behavior in the mole rat functions to deter neighboring competitors from territory, food, and mates and includes seismic and odor signals. The aim of the present study was to determine whether the aggressive defense behavior displayed by male mole rats is testosterone dependent. Five behavioral variables were taken as being representative of such aggressive interaction: exposing teeth, biting, bulldozing movements of the head, soil blocking, and self‐grooming. We monitored male testosterone levels and aggressiveness throughout the annual cycle, which can be divided into three main climatic periods: cold and rainy (September–February); warm, during which the soil is still moist and easily excavated (March–May); and hot (June–August), when the soil is hard and dry. In a second experiment the effect of endogenous and exogenous testosterone on male aggressive defense behavior was determined before and after castration and following testosterone propionate replacement. We found fluctuations in male testosterone concentrations, with three peaks: in November, May, and August, one in each of the three climatic periods. However, these fluctuations did not correlate with male aggressive behavior, which remained constant throughout the year. Furthermore, because neither castration nor testosterone propionate replacement in castrated individuals affected their defense behavior, we suggest that such behavior in male mole rats is testosterone independent. The continuous excavation and maintenance of the mole rat’s underground tunnel system demands high energy expenditure year‐round and constant defense of territory sites and food caches from intraspecific rivals. Thus, although testosterone may fluctuate as a result of seasonal breeding cycles, constant high levels of aggressive defense throughout the year are crucial for the survival of the male mole rat in its solitary subterranean environment. Aggr. Behav. 27:64–72, 2001. © 2001 Wiley‐Liss, Inc.     

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.     

Maternal aggression toward infanticidal males of different social status in wild house mice (Mus musculus domesticus)

Maternal aggression was examined in wild female mice (Mus musculus domesticus) derived from animals trapped in Alberta, Canada. Lactating females were tested for their behavior toward intruder males during the time of postpartum estrus while housed in a two-cage apparatus containing a defensible nest area. Prior to being used as intruders, sexually naive males were screened for their behavior toward a newborn pup (83% exhibited infanticide). Only infanticidal males were then housed in pairs and allowed to establish a dominance hierarchy. Dominance status was further verified by a urine marking test. The dominant and subordinate infanticidal males were then placed into a lactating female's cage and observed for 1 hr. The test was terminated immediately when a male began to attack the pups. Lactating females attacked the males in both groups, but subordinate males received more intense attacks than dominant males. Dominant males elicited significantly more fear/defense behavior than subordinate intruders. All of the dominant males and only one submissive male attacked the pups. Females were thus successful in blocking infanticide only by infanticidal subordinate males. Since females do not persist in attacking males with high fighting ability, one function of maternal aggression could be to assess the fighting, and resource holding, potential of a future mate. © 1994 Wiley-Liss, Inc.     

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.     

Detailed analysis of the male copulatory motor pattern in mammals: hormonal bases

Data obtained, using a polygraphic technique, on the characteristics of the motor and genital copulatory responses of male rabbits, rats, mice, hamsters, and guinea pigs are reviewed. This methodology provided detailed information, not accessible to other analyses, on the frequency and dynamic organization of copulatory pelvic thrusting trains of the species studied. This comparative analysis showed that: (1) The male rat may display two types of ejaculatory responses, differing in the dynamic organization of the pelvic thrusting train, and in the duration of the intravaginal thrusting period preceding ejaculation. (2) In the guinea pigs and small rodents, but not in rabbits, pelvic thrusting at ejaculatory responses persists during intromission, and a period of fast intravaginal thrusting is associated with ejaculation. (3) The motor copulatory pattern of the rabbit, but not of the rat, hamster, or guinea pig, is affected by castration and hormone treatment, suggesting that, in rabbits, androgen acts both on motivation and on the spinal neural systems related to copulation.     

Behavioral changes over several successful agonistic encounters between male mice: Effects of type of “standard opponent”

This study assessed whether two types of non-aggressive “standard opponents” (“intact” and “anosmic” group-housed males) produced similar behavioral changes in isolated OF1 male mice given several experiences of victory. Experimental groups confronted either intact or anosmic opponents every two days until they had completed four encounters. The behavioral changes were recorded using a detailed ethologically inspired analysis. These changes were clearly different depending on the opponent type. When intact opponents were used, experimental subjects increased the time spent in digging, non-social exploration, explore from a distance, and attack over encounters, but showed decreased time spent in threat and a decreased latency to the first attack. In encounters with anosmic opponents, only declines in the latencies to threat and attack were noted. Moreover, the experimental groups differed in their behaviors over encounters. Those confronting intact opponents spent less time in social investigation, more time in explore from a distance and threat, and showed a shorter latencies to threat and attack than counterparts confronting anosmics. These results suggest that, although both types of “standard opponents” are similar in their non-aggressiveness, they elicit rather different behavioral responses in their adversaries. These findings provide additional support for the view that the type of opponent used in studies on intermale aggression is of paramount importance. Indeed, the use of different types of “standardized non-aggressive opponents” appears to be an important source of variability between studies. © 1994 Wiley-Liss, Inc.     

Behavioral profile of amisulpride in agonistic encounters between male mice

Amisulpride is a substituted benzamide derivative that acts as a selective dopamine D2/D3 receptor antagonist. Although the anti‐aggressive properties of neuroleptic drugs are well known, the effects of amisulpride on agonistic interactions have not been explored, and there are no studies comparing acute and subchronic effects of this compound on aggression in rodents. In this study, we examined the action of amisulpride (5–25 mg/kg, i.p), administered acutely or subchronically for 10 days, on agonistic behavior elicited by isolation in male mice. Individually housed mice were exposed to anosmic "standard opponents" 30 min after drug administration, and the encounters were videotaped and evaluated using an ethologically based analysis. After acute treatment, amisulpride (5–20 mg/kg) exhibited an ethopharmacological profile characterized by a marked decrease of offensive behaviors (threat and attack) without an impairment of motor activity. By contrast, the anti‐aggressive action of the highest dose used (25 mg/kg) was accompanied by a weak increase of immobility. Body care was also significantly enhanced after treatment with the drug (20 and 25 mg/kg), emphasizing the involvement of dopaminergic receptors in this behavior. After subchronic treatment, no tolerance to amisulpride anti‐aggressive activity was observed. Overall, this behavioral profile is similar to that observed by other atypical neuroleptics. Aggr. Behav. 25:225–232, 1999. © 1999 Wiley‐Liss, Inc.     

The decline of aggressiveness in male mice during group caging as determined by punishment delivered by the cage mates

Group-housed rodents are generally less aggressive than isolated counterparts. The present study examined the role of defeat by cage mates as a reason for this decline in aggressiveness. In Experiment I, highly aggressive isolated male mice were introduced into aggressive or nonaggressive resident groups. The intruder's level of aggressiveness directed toward a group-housed standard opponent declined more rapidly after daily exposure to the aggressive than to the nonaggressive groups. Intruders in the aggressive groups received more attacks from their cage mates, and delivered fewer attacks to them than did the intruders in the nonaggressive groups. In Experiment II, the intruders lived for seven days in small wire net cages in the middle of the group cages. Their level of aggressiveness toward standard opponents decreased little during the preexposure but after being put freely into the groups, their aggressiveness declined to a minimal level within a day. Experiment III showed that when the wire net protection in the middle of the cage was installed after the group caging experience, the aggressiveness of the intruders did not return to the isolation level as effectively as it did in isolation. This is explained by the aggression-inhibiting content that the cues from the cage mates have acquired during group caging. The decline of aggressiveness in male mice during group caging is determined by punishment delivered by the cage mates.