Assessing the Ideal Free Distribution: Do Guppies Use Aggression as Public Information about Patch Quality?

Aggression can be costly to foragers, yet some recent research suggests that foragers should use aggression as a cue to patch quality (the attractive aggression hypothesis). If aggression is predictive of patch quality, then the attractive aggression hypothesis predicts that the distribution of foragers should follow the distribution of aggression. If, instead, aggression is repulsive because it is costly, then the distribution of foragers should diverge from the distribution of aggression. We tested the attractive aggression hypothesis using female guppies, Poecilia reticulata , and found that the distribution of foragers followed the distribution of food, but was unaffected by the distribution of aggression. These data do not support the attractive aggression hypothesis, but instead suggest that the distribution of aggression is a consequence of the distribution of foragers, and that aggression is not used as public information about patch quality.     

Fight for your breeding right: hierarchy re-establishment predicts aggression in a social queue

Social aggression is one of the most conspicuous features of animal societies, yet little is known about the causes of individual variation in aggression within social hierarchies. Recent theory suggests that when individuals form queues for breeding, variation in social aggression by non-breeding group members is related to their probability of inheriting breeding status. However, levels of aggression could also vary as a temporary response to changes in the hierarchy, with individuals becoming more aggressive as they ascend in rank, in order to re-establish dominance relationships. Using the group-living fish, Neolamprologus pulcher, we show that subordinates became more aggressive after they ascended in rank. Female ascenders exhibited more rapid increases in aggression than males, and the increased aggression was primarily directed towards group members of adjacent rather than non-adjacent rank, suggesting that social aggression was related to conflict over rank. Elevated aggression by ascenders was not sustained over time, there was no relationship between rank and aggression in stable groups, and aggression given by ascenders was not sex-biased. Together, these results suggest that the need to re-establish dominance relationships following rank ascension is an important determinant of variation in aggression in animal societies.     

What can animal aggression research tell us about human aggression?

Research on endocrinological correlates of aggression in laboratory animals is implicitly motivated by an expectation that the results of such studies may be applicable to human aggression as well. Research with a focus on the stimulus antecedents of aggression, its response characteristics, and its outcomes suggests a number of detailed correspondences between offensive aggression in laboratory rodents and human angry aggression. These include resource (including status and territory) competition as motives that are particularly elicited by conspecific challenge situations and, when the aggression is successful, outcomes of reduction of challenge and enhancement of resource control and status. Although the response characteristics of human aggression have been dramatically altered by human verbal, technological, and social advancements, there is some evidence for targeting of blows, similar to a well-established pattern for offensive aggression in many nonhuman mammals. Finally, for people as well as for nonhuman mammals, fear of defeat or punishment is a major factor inhibiting the expression of offensive aggression. While defensive aggression has been very little researched in people, it may represent a different phenomenon than angry aggression, again providing a parallel to the offense-defense distinction of laboratory rodent studies.     

Family Feuds: Severe Aggression among Cooperatively Breeding Cotton-Top Tamarins

A survey of severe aggression occurring over the 20 year history of a cotton-top tamarin (Saguinus oedipus) colony indicated that most aggression was between same-sex individuals, with fights among siblings more common than parent-offspring conflict. Males engaged in severe aggression more often than females did, paralleling the dimorphic aggressive response to same-sex intruders in this species. Female-female aggression occurred at larger group sizes than male-male aggression, suggesting a higher threshold for female aggression. Much sibling aggression was directed by postpubertal subadults toward prepubertal siblings. Only 17% of aggression occurred in association with infant births, and these cases rarely involved parents and offspring suggesting that aggression was not used by reproductive animals to defend their breeding position. Severe aggression was often associated with attempts to introduce stepparents or movement of individuals in and out of the group. The mean group sizes when aggression is observed in captivity are close to the maximum group sizes observed in wild tamarins, which suggests that severe aggression in captive groups may reflect processes related to dispersal in wild tamarins.     

Sex differences in indirect aggression: Psychological evidence from young adults

Many studies have found differences in the types of aggression used by males and females, at least in children and adolescents. Boys tend to use direct physical or verbal aggression, whereas girls tend to use more indirect forms of aggression that prominently feature gossip. Evolutionary theories of sex differences in indirect aggression propose selection pressures that would have acted on older teenagers and adults. Evidence for sex differences in indirect aggression in adults, however, is equivocal. Virtually all studies of adults have found a sex difference in physical aggression, but most have failed to find sex differences in the use of the more indirect forms of aggression. Almost all of these studies have measured indirect aggression using self-reports of aggressive behavior. We investigated sex differences in the psychology of indirect aggression by exposing young adult women and men to the same aggression-evoking stimulus. As evolutionary models predict, we found that women had a stronger desire than men to aggress indirectly, even after controlling for perceptions of social norms and approval. Future work on both evolutionary and social norm models of indirect aggression is warranted.     

Football Fan Aggression: The Importance of Low Basal Cortisol and a Fair Referee

Fan aggression in football (soccer) is a societal problem that affects many countries worldwide. However, to date, most studies use an epidemiological or survey approach to explain football fan aggression. This study used a controlled laboratory study to advance a model of predictors for fan aggression. To do so, football fans (n = 74) saw a match summary in which their favorite team lost against their most important rival. Next, we measured levels of aggression with the hot sauce paradigm, in which fans were given the opportunity to administer a sample of hot sauce that a rival football supporter had to consume. To investigate if media exposure had the ability to reduce aggression, before the match fans saw a video in which fans of the rival team commented in a neutral, negative, or positive manner on their favorite team. Results showed that the media exposure did not affect aggression. However, participants displayed high levels of aggression and anger after having watched the match. Also, aggression was higher in fans with lower basal cortisol levels, which suggests that part of the aggression displayed was proactive and related to anti-social behavior. Furthermore, aggression was higher when the referee was blamed and aggression was lower when the performance of the participants’ favorite team was blamed for the match result. These results indicate that aggression increased when the match result was perceived as unfair. Interventions that aim to reduce football fan aggression should give special attention to the perceived fairness of the match result.     

The Dynamic of Aggression: How Individual and Group Factors Affect the Long‐Term Interspecific Aggression Between Two Sympatric Species of Dolphin

Interspecific aggression, similar to intergroup conspecific aggression, has been observed in a variety of taxa. The dominant group or individual is determined by multiple aggressive events and can be influenced by the size, age, or group size of the participating individuals. Interspecific aggression between Atlantic bottlenose (Tursiops truncatus) and spotted (Stenella frontalis) dolphins, both resident and sympatric to Little Bahama Bank, the Bahamas has been consistently observed for over two decades. However, it is unclear whether one species is more dominant and little is known about the factors that influence the progression of aggression. For this study, underwater video recordings of 32 aggressive encounters composed of 451 aggressive behavioural events were analysed over a 12‐yr period (1993–2004). These were used to describe the interspecific aggression observed and quantify which factors (the species and age class of the participants or the group size and behaviour of spotted dolphin groups) had the strongest impact on the progression and outcome of aggression. Over the long term, interspecific aggression was bidirectional with neither species being more dominant. During a single encounter, spotted dolphin group synchrony had the strongest impact on the dynamic of aggression, specifically impacting which group (1) initiated aggression, (2) the direction of aggression and (3) the occurrence of dynamic shifts or dominance reversals. This is the first study to quantify the dynamic of aggression for this population, to document bidirectional aggression and dynamic shifts during long‐term interspecific aggression in free‐ranging delphinids, and this study quantifies the role of synchrony during interspecific aggression using underwater observations.     

Predatory aggression, but not maternal or intermale aggression, is associated with high voluntary wheel-running behavior in mice

Predatory (towards crickets), intermale, and maternal aggression were examined in four replicate lines of mice that had been selectively bred for high wheel-running (S) and in four random-bred control lines (C). In generation 18, individual differences in both predatory and intermale aggression were significantly consistent across four trial days, but predatory and intermale aggression were uncorrelated both at the individual level and among the eight line means. Latencies to attack crickets were significantly lower in S lines as a group. Intermale aggression, however, did not differ between S and C lines. S lines were significantly smaller in body mass, but did not differ in either testes mass or plasma testosterone. In generations 28 and 30, respectively, S and C lines did not differ in either maternal or intermale aggression. However, significant differences among the individual lines were found for maternal aggression, and one S line exhibited an extremely high mean time of aggression (>120 sec for a 5-min test). Maternal and intermale aggression were not correlated among the eight line means or at the level of individual variation. Overall, our results suggest: (1) predatory aggression and voluntary wheel-running are positively related at the genetic level; (2) predatory and intermale aggression are unrelated at a genetic level; and (3) maternal and intermale aggression are not tightly related at the genetic level. Possible relationships between predatory aggression, dopamine, and wheel-running behavior are discussed.     

Juvenile Female Aggression in Cooperatively Breeding Pied Babblers: Causes and Contexts

Sex biases in adult aggression have been well studied and commonly arise when resources which affect survival or lifetime reproductive success are less abundant or more valuable for individuals of one sex. Despite the prevalence of sex biases in adult aggression, evidence for sex biases in juvenile aggression is scant. Here, we present evidence for female‐biased juvenile aggression in cooperatively breeding pied babblers (Turdoides bicolor). Unlike most cases of non‐lethal sibling aggression, juvenile aggression in pied babblers does not seem to be determined by food availability. Instead, we found that juvenile aggression was related to adult dispersal patterns. This study shows that females that were more aggressive as juveniles attempted dispersal earlier than less aggressive females. Potential explanations for the association between juvenile aggression and adult dispersal patterns are discussed.     

Maternal aggression in endothelial nitric oxide synthase-deficient mice

Lactating female rodents protect their pups by expressing fierce aggression, termed maternal aggression, toward intruders. Mice lacking the neuronal nitric oxide synthase gene (nNOS-/-) exhibit significantly impaired maternal aggression, but increased male aggression, suggesting that nitric oxide (NO) produced by nNOS has opposite actions in maternal and male aggression. In contrast, mice lacking the endothelial nitric oxide synthase gene (eNOS-/-) exhibit almost no male aggression, suggesting that NO produced by eNOS facilitates male aggression. In the present study, maternal aggression in eNOS-/- mice was examined and found to be normal relative to wild-type (WT) mice in terms of the percentage displaying aggression, the average number of attacks against a male intruder, and the total amount of time spent attacking the male intruder. The eNOS-/- females also displayed normal pup retrieval behavior. Because a significant elevation of citrulline, an indirect marker of NO synthesis, occurs in neurons of the hypothalamus of lactating WT mice in association with maternal aggression, we examined the brains of eNOS-/- females for citrulline immunoreactivity following an aggressive encounter. The aggressive eNOS-/- females exhibited a significant elevation of citrulline in the medial preoptic nucleus and the subparaventricular zone of the hypothalamus relative to unstimulated lactating eNOS-/- females. Taken together, these results suggest that NO produced by eNOS neither facilitates nor inhibits maternal aggression and that NO produced by eNOS has a different role in maternal and male aggression.     

Interspecific aggression in mixed ungulate species exhibits

Mixed ungulate species exhibits are often plagued with difficulties stemming from interspecific aggression. Several aspects of interspecific aggression were investigated in mixed ungulate species exhibits at the Audubon Zoolnogical Garden in New Orleans, Louisiana. Success of a mixed species exhibit was found to be correlated with the rate of male-initiated aggression, but not with the total rate of aggression. Neither taxonomic relatedness nor size difference between the species could be used to predict the success of a species pairing. The total rate of aggression in an exhibit was related to taxonomic relatedness, aggression being highest between distantly related species. Increases in aggression were triggered by births, mating activity, and introduction of an animal to an exhibit.     

Further evidence for the role of nitric oxide in maternal aggression: effects of L-NAME on maternal aggression towards female intruders in Wistar rats

It has been shown that nitric oxide (NO) increases aggression in male mice, whereas it decreases aggression in lactating female mice and prairie voles. It is also known that aggression can be exhibited at different levels in rodent species, strain or subtypes. The aims of this study were to investigate the proportion of aggressiveness in Wistar rats, the effect of intraperitoneally administered nonspecific nitric oxide synthase (NOS) inhibitor L-NAME (NG-nitro L-arginine methyl ester) on maternal aggression towards female intruders, and whether these effects are due to NO production or not. Rats were given saline intraperitoneally on the postpartum Day 2 and aggression levels were recorded. The same rats were given 60 mg/kg L-NAME or D-NAME (NG-nitro D-arginine methyl ester) on the postpartum Day 3 and their effects on aggression levels were compared to saline. While L-NAME administration did not cause any differences in the total number of aggressive behavior, aggression duration and aggression intensity, it reduced the proportion of animals showing aggressive behavior. In addition, the latency of the first aggression was significantly increased by L-NAME. In the D-NAME group, however, no significant change was found. Our results have shown that L-NAME reduces maternal aggression towards female intruders in Wistar rats through inhibition of NO production. These results suggest that the role of NO in offensive and defensive maternal aggression shares neural mechanisms.     

Relationships between aggression and pubertal increases in testosterone: A panel analysis of adolescent males

Abstract

Existing data linking testosterone (T) and aggression in human adult males are surprisingly tenuous. In one of the few studies based on adolescent males, Olweus et al. (1988) demonstrated strong relationships between concurrent measures of T and aggression. However, the conclusions that could be drawn regarding developmental change were limited. Using data from a three‐year panel study of 100 adolescent males (ages 12 to 13 at study entry), we examined whether there are significant relationships between concurrently collected measures of T and self‐ratings of aggression, and whether the dramatic pubertal rise in T predicts subsequent change in aggression ratings. Panel analyses incorporating concurrent, lagged, and change measures found few significant relationships between aggression and T or pubertal development. The general absence of T/aggression relationships is discussed in the context of other empirical findings, the aggression measures used, and prepubertal differentiation on aggression.     

Sibling Age and Intragroup Aggression in Captive Saguinus midas midas

Different species of Callitrichidae show a consistent pattern in intragroup aggression. Aggression is more frequent between same-sex individuals, with males and older siblings being more aggressive. These findings have been associated with reproductive competition and dispersal events. However, the few studies dealing with intragroup aggression have not fully explored the effects of food availability on aggression or the relationship between age and aggression. I observed 3 family groups of Saguinus midas for 50 weeks and recorded all occurrences of aggression. A total of 138 agonistic events occurred at an average of 1.16 aggressive acts/hour per group, and 52.2% of aggressive acts occurred during a food shortage condition, which accounted for about 12% of all meals in the groups. During the food shortage, aggression was significantly higher, which suggests that food competition promoted an increase in aggression levels. Aggression amongst siblings accounted for 65.2% of all aggressive acts. Aggression from brothers to sisters was significantly more frequent than aggression between brothers. Aggression rates were significantly different between age classes. Young siblings were significantly more aggressive toward old ones than the reverse. Age and aggression received followed a linear relationship, while age and aggression initiated tended to follow a curvilinear relationship. Higher rates of aggression in young siblings probably were prompted by puberty and associated hormonal changes.     

Patterns of injury in zoo-housed spider monkeys: A problem with males?

Aggression among wild spider monkeys is most frequently reported to occur between the sexes, with adult males directing aggression towards adult females and the aggression is normally non-injurious. After two severe instances of aggression in the group of spider monkeys housed at Chester Zoo, we developed a questionnaire to investigate the frequency, direction and possible reasons for aggression in zoo-housed spider monkeys. We sent our questionnaire to 55 zoos worldwide and obtained records from 26 groups, which yielded detailed accounts of 143 aggressive incidents: 56 events for the actors and 127 events for the targets of aggression. We found that zoo-housed spider monkeys are predominantly maintained in small social groups, with a single adult male, two adult females and their offspring. Of the aggression reported, 23.1% of incidents resulted in severe or lethal injuries. Adult males were the most frequent actors of aggression and accounted for 66.7% of incidents. Six cases of male–male aggression were lethal. The most striking pattern was that adult males directed aggression towards non-adult males more than any other age/sex category. The most frequently reported context of aggression was tension between adult and non-adult males. These findings contradict previous reports from wild spider monkeys where female-directed male aggression is most frequently reported. In light of our findings, we recommend that males form the core of the group and that females be relocated among groups to reflect the wild condition of male philopatry and female dispersal. In addition, enclosure design should allow opportunities for the monkeys to segregate themselves from other group members, simulating fission, which is a conflict management strategy for avoiding aggression in wild spider monkeys.     

Factors affecting aggression among females in captive groups of rhesus macaques (Macaca mulatta)

Captive groups of primates often exhibit higher rates of aggression than wild, free-ranging groups. It is important to determine which factors influence aggression in captivity because aggression, particularly intense aggression, can be harmful to animal health and well-being. In this study, we investigated the effect of ground substrate as well as season, rank, age, and group size on rates of agonistic interactions per female in seven captive groups of rhesus macaques (n = 70 females, 1,723 focal samples) at the California National Primate Research Center. Agonistic interactions were divided into three categories: displacements, mild aggression, and intense aggression. Females living in enclosures with gravel substrate were 1.7 times more likely to be involved in intense aggression (e.g. chases and physical contact) than females living in enclosures with grass (Poisson regression model: P < 0.001). High-ranking females were at least 1.3 times more likely to be involved in mild (e.g. threats and lunges) aggression than lower-ranking females (low rank: P = 0.03; mid rank: P = 0.001). Females of all ranks were 1.5-1.9 times more likely to be involved in both intense and mild aggression during the breeding season than other seasons. Age and group size did not affect rates of mild or intense aggression. These findings indicate that although some aggression appears to be natural and unavoidable, i.e. aggression during the breeding season, the well-being of captive macaques can be improved by developing grass substrate in outdoor enclosures.     

Opposing hormonal mechanisms of aggression revealed through short-lived testosterone manipulations and multiple winning experiences

Territorial aggression is influenced by many social and environmental factors. Since aggression is a costly behavior, individuals should account for multiple factors such as population density or reproductive status before engaging in aggression. Previous work has shown that male California mice (Peromyscus californicus) respond to winning aggressive encounters by initiating aggression more quickly in future encounters, and we investigated the physiological basis for this effect. We found that injections that produced a transient increase in testosterone (T) following an aggressive encounter caused males to behave more aggressively in an encounter the following day. Experience alone was not enough to change aggression, as males treated with saline injections showed no change in aggression. The effect of T injections on aggression was androgen-based, as the inhibition of aromatase did not block the T injections from increasing aggression. Aromatase inhibition did, however, increase aggression in the initial aggression tests (before application of T or saline injections), and aromatase activity in the bed nucleus of the stria terminalis (BNST) was negatively correlated with aggression. A previous study suggested that aromatase activity in the BNST decreases after males become fathers. Thus, distinct neuroendocrine mechanisms allow male California mice to adjust aggressive behavior in response to changes in social and reproductive status.     

Kin recognition and the paradoxical patterns of aggression between colonies of a Mojave desert Pheidole ant

Populations of the desert seed-harvesting ant Pheidole xerophylla are often characterized by high nest density leading to competitive interactions between foragers from different nests. We investigated the inter-nest aggression, spatial distribution and genetic structure of a P. xerophylla population of the Mojave Desert in Southern California. Inter-nest aggression was quantified by standardized staged encounters in a neutral arena. Genetic relatedness within nests and relatedness between nests were calculated using allelic frequencies at four microsatellite-DNA loci. We found a bimodal distribution of inter-colony aggression levels with a first mode at low aggression levels and another mode at much higher aggression levels. Inter-colony aggression levels were largely non-transitive. No effect of geographical distance on inter-nest aggression levels was detected. Despite high amounts of variation in inter-colony relatedness ( − 0.24 to 0.37) this variable did not correlate with the level of aggression between nests. Intra-nest relatedness ranged from 0.40 to 0.75 and close inspection of worker genotypes within colonies revealed a high proportion of polygynous colonies or a mixture of polygyny and polyandry. Aggression levels among nests was found to decrease with increasing intra-nest relatedness. These results do not support the idea that aggression is modulated by a nestmate recognition mechanism based on overall genetic similarity. Instead, the absence of transitivity found in inter-colony aggression and bimodal distribution of aggression levels are compatible with a common label acceptance model of nestmate recognition and suggest that label diversity may be encoded by a limited number of loci. Received 29 March 2005; revised 8 September 2005; accepted 27 September 2005.     

Is pain-induced aggression actually a defensive form of that behavior?

25-minute testing of aggressive reactions in constant pairs of male rats, elicited by electric shocks shows that electro-pain aggression of rats is not a homogeneous process, but consists of three successive stages: orienting-investigatory activity and attempts to get out of the chamber; defensive aggression; establishing of relations of domination-subordination and attacking aggression. Division in attacking rats and defending themselves, occurs mainly at final stages of testing (15-25 min); in some pairs reactions of attacking aggression are accomplished by the same rats. It is supposed that rats pain aggression is not a purely defensive form of this behaviour, but a modification of intermale aggression caused by specificity of laboratory conditions.     

Temperament in a Fish: A Longitudinal Study of the Development of Individual Differences in Aggression and Social Rank in the Midas Cichlid

A longitudinal design was applied in a study of the development of individual differences in aggression, and their relationship to growth and sexual differentiation in the Midas cichlid, Cichlasoma citrinellum. Weight and standard length measurements, as well as several measures of aggression, were obtained at regular intervals. Size ranks within groups were stable over a period spanning an early juvenile phase through sexual maturity. Two of three aggression rank scores were also stable over this interval, but they did not relate in any direct way to social rank. As juveniles, males showed higher levels of aggression than females, but the reverse was true in adults. This sex-specific developmental change resulted both from an increase in female aggression at sexual maturity and a decline in male aggression at sexual maturity. Individuals showed distinct and stable behavioral profiles with respect to the combined aggression tests.