Social dominance, reproduction, and release of the maturation-delaying chemosignal in the urine of female house mice (Mus musculus)

Five experiments were performed to investigate the effects of social status in groups of female mice on reproduction and on the release or urinary chemosignals that accelerate or delay the onset of sexual maturation in young females. Treatment of young female mice with urine from bottom-ranking mice in groups of 5 adult females resulted in delays in puberty comparable to those produced by treatment with urine pooled from females housed at moderate to high densities. Treatment of young females with urine from top-ranking females from the same groups resulted in ages for puberty not different from those of control females treated with water. There was an interaction between the social rank of a female and the stages of the estrous cycle with respect to the presence in the urine of chemosignals from grouping that delay puberty and estrus that accelerate puberty. Within groups of 5 adult mice, top-ranking females were in estrus more frequently than bottom-ranking females. Individually caged adult females treated with urine from top-ranking females were in estrus more frequently than females treated with urine from bottom-ranking females. When grouped females were separated into individual cages and mated, there was differential reproductive success: More top-ranking females conceived and bore litters than bottom-ranking females. Bottom-ranking females produced more female pups, relative to top- and middle-ranking females.     

Rare male aggression directed toward females in a female‐dominated society: Baiting behavior in the spotted hyena

Spotted hyenas (Crocuta crocuta) are gregarious carnivores. The females are socially dominant to males, and adult males rarely direct aggression toward adult females. This study analyzed all cases in which adult immigrant males behaved aggressively toward adult females in a large population of free‐living hyenas in Kenya, observed for 11 years. Our goals were to describe the conditions under which male attacks on females occur, and address possible adaptive functions. Most aggression directed by adult immigrant males against females occurred when coalitions of two or more males attacked a single adult female, who typically responded by defending herself and fighting back. Male aggression against females frequently occurred at sites of ungulate kills, but males never behaved aggressively toward females over food, and all male attacks on females were unprovoked. Although no mounting or other copulatory behaviors ever occurred during or immediately after an attack, the number of male attacks on females peaked around the time of conception. Daily rates at which males attacked females did not vary with female social rank. However, daily attack rates did vary significantly with female reproductive state, and the highest rates of male attack on females were observed during the two stages of the reproductive cycle during which females were most likely to conceive litters. The adaptive significance of male aggression against females in this species remains unknown, but a tight association between male attacks on females and a female's time of conception provides strong evidence of some role for male aggression in hyena sexual behavior. In particular, our data are consistent with hypotheses suggesting that male aggression toward females in this species either serves to inform females about male fitness or represents sexual harassment. Aggr. Behav. 29:457–474, 2003. © 2003 Wiley‐Liss, Inc.     

Visual preferences for sex and status in female rhesus macaques

Most primates are both highly visual and highly social. These qualities predict that visual cues to social variables, such as identity, sex, social status, and reproductive quality, would be intrinsically valuable and systematically attract attention. Supporting this idea, thirsty male rhesus macaques (Macaca mulatta) will forego fluid reward to view images of the faces of high-ranking males and the sexual skin of females. Whether female rhesus macaques, who experience dramatically different social pressures and reproductive costs than male macaques, also systematically and spontaneously value visual cues to social information remains untested experimentally. We probed the preferences of female rhesus macaques, given the opportunity to display an image from a known class of social stimuli or touch a second target to display a blank screen. We found that females preferred faces of high-status males and also images of the perinea of both males and females, but were not motivated to display images of subordinate males or control stimuli. These findings endorse the view that both male and female rhesus macaques—and presumably other highly social primates—seek information about other individuals in a way that matches the adaptive value of that information for guiding social behavior.     

Effect of intrauterine position and social density on age of first reproduction in wild-type female house mice (Mus musculus)

In laboratory strains of mice, reproductive maturation is influenced by both the fetal and the peripubertal social environments experienced by females. Intrauterine position (IUP) for female fetuses is identified by the number of adjacent males; where 0M have zero, 1M have one, and 2M have two male neighbors. We sought to confirm, using wild-type female house mice (Mus musculus), the previous finding in the CF-1 strain of laboratory mouse that males prefer 0M over 2M females as mates. We recorded the age at first reproduction for females of known IUP housed either individually with a male or in a group of 6 females and a male. In neither housing condition were there significant differences in age of first reproduction among females of different IUPs, but 0M females that were group housed had perforate vaginas at an earlier age than other group-housed females. Mean (+/- SE) age at first reproduction was 58.1 (+/- 3.3) for paired and 126.6 (+/- 5.1) for group-housed females. The reproductive suppression observed in the grouped females was probably due to the interaction of inhibitory urinary chemosignals, low body weights, and female dominance hierarchies.     

Social mediation of puberty: an adaptive female strategy?

Females of two hamster species with contrasting degrees of gregariousness were tested for social influences on the timing of sexual maturation. When female dwarf hamsters (Phodopus sungorus campbelli), a gregarious species, were housed with an adult male at weaning, they began estrous cycles significantly earlier than when they were housed alone or with their family. Females housed with one or two female siblings at weaning matured significantly later than did all other females. Once mature, females housed with familiar males conceived later than did females housed with unfamiliar males. Rearing conditions also affected body weight; those housed with female siblings grew more slowly and attained a lower weight at 8 weeks of age than did females in all other groups. In contrast, when weanling female golden hamsters (Mesocricetus auratus), a solitary species, were housed with either an adult male, two female siblings, or alone, they did not differ in their rate of sexual maturation or growth. It is suggested that the degree to which social factors can accelerate or delay puberty is an adaptive characteristic and may be correlated with the degree of gregariousness of a species.     

Gender differences in advertising response and self-consciousness variables

This study assesses gender differences in self-consciousness traits and advertising responses across a sample of adult Americans. The results indicate that there are gender differences in public self-consciousness and social anxiety, with the effects particularly pronounced for younger females. Younger females also recalled more television commercials than other male and female groups. The social implications of these findings are considered.     

Clues for dominance in female chamois: Age,weight, or horn size?

A study of social interactions among female Apennine chamois Rupicapra pyrenaica ornata was made in Abruzzo National Park, central Italy, between 1981 and 1982. A linear hierarchy among females was observed, rank order being highly correlated with age, weight, and horn size. An analysis of which physical clues are used by females to assess dominance suggests that body weight may be the most important attribute. The percentages of threats and dominance displays decrease beyond 7–8 years of age when females usually start to lose weight, whereas horns keep growing throughout life. Furthermore, the greater effect of weight compared to that of horn size on the rank/age correlation supports our conclusion.     

Ontogeny of sex differences in defensive burying behavior in rats: effect of social isolation

The aim of the present experiments was to clarify sex differences in socio-developmental factors that affected defense behavior in rats. Sex differences in the defensive burying behavior of rats, and related social factors, were explored in three developmental stages: juvenile, puberty, and adult; 30, 50, and 80 days of age, respectively. The duration of burying, digging into bedding material, stretch-attend postures, and crouch/freezing were measured in a shock-prod test. For males, the duration of burying was longer in the juvenile and pubertal stages than in adulthood. For females, no age differences in the duration of burying were found. Males showed longer burying durations than females in both the juvenile and pubertal stages. For both sexes, the highest duration of digging was found in the juvenile stage, and females showed longer durations of digging than males. Both male and female rats isolated during the juvenile stage, from 26 to 40 days of age, showed smaller durations of burying behavior compared to pair-reared rats. This effect of juvenile isolation was maintained among both adult males and females even when they were returned to pair rearing after isolation. Isolation during adulthood, from 66 to 80 days of age, increased burying behavior in males, but decreased it in females. The durations of digging, stretch-attend postures, and crouch/freezing were not affected by isolation. The decrease in defensive burying and its increase resulting from isolation in adult male rats, suggest that the emergence of adult-like social relationships in males suppressed the duration of burying. Male and female rats isolated during the juvenile stage maintained lower levels of burying, suggesting that social experience as juveniles is important for the emergence of defensive burying behavior.     

The structure of social relationships among captive female giraffe (Giraffa camelopardalis)

Giraffe herds have been characterized as random associations of individuals, but recent evidence suggests giraffe have a more complex social structure. The authors formulated 3 hypotheses designed to evaluate whether a herd of captive giraffe (Giraffa camelopardalis) associated randomly or patterned their behavior and proximity in a manner indicative of social relationships. Affiliative interaction, proximity, and nearest neighbors for 6 captive female giraffe living in a large outdoor enclosure were analyzed, and all three measures were nonrandomly distributed, indicating female giraffe had social preferences. Furthermore, preferences were consistent across measures and time, suggesting that adult female giraffe maintain relationships. Mother-daughter pairs and pairs with large age differences between members interacted and associated most often. The social structure of this captive herd is influenced by social relationships between individual adult females, and the social behavior of individual females should be examined more closely in the wild.     

A status theory of the evaluation of sex-role and age-role behavior

An earlier investigation formulated a status theory of behavioral choice evaluation to explain the lesser approval for cross-sex-role behavior of males than of females. Since males are often assigned higher prestige, their deviation from male to female behavior represents a movement from higher to lower status, resulting in a loss of approval. To determine that the fit of previous data with the theory was indeed due to the status characteristic of sex roles, the current study used the theory to predict the evaluations of appropriate and cross-role behavior concerning age roles as well as sex roles. Furthermore, the effect of status upon evaluation was hypothesized to reside in the association of status with social value and, in turn, the effect of social value upon evaluation. Subjects were 57 male and 40 female university students who provided approval ratings of either appropriate or cross-age-role and sex-role behavior. For sex and age, cross-role behavior received less approval for the higher status actor. This indicated that the lesser approval of cross-sex-role behavior of males was due to the differential status ranking of male and female roles, rather than to some other feature more specific to sex roles. The proposition that social value is the explanatory link in the effect of status upon evaluation is supported by the results.     

Effects of male social status on reproductive success and on behavior in mice (Mus musculus)

Differences in reproduction as well as in behavior in the presence of females were evaluated according to dominant and subordinate male rank in albino mice, in the temporary absence of each male's antagonist. Dominant males reproduced more successfully than subordinate males. Subordinate males were generally inactive, except for displacement activities, during the first 15 min they were exposed to female partners. These findings suggest that mechanisms other than male-male interference or mating order may be operating or influencing behavior and reproductive results.     

Permanent and transient effects of repeated preweaning stress on social and sexual behaviors of rats

We have reported that exposure of preweaning male and female rats to a model of unpredictable mild physical stressors (Neo-A) can decrease the behavioral and hormonal responses to acute and chronic stress as adults. In this paper we have analyzed the effect of Neo-A on development of social behaviors, including aggressiveness, social dominance, and sexual behavior in adulthood. The subjects were divided into two groups: Neo-A (daily exposed to unpredictable mild stresses- from day 2 up to day 15 of suckling; n = 30 litters) and controls (C) (undisturbed rats, except for testing, during the same period of life; n = 26 litters). When day 6 pups were submitted to a social clustering test the Neo-A group showed a higher rate of litter-mate clustering than C. The 35 days Neo-A males and Neo-A females submitted to a social behavior test after 24 h of social isolation also showed higher scores of time spent in active social interaction than controls, as well as a higher ratio of animals showing aggressive playing. A second social behavior test performed after 48 h of social isolation at days 75-80 of age revealed that only Neo-A females displayed increased social behavior and aggressive behaviors, whereas controls did not. A water competition test performed at 24 and 48 h after water deprivation showed that Neo-A adult males spent more time in possession of the drinking device and drank more frequently than C. When adult proestrous females were exposed to a sexual behavior test, the Neo-A group showed shorter latency and higher scores of lordosis quotient. These results support the view that exposure to this model of repeated mild stress early in life stimulates the development of social behavior, dominance and sexual behavior.     

Gender‐role egalitarianism predicts desirable traits of potential marriage partners: A cross‐cultural comparison

We examined whether gender‐role egalitarianism predicted participants' rank‐order preferences for traits in potential marriage partners of the opposite sex, and whether gender‐role egalitarianism mediated cultural differences between participants from North America, Polynesia and East Asia. Participants completed the Sex‐Role Egalitarianism Scale and ranked the following traits in terms of their importance in choosing a potential marriage partner: kindness, physical attractiveness, social level, athleticism, creativity and liveliness. Parallel analyses for male and female participants reveal that traditional males value physical attractiveness more than egalitarian males, and that traditional females value social level more and kindness less than egalitarian females. Gender‐role egalitarianism fully mediated the effect of culture on kindness rankings, but no others. These results expand upon previous findings by accounting for individual differences regarding beliefs about traditional gender roles.     

Relationship of social rank in mice to growth,endurance, and fertility

The influence of the social rank of male mice, determined by the outcome of fights, was assessed on their growth, treadmill performance, open-field behavior, and morphometric traits. Fertility of mated females was also investigated. Special attention was paid to the relationship between the male's social rank and body weight. Winners of fights were heavier than losers; their latencies were shorter, and they showed more locomotor activity in an open field test. Winners also had higher absolute testicular and epididymal weights. These males had a positive influence on the reproductive fitness of the females with which they were mated.     

Social variables influence female sexual behavior in the musk shrew (Suncus murinus)

The role of social variables in the mediation of sexual behavior was examined in the female musk shrew (Suncus murinus). Two social variables were manipulated: amount of reproductive experience and exposure to male-related chemical cues. Virgin females took significantly longer to achieve receptivity than did sexually experienced females. In addition, exposure to soiled bedding taken from a male's cage for 24-hr prior to testing reduced receptivity latencies in all females. Even a brief (30 min) exposure to male-related cues was effective in facilitating receptivity in virgins. The converse was noted for female aggressive behavior. Virgin females attacked more frequently than experienced females, and preexposure to male-related cues reduced aggressiveness. These findings suggest that social variables play an important role in female sexual behavior in this primitive eutherian mammal.     

Developmental consequences of behavioral inhibition: a model in rhesus monkeys (Macaca mulatta)

In children, behavioral inhibition is characterized by a disposition to withdraw in the presence of strangers and novel situations. Later in life, behavioral inhibition can result in an increased risk for anxiety and depression and a decrease in social behavior. We selected rhesus monkeys that, during infancy, showed evidence of behavioral inhibition in response to separation, and contrasted them with non‐inhibited peers. To understand the development of behavioral inhibition at juvenile age, we collected behavioral data in response to relocation; in response to a human intruder challenge; and in naturalistic outdoor field corrals. At 4 years of age (young adulthood), we again collected behavioral data in the outdoor field corrals to understand the adult social consequences of behavioral inhibition. We also included sex, dominance rank, and number of available kin in our analyses. Finally, to understand the consistency in behavior in behaviorally inhibited animals, we conducted exploratory analyses contrasting behaviorally inhibited animals that showed high vs. low durations of non‐social behaviors as adults. At juvenile age, behaviorally inhibited animals continued to show behavioral differences in the novel testing room and during the human intruder challenge, generally showing evidence of greater anxiety and emotionality compared to non‐inhibited controls. In their outdoor corrals, behaviorally inhibited juveniles spent more time alone and less time in proximity and grooming with mother and other adult females. In young adulthood, we found that behavioral inhibition was not related to time spent alone. We did find that duration of time alone in adulthood was related to time alone exhibited as juveniles; sex, dominance rank, or the number of kin were not influential in adult non‐social duration, either as main effects or as moderators. Finally, exploratory analyses revealed that behaviorally inhibited females that were more sociable (less time spent alone) as adults had spent more time grooming as juveniles, suggesting that high‐quality social interaction at a young age might mitigate the social consequences of behavioral inhibition. Overall, we believe that the many similarities with the human data that we found suggest that this monkey model of naturally occurring behavioral inhibition can be valuable for understanding social development.     

Aggressive interactions among female,semi-captive pampas deer (Ozotoceros bezoarticus) increase within the hierarchy and after short-term removal of the male

Two trials were carried out to determine: (a) if there is a positive relation between the frequency of aggressive interactions among female pampas deer and their position within the hierarchy (HI), (b) if short-term removal of the male triggers an increase in the frequency of aggression, and (c) if the magnitude of this increase is related to the individual rank position of the female. Each of 19 breeding groups comprised one adult male and from four to six adult females. The HI was determined for each female and all aggressive interactions were recorded. These were recorded while the male was present (i.e., all of Trial 1 and the “with male” period in Trial 2) and after removal of the male (i.e., the “without male” period in Trial 2). The individual percentage change in the frequency of aggressive interactions after male removal was calculated. In Trial 1 the HI, the frequency of different types of aggressive interaction and the total of aggressive interactions were positively related (all: p < .001; General Linear Mixed Model [GLMM]). In Trial 2, the frequency of total aggressive interactions increased after male removal (F(1, 27) = 3.5; p < .001; GLMM). The individual percentage changes in aggressive interaction between periods were positively related to HI (F(6, 24) = 2.56; p = .05; GLMM). For female pampas deer maintained in breeding groups, we conclude that the frequency of aggressive interactions increases within the hierarchy. Aggression also increases after the short-term removal of the male, mainly among females of higher social status.     

Aggressive behavior during the breeding season of adult female rhesus monkeys (Macaca mulatta)

The aggressive behavior of eight adult female rhesus living in a captive social group was studied prior to and during a breeding season extended by vasectomizing all the adult males in the group. Female reproductive status was ascertained by: recording all adult female-adult male copulations; detecting menstruation by vaginal swabbing; and analyzing serum progesterone levels by radioimmunoassay. Females showed more non-contact aggression during the breeding season, but wounding did not increase. Individual cycling females directed more frequent aggression to: particular adult males subordinate to them, subordinate females also in estrus, and (in a few cases) juveniles and infants.     

A comparison of adult women's and men's ascriptions of negative traits to the same and opposite sex

College students (N=135), ranging from 19 to 55 years of age, were studied to determine their sex stereotypes. Results from the present study indicated that adult males were significantly more negative than adult females in their evaluations of both sexes. One possible explanation that may be offered to account for these findings is that current emphasis of female rights may be causing negativistic reactions on the part of males toward both sex groups.     

Early tutoring and adult reproductive behaviour in female domestic canary (Serinus canaria)

We studied the effect of early tutoring on the subsequent sexual preferences and reproductive activity of female domestic canaries (Serinus canaria). Young female canaries were exposed during the first 4 months of life to songs of either domestic or wild canaries. When adult, these females were again exposed to domestic or wild songs. In the first experiment, the sexual responses of the females to unfamiliar domestic and wild songs were quantified with the copulation solicitation display (CSD) assay. In the second experiment, the same females were tested again with modified tutoring songs. In the third experiment, song stimulation of nest-building and egg-laying was studied. Domestic-strain-tutored females gave more CSDs to domestic than to wild songs. In contrast, wild-strain-tutored females showed no sexual preference. We propose that the sexual preference of adult domestic-strain-tutored female canaries for domestic songs is the consequence of learning and categorisation processes. The discrepancy between the results of the domestic-strain-tutored females and those of the wild-strain-tutored females suggests that female canaries have a predisposition to learn songs of their own strain rather than songs of an alien strain. In the third experiment nest-building and egg-laying activities appeared to be unaffected by early tutoring conditions: there was no significant differential effect of the different tutoring and exposure conditions on nest-building and egg-laying scores. Mate attraction and stimulation of females’ reproductive activity appear to be two separate functions of male song, which may have been shaped by different evolutionary constraints. Received: 24 July 1999 / Accepted after revision: 22 February 2000