Fighting in NIH/S male mice: consequences for behaviour in resident-intruder tests and physiological parameters

Fighting is known to occur frequently in male mouse groups. In this study with outbred NIH/S mice, the possible impact of individual aggressiveness on fighting in groups and on the social status of animals was studied. Male mice were pre-tested in a resident-intruder (RI) test and rated as initially aggressive or non-aggressive according to their attack behaviour against an intruder. Thereafter they were randomly allocated to new social groups, with four mice per cage. Fighting in groups was increased when several initially aggressive animals were included in the group. Within the groups, animals were rated as dominants and subordinates according to their behaviour toward a strange intruder introduced into their home-cage (Group Intruder, GI) test and the occurrence of wounds. Additionally, subordinates were divided into aggressive and non-aggressive categories according to their behaviour in the second RI test, which was performed 3 weeks after grouping. The behaviour in the RI test prior to group-housing did not predict the individual social status or possibility of being wounded in the new social environment. On the other hand, the social relationships in the new group affected the behaviour in a subsequent RI test. All dominants showed aggressive behaviour during the second RI test. Those subordinates which behaved aggressively during this test received the most numerous and serious wounds, suggesting that in the new groups their interactions with the other group members were mostly aggressive. The reduced weight of epididymal adipose tissue in dominant and aggressive subordinates may indicate that they had fought continuously. Social status or levels of fighting in a group did not affect individual weight gain or the other physiological parameters measured. The wounded animals had enlarged spleens and reduced weights of epididymal adipose tissue, which were probably the results of increased activity of the immune system and reduced welfare, respectively. In conclusion, individual aggressiveness seems to be greatly affected by the demands of the social environment. Fighting in mouse groups leading to wounded animals may have effects on physiological research parameters.     

Preference for social contact versus environmental enrichment in male laboratory mice

Due to their aggressive nature, male mice are less frequently used than female mice in biomedical research. When aggressive males are being used, individual housing is common practice. The question arises whether this is an acceptable housing for a social species. The present study was designed to gain more insight into the nature of inter-male social contact and into the potential of a form of environmental enrichment (nesting material) to compensate for the lack of social contact. In a series of tests, we analysed whether male mice of different ages preferred to spend time (1) near a familiar cage mate versus an empty cage, or (2) near to a familiar cage mate versus direct contact with nesting material (tissues). Dwelling time in each of the test cages and sleeping sites was recorded, as was the behaviour of the test mice. Results indicated that when other conditions were similar, male mice preferred to sleep in close proximity to their familiar cage mate. Furthermore, the need to engage in active social behaviour increased with age. Tissues were used to a large extent for sleeping and sleep-related behaviour. It is concluded that single housing in order to avoid aggression between male mice is a solution with evident negative consequences for the animals. When individual housing is inevitable due to excessive aggressive behaviour, the presence of nesting material could partly compensate for the deprivation of social contact.     

On the role of brain serotonin system in the pathway from gene to behaviour

This paper concentrates on involvement of protein elements in the brain neurotransmitter serotonin system (key enzymes in serotonin metabolism and 5-HT(1A) receptors) in the genetic control of behaviour. The data were obtained using Norway rats selected for more that 50 generations for lack of aggressive response and for aggressive behaviour towards humans (fear-induced aggression), inbred mouse strains, and MAO A knockout mice. The review provides converging line of evidence that: 1) brain serotonin contributes to critical mechanism underlying genetically defined individual differences in aggressiveness, and 2) genes encoding pivotal enzymes in serotonin metabolism (tryptophan hydroxylase, MAO A) and 5-HT(1A) receptors belong to a group of genes that modulate aggressive behaviour.     

Photoperiod influences the development and the expression of personality traits and social behaviour in wild cavies (Cavia aperea)

Seasonality influences behaviour, physiology and life history of organisms, and photoperiod is a reliable and influential cue gearing individual adaptation to seasonal changes in the environment. Plastic phenotypic adjustments according to the prevailing season are a widespread, well-studied phenomenon. Less well known are effects on developmental trajectories of animals born into different seasons. By manipulating the photoperiod during pregnancy and lactation independent of food availability and temperature, we studied if maternal behaviour in the precocial wild cavy (Cavia aperea) responds to this seasonal cue and if maternal behaviour and photoperiod shape offspring development and behaviour. We repeatedly observed mothers before and after birth. We investigated if pups differ in risk-taking behaviours directly after birth (indicating direct prenatal effects) or only after gaining independence of the mother (indicating delayed prenatal or postnatal effects due to own cue sampling). Furthermore, we tested if different simulated seasons of birth affect social and aggressive behaviour of adult animals. While theoretical predictions according to risk-taking are quite clear, they are contradictory for social behaviours that are much less well studied. We predicted that animals born into spring photoperiods would be aggressive because of a need to gather enough resources for early reproduction and successfully establishing a territory at least in males. Spring-born males were more aggressive than autumn-borns, while females did not differ with respect to season. Spring-born females, however, lost more body mass when they had to integrate into an established group and autumn-born females initiated more aggressive interactions. Our data demonstrate flexible and long-term stable seasonal effects on behaviours that likely affect fitness outcomes under natural conditions.     

Analysis of the effect of phenamine, L-DOPA and parachlorophenylalanine on the zoo-social behavior of isolated mice]

Abnormal changes in the structure of the individual and zoo-social behaviour of isolated mice due to phenamine (amphethamine), L-DOPA or PCPA were shown. Several elements of the "pathological syndrome of isolation" in mice were found to increase under the action of the drugs studied. The extension or reduction of contacts between animals of the same species was used as an integrative indicator of recovering (resocializing) or aggravating (desocializing) effect of psychotropic drugs on the pathology of animal behaviour.     

Enhancement of social isolation-induced aggressive behavior of young mice by zinc deficiency

Neuropsychological behavior via activation of the hypothalamic-pituitary-adrenal (HPA) axis was analyzed using young mice fed a zinc-deficient diet for 2 weeks. Serum corticosterone concentration was significantly increased after 2-week zinc deprivation, whereas zinc concentration in the brain was not decreased. In the resident-intruder test, the rate of mice that exhibited aggressive behavior to the total mice was significantly higher in isolated zinc-deficient mice than in isolated control mice. The duration of aggressive behavior was more in isolated zinc-deficient mice. These results indicate that aggressive behavior of young mice elicited by social isolation is enhanced by zinc deficiency. On the other hand, social isolation-induced aggressive behavior was enhanced in isolated pair-fed mice with food restriction that can activate the HPA axis. Serum corticosterone concentration was also significantly higher in isolated zinc-deficient mice. To see the effect of the increased serum corticosterone on behavioral abnormality, neurotransmitter concentrations in brain tissue were checked. The concentrations of glutamate and GABA in brain tissue were significantly higher in both grouped and isolated zinc-deficient mice. Furthermore, the concentration of extracellular glutamate in the amygdala before the resident-intruder test was significantly higher in isolated zinc-deficient (aggressive) mice and the higher concentration was maintained during the test. The changes in neurotransmitter homeostasis, probably via the increase in serum corticosterone, seem to be linked to aggressive behavior elicited by social isolation in zinc deficiency.     

Ontogenetic and gender-related variation in the isotopic niche within and between three species of fur seals (genus <Emphasis Type="Italic">Arctocephalus</Emphasis>)

Differences in aggressiveness when competing for environmental resources are the main factor leading to social hierarchy in group living fish. Social status acquired is related to changes in physiological parameters, as metabolic rate. Habitat variation can interfere with aggressive behaviour and promote changes in physiological parameters associated with social status. The primary goal of our study was to investigate how differences in habitat complexity affect the relationship between resting metabolic rate (RMR) and social status in the Amazonian dwarf cichlid Apistogramma agassizii. We compared agonistic interactions between pairs of males in aquaria with different habitat enrichment levels, manipulated by adding shelters. RMR was measured before and after hierarchy establishment. Habitat enrichment promotes changes in aggressive behaviour and influences differences in metabolic rate between dominant and subordinate fish. We observed an increase in biting by dominant fish at high enrichment habitat, which could be related to the increase in territory value. We observed an increase in metabolic rate in dominant fish after hierarchy establishment. However, it occurs only in enriched habitats. We concluded that habitat structure interfere with behavioural characteristics in social hierarchies, as aggressiveness, and changes in aggressive interactions affect metabolic rate in different social ranks in the dwarf cichlid Apistogramma agassizii.     

Aggressive behaviour in related and unrelated wild house mice (Mus musculus L.)

Aggressive behaviour was observed to be rare in small family groups of confined wild house mice, Mus musculus L. Unrelated mice were attacked when they were introduced to a family group and in their presence intra-family aggressive behaviour increased. When two family groups of mice were allowed to meet there were frequent aggressive encounters between unrelated animals and the two groups remained separate. Resident mice were found to be aggressive towards males and females individually isolated and returned to their own family after 2 or 3 weeks absence but not after 1 week. The possibility is discussed that in wild mice odour discrimination influences the dispersal and build-up of free-living populations.     

The neuropeptide arginine vasotocin alters male call characteristics involved in social interactions in the grey treefrog, Hyla versicolor

We investigated the effects of different doses (0, 2.5, 25 and 250 μg) of the neuropeptide arginine vasotocin (AVT) on the calling characteristics of the grey treefrog in a chorus in its natural habitat. AVT changed some call characteristics known to influence social behaviour in grey treefrogs. It increased call duration and number of pulses in a call, but not dominant frequency, call rate or pulse effort. Saline injections and handling did not produce significant changes in any of the call characteristics. In addition, individual animals injected with AVT only rarely produced call characteristics that were outside of the range found in the preinjection measurements, suggesting that AVT does not cause abnormal calling behaviour. Other researchers have demonstrated that longer calls with more pulses are produced by males when chorus densities increase, and females display a strong preference for longer calls with more pulses. This suggests that the changes induced by AVT injections may have functional consequences in social interactions. We previously demonstrated that AVT-injected males (25 μg AVT) displaced resident males from calling sites through changes in calling behaviour under natural field conditions. Our results indicate that changes in call duration and pulse number could contribute to the unmanipulated resident male's behaviour towards the AVT-injected intruder, perhaps because the calls are more attractive to females or because the calls are perceived as more aggressive. Copyright 2000 The Association for the Study of Animal Behaviour.     

Socio-biological basis of “power” in man

The difference between individual aggressive behaviour and group violence is discussed. While individual aggressive behaviour has a biological background and has evolutionary significance for the survival of the individual and the species, group violence, like human character, is due to cultural imprinting and is against the survival of both individuals and populations (war).     

Territorial Behaviour and Social Organization as a Function of the Level of Aggressiveness in Male Mice

Territoriality and social organization were examined in relation to different genetic dispositions for aggressive behaviour. The animals used in the study were male mice of the 51st and 52nd generation of selection for high (Turku Aggressive, TA) and low (Turku Non-Aggressive, TNA) levels of aggressiveness. The level of aggressiveness of the animals was assessed by means of individual tests with non-aggressive standard opponents, after which they were allowed to form individual territories in a 102 times 204 times 90 cm enclosure. TA and TNA males were placed in different enclosures. After 2 wk, when the partitions between individual pens were removed, the behaviour of the animals was observed for a 7-d period. Excessive fighting between the highly aggressive TA males occurred, resulting in the formation of dominant-subordinate relationships. A great number of attacks inflicted were found to be associated with dominance in the colony, and correlated with a high level of aggressiveness when the animals were individually tested for aggression after having been in colony environments. The level of aggressiveness of the TA males that had become subordinates had significantly decreased. The TNA males fought less and were more often found to stay in their original territory for the entire period of observation. The results suggest that different genotypes for aggression arc related to differences in territoriality and social organization in mice.     

Food sensory characteristics: their unconsidered roles in the feeding behaviour of domestic ruminants

When domestic ruminants are faced with food diversity, they can use pre-ingestive information (i.e. food sensory characteristics perceived by the animal before swallowing the food) and post-ingestive information (i.e. digestive and metabolic consequences, experienced by the animal after swallowing the food) to evaluate the food and make decisions to select a suitable diet. The concept of palatability is essential to understand how pre- and post-ingestive information are interrelated. It refers to the hedonic value of the food without any immediate effect of post-ingestive consequences and environmental factors, but with the influence of individual characteristics, such as animal's genetic background, internal state and previous experiences. In the literature, the post-ingestive consequences are commonly considered as the main force that influences feeding behaviour whereas food sensory characteristics are only used as discriminatory agents. This discriminatory role is indeed important for animals to be aware of their feeding environment, and ruminants are able to use their different senses either singly or in combination to discriminate between different foods. However, numerous studies on ruminants’ feeding behaviour demonstrate that the role of food sensory characteristics has been underestimated or simplified; they could play at least two other roles. First, some sensory characteristics also possess a hedonic value which influences ruminants’ intake, preferences and food learning independently of any immediate post-ingestive consequences. Further, diversity of food sensory characteristics has a hedonic value, as animals prefer an absence of monotony in food sensory characteristics at similar post-ingestive consequences. Second, some of these food sensory characteristics become an indicator of post-ingestive consequences after their initial hedonic value has acquired a positive or a negative value via previous individual food learning or evolutionary processes. These food sensory characteristics thus represent cues that could help ruminants to anticipate the post-ingestive consequences of a food and to improve their learning efficiency, especially in complex environments. This review then suggests that food sensory characteristics could be of importance to provide pleasure to animals, to increase palatability of a food and to help them learn in complex feeding situations which could improve animal welfare and productivity.     

Effects of previous experience on the agonistic behaviour of male crickets, Gryllus bimaculatus

Male solitary animals frequently enter aggressive interactions with conspecific individuals to protect their territory or to gain access to females. After an agonistic encounter, the loser (subordinate individual) changes its behaviour from aggression to avoidance. We investigated agonistic interactions between pairs of male crickets to understand how dominance is established and maintained. Two na?ve males readily entered into agonistic interactions. Fights escalated in a stereotyped manner and were concluded with the establishment of dominance. If individuals were isolated after the first encounter and placed together 15 minutes later, subordinate crickets tended to avoid any further contact with the former dominant opponent. Moreover, subordinate males also avoided unfamiliar dominant and na?ve opponents. They displayed aggressive behaviour only towards unfamiliar subordinate opponents. This suggests that the subordinate male change their behaviour depending on the dominance status of the opponent. Dominant crickets, in contrast, displayed aggressive behaviour towards familiar as well as unfamiliar opponents. If the interval between the first and second encounter was longer than 30 minutes, the former subordinate male showed aggressive behaviour again. However, if the subordinate cricket was paired with the same opponent three consecutive times within 45 minutes, it avoided the former dominant opponent for up to 6 hours following the third encounter. Our results suggest that the maintenance of dominance in male crickets depends largely on the behavioural change of subordinate individuals. Possible mechanisms to maintain dominance are discussed.     

Imidazole modification of aggressive behaviour in rats and mice

Imidazole (IMID) strongly affected aggressive behaviour in rodents, the type of influence varying according to the experimental model considered. In morphine-dependent rats, during naloxone-induced abstinence syndrome, signs of irritability and mild aggressiveness were observed after treatment with IMID. Moreover, IMID enhanced aggressive posturing elicited by the dopaminergic (DA) agonist lisuride, whether rats were affected by morphine-withdrawal symptoms or not. In isolation test in mice, on the other hand, IMID inhibited aggression.Imidazolacetic acid, one of the metabolites of histamine, comparatively investigated in the same behavioural tests, never potentiated lisuride-induced aggressiveness in rats; moreover, it was more effective than IMID in inhibiting aggression in isolated mice.     

Wood mice aggressiveness and flight response to human handling: Effect of individual and environmental factors

Numerous studies have examined human disturbance repercussions on wildlife, mainly focused on the effects on behaviour, reproductive success and population dynamics. However, few studies have addressed the behaviour of prey species during and after human capture and handling and how this may correlate to individual characteristics or variation in their physical environment they inhabit. We explored wood mouse’s fleeing and aggressive behaviours in response to captures by human in their natural habitat. Eighty‐seven wood mice were caught using Sherman live traps. For each trapped individual, aggressiveness was measured as the total number of bites inflicted upon the investigator during handling time. Afterwards, each mouse was released in a two‐metre radius partially covered vegetation area that allowed visual mouse tracking by the observer and flight behaviour was registered by individual one‐zero focal sampling technique during 2 min. Both aggressiveness and fleeing behaviour were analysed regarding individual (sex, reproductive status, age) and environmental factors (habitat and season). Males, adults and breeding individuals showed heightened aggression levels. Higher aggressiveness levels were found in wood mice occupying scrubland and during summer and autumn. The flight response was exclusively explained by reproductive status, whereby breeding individuals spent more time on fast escape than nonbreeding ones. These results indicate that both individual and environmental factors seem to influence defensive behaviours in the wood mouse during and after being captured by a human. Since human disturbance shares many aspects with the predation risk, behavioural responses found to captures may likely be influenced by previous experience of individuals with predators as well as to seasonal and habitat features conditioning predators’ densities but also protection against them.     

Role of the pituitary-adrenocortical axis in the control of agonistic behaviour after single and repeated footshock in castrated male mice

Two experiments were conducted to examine the role of the pituitary-adrenocortical axis in the mediation of the effects of single and repeated electric footshock on subsequent agonistic responding in castrated male mice. It was found that (1) preventing corticosterone responses to shock occludes the facilitatory effects of single shock on both aggressive and submissive behaviour and occludes the additional increases in submissive behaviour which normally occur after repeated shock, and (2) blocking pituitary release of ACTH by dexamethasone treatment restores aggressive behaviour after repeated shock, independently of the initial levels of corticosterone and testosterone. These findings suggest that (1) increases in aggressive and submissive behaviour in response to single shock depend on shock-induced increases in corticosterone levels; (2) further increases in submissive behaviour in response to repeated shock require further increases in the corticosterone levels; and (3) inhibition of aggressive behaviour after shock repetition appears to depend on increases in ACTH levels, and occurs independently of the initial corticosterone and testosterone levels.     

野生雄性成年小家鼠行为

本实验以在英格兰捕获的野生小家鼠（Ｍｕｓｍｕｓｃｕｌｕｓｄｏｍｅｓｔｉｃｕｓ）的雄性后代为材料,研究同父异母断乳鼠组和无亲缘关系断乳鼠组在鼠成年后,鼠组成员在自由活动条件下的社会行为,以及独居和亲缘关系对其行为的影响。主要结论如下：１．成年优势鼠和成年从属鼠除打斗行为有显著差别外,优势鼠的嗅底物、社会探究、尿标记等行为也显著地高于从属鼠。从属鼠接触从属鼠显著地多于优势鼠。２．在一小时观察期内,打斗行为和社会探究逐渐减少,而和睦相处行为逐渐增加。社会行为主要发生在现在初期（０—１０分钟）。３．基于非打斗行为,尤其是社会探究和接触行为,通过判别分析,可能辩别出社会等级不清楚的成年雄鼠组中谁是优势鼠,谁是从属鼠。４．独居２３小时后,社会行为中,打斗行为和社会探究均明显上升。但优势鼠的多数行为基本保持原有水平,独居主要是使从属鼠的多数行为发生了改变,并且以针对另一从属鼠为主。５．有、无亲缘关系组的个体共同生活很长一段时间后,亲缘关系依然对小家鼠行为有深刻的影响,有亲缘关系组的社会稳定性、容忍性强于无亲缘关系组。     

Delayed development of aggressive behavior in castrate isolated male mice

Male mice were castrated at 21–22 days of age. Intact and castrated mice were isolated to induce aggressive behavior. The incidence of fighting between paired nonisolated and isolated mice was measured at 3, 6, 12, and 23 weeks to determine the effect of time of isolation on aggressive behavior. After 3 weeks isolation, 90% of the intact isolated mice fought, but none of the castrate isolated mice fought. Aggressive behavior equivalent to that of intact isolated mice developed in the castrate mice after 23 weeks of isolation. These results suggest that the presence of gonadal androgen is important in expediting the onset of aggressive behavior in isolated mice, but its absence does not preclude its eventual development.     

Effects of repeated exposure to electric footshock on subsequent agonistic behaviour and adrenocortical secretion in male mice of different androgen status

Two experiments were conducted to examine effects of repeated exposure to electric footshock on subsequent agonistic behaviour and adrenocortical secretion in male mice of different androgen status. Aggressive and submissive behavioural components were independently studied in the two experiments. It was found that repetition reduced aggressive, and stimulated submissive and adrenocortical responses to shock, particularly in castrates. The direction of the shock effects on aggressive behaviour was reversed by repetition in castrates, whereas only the magnitude of the behavioural responses was changed at normal androgen levels. It is suggested that the changes in agonistic responses to shock induced by repetition are mediated by changes in pituitary-adrenocortical secretion, and that androgen inhibits the shock effects on agonistic behaviour through inhibition of the pituitary-adrenocortical responses to shock.