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.     

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.     

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.     

Short-term early exposure to pups alters infanticide in adulthood in male but not in female wild house mice (Mus domesticus)

Male and female wild house mice (Mus domesticus) were allowed to remain in the cage of their parents until 30-35 days of age. When a second litter was delivered, the first litter was exposed to the younger pups for 2-10 days. In adulthood the male and female mice that had been exposed to pups as juveniles and an additional group that had cohabitated with their parents for the same length of time but were not exposed to pups were tested for infanticidal behavior. The frequency of infanticide by the adult female mice was not significantly different (55% vs. 70%, respectively). In contrast, the adult males that were exposed to pups as juveniles were significantly less likely to kill young in adulthood when compared with males that were not similarly exposed (35% vs. 80%, respectively). These data further demonstrate the strong influence of experience on the expression of infanticide by male mice and its relative unimportance to the expression of female infanticide.     

Agonistic onset marks emotional changes and dispersal propensity in wild house mouse males (Mus domesticus)

The authors investigated implications of agonistic onset for anxiety and dispersive motivation in maturing wild house mouse males (Mus domesticus). Laboratory-kept fraternal pairs either developed agonistic dominance or stayed amicable during their first 2 months of life, when the authors assessed open-field behavior and dispersal propensity. State anxiety was lower in amicable than agonistic males and higher in subordinate than dominant ones. During subsequent dispersal trials, 1 dominant and 1 amicable male from 2 fraternal pairs were concomitantly introduced into seminatural enclosures containing 3 females. One male invariably became territorial. The defeated males, if previously dominant, dispersed at significantly higher rates than if previously amicable. The authors conclude that agonistic onset during development represents an adaptive behavioral switch from a submissive-philopatric to agonistic-dispersive coping strategy.     

The reinforcing properties of aggressive vs nonaggressive social interactions in isolated male ICR mice (Mus musculus)

Isolated male ICR mice in a T-maze consistently selected the goal box which enabled them to fight another mouse if the alternative goal box allowed no social interaction (Experiment 1). However, if the alternative choice enabled the isolated mice to interact with another mouse through a mesh screen which prevented fighting, the preference for the opportunity to fight did not appear (Experiment 2). Because the visual, olfactory, and auditory stimuli available through the screen appeared to be as attractive as the stimuli provided by the additional opportunity to fight, it is not necessary to conclude that the stimuli reinforcing the choice behavior in Experiment 1 were provided by fighting. Since there is no compelling reason to conclude that fighting is a primary reinforcer for these isolated mice, it is not necessary to argue that the high incidence of isolation-induced fighting is the reflection of a primary aggressive motive.     

Studies on wild house mice VI: Differential effects of the Y chromosome on intermale aggression

The aim of this study is to determine the effects of different parts of the Y chromosome of wild house mice on aggression. To reach this goal, intercrosses were made between two selection lines for attack latency (SAL and LAL) and their congenic strains (SAL. LY and LAL. SY). This procedure resulted in F₁ hybrids that carried the same autosomes, but differed in their X chromosome and the two different parts of their Y chromosomes, the different parts of the Y chromosome being a recombining part called the pseudoautosomal region (PAR) and a non-recombining part (non-PAR). We conclude that both parts of the Y chromosome contribute slightly but significantly to variation in aggression. The major effect is accomplished by the PAR of the aggressive parent; a mirror effect is achieved by the non-PAR of the aggressive parent in interaction with the PAR. © 1994 Wiley-Liss, Inc.     

Anxiety and maternal aggression in house mice (Mus musculus): a look at interindividual variability

The hypotheses were tested that mouse motherhood is accompanied by decreased reactivity to aversive stimuli and that female anxiety is inversely related to the probability of displaying intense forms of postpartum aggression. Outbred Swiss female mice were tested for anxiety in a light/dark choice test when virgin, pregnant, or lactating, and then tested for maternal aggression (5-min exposure to a male intruder) on postpartum Day 7. Anxiety declined in pregnant and lactating females when compared with virgin animals. Furthermore, females who displayed higher scores of postpartum fighting were less anxious in the previous test regardless of reproductive stage. Part of interindividual variability in postpartum aggression might thus be related to differences in the extent to which individuals perceive and react to anxiogenic situations. In addition, the higher emotionality characterizing the C57BL/6 and DBA/2 inbred strains may be responsible for the lack of a clear-cut exhibition of maternal aggression in these two strains.     

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.     

Pre-breeding aggression in male and female three-spined sticklebacks (gasterosteus aculeatus)

The reactions of 34 female and 32 male three-spined sticklebacks to a conspecific were observed in the month before the breeding season. Factor analysis indicated that the organization of the response in the two sexes was very similar; in both cases, axes labelled “aggression,” “threat,” “curiosity,” and “sex” emerged, with male fish having significantly higher scores on the first factor and females on the second. Any theory of the causes of aggression in sticklebacks should accommodate these facts.     

Aversive potency of urine from dominant and subordinate male laboratory mice (Mus musculus): Resolution of a conflict

The present study assessed the aversive potency of urine collected from male albino mice that had been clearly identified as dominants/winners or subordinates/losers of paired aggression tests and then housed either individually or in a quasi-paired situation in which only a wire-mesh divider separated the two mice. This divider permitted constant visual, olfactory, auditory, and some tactile contact. The responses of individually tested, group-housed males were recorded when half of the substrate in a test box was treated with either water or one of the four urine types; the other half remained untreated. Significant preferences for the untreated half were found when the urine of winners or losers housed in individual metabolism cages or that of pair-housed dominants was used as the test stimulus. On the other hand, neither water nor the urine of cohabiting subordinate males was avoided. The present findings confirmed our earlier reports that the urine of dominant male mice was aversive, whereas that of their cohabiting subordinate partners was not. They also identified Sawyer's [1978] procedure of housing winners and losers in individual cages, with the consequent interruption of social contact as the likely reason for his failure to replicate our reports that subordinate male urine lacked aversive properties. The territorial implications of the aversive factor and other urinary signals are discussed.     

Learning to cope with two different food distributions: the performance of house mice (Mus musculus domesticus)

Search abilities of mice (Mus musculus domesticus) were evaluated using an arena closed by a ceiling in which 9 food sources (which mice could reach standing on their hind legs) could be arranged according to 2 configurations: a 3 x 3 square matrix and 3 clusters each containing 3 food sources. Testing conditions prevented olfactory and visual cues from being left after visits to food sources, and mice were able to choose alternative routes between food sources. Results showed that mice were more efficient with the matrix than with the cluster configuration. Sex differences were observed: Females improved their performance with both configurations, whereas males improved only with the matrix one. Mice did not develop evident search strategies that would minimize task complexity. Comparison with data published on capuchin monkeys revealed differences, with monkeys performing better with the cluster configuration than with the matrix and applying searching strategies.     

Ultrasonic vocalizations during sex behavior of male house mice (Mus musculus): a description

After placing a female house mouse into the home cage of a male, the occurrences of four behaviors were recorded on separate channels of an event recorder: (1) male sniffing female, (2) male mounting female, (3) male intromitting female, and (4) 70-kHz vocalizations. The amount of vocalizing was greatest shortly after pairing and was associated with the male sniffing the female. After the male began mounting, vocalizations also were associated with mounting. Vocalizations were recorded during intromissions and occasionally occurred coincident with pelvic thrusts. Very few vocalizations were detected when the male was not sniffing or mounting the female. Vocalizations ceased following ejaculation but typically resumed several minutes before the resumption of another mounting sequence. Thus 70-kHz vocalizations appear to be closely linked to male sexual arousal.     

The potential effects of protected nests and cage complexity on maternal aggression in house mice

I studied the behavior of nursing house mice (Mus musculus) in captivity and used a two-by-two factorial design to test the hypothesis that the combination of a protected nest along with a chance for the intruders to retreat would improve the ability of resident females to defend their litters from infanticidal males. A chance for the intruder to retreat was manipulated by testing the resident females in either a single- or a two-compartment cage. The effect of a protected nest was examined by providing females with a nest box having a narrow entrance. During each test, an infanticidal adult male was introduced into the cage of a resident female and her pups. I observed that neither the presence of a protected nest nor the chance for the intruders to retreat to a different compartment, or a combination of the two, increased the ability of a female to defend her litter against an intruder male. Moreover, neither of these two factors influenced the overall behavior of the resident females. I obtained similar results after using data from previous studies to examine the influence of both of these factors on the efficiency of maternal aggression. Overall, these two approaches showed that females are often unable to prevent intruders from committing infanticide. I discuss the validity of the hypothesis that maternal aggression evolved as a mechanism to protect offspring from infanticide. Aggr. Behav. 24:385–396, 1998. © 1998 Wiley-Liss, Inc.     

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.     

Acceleration and delay of sexual maturation in female house mice (Mus domesticus) by urinary chemosignals: mixing urine sources in unequal proportions

Urine from male mice, from estrous female mice, and from pregnant or lactating female mice accelerate first vaginal estrus in females, whereas urine from grouped female mice delays first estrus. Nine experiments were used to test the effects of treatment of young female mice with urinary chemosignals that influence the onset of first estrus using unequal proportions of urine from the different sources. At ratios of 10-20 parts acceleratory chemosignal to 1 part delay chemosignal the acceleratory effect overrides the delay chemosignal, and the mice attain first estrus at earlier ages than controls. Ratios of about 4 to 1 up to 7 to 1 result in mean ages for puberty that are not accelerated or delayed relative to controls. Over a modest range of actual dose amounts of urine, the ratio effects are the same regardless of the actual quantities of urine employed in treating test females.     

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.     

Different patterns of biting attack employed by lactating female mice (Mus domesticus) in encounters with male and female conspecific intruders

Attacks by resident lactating female mice were examined in a variety of situations. Relatively few attack bites to vulnerable body regions were seen when pairs of unfamiliar lactating females fought, establishing social status prior to communal nesting. Sexually naive male and female intruders were equally prone to attack by lactating females, but patterns of bite attack generated by them were very different; males received the more damaging attacks. More signs of "fear" were seen in the lactating females' responses to male rather than female intruders. Varied motivations may underlie attacks by lactating females directed to conspecific intruders. Defensive patterns of biting by lactating females are more consistently directed towards males, intruders that are more likely to harm or destroy the litter. Although attacks by females rarely thwarted infanticide by male intruders, the behavior may acutely protect parental investment.     

The introduction of a group of alien mice (Mus musculus L.) into hierarchically organized groups of five male mice

Groups of 3 male or female Mus musculus were introduced into hierarchically organized colonies of 5 male mice for a period of 8 days. The colonies were of 2 kinds; high-level aggressive (HLA), which had been set up 3 days prior to the introduction of the aliens, and low-level aggressive (LLA), which had been established for 21 days before strangers were introduced. Both males and anestrous females were attacked, but males were attacked 5 times more frequently than females. In HLA colonies most of the attacks on the aliens were by the dominant; in LLA colonies there was no difference in the behavior of dominant and subordinate mice toward strangers. Both aggression toward aliens and intracolony aggression declined over the 8 day experimental period. In HLA colonies the dominant mouse mounted females 5 times more frequently than did either his subordinates or male mice in the LLA colonies. In HLA colonies aliens huddled with subordinates to form a single colony with 1 dominant and 7 subordinates. In LLA colonies alien males remained as a discrete group spatially separated in the cage. Female aliens were incorporated into the main colony. In all cases dominant male mice made more attacks on aliens as compared with familiar mice.     

Ultrasonic vocalizations by male house mice (Mus musculus) to novel odors: roles of infant and adult experience

Two experiments were conducted to examine 70-kHz ultrasonic courtship vocalizations by adult male mice (Mus musculus) to novel odors following exposure to these odors in infancy and/or adulthood. The research was performed in hopes of better understanding the experiences giving rise to vocalizations to naturally occurring chemosignals. Experiment 1 demonstrated that adult males normally do not vocalize to the urine of female rats but would come to do so if adult female mice odorized with female rat urine were repeatedly encountered postpubertally. On the other hand, encountering their own mother odorized with female rat urine from birth until weaning did not promote vocalizations to the urine of female rats. Experiment 2 was designed to examine vocalizations to the urine of female mice whose urinary odor was altered by the ingestion of fenugreek, a spice. Although the magnitude of the effect was smaller in this experiment, greater amounts of vocalization again were seen by males that as adults encountered females that had ingested fenugreek. Males with such experience also showed a small but significant elevation in vocalizations to the fenugreek odor itself. Again, experience with the novel odor during infancy was not associated with elevated vocalizations during adulthood either to fenugreek-altered urine or to the fenugreek odor itself. Thus vocalizations to two different novel odors occurred only after an adult male had encountered an adult female odorized with the novel odor. On the other hand, none of the novel odor experiences eliminated vocalizations to the naturally occurring chemosignal in female mouse urine.(ABSTRACT TRUNCATED AT 250 WORDS)