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.     

Content analysis of infanticide and neonaticide cases in the UK

Twenty cases, 14 infanticides and 6 neonaticides committed between 1989 and 2020 by biological mothers were analysed using Smallest Space Analysis for the presence of themes. Three themes associated with offender motivation were identified: Desperation, Disturbance and Rejection. Desperation theme included variables suggesting the mother committed the crime as a result of distress or perceived necessity. Disturbance suggested the motivation behind the offence to be as a result of the mother's caregiving role being disturbed; and the Rejection theme explained complete maternal rejection of the infant or new-born as the motivation behind the crime. Alongside the themes, three core variables were identified to be common for the crime regardless of motivation: the crime being committed at Home, the victim Female, and the crime being Denied by the mother. The implications of the findings are discussed including the potential for an investigative support tool and developing understandings of neonaticide and infanticide as separate crimes.     

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.     

Agonistic rank,aggression, social context,and testosterone in male pigtail monkeys

Two groups of pigtail monkeys were merged, a third was formed, and individual males were introduced into a group in a series of experiments examining the effects of social context upon agonistic rank, aggressive expression, and testosterone levels. In the first experiment, two heterosexual groups, containing adult males unfamiliar to the other group, were merged. The two groups fought, and the smaller group was defeated. The alpha and beta males of the defeated group were singled out for repeated attack and both showed significant drops in circulating levels of testosterone. Both males were removed from the group during the first day, but testosterone levels did not recover to baseline levels for several days. The alpha male of the victorious group, on the other hand, showed a significant rise in testosterone, which was apparent only on the day following the merger. In order to study the influence of previous social familiarity on male reception into a group, another group was formed by removing males from the victorious group and placing them in a separate enclosure. The males in the new group established a dominance hierarchy unrelated to their previous social ranks with one another. Three months later, each of the six adult males remaining in the parent group was individually introduced into the new group for one day or less. Each of the males introduced into the new group accepted a social position at the lower end of the dominance hierarchy without regard to his previous rank relationships with the host males when they were all in the parent group. Even the alpha and beta males of the parent group were relegated to low rank positions in the new group, despite having ranked over each of the host males since birth. In contrast to the aggression directed at the unfamiliar males in the first experiment, a minimum of aggression was directed to the familiar males introduced into the new group in the second experiment. Although the males introduced accepted low social ranks, it appeared that each was readily integrated into the group with a minimum of aggressive interaction during the time he was scheduled to remain in the group. There were no significant changes in circulating levels of testosterone in any of the males during the introductions of familiar males to one another.     

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.     

Intersexual aggression and male sexual activity in captive rhesus macaques

Rape has been posited to be an outgrowth of male reproductive strategies. Forced copulations may have evolved as a consequence of the low parental investment made by males in producing and raising offspring. We designed a laboratory experiment which paired rhesus macaque males with females in order to assess the influence of intersexual aggression on male sexual activity. Younger and older adult males had comparable levels of sexual behavior, but younger males were more aggressive towards females than were older males. In addition, females threatened younger males more than older males. Male attacks on females did not result in sexual intercourse. On the contrary, a negative correlation existed between male aggression towards females and male success at achieving intromissions. Female aggression towards males appeared to be an effective tactic which reduced the chances of sexual intercourse. We conclude that intersexual aggression acts either as a mechanism of dominance assertion or as a means to increase spatial distance between individuals. These data do not support the idea that rape in humans has an evolutionary foundation derived from male reproductive strategies.     

The evolution of aggression and the level of selection controversy

This paper has two objectives. The first is to examine the “level of selection” controversy in an historical light, particularly as it relates to the evolution and function of aggressive behaviors. Individual and kin selection, on the one hand, and group selection, on the other, are viewed as alternative scientific paradigms for interpreting aggression and other behaviors. It is suggested that the crux of the conflict between these positions involves different ways of explaining altruism. Often, restraints in fighting are tacitly assumed to function first and foremost for the good of the group or species to the detriment of the actor – ie, to be altruistic and to have evolved by group selection. The frequent use of the group level “good for the species” explanations in various disciplines is noted. A second and overlapping objective of this paper is to present evidence against group selection level interpretations and to propose instead that individual level selection and inclusive fitness theory explain better and provide a heuristically more useful way of examining aggressive behavior. Toward these ends, ritualized aggressive behaviors, formerly assumed to exist for species preservation, are reinterpreted along individualistic lines. Next, the concept of inclusive fitness [Hamilton, 1964] is discussed as a theoretical breakthrough which adds support to an individual level approach. In short, the argument is set forth that animals, by and large, do not kill or seriously injure members of their own species because it usually is not in their genetic self-interest to do so; social patterns of interaction such as aggressive encounters should be examined in terms of their effects on the fitness of the individuals engaging in the behaviors before group adaptations are simply assumed. In illustration, data from several animal behavior studies are discussed. Consideration is also given to instances of intraspecific killing and wounding, which in fact occur much more frequently than has been suggested by members of a group selectionist school of thought. Infant killing reported in lions and various primate species is examined and shown to be explicable through individual selection and inclusive fitness theory. It is concluded that this approach represents a more viable theoretical framework for the evolutionary and functional study of both ritualized and other forms of limited animal aggression as well as more violent incidents of intraspecific wounding and killing.     

The effect of environment on visual cliff performance in the Mongolian gerbil

Depth perception in the Mongolian gerbil was investigated as a function of age and environment. Thirty-two gerbils were raised in either a cliff or flat environment, and half the gerbils in each condition were tested on the visual cliff from 21 to 57 days of age. All gerbils were tested at 60–61 days on a standard visual cliff, a barrier cliff which prevented movement along the centerboard, and a jumping platform. While the gerbils did not display a preference for the shallow side when tested at 21 days, those living in a cliff environment showed rapid acquisition of such a preference, whereas those living in a flat environment did not. By 60–61 days, however, all gerbils demonstrated a strong preference for the shallow side on both versions of the visual cliff, regardless of environment or pretesting experience.     

Formation of leap orders in pairs of male domestic chickens

There is disagreement concerning the role or importance of social leaping, compared with pecks and threats, in the dominance relations of fowl. As an approach to this issue, the current paper reports two experiments that used aggression-inducing isolation-rearing conditions of either 8 days or 8 weeks. In 5-min tests in pairs after isolation it was found that leaping was the key aggressive response in conflicts between 14- to 15-week-old roosters. Leaps were more frequent overall and occurred earlier than did pecks. Although both dominant and subordinate birds leaped at one another to some degree, only the dominant birds had both “leap rights” and “peck rights.” The data indicated that leaping is a behavior that has an important, central role in the social organization of male domestic chickens. These laboratory results were comparable to certain archival data from classic field research.     

Dominance,aggression, and the functional use of space in institutionalized female adolescents

This is a study of an institutionalized group of female adolescents observed for a nine-week period. These girls were observed to determine the characteristics of their dominance relations and how, in turn, this aspect of their social environment was related to use of their physical environment. Correlational analyses between observational and sociometric data suggested that dominance rank was based upon the frequency of being the recipient of a dominance act. Fewer dominance acts were initiated against higher ranking girls. Dominance ranking was not based upon frequency of initiating a dominance act towards others. Higher ranking girls were the ones most frequently observed alone in their own bedroom. Bedrooms were highly desiuable areas used for grooming (eg, setting hair, ironing clothes, putting on cosmetics, resting) as girls sought to gain popularity with the institution's male population. Comparison of results with findings in similar studies on male adolescents suggest some tentative generalizations as to sex difference in dominance and territoriality.     

Development and expression of autogrooming in the Mongolian gerbil, Meriones unguiculatus

Adult gerbils, Meriones unguiculatus, autogroom their body parts in the order: mouth--nose, face, ears, flank, ventrum, and tail. This is the identical order in which the autogroom matures during the first 33 days of life. The parallel sequencing increases our understanding of neurophysiological processes underlying movement patterns and also indicates how movement patterns evolve.     

When ostracism leads to aggression: The moderating effects of control deprivation

We hypothesized that increasing or decreasing levels of control in an ostracized individual could moderate aggressive responding to ostracism. Participants were either ostracized or included in a spontaneous game of toss, and then exposed to a series of blasts of aversive noise, the onsets over which they had either control or no control. Aggression was defined as the amount of hot sauce participants allocated to a stranger, knowing the stranger did not like hot foods, but would have to consume the entire sample. Ostracized participants without control allocated more than four times as much sauce as any other group; ostracized participants who experienced restored control were no more aggressive than either of the groups who were included. Aggressive responding to ostracism may depend on the degree to which control needs are threatened in the target, and is discussed in terms of Williams’s (2001) needs threat model of ostracism.     

Heightened male aggression toward sexualized women following romantic rejection: The mediating role of sex goal activation

Research from a variety of disciplines suggests a positive relationship between Western cultural sexualization and women's likelihood of suffering harm. In the current experiment, 157 young men were romantically rejected by a sexualized or non‐sexualized woman then given the opportunity to blast the woman with loud bursts of white noise. We tested whether the activation of sexual goals in men would mediate the relationship between sexualization and aggressive behavior after romantic rejection. We also tested whether behaving aggressively toward a woman after romantic rejection would increase men's feelings of sexual dominance. Results showed that interacting with a sexualized woman increased men's sex goals. Heightened sex goal activation, in turn, predicted increased aggression after romantic rejection. This result remained significant despite controlling for the effects of trait aggressiveness and negative affect. The findings suggest that heightened sex goal activation may lead men to perpetrate aggression against sexualized women who reject them.

     

Genotype modulates prenatal stress effects on aggression in male and female mice

Prenatal stress (heat and restraint) significantly increased postpartum aggression (proportion of animals fighting and/or the intensity of the behavior) in C57BL/6J female mice and reduced the behavior in DBA/2J females. For intermale aggression, prenatal stress increased the behavior (intensity of aggression) in C57BL/6J males but did not affect aggressive behavior in DBA/2J animals. Infanticidal behavior (the killing of young) exhibited by male mice was not influenced by prenatal stress in either strain. Relative anogenital distance measurements in neonates at birth did not serve as a reliable predictor of strain variation in prenatal stress effects. Prenatal stress did not influence this measure of prenatal androgen exposure in DBA/2J or C57BL/6J females. For males, prenatal stress elevated relative anogenital distance in C57BL/6J mice and decreased this measure in DBA/2J animals. Prenatal stress effects on aggressive behavior in male and female mice therefore depend upon genotype. Strain-dependent differences may be modulated by differences in endocrine reactivity to prenatal stress/and or differential central neural tissue sensitivity to hormones.