Effects of group composition on agonistic behavior of captive pigtail macaques,Macaca nemestrina

We surveyed agonistic behaviors of 20 captive groups of pigtail macaques (Macaca nemestrina) housed under identical spatial conditions. Fifteen groups contained one male each; the other five groups contained no adult males. Groups included six to twelve adult females, some of which had infants with them. We found no relationship between social density of groups and incidence of agonistic behavior, but significantly more contact aggression (grab, hit, push, bite) and noncontact aggression (chase, open-mouth “threat,” bark vocalization) occurred among females in groups containing no males than in those containing one male each. Apparently, males played an important role in the inhibition of intragroup conflict. We also found that females in groups containing males exhibited less noncontact aggression if infants were present than if no infants resided in their groups. Thus, competition of females over infants must not have been an important constituent of intragroup conflict under the conditions of this survey.     

Postweaning environmental and social factors influencing the onset and expression of agonistic behavior in Norway rats

Two studies were conducted to determine the importance of the postweaning environment and social milieu in regulating the expression of intraspecific aggression in Norway rats. In Experiment 1, male rats were housed either individually or in pairs at 21 days of age. In addition, one-half of the singly housed and paired animals were given experiences with intruders during maturation. At 85 days of age, all animals were given a brief intruder test and then removed from their postweaning environment and provided individually with homecages for a two week period until tested for aggression toward intruders. Results of intruder tests given during maturation indicated agonistic exchanges appeared earlier and more frequently in cages housing a single resident than cages with cohabiting males. However, agonistic exchanges between singly reared residents and intruders had detrimental consequences in adulthood especially under long-term combat situations. That is, although individually reared animals, with early fighting experiences, were capable of initiating intraspecific aggression, such individuals were unable to defend their homecage over a long period of time as evidenced by the high number of wounds and tendency to lose body weight during adult fighting.In Experiment 2, male Norway rats were reared in pairs from 21 days of age and identified as dominant or subordinate on the basis of intracolony social interactions shown during maturation. At 80 days of age, animals were paired with individually reared males in an unfamiliar cage for a 20 day period and examined for agonistic behavior toward intruders at 100 days of age. Group-reared subordinate males exhibited defensive behavior during confrontations with individually reared animals and incurred more wounds and lost more body weight than their cohabiting partner. In addition, subordinate males showed significantly fewer offensive postures toward intruders than individually reared cohabitants. In contrast, group-reared dominant animals did not differ from individually reared males in display of agonistic patterns, in number of wounds, and body weight changes during the period of cohabitation. These findings demonstrate that early rearing factors have pronounced effects on agonistic behavior. Animals experiencing defeat during development are more likely to lose agonistic confrontations in unfamiliar territory than either animals dominant in their early social interactions or animals without the experience of winning or losing agonistic encounters. These results have implications for the understanding of agonistic behavior and predicting outcomes of animal contests, and reveal important differences in agonistic experiences among animals reared in groups.     

Involvement of metabotropic glutamate receptors in excitatory amino acid and GABA release following spinal cord injury in rat

Spinal cord injury (SCI) leads to an increase in extracellular excitatory amino acid (EAA) concentrations resulting in glutamate receptor-mediated excitotoxic events. The glutamate receptors include ionotropic (iGluRs) and metabotropic (mGluR) receptors. Of the three groups of mGluRs, group-I activation can initiate intracellular pathways that lead to further transmitter release. Groups II and III mGluRs function mainly as autoreceptors to regulate neurotransmitter release. In an effort to examine the role of mGluRs in the increase in EAAs following SCI, we administered AIDA, a potent group-I mGluR antagonist immediately after injury. To determine subtype specific roles of the group-I mGluRs, we evaluated EAA release following LY 367385 (mGluR1 antagonist) and MPEP (mGluR5 antagonist) administration. To evaluate group-II and -III mGluRs we administered APDC (group-II agonist) and L-AP4 (group-III agonist) immediately following injury; additionally, we initiated treatment with CPPG (group-II/-III antagonist) and LY 341495 (group-II antagonist) 5 min prior to injury. Subjects were adult male Sprague-Dawley rats (225-250 g), impact injured at T10 with an NYU impactor (12.5 mm drop). Agents were injected into the epicenter of injury, amino acids where collected by microdialysis fibers inserted 0.5 mm caudal from the edge of the impact region and quantified by HPLC. Treatment with AIDA significantly decreased extracellular EAA and GABA concentrations. MPEP reduced EAA concentrations without affecting GABA. Combining LY 367385 and MPEP resulted in a decrease in EAA and GABA concentrations greater than either agent alone. L-AP4 decreased EAA levels, while treatment with LY 341495 increased EAA levels. These results suggest that mGluRs play an important role in EAA toxicity following SCI.     

Exposure to the steroid hormone 20-hydroxyecdysone modulates agonistic interactions in male Homarus americanus

In this study we present evidence that 20-hydroxyecdysone (20E) affects agonistic behavior in male American lobsters and that male and female animals differ in their response to the hormone. Thirty-minute staged fights were conducted between large males exposed either to artificial seawater (ASW) or 20E and small, anosmic opponents. The nephropores of both combatants were blocked. Fights were videotaped and quantitatively analyzed for aggressive, defensive and avoidance behaviors using an ethogram in which behaviors are ranked according to aggressiveness. Unlike female lobsters, exposing male lobsters to 20E did not increase their aggressive behavior; however, there was a marginally significant trend toward an increase in defensive behaviors with a lower aggressive content than in their ASW-exposed counterparts. The opponents of 20E-exposed animals performed significantly more aggressive behaviors than their counterparts. In fights with 20E-exposed animals, the overall aggressive intensity of the fight was increased and the animals performed a greater number of avoidance behaviors. Unlike the effects of 20E on females, where exposure to 20E caused an increase in overall agonistic arousal, males only exhibited a change in frequency of their behaviors. These findings suggest that while 20E affects both males and females in agonistic encounters, the nature of the effect is different for the two sexes.     

Seasonal dynamics of agonistic displays in territorial and non-territorial males of goitered gazelle

Aggression serves a great variety of social functions, one of which is protection of individual territories from intruders. Territorial males of many antelope species show aggressive noncontact displays, and only rarely fight. It has been suggested that ungulate males tend to have more frequent and longer aggressive interactions with rivals of similar age or social status than with males of dissimilar status. In the present paper, we test whether territorial and non-territorial males behave in a similar manner and avoid fights, and whether or not they preferentially direct aggressive and longer agonistic interactions towards males of similar age or social status, rather than towards other classes of males. We found that territorial males usually avoided straight fights with peers, and instead mainly used noncontact displays in aggressive interactions. In contrast, non-territorial males used fights considerably more often, especially during the onset of territoriality in April to May, when these males had their most frequent aggressive interactions. Territorial bucks aggressively interacted most frequently with non-territorial males and significantly less often with other territorial males, but agonistic noncontact displays between territorial males lasted the longest. In contrast, non-territorial males addressed their aggressive noncontact displays and fights most often to peers and less frequently to sub-adults. Asymmetry in the social status of territorial vs. non-territorial males was likely responsible for the distinctively different agonistic behaviors shown by the two types of males, which in turn are likely due to the different costs and benefits each male can accrue from these aggressive interactions.     

条纹短攀鲈的雄性个体大小、雌性偏好以及雄性之间的竞争

本研究考察了条纹短攀鲈(Trichopsis vittata)雄性个体的身体大小对雌性个体性偏好的影响以及对雄性之间竞争的影响。本研究设立了两种处理来研究雌性个体的性偏好以及雄性之间的竞争。在一种处理中,放入同样大小的雄性个体,而在另一种处理中,放入大小不同的雄性个体。结果表明,雄性个体的大小不影响雌性条纹短攀鲈的性偏好。在对雄性之间竞争的研究中,发现个体较大的个体获胜的次数比较多。在个体大小相同的处理中,雄性之间打斗的持续时间比另一种处理中的打斗持续时间长。对这两种处理中不同对抗行为的比较表明,个体大小相同处理组中的发声、咬、以及总体对抗行为发生得更为频繁。对个体大小不同处理组中的大、小个体的进一步观察也揭示出体型大的个体比体型小的个体有更多的追逐行为和更少的逃脱行为。这些结果表明,在雄性个体比雌性个体大的物种中,体型的性两型可能与雄性之间的竞争有关,而不是与雌性偏好有关。     

Kinship shapes affiliative social networks but not aggression in ring-tailed coatis

Animal groups typically contain individuals with varying degrees of genetic relatedness, and this variation in kinship has a major influence on patterns of aggression and affiliative behaviors. This link between kinship and social behavior underlies socioecological models which have been developed to explain how and why different types of animal societies evolve. We tested if kinship and age-sex class homophily in two groups of ring-tailed coatis (Nasua nasua) predicted the network structure of three different social behaviors: 1) association, 2) grooming, and 3) aggression. Each group was studied during two consecutive years, resulting in four group-years available for analysis (total of 65 individuals). Association patterns were heavily influenced by agonistic interactions which typically occurred during feeding competition. Grooming networks were shaped by mother-offspring bonds, female-female social relationships, and a strong social attraction to adult males. Mother-offspring pairs were more likely to associate and groom each other, but relatedness had no effect on patterns of aggressive behavior. Additionally, kinship had little to no effect on coalitionary support during agonistic interactions. Adult females commonly came to the aid of juveniles during fights with other group members, but females often supported juveniles who were not their offspring (57% of coalitionary interactions). These patterns did not conform to predictions from socioecological models.     

Social interactions and aggression among male Madagascar hissing cockroaches (Gromphadorhina portentosa) in groups (Dictyoptera: Blaberidae)

We studied agonistic interactions among male Madagascar hissing cockroaches,Gromphadorhina portentosa, in groups of five (low-density) or 10 (high-density) males. Consistent with previous studies of male pairs, we observed aggression (Abdomen Flick, Abdomen Push, Butt, Lunge), submission (Crouch, Retreat), and noncontact behavior (Abdominal Extension, Abdomen Thrash, Agonistic Hiss, Stilt). Males at both densities performed all acts. However, males in the high-density group performed Abdomen Push significantly more often than males at a low density. The rate of each remaining act was unaffected by density. Regardless of density, males within social groups varied in aggression. More aggressive males utilized frontal assaults (Butt and Lunge) during interactions, while males displaying lower levels of aggression preferentially used the abdomen during interactions. More aggressive males performed Abdomen Flick more frequently, while males displaying lower levels of aggression performed Abdomen Push. We also investigated the relationship between male aggression and the four noncontact behaviors. We found that Abdominal Extension, Abdomen Thrash, and Agonistic Hiss were positively correlated with our aggregate measure of male aggression suggesting these are aggressive displays. Stilt was positively correlated with measures of both aggression and submission, leaving its function unclear. None of the behavioral acts examined in this study were highly correlated with male weight. Our results are discussed in light of possible hypotheses addressing the function of specific behavior during male-male competition.     

Neighbor effect: evidence of affiliative and agonistic social contagion in captive chimpanzees (Pan troglodytes)

Previous studies of captive chimpanzees have demonstrated the "neighbor effect," or social contagion, with respect to agonistic vocalizations and behaviors. The present study considers whether there is a relationship between behavior patterns in focal animals and the auditory signals of neighboring social groups. Using focal-group sampling, we collected 172.5 hr of data on 51 subjects (25 females and 26 males) housed in 10 social groups. We performed two-tailed Wilcoxon matched-pairs signed-rank tests to determine whether the relative frequency of the vocalizations (high vs. low) affected the behaviors. In keeping with past research, we found that agonistic noises and vocalizations from neighboring social groups had a significant effect on the rates of focal-group bluff displays, pant-hoots, and aggression (P<0.05). In addition, we also found significant relationships between grooming behavior and vocalizations in focal groups, and grooming vocalizations from neighboring groups (P<0.05). The results suggest that social contagion is not limited to aggressive behaviors, but also occurs for affiliative behavior patterns.     

Exogenous vasotocin alters aggression during agonistic exchanges in male Amargosa River pupfish (Cyprinodon nevadensis amargosae)

Pupfishes in the Death Valley region have rapidly differentiated in social behaviors since their isolation in a series of desert streams, springs, and marshes less than 20,000 years ago. These habitats can show dramatic fluctuations in ecological conditions, and pupfish must cope with the changes by plastic physiological and behavioral responses. Recently, we showed differences among some Death Valley populations in brain expression of arginine vasotocin (AVT). As AVT regulates both hydromineral balance and social behaviors in other taxa, these population differences may indicate adaptive changes in osmoregulatory and/or behavioral processes. To test whether AVT is relevant for behavioral shifts in these fish, here we examined how manipulations to the AVT system affect agonistic and reproductive behaviors in Amargosa River pupfish (Cyprinodon nevadensis amargosae). We administered exogenous AVT (0.1, 1, and 10 microg/g body weight) and an AVP V1 receptor antagonist (Manning compound, 2.5 microg/g body weight) intraperitoneally to males in mixed-sex groups in the laboratory. We found that AVT reduced the initiation of aggressive social interactions with other pupfish but had no effect on courtship. The effects of AVT were confirmed in males in the wild where AVT (1 microg/g body weight) reduced the aggressive initiation of social interactions and decreased aggressive responses to the behavior of other males. Combined, these results show that AVT can modulate agonistic behaviors in male pupfish and support the idea that variation in AVT activity may underlie differences in aggression among Death Valley populations.     

Aggressive behavior in female golden hamsters: development and the effect of repeated social stress

In male golden hamsters, agonistic behavior matures during puberty, changing from play fighting to adult-like aggression. In addition, this transition is accelerated by repeated social subjugation early in puberty. However, little is known about the development of agonistic behavior in females. In the present study, we compared the development of agonistic behavior in male and female golden hamsters. Furthermore, we also tested the effects of repeated social subjugation on the development of agonistic behavior during puberty. Hamsters were tested for agonistic behavior in the presence of a smaller intruder at different intervals during puberty. Several observations were made. First, the frequency of attacks remained stable in females, while varying in males. Second, the transition from play fighting to adult-like aggression occurred at earlier time periods in females than in males. Finally, a clear transitional period marked by attacks focused on the flanks was observable in males around mid-puberty. However, this transitional period was not apparent in females. In addition, juvenile females were exposed to aggressive adult males or females. In both cases, repeated exposure to stress had no statistically significant effect on the development of agonistic behavior. After 2 weeks of subjugation, exposure to aggressive adults had no effect on serum cortisol levels, indicating that juvenile females habituate to repeated social stress. These data show significant sex differences in the development of agonistic behavior and adaptation to repeated stress in juvenile golden hamsters.     

Role of loud calls in brown howlers,Alouatta fusca

The loud calls of brown howler monkeys were studied during a year at the Santa Genebra Reserve, in southeastern Brazil. The study group emitted roars and barks on a total of 47 occasions, the majority of which (92%) were restricted to intergroup visual encounters. Loud calls were also elicited by the roars of distant groups (6%) and during intragroup agonistic interactions (2%). Intergroup visual encounters (n = 42) occurred predominantly in seldom used quadrats of the study group home range. In these instances, the loud calls were produced chiefly by the adult male alone (69% of cases), while the study group's two adult females joined the male in the remaining cases. Intergroup physical aggression, such as chase and displacement, was observed during 15 encounters (35% of cases). A dawn chorus does not occur in Santa Genebra—the loud calls were heard most frequently in mid-morning and again during mid-afternoon—and they were more abundant during the dry season, when the availability of food (new leaves) in the forest was lower. The data presented here provide some support for the hypothesis that roars of howler adult males are used in assessment of opponents, providing an alternative to energetically expensive chases and fights. However, given the relatively high rate of physical aggression observed during intergroup encounters, a result probably related to the high density of howlers and the consequent high frequency of intergroup encounters observed in this forest (0.7/day), ritualized aggression, in the form of loud calling, is apparently often insufficient to settle disputes. © 1995 Wiley-Liss, Inc.     

Sounds Modulate Males’ Aggressiveness in a Cichlid Fish

Acoustic signals are produced in many fish species during agonistic or courtship interactions. A way to test the biological role of these sounds is the use of acoustic playback experiments. However, sounds are usually associated with visual displays and playback experiments performed in fish so far, often failed to match acoustic and visual stimuli. To avoid this mismatch issue, we experimentally separated or coupled visual and acoustic channels to test the role of sounds produced during male–male aggressive interactions in a cichlid fish, Metriaclima zebra. Results show that aggressive behaviour is based on visual stimuli and that acoustic signals alone never trigger aggression. Furthermore, the association between visual and acoustic channels lowers the level of aggressiveness found when fish can only interact visually. This suggests that acoustic signals used during a dispute may complement visual displays to modulate males’ behaviour by reducing their aggressiveness and the risk of escalated fights.     

Sociality in Callithrix penicillata: II. Individual Strategies During Intergroup Encounters

In social animals, intergroup interactions, whether through agonistic and competitive behaviors or affiliative ones, can influence important parameters such as home range, territory sizes, and access to resources, which may directly affect both female and male fitness. We studied the intergroup interaction patterns of a wild group of black-tufted-ear marmosets (Callithrix penicillata) in central Brazil. Agonistic interactions occurred at low frequencies during intergroup encounters. The marmosets directed agonistic interactions without physical aggression primarily against same-sex individuals, suggesting that male and female aggression patterns are shaped by their sexual interests. However, females of the focal group also directed agonistic behavior toward extragroup males that attempted copulation. The marmosets appeared to use intergroup encounters to gather information about possible partners and extragroup reproductive opportunities. Intergroup sexual interactions occurred mainly in the form of copulations or attempted copulations by all adults, with the exception of the dominant female. Our results suggest that a possible reproductive strategy used by males is to attempt fertilization of extragroup females. Adult males copulated with the same extragroup female during several opportunities, which suggests sperm competition or the establishment of social bonds with neighboring females.     

Social compatibility in a newly formed all‐male group of white crowned mangabeys (Cercocebus atys lunulatus)

Surplus males in primate captive populations are a common problem for zoos. Some captive breeding programs promote all‐male groups as an adequate option to house surplus males, but there have been few attempts to assess the feasibility of this management technique across primate species. The present study provides preliminary data regarding social compatibility within a newly formed all‐male group of four white crowned mangabeys (Cercocebus atys lunulatus). The study was conducted at the Valencia Zoo (Spain), where data on social behavior were collected over 6 months using continuous focal animal sampling for a total of 87 hr of observation. Results show that low intensity aggressive behaviors (facial threats) were expressed at high rates, whereas physical aggression (fights) rarely occurred. Aggression was more frequent among individuals belonging to the same age–gender class. Regarding affiliative behaviors, every individual actively sought proximity to all other group members through positive approaches, and although not all males carried out social grooming, every male was groomed by at least one group member. Our results suggest that the group was compatible socially because social relationships among the individuals were not neutral, and physical aggression occurred at low rates. The present study provides preliminary data supporting the feasibility of all‐male groups as a management option for surplus males in captive populations of white crowned mangabeys. Nevertheless, further studies are needed to be able to generalize both within and across species. Zoo Biol 0:1–7, 2007. © 2006 Wiley‐Liss, Inc.     

Effects of physical and social experiences and octopamine receptor agonist on fighting behavior of male crickets Velarifictorus aspersus (Orthoptera: Gryllidae)

Fighting commonly occurs among animals and is very important for resolving conflicts between conspecific individuals over limited resources. The plasticity of fighting strategies and neurobiological mechanisms underlying fighting behavior of insects are not fully understood. In the present study, we examined whether physical and social experiences affected the aggressiveness of males of the cricket Velarifictorus aspersus Walker, and whether an octopamine (OA) receptor agonist could affected the aggressiveness of males exposed to different experiences. We found that flight and winning a fight significantly enhanced male aggressiveness, while losing a fight significantly suppressed male aggressiveness, consistent with the findings of existing studies on other cricket species. We also found that female presence had a stronger enhancing effect on male aggressiveness than flight or winning a fight. These findings demonstrated that physical and social experiences can affect the fighting behavior of male V. aspersus. Topical application of a 0.15?M solution of an OA receptor agonist (chlordimeform, CDM) significantly increased male aggression level, suggesting that OA may play an important role as a neuromodulator in controlling fighting behavior of males of this species. Despite displaying a significantly higher aggression level (level 5 or 6), CDM-treated losers did not escalate to physical combat, while fights between courting males usually resulted in physical escalation. It is likely that fighting behavior is only partly regulated by OA, and additional regulatory pathways may be involved in achieving physical combat.     

Agonistic interactions with asymmetric body size in two adult-age groups of the annual killifish Millerichthys robustus (Miller & Hubbs, 1974)

In this study, the author evaluated two adult age groups of the Mexican rivulus Millerichthys robustus with body size asymmetries to determine the strategies used by an annual killifish during agonistic interactions of different ontogenetic stages. To achieve this goal, the author first characterized the ethogram of agonistic interactions of M. robustus composed of seven behavioural units in males and five behavioural units in females. The author then analysed agonistic interaction strategies used by males and females with body size asymmetries in two groups of different adult ages that represent different ontogenetic stages: (a) just after sexual maturity was reached, at 5 weeks of age, and (b) near natural death, at 24 weeks of age. The agonistic behaviour patterns of M. robustus were compatible with the logic of mutual assessment. Large males had an advantage during their interactions in both age groups, winning all of the encounters. Nonetheless, there was more aggression in 5-week-old fish encounters. In addition, small 24-week-old fish were more aggressive than small 5-week-old fish. These changing strategies may be because of the cost–benefits required during a fight at each ontogenetic stage. In the female encounters, size did not predict winners, as both small and large fish won a similar number of encounters, and some contests remained unresolved regardless of age group. There was a tendency for small females of any age to risk more than males in fights to maintain reproductive fitness.     

Seasonal changes in and effects of familiarity on agonistic behaviors of rat-like hamsters (Cricetulus triton)

The seasonal changes in agonistic behaviors and effects of familiarity on agonistic behaviors in wild-caught adult rat-like hamsters (Cricetulus triton) were observed in dyadic encounters in a neutral arena. The aggression of opposite- and same-sex encounters became higher or remained the same during the non-breeding season. This indicates that the hamsters were solitary during both seasons. Familiarity increased the aggression in male–male encounters and decreased the aggression in female–female encounters during both seasons. Familiarity also increased the aggression in female–male encounters during the non-breeding season and had no effect on the aggression in female–male encounters during the breeding season. These results may be related to the hamsters social structure. The more agonistic acts both male and female hamsters had, the more frequently they marked using flank glands during both seasons. This implies that flank gland marking can be used to advertise status and can be assessed by opponents to reduce the agonistic costs.     

Social cues influence growth and sexual maturation of the male musk shrew (Suncus murinus)

Musk shrews were maintained from weaning (20 days of age) for 20 or 40 days in one of several social conditions. In Exp. 1, young males housed with adult females gained more weight and had heavier sex accessory organs than did young males housed with an adult male or reared alone. In Exp. 2 this same pattern of accelerated growth and sexual maturation was found when males were reared directly with an adult female or in a split cage where a wire barrier served to separate the male and his adult female cagemate. In Exp. 3, males were reared in cages containing clean or soiled bedding: soiled bedding was taken once every 5 days from the cage of an adult male, or a female. Under these conditions differences in the weights of reproductive tissues showed minimal variation with housing condition after 20 days of treatment. At that time males reared in soiled bedding taken from the cage of an adult female had accelerated development compared with control males. In Exp. 4, males were housed alone or in a split cage with an adult female which was separated by a wire mesh or a solid, opaque barrier. Males separated by a solid barrier from their female cagemates for 40 days had reproductive tissue weights equivalent to those measured in males reared alone. Taken together these results suggest that the presence of an adult female has dramatic effects on body growth and development of reproductive target tissues in young male musk shrews. Male-female social interactions could play an important role in the timing of puberty in this opportunistically breeding tropical mammal.     

Gender effects on aggression, dominance rank, and affiliative behaviors in a flock of captive adult cockatiels (Nymphicus hollandicus)

Agonistic and affiliative behaviors and spatial positioning were studied in a small psittacine species, Nymphicus hollandicus. Subjects studied were flock-housed breeders including five hens and seven cocks. Fifteen-minute focal animal samples were collected for the entire flock in a randomly distributed order during mate selection and the onset of the breeding season. All agonistic behaviors were recorded, including the winner and loser of each interaction, along with allopreening and copulation behavior. Point samples were recorded every 60s to determine social spacing. Rates of aggression were significantly higher for male cockatiels than female cockatiels. Results based on dyadic agonistic interactions showed males to rank significantly higher in the social hierarchy than females. Associations within the flock were not random. Individual birds associated more with specific birds than would be predicted by chance. Analysis of spatial data revealed that there were both same-sex and opposite-sex preferred associations within the flock. Male cockatiels engaged in allopreening behavior with females significantly more than with other males. Observations of breeding and nesting behaviors revealed pairs, a triad, and extra-pair mating.