Sickness and Aggressive Behavior in Dominant and Subordinate Mice*

Sick animals show a set of organized behavioral changes (sickness behavior), which is the result of a motivational re‐organization of the behavior as a whole. Sickness behavior display can be influenced by the social context. In this work, we sought to investigate the regulation of sickness behavior within a pair of mice in the presence of an intruder mouse. Dominant and subordinate mice were treated with the bacterial endotoxin lipopolysaccharide (LPS) and were challenged with the presence of an intruder mouse. LPS effects depended on ranking and social context. Even though dominant mice displayed more agonistic interaction towards the intruder, subordinate mice displayed agonistic behavior towards the intruder when their dominant companion was treated with LPS. The results show that, not only sickness behavior is differentially expressed among different social ranks, but also that sickness behavior is related to different reactions among surrounding animals. These data are relevant for a biological approach to the relation between sickness behavior and social behavior.     

Modulation of social behavior and dominance status by chronic pain in mice

The potential influence of pain on social behavior in laboratory animals has rarely been evaluated. Using a new assay of social behavior, the tube co‐occupancy test (TCOT), we assess propinquity—the tendency to maintain close physical proximity—in mice exposed to pain using subcutaneous zymosan or spared nerve injury as noxious stimuli. Our previous experience with the TCOT showed that outbred mouse sibling dyads show higher levels of tube co‐occupancy than stranger dyads. We find here that long‐lasting pain from spared nerve injury given to both mice in the dyad abolishes this effect of familiarity, such that strangers also display high levels of propinquity. We performed a separate experiment to assess the effect on dominance behavior of nerve injury to one or both mice of a dyad in which relative dominance status had been previously established via the confrontation tube test. We find that neuropathic pain given only to the dominant mouse reverses the relationship in male but not female mice, such that the previously subordinate mouse becomes dominant. These observations bolster the scant but growing evidence that pain can robustly affect social behavior in animals.     

Interplay between various aspects in social relationships of young rhesus monkeys: Dominance,agonistic help,and affiliation

Relationships between group-living primates depend strongly on their position in the group dominance hierarchy and on their relationships with other group members. The influence of various behaviours on social relationships of immature rhesus monkeys (Macaca mulatta) was investigated here. Dominance ranks were established and related to the degree of affiliation in a dyad. Older monkeys were mostly dominant to the younger ones, regardless of kinship. Subordinate monkeys left proximity of their dominant members more often than they were left by them both among siblings and non-siblings, but the effect of dominance rank on the amount of play initiation and grooming in a dyad differed between these two types of dyads. The amount of agonistic help two individuals provided for each other was low among immatures. Nevertheless, pairs of siblings gave help to each other in agonistic conflicts more often than non-siblings, and such help was more often reciprocated between siblings than between non-siblings. Help in agonistic conflicts was positively correlated with the amount of time monkeys spent playing, grooming, or in proximity. Adults tended to interfere less in conflicts of frequent sibling play partners or non-sibling grooming partners. No evidence was found for young monkeys to exchange reciprocally grooming for agonistic help. It is argued that the time monkeys spend interacting with each other in affiliative interactions increases their familiarity and thus promotes close relationships between them. On the whole, young monkeys' relationships, like those between adults, are influenced strongly by their kinship, and position in the dominance hierarchy.     

Longitudinal study of dominance relations among captive patas monkeys

Eight and a half years of dominance relations within a captive group of patas monkeys were analyzed. It was found that matrilineal kinship significantly influenced individuals' ranks. In contrast, with the exception of certain intramatriline changes, increasing age had no predictable effect on overall rank, at least for females (this was untestable for males). Offspring typically challenged maternal dominance and in eight of twelve dyads, offspring either rose fully over their mothers (three cases, all daughters) or at least achieved dominance ambiguity with them. Additionally, two of the four younger sisters with an opportunity to rise in rank over an older sister did so. The group dominance hierarchy was unstable for 75% of the study due to a combination of agonistically induced and demographically induced rank changes. Concentration of the highest ranks in a single matriline showed a stronger association with group hierarchy stability than did the presence of an adult, nonnatal male. Group hierarchy stability was associated with increased affiliation (sitting close and sitting touching), but otherwise there were no behavioral correlations. Individuals' ranks within the group hierarchy were unrelated to their chances of being wounded or having diarrhea. Adult females' ranks were over twice as stable as the group hierarchy (57.1% stability), but stability/instability was not correlated with any behavioral changes. Available evidence suggests that dominance relations play only a minor role in the organization of patas monkeys' intragroup behavior. Am. J. Primatol. 42:41–51, 1997. © 1997 Wiley-Liss, Inc.     

Testosterone treatment diminishes sickness behavior in male songbirds

Males of many vertebrate species are typically more prone to disease and infection than female conspecifics, and this sexual difference is partially influenced by the immunosuppressive properties of testosterone (T) in males. T-induced immunosuppression has traditionally been viewed as a pleiotropic handicap, rather than an adaptation. Recently, it has been hypothesized that suppression of sickness behavior, or the symptoms of infection, may have adaptive value if sickness interferes with the expression of T-mediated behaviors important for male reproductive success. We conduct a classic hormone replacement experiment to examine if T suppresses sickness behavior in a seasonally-breeding songbird, Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii). Triggered experimentally by bacterial lipopolysaccharide (LPS), sickness behavior includes decreased activity, anorexia, and weight loss. Gonadectomized (GDX) males that were treated with silastic implants filled with T exhibited suppression of behavioral and physiological responses to LPS compared to GDX and sham-GDX controls given empty implants. Sickness responses of control groups were statistically indistinguishable. T-implanted birds had significantly higher plasma T than control groups and levels were within the range associated with aggressive interactions during male-to-male contests. These findings imply that suppression of sickness behavior could occur when T is elevated to socially-modulated levels. Alternatively, it is possible that this suppressive effect is mediated through a stress-induced mechanism, as corticosterone levels were elevated in T-implanted subjects compared to controls. We propose that males wounded and infected during contests may gain a brief selective advantage by suppressing sickness responses that would otherwise impair competitive performance. The cost of immunosuppression would be manifested in males through an increased susceptibility to disease, which is presumably offset by capitalizing upon limited reproductive opportunities.     

不同生活史阶段长爪沙鼠尿标记行为的遗传和空间距离效应

气味标记普遍存在于哺乳动物类群中,它能向同类传达领地占有、社会等级及繁殖状态等多种信息。2014年4月至10月,我们在内蒙古锡林郭勒正蓝旗对长爪沙鼠 (Meriones unguiculatus) 野外种群进行了标志重捕,采用中立场的方式测定了不同社群间同性别长爪沙鼠的尿标记行为。通过建立洞群样地坐标后用勾股弦方法计算群间距离,并用微卫星DNA分子标记估算个体间的亲缘系数,以探讨野生动物标记行为是否受个体间空间和遗传距离的影响。广义线性混合效应分析显示,雄鼠间的尿标记强度在繁殖期和贮食期受空间距离或遗传距离的影响均不显著。繁殖期雌鼠间的尿标记强度受空间或遗传距离的影响亦不明显,但在贮食期,遗传距离对雌鼠间标记的强度有显著影响,且遗传距离与空间距离对标记强度有明显的交互作用。本研究结果暗示亲缘关系和空间距离对长爪沙鼠的尿标记行为具有一定影响,这与长爪沙鼠的繁殖或贮食行为相适应。     

Social organization of a stable natal group of captive Guyanese squirrel monkeys (<Emphasis Type="Italic">Saimiri sciureus sciureus</Emphasis>)

Socioecological models suggest competition for food, foraging efficiency, predation, infanticide risk, and the costs of dispersal regulate primate social structure and organization. Wild populations of squirrel monkeys (Saimiri spp.) appear to conform to the predictions of the predation/competition socioecological model (Sterck et al. in Behav Ecol Sociobiol 41:291–309, 1997) and the dispersal/foraging efficiency model (Isbell in Kinship and behavior in primates. Oxford University, New York, pp 71–108, 2004). However, squirrel monkeys in captivity are reported to maintain patterns of social behavior observed in their wild conspecifics despite different food distribution, predation risk, and dispersal options. This behavioral similarity suggests squirrel monkeys’ social behavior has limited flexibility to respond to environmental changes. In this study, we experimentally evaluated the flexibility of social behavior within a captive group of S. sciureus. First, we determined whether dominance and affiliative relationships observed under normal laboratory conditions (with abundant, widely distributed, food; no dispersal option; and no predators) better matched published reports of relationships among wild conspecifics or the predictions of the predation/competition model. Second, we made preferred food items defensible to determine whether dominance interactions would become more frequent and linear, as predicted by the model. The model correctly predicted rates of dominance behavior in both conditions and a linear hierarchy in the defensible food condition but did not predict the consistent affiliative relationships and linear dominance hierarchy observed in normal lab conditions. Although hierarchies were linear and male dominant, manipulating food distribution changed the dominant individual within each sex. Our findings suggest interaction rates adapt more rapidly than social structure to environmental changes in Saimiri and recommend caution in interpreting tests of socioecological models.     

Early social isolation alters behavioral and physiological responses to an endotoxin challenge in piglets

Psychosocial stress in the form of maternal deprivation and social isolation during early postnatal life induces persistent alterations in behavioral and physiological mechanisms of adaptation. One consequence may be an increased susceptibility to diseases in later life. Therefore, the aim of the present study was to investigate in domestic piglets the effects of a repeated social isolation (2 h daily from day 3 to day 11 of age) on behavioral, endocrine and immune responses to an endotoxin challenge with lipopolysaccharide (LPS) 1 day or 45 days after the isolation period. Peripheral LPS administration caused serious sickness behavior (somnolence, shivering, vomiting) and provoked profound increases in circulating tumor necrosis factor-alpha (TNF-alpha), ACTH and cortisol concentrations. The prior social isolation treatment enhanced signs of sickness and impaired suckling behavior. Early isolated piglets responded to LPS by an increase of shivering on day 12 and by increased vomiting on day 56 compared to controls. Further, there were considerable delays and reductions of time isolated piglets spent suckling on day 12. The repeated isolation stressor diminished TNF-alpha increases after LPS, whereas stress hormone levels were not significantly affected by isolation treatment. Finally, stronger relationships between signs of sickness and physiological measures were revealed in early isolated piglets. The duration of somnolence in isolated piglets was related to changes of cortisol and TNF-alpha concentrations, and the highest impact on duration of shivering was found for changes in cortisol and corticosteroid binding globulin levels. The present results suggest a sustained adaptive sensitization of coping with infection by social stress experience during early development in piglets.     

Early social isolation alters behavioral and physiological responses to an endotoxin challenge in piglets

Psychosocial stress in the form of maternal deprivation and social isolation during early postnatal life induces persistent alterations in behavioral and physiological mechanisms of adaptation. One consequence may be an increased susceptibility to diseases in later life. Therefore, the aim of the present study was to investigate in domestic piglets the effects of a repeated social isolation (2 h daily from day 3 to day 11 of age) on behavioral, endocrine and immune responses to an endotoxin challenge with lipopolysaccharide (LPS) 1 day or 45 days after the isolation period. Peripheral LPS administration caused serious sickness behavior (somnolence, shivering, vomiting) and provoked profound increases in circulating tumor necrosis factor-α (TNF-α), ACTH and cortisol concentrations. The prior social isolation treatment enhanced signs of sickness and impaired suckling behavior. Early isolated piglets responded to LPS by an increase of shivering on day 12 and by increased vomiting on day 56 compared to controls. Further, there were considerable delays and reductions of time isolated piglets spent suckling on day 12. The repeated isolation stressor diminished TNF-α increases after LPS, whereas stress hormone levels were not significantly affected by isolation treatment. Finally, stronger relationships between signs of sickness and physiological measures were revealed in early isolated piglets. The duration of somnolence in isolated piglets was related to changes of cortisol and TNF-α concentrations, and the highest impact on duration of shivering was found for changes in cortisol and corticosteroid binding globulin levels. The present results suggest a sustained adaptive sensitization of coping with infection by social stress experience during early development in piglets.     

四川短尾鼩尿液气味在社会等级识别中的作用

本文在中立竞技场中通过两两互作确定四川短尾鼩(Anourosorex squamipes)同性个体间的社会等级,并在此基础上利用其尿液,研究不同社会等级个体的自我/非自我识别能力及模式、尿液气味的行为响应机制,以及社会等级识别能力。结果表明：(1)四川短尾鼩优势个体表现攻击行为较多,从属个体防御行为较多,优势个体的标记行为显著高于从属个体。攻击行为表现为同等级雄性高于同等级雌性,且雌性间的攻击强度低于雄性。(2)从属个体和优势个体分别对自身尿液气味和非自身尿液气味存在明显偏好差异。不同性别、等级个体自我识别模式差异不明显,不同社会等级个体对于自身识别模式和非自身尿液的行为反应模式均不同。不同社会等级个体具有自我识别能力且能力不同。(3)四川短尾鼩能够识别不同社会等级个体的尿液气味,雌性对雄性尿液更感兴趣,雄性对优势雄性尿液选择回避。雄性对其他个体的访问时间与嗅舔频次均显著高于雌性,雌雄个体在识别不同社会等级的尿液气味时存在性二型。     

Gonadectomy negatively impacts social behavior of adolescent male primates

Social behavior changes dramatically during primate adolescence. However, the extent to which testosterone and other gonadal hormones are necessary for adolescent social behavioral development is unknown. In this study, we determined that gonadectomy significantly impairs social dominance in naturalistic settings and changes reactions to social stimuli in experimental settings. Rhesus macaques were castrated (n =  6) or sham operated (n = 6) at age 2.4 years, group-housed for 2 years, and ethograms were collected weekly. During adolescence the gonadally intact monkeys displayed a decrease in subordinate behaviors and an increase in dominant behaviors, which ultimately related to a rise in social status and rank in the dominance hierarchy. We measured monkey's reactions to emotional faces (fear, threat, neutral) of conspecifics of three ages (adult, peer, infant). Intact monkeys were faster to retrieve a treat in front of a threatening or infant face, while castrated monkeys did not show a differential response to different emotional faces or ages. No group difference in reaction to an innate fear-eliciting object (snake) was found. Approach and proximity responses to familiar vs unfamiliar conspecifics were tested, and intact monkeys spent more time proximal to a novel conspecific as compared to castrates who tended to spend more time with a familiar conspecific. No group differences in time spent with novel or familiar objects were found. Thus, gonadectomy resulted in the emergence of significantly different responses to social stimuli, but not non-social stimuli. Our work suggests that intact gonads, which are needed to produce adolescent increases in circulating testosterone, impact social behavior during adolescences in primates.     

Prolonged depression-like behavior caused by immune challenge: influence of mouse strain and social environment

Immune challenge by bacterial lipopolysaccharide (LPS) causes short-term behavioral changes indicative of depression. The present study sought to explore whether LPS is able to induce long-term changes in depression-related behavior and whether such an effect depends on mouse strain and social context. LPS (0.83 mg/kg) or vehicle was administered intraperitoneally to female CD1 and C57BL/6 mice that were housed singly or in groups of 4. Depression-like behavior was assessed with the forced swim test (FST) 1 and 28 days post-treatment. Group-housed CD1 mice exhibited depression-like behavior 1 day post-LPS, an effect that leveled off during the subsequent 28 days, while the behavior of singly housed CD1 mice was little affected. In contrast, singly housed C57BL/6 mice responded to LPS with an increase in depression-like behavior that was maintained for 4 weeks post-treatment and confirmed by the sucrose preference test. Group-housed C57BL/6 mice likewise displayed an increased depression-like behavior 4 weeks post-treatment. The behavioral changes induced by LPS in C57BL/6 mice were associated with a particularly pronounced rise of interleukin-6 in blood plasma within 1 day post-treatment and with changes in the dynamics of the corticosterone response to the FST. The current data demonstrate that immune challenge with LPS is able to induce prolonged depression-like behavior, an effect that depends on genetic background (strain). The discovery of an experimental model of long-term depression-like behavior after acute immune challenge is of relevance to the analysis of the epigenetic and pathophysiologic mechanisms of immune system-related affective disorders.     

不同社群序位布氏田鼠的繁殖行为

在实验室条件下观察了捕自内蒙古草原的不同序位布氏田鼠的繁殖行为特征。结果表明, 雌鼠对雄性配偶存在着激烈的竞争, 高序位雌鼠获得被选择、交尾及产仔的机会最多, 较低序位雌鼠若被选择并且产仔, 则其序位将随之上升; 高序位雄鼠对各个序位雌鼠均可选择, 且在繁殖期间对同性个体表现很强的攻击性, 以获得更多的交配机会。在社群繁殖中高序位雌、雄个体的作用明显高于低序位个体, 这是布氏田鼠种群长期选择进化的生存策略。实验支持了布氏田鼠为混交制、一雄多雌的婚配制度推论。     

Monitoring the social behavior of a bachelor mandrill (Mandrillus sphinx) dyad participating in touchscreen‐mediated cognitive testing

Cognitive testing of primates in zoos is becoming increasingly common. Cognition experiments are generally thought to be beneficial as they provide participants with an opportunity to engage in species‐specific cognitive functioning, perhaps more so than with traditional forms of environmental enrichment. However, testing may increase competition and aggression between conspecifics if it has monopolizable features or creates social tension within groups. The purpose of this study was to monitor the social behavior of a bachelor mandrill (Mandrillus sphinx) dyad participating in a touchscreen‐mediated cognition study. The mandrills' behavior was monitored before and after testing sessions for 8 months. Positive changes in the mandrills' affiliative behavior were observed. Rates of play, presentations, and silent bared‐teeth face increased posttesting. No change in rates of agonism were observed between pre‐ and posttesting conditions. The observed positive changes in affiliative behavior suggest cognitive testing was enriching for the mandrills and participating in testing improved their welfare. Zoos beginning cognitive studies should monitor participant behavior to ensure their welfare is not compromised and is, ideally, enhanced.     

Does animal behavior underlie covariation between hosts' exposure to infectious agents and susceptibility to infection? Implications for disease dynamics

Animal behavior is unique in influencing both components of the process of transmission of disease: exposure to infectious agents, and susceptibility to infection once exposed. To date, the influence of behavior on exposure versus susceptibility has largely been considered separately. Here, we ask whether these two key mechanisms act in concert in natural populations, whereby individuals who are most exposed to infectious agents or have the most contact with conspecifics are also the most susceptible or infectious. We propose three mechanisms that can generate covariation between these two key elements of the transmission of disease within and among hosts, and we provide empirical examples of each. We then use a mathematical model to examine the effect of this covariation on the dynamics of disease at the population level. First, we show that the empirical mechanisms generating covariation between behavioral and physiological components of disease transmission are widespread and include endocrine mediators of behavior, mate choice, group size, sickness behaviors, and behavioral avoidance of infectious conspecifics. The diversity of these empirical mechanisms underscores the potential importance and breadth of covariation in the disease process. Second, we show mathematically that the variability in hosts' exposure to infectious agents and susceptibility or infectiousness, and how tightly they are coupled, strongly influences the ability of a disease to invade a host population. Overall, we propose that covariation between behavioral and physiological components of transmission is likely widespread in natural populations, and can have important consequences for the dynamics of disease at the population level as well as for our understanding of sexual selection, social behavior, and animal communication.     

Detecting instability in animal social networks: genetic fragmentation is associated with social instability in rhesus macaques

The persistence of biological systems requires evolved mechanisms which promote stability. Cohesive primate social groups are one example of stable biological systems, which persist in spite of regular conflict. We suggest that genetic relatedness and its associated kinship structure are a potential source of stability in primate social groups as kinship structure is an important organizing principle in many animal societies. We investigated the effect of average genetic relatedness per matrilineal family on the stability of matrilineal grooming and agonistic interactions in 48 matrilines from seven captive groups of rhesus macaques. Matrilines with low average genetic relatedness show increased family-level instability such as: more sub-grouping in their matrilineal groom network, more frequent fighting with kin, and higher rates of wounding. Family-level instability in multiple matrilines within a group is further associated with group-level instability such as increased wounding. Stability appears to arise from the presence of clear matrilineal structure in the rhesus macaque group hierarchy, which is derived from cohesion among kin in their affiliative and agonistic interactions with each other. We conclude that genetic relatedness and kinship structure are an important source of group stability in animal societies, particularly when dominance and/or affilative interactions are typically governed by kinship.     

Influence of prenatal iron deficiency and MAOA genotype on response to social challenge in rhesus monkey infants

Social and emotional behaviors are known to be sensitive to both developmental iron deficiency (ID) and monoamine oxidase A (MAOA) gene polymorphisms. In this study, male rhesus monkey infants deprived of dietary iron in utero were compared with iron sufficient (IS) controls (n = 10/group). Half of each group had low MAOA activity genotypes and half had high MAOA activity genotypes. A series of social response tests were conducted at 3-14 months of age. MAOA genotype influenced attention to a video of aggressive behavior, emotional expression (fear, grimace and sniff) in the social intruder test, social actions (displacement, grooming) in the social dyad test, and aggressive responses to a threatening picture. Interactions between MAOA and prenatal ID were seen in response to the aggressive video, in temperament ratings, in affiliative behavior in the social dyad test, in cortisol response in the social buffering test and in response to a social intruder and to pictures with social and nonsocial themes. In general, the effects of ID were dependent on MAOA genotype in terms of both direction and size of the effect. Nutrition/genotype interactions may shed new light on behavioral consequences of nutritional deprivation during brain development.     

A Comparison of Behavioral Interactions in Solitary and Presocial Zetoborinae Cockroaches (Blattaria,Blaberidae)

The social behavior of five species of Zetoborinae cockroaches is compared with respect to inter-individual interactions of nymphs in the laboratory. These species belong to the same Neotropical subfamily and were characterized as gregarious (Lanxoblatta emarginata, Parasphaeria boleiriana, Phortioeca nimbata, Schultesia lampyridiformis) and solitary (Thanatophyllum akinetum) by previous field studies. Our results show that gregarious species accept closer contacts than does the solitary one. The solitary species did not display especially short, infrequent or less diverse behavioral sequences when forced to remain aggregated, but its interactions are characterized by fewer acts promoting contact and more dominance-like acts. The solitary species symmetrically interacts with conspecifics and does not show specific dispersal-promoting behaviors. This suggests that the solitary behavior observed in the field for species of Zetoborinae mainly results from a passive spacing tendency and a lack of attraction for conspecifics. One of the gregarious species, P. boleiriana, was previously described as subsocial with nymphs remaining with the female in a wood chamber after brood birth. This species does not show a peculiar behavioral repertoire but its interactions are characterized by more dominance-like behaviors than are those of the non-subsocial gregarious species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Behavioral and physiological plasticity: Rapid changes during social ascent in an African cichlid fish

In many vertebrates, reproduction is regulated by social interactions in which dominant males control access to females and food. Subordinate males that displace dominant individuals must rapidly adopt behavioral and physiological traits of the higher rank to gain reproductive success. To understand the process of phenotypic plasticity during social ascent, we analyzed the temporal expression pattern of dominance behaviors and circulating androgen levels when socially-suppressed males of an African cichlid fish Astatotilapia burtoni ascended in status. These experiments tested a prediction of the ‘challenge hypothesis’ that, during periods of social instability, male androgen levels are higher than during socially stable times. We found that socially and reproductively suppressed males perform territorial and reproductive behaviors within minutes of an opportunity to ascend in status, and that animals switch from initial expression of territorial behaviors to more reproductive behaviors during territory establishment. Following this rapid response, social stability may be achieved within 1-3 days of social ascent. Consistent with predictions of the ‘challenge hypothesis’, circulating 11-ketotestosterone (11-KT) levels were elevated within 30 min following social opportunity, coincident with increased aggressive behavior. However, territorial behaviors and serum 11-KT levels were then dissociated by 72 h after social ascent, suggesting either rapid social stability and/or increased physiological potential for androgen production. This behavioral and physiological plasticity in male A. burtoni suggests that perception of social opportunity triggers a suite of quick changes to facilitate rapid transition towards reproductive success, and reveals important features of social ascent not previously recognized.     

Social interactions between captive adult male and infant lowland gorillas: Implications regarding kin selection and zoo management

Interactions between unrelated and related silverback‐infant dyads are compared in an attempt to assess the influence that kinship may have on male parental behavior. Observational data were collected on each member of two silverback‐infant dyads, in two separate enclosures at the Lincoln Park Zoo in Chicago, IL. The silverback was the father of the infant in one dyad, and unrelated to the infant in the other. Each infant was responsible for initiating most of the encounters with its respective group silverback. However, based on the frequency and duration of interactions, there is a significantly higher degree of affiliation and tolerance within the silverback‐offspring dyad. Furthermore, the unrelated infant was the recipient of more than 40% of the agonistic behaviors exhibited by the silverback, whereas no such encounters were recorded within the related dyad. Although alternative explanations must be considered, these findings are consistent with kin selection theory, are similar to observations documented for wild mountain gorillas, and provide uncommon comparative data on adult male interactions with related and unrelated infants. In addition, this study offers behavioral information relevant to the management of captive gorillas, which often requires the introduction of immatures into non‐natal groups. Zoo Biol 18:53–62, 1999. © 1999 Wiley‐Liss, Inc.