Submissive Signals Research Articles

Benefits but not the dual functions of submissive signals differ between two Malagasy primates.

Many animals use formalized signals to communicate dominance relationships. In some primates, such as macaques, the function of such signals varies with dominance style. Despotic species produce unidirectional submission signals that have a dual function: in conflict contexts, they signal a willingness to withdraw, whereas in peaceful contexts, they indicate the agreement to subordination. More despotic species produce these calls to a lesser extent than less despotic species. Here, we investigated whether the use of unidirectional submission signals is also related to dominance style in two lemur species and whether signalling subordination stabilizes social relationships at the group level. Ring-tailed lemurs (Lemur catta) exhibit a more despotic dominance hierarchy than Verreaux's sifakas (Propithecus verreauxi). We observed social interactions in 75 dyads of Verreaux's sifakas and 118 dyads of ring-tailed lemurs. Both species used unidirectional submissive calls that have a dual function, potentially suggesting convergent evolution of the function of these signals in independent primate lineages. However, signalling subordination did not stabilize social relationships at the group level in both species. Additionally, subordination occurred more frequently in dyads of the more despotic ring-tailed lemurs than in Verreaux's sifakas, indicating opposite patterns to macaques in the coevolution of social traits with dominance style. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'.

Characterization of the agonistic behavior of the weakly electric fish Gymnotus sylvius

AbstractElectric fish are good models in neuroethology as any behavior in electric fish involves both locomotor and electrical displays, which are experimentally accessible and controlled by well‐known neural circuits. The agonistic behavior within the genus Gymnotus has been evaluated in Gymnotus carapo and Gymnotus omarorum, providing an advantageous model system to address comparative analyses. Gymnotus sylvius is a weakly electric fish which occurs in sympatry with G. omarorum in freshwater environments of Argentina. Here, we describe the agonistic behavior of G. sylvius in laboratory conditions. All dyads engaged in intense fights, with a latency to the first attack of 8 ± 7.8 s and a contest phase of 42.71 ± 31.7 s. Individual initiative in the first attack predicted contest outcome with no apparent influence of body weight asymmetry between contenders. Contenders did not escalate in their aggression during the short contest; in turn, subordinates tended to retreat in response to dominants' attacks. Submission and dominance were expressed by electric signals: dominants increased their basal electric organ discharge (EOD) rate after contest resolution, resulting in a persistent EOD rate rank. Subordinates also emitted chirps and offs during the contest and post‐resolution phases without a clear temporal pattern. The agonistic behavior of G. sylvius presents some similarities with other species of the genus Gymnotus: EOD rank between dominants and subordinates, electric signals of submission, and the presence of attacks in the post‐resolution phase. On the other hand, it also presents differences: a shorter evaluation phase in G. sylvius, initiative as a determinant of outcome, a higher attack rate of dominants in G. sylvius, a different temporal pattern of chirps, and different mechanisms to separate EOD rate of dominants and subordinates. These facts open a promising road to analyze the evolution of different neuroendocrine strategies, operating on homologous neural pathways, to command the same behavior.

Sex and dominance: How to assess and interpret intersexual dominance relationships in mammalian societies

The causes and consequences of being in a particular dominance position have been illuminated in various animal species, and new methods to assess dominance relationships and to describe the structure of dominance hierarchies have been developed in recent years. Most research has focused on same-sex relationships, however, so that intersexual dominance relationships and hierarchies including both sexes have remained much less studied. In particular, different methods continue to be employed to rank males and females along a dominance hierarchy, and sex biases in dominance are still widely regarded as simple byproducts of sexual size dimorphism. However, males and females regularly compete over similar resources when living in the same group, and sexual conflict takes a variety of forms across societies. These processes affect the fitness of both sexes, and are mitigated by intersexual hierarchies. In this study, we draw on data from free-ranging populations of nine species of mammals that vary in the degree to which members of one sex dominate members of the other sex to explore the consequences of using different criteria and procedures for describing intra- and intersexual dominance relationships in these societies. Our analyses confirmed a continuum in patterns of intersexual dominance, from strictly male-dominated species to strictly female-dominated species. All indices of the degree of female dominance were well correlated with each other. The rank order among same-sex individuals was highly correlated between the intra- and intersexual hierarchies, and such correlation was not affected by the degree of female dominance. The relative prevalence of aggression and submission was sensitive to variation in the degree of female dominance across species, with more submissive signals and fewer aggressive acts being used in societies where female dominance prevails. Thus, this study provides important insights and key methodological tools to study intersexual dominance relationships in mammals.

Greetings among female chimpanzees in Mahale, Tanzania.

Greeting behaviors have been reported in several primate species, although their forms and context may vary across species. Chimpanzees (Pan troglodytes) greet each other in various ways when they meet; however, many recent studies of greetings in chimpanzees have mostly focused on pant grunt vocalizations, which are often viewed as equivalent to submissive signals. Asmost greetings in chimpanzees are directed toward adult males, either from other males or females, relatively few studies have focused on female-female greetings. Thus, the primary aim of this study was to describe the greetings (not limited to pant grunts) between chimpanzee females in the Mahale Mountains National Park based on long-term observational data. I observed 405 female-female greeting events (10.9 instances per 100 observation hours [obsn. h]) between 1994 and 2018, of which 242 were pant grunts (6.5 instances per 100 obsn. h); 42.3% of greetings were nonaudible, such as tactile or gestural greetings. Most pant grunts were directed toward older females; females under 20 years of age were generally responsible for this trend, as they were the most frequent greeters among females and tended to perform pant grunts toward older females. Nonetheless, among females 20 years of age or older, pant grunts from an older to a younger female were not rare (37%). Compared to previous studies in Mahale, pant grunts between females were an order of magnitude less than those directed toward males. There may also be a large difference in the frequencies of female-female pant grunts across study sites, which may be attributed to differences in female gregariousness.

The Indispensable Dog

Dogs’ remarkable success in living in a human-dominated world rests on a set of adaptations to cohabitation with humans. In this paper, I review the nature of these adaptations. They include changes in reproductive and foraging behavior from their ancestor species, wolves, which can be understood as adaptations to the change from hunting live prey to feeding on human food residues. Dogs also show several changes in social behavior which are more controversial and even somewhat paradoxical. Contrary to theories of canine domestication which view dogs as less aggressive and more cooperative than wolves, several studies show that dogs’ social interactions with conspecifics are more hierarchical and competitive than are wolves’. As scavengers rather than hunters, dogs do not need to cooperate with conspecifics the way that wolves do. But how then can we understand dogs’ willingness to cooperate with humans? I propose an integrated account of dogs’ social behavior that does not assume that dogs need to recognize the species-identity of the individuals with whom they interact. Because of the overlap in formal signals of dominance and submission between dog and human and people’s complete control over the resources dogs need, I propose that people occupy a status of “super-dominance” over dogs. This conception suggests several new lines of research which could shed light on the human-dog relationship to the benefit of both partners.

Agonistic vocalization behaviour in the male ring-tailed lemur (Lemur catta).

Vocalizations are used by group-living animals as aggressive and submissive signals during agonistic interactions, and are also used to maintain dominance hierarchies in many species. For gregarious strepsirrhines with large vocal repertoires and differentiated dominance ranks like the ring-tailed lemur (Lemur catta), agonistic vocalization use is important to study to better understand their social adaptations.To determine whether ring-tailed lemur vocalizations such as the yip, cackle, twitter, chutter, and plosive bark were used as aggressive or submissive signals during agonism and uttered at different rates by males of differing dominance ranks and ages, 565 h of focal data were collected on 31 individual males aged ≥ 1 year from Beza Mahafaly Special Reserve, Madagascar. Yip, cackle, and twitter vocalizations were consistently used during agonistic submissive interactions with both males and females, chutter vocalizations were used during aggressive agonistic interactions with males and submissive agonistic interactions with males and females, and plosive bark vocalizations were used across behavioural contexts but not particularly during agonism. Males of all ages employed all vocalizations, and while low-ranking males uttered yip calls at higher rates, males of all dominance ranks uttered cackle, twitter, chutter, and plosive bark vocalizations. These results advance our knowledge of how male lemurs utilize agonistic vocalizations to maintain inter-individual relationships with males and females, and improve our overall understanding of the function of different agonistic vocalizations in wild lemurs.

Head up displays are a submission signal in the group-living daffodil cichlid

Dominance hierarchies can reduce conflict within social groups and agonistic signals can help to establish and maintain these hierarchies. Behaviours produced by subordinates in response to aggression are often assumed to function as signals of submission, however, these behaviours may serve other purposes, for example, defence or escape. For a behaviour to act as a submission signal, the receiver must respond by reducing their likelihood of further aggression towards the signaller. In the current study, we examine the receiver response to a putative signal of submission, the head up display, within established social groups of the cooperatively breeding fish, the daffodil cichlid (Neolamprologus pulcher). We found that when subordinate signallers produce the head up display in response to aggression from the breeder male, he exhibited a longer latency to behave aggressively towards that individual again. We also report that head up displays are rarely produced without being elicited by aggression, and the number of head up displays correlates with the amount of aggression received. Our results demonstrate that the head up display is used as a signal of submission in the daffodil cichlid and provide insight into intragroup communication in an emerging model system for the study of social behaviour.

Predefinitive Plumage in the Golden Eagle (Aquila chrysaetos): A Signal of Aggression or Submission?

Predefinitive Plumage in the Golden Eagle (Aquila chrysaetos): A Signal of Aggression or Submission?

A JAR of Chirps: The Gymnotiform Chirp Can Function as Both a Communication Signal and a Jamming Avoidance Response.

The weakly electric gymnotiform fish produce a rhythmic electric organ discharge (EOD) used for communication and active electrolocation. The EOD frequency is entrained to a medullary pacemaker nucleus. During communication and exploration, this rate can be modulated by a pre-pacemaker network, resulting in specific patterns of rate modulation, including stereotyped communication signals and dynamic interactions with conspecifics known as a Jamming Avoidance Response (JAR). One well-known stereotyped signal is the chirp, a brief upward frequency sweep usually lasting less than 500 ms. The abrupt change in frequency has dramatic effects on phase precession between two signalers. We report here on chirping in Brachyhypopmus cf. sullivani, Microsternarchus cf. bilineatus Lineage C, and Steatogenys cf. elegans during conspecific playback experiments. Microsternarchus also exhibits two behaviors that include chirp-like extreme frequency modulations, EOD interruptions with hushing silence and tumultuous rises, and these are described in terms of receiver impact. These behaviors all have substantial impact on interference caused by conspecifics and may be a component of the JAR in some species. Chirps are widely used in electronic communications systems, sonar, and other man-made active sensing systems. The brevity of the chirp, and the phase disruption it causes, makes chirps effective as attention-grabbing or readiness signals. This conforms to the varied assigned functions across gymnotiforms, including pre-combat aggressive or submissive signals or during courtship and mating. The specific behavioral contexts of chirp expression vary across species, but the physical structure of the chirp makes it extremely salient to conspecifics. Chirps may be expected in a wide range of behavioral contexts where their function depends on being noticeable and salient. Further, in pulse gymnotiforms, the chirp is well structured to comprise a robust jamming signal to a conspecific receiver if specifically timed to the receiver’s EOD cycle. Microsternarchus and Steatogenys exploit this feature and include chirps in dynamic jamming avoidance behaviors. This may be an evolutionary re-use of a circuitry for a specific signal in another context.

Social relationships and greetings in wild chimpanzees (Pan troglodytes): use of signal combinations.

Signals of submission, so-called 'greetings', represent an important tool for the regulation of social life in primates. In chimpanzees, vocalizations and gestures are commonly employed to communicate greetings, however, the topic of signal complexity (i.e., combinations of signals) during greeting instances has been neglected by research to date. Here, we investigate combinatorial possibilities in vocal greetings in a free-ranging group of chimpanzees (Pan troglodytes) and study how greeter sex, rank relationship between an interacting pair, and strength of the social bond of a greeting dyad influence signal complexity. Results show that the social bond and the dominance distance between individuals engaged in a greeting bout are important determiners for vocal combinations. The findings indicate that greeting signals in chimpanzees, like other vocal signals of the species, can become subject to social influences.

Submissive behaviour is mediated by sex, social status, relative body size and shelter availability in a social fish

Acting submissively may inhibit aggression and facilitate the termination of contests without further escalation. The need to minimize conflict is vital in highly social species where within-group interactions are frequent, and aggression can dampen group productivity. Within social groups, individual group members may modulate their use of submissive signals depending on their phenotype, the value of the contested resource, their relationship to the receiver of the signal and the characteristics of the local environment. We predicted that submissive behaviour would be more common when signallers had limited ability to flee from conflict, when signallers were of a low rank within the group, when signallers and receivers differed substantially in body size (and thus in fighting ability), and when signallers and receivers were of opposite sex and therefore not directly in competition over reproductive opportunities. We tested these predictions using social network analyses on detailed behavioural observations from 27 social groups of the cooperatively breeding cichlid fish Neolamprologus pulcher. Congruent with our prediction, submissive behaviour was more common when there were fewer shelters available, suggesting that constraints on fleeing behaviour may increase the use of submission. Also fitting with predictions, submissive behaviour was more common with increasing body size asymmetry between the competitors, among lower ranked fish and in interactions between opposite-sex dyads, which supports the idea that signalling submission is adaptive in contests over low-value resources. Our findings suggest that subordinate N. pulcher are primarily concerned with being tolerated within the social group and may use submissive behaviour to avoid escalated conflict. Our findings offer a window into the factors that influence signals of submission in a highly social vertebrate.

Subordination signals improve the quality of social relationships in Verreaux's Sifaka: Implications for the evolution of power structures and social complexity.

Unidirectional dominance-related signals can be used to communicate submission (an immediate behavioral response) or subordination (the status of an established relationship). Subordination signals are defined as emitted during peaceful interactions and are hypothesized to be critical for the evolution of social complexity and robust power structures because they reduce uncertainty in social relationships. The chatter vocalization in Verreaux's sifaka (Propithecus verreauxi) is a unidirectional submissive signal. I tested the hypothesis that chatter vocalizations can signal subordination and thereby reduce agonism in a dyad. I examined 780 chatters from 18 dyads collected over 881 observation hours on four groups of sifaka in Kirindy Forest, Madagascar. Sifaka emitted 63% of chatters in the peaceful context. Peaceful chatters significantly predicted grooming rate, fighting rate, reconciliation, and proportion of wins in a dyad but did not predict time in proximity. Dyad-type significantly predicted the frequency of peaceful chatters, with intrasexual dyads exhibiting chatters in peaceful contexts more often than intersexual dyads. Sifaka communicate both submission and subordination with chatter vocalizations. Subordination signaling increased tolerance and affiliation. It reduced conflicts and the probability dominant individuals usurped resources. Moreover, intrasexual power may be more institutionalized than intersexual power in sifaka. The finding of complex and cognitively demanding social communication in a lemur with low levels of cooperation (1) challenges previous assumptions that the evolution of social complexity is dependent on frequent triadic interactions and high levels of cooperation, and (2) highlights the need for taxonomic diversity in studies of social complexity.

Distinctive mechanisms underlie the emission of social electric signals of submission in Gymnotus omarorum.

South American weakly electric fish (order Gymnotiformes) rely on a highly conserved and relatively fixed electromotor circuit to produce species-specific electric organ discharges (EODs) and a variety of meaningful adaptive EOD modulations. The command for each EOD arises from a medullary pacemaker nucleus composed of electrotonically coupled intrinsic pacemaker and bulbospinal projecting relay cells. During agonistic encounters, Gymnotus omarorum signals submission by interrupting its EOD (offs) and emitting transient high-rate barrages of low-amplitude discharges (chirps). Previous studies in Gymnotiformes have shown that electric signal diversity is based on the segregation of descending synaptic inputs to pacemaker or relay cells and differential activation of the neurotransmitter receptors -for glutamate or γ-aminobutyric acid (GABA) - of these cells. Therefore, we tested whether GABAergic and glutamatergic inputs to pacemaker nucleus neurons are involved in the emission of submissive electric signals in G. omarorum We found that GABA applied to pacemaker cells evokes EOD interruptions that closely resemble natural offs. Although in other species chirping is probably due to glutamatergic suprathreshold depolarization of relay cells, here, application of glutamate to these cells was unable to replicate the emission of this submissive signal. Nevertheless, chirp-like discharges were emitted after the enhancement of excitability of relay cells by blocking an IA-type potassium current and, in some cases, by application of vasotocin, a status-dependent modulator peptide of G. omarorum agonistic behavior. Modulation of the electrophysiological properties of pacemaker nucleus neurons in Gymnotiformes emerges as a novel putative mechanism endowing electromotor networks with higher functional versatility.

Status-Dependent Vasotocin Modulation of Dominance and Subordination in the Weakly Electric Fish Gymnotus omarorum.

Dominant-subordinate status emerges from agonistic encounters. The weakly electric fish, Gymnotus omarorum, displays a clear-cut example of non-breeding territorial aggression. The asymmetry in the behavior of dominants and subordinates is outstanding. Dominants are highly aggressive and subordinates signal submission in a precise sequence of locomotor and electric traits: retreating, decreasing their electric organ discharge rate, and emitting transient electric signals. The hypothalamic neuropeptide arginine-vasotocin (AVT) and its mammalian homolog arginine-vasopressin, are key modulators of social behavior, known to adapt their actions to different contexts. By analyzing the effects of pharmacological manipulations of the AVT system in both dominants and subordinates, we show evidence of distinct status-dependent actions of AVT. We demonstrate an endogenous effect of AVT on dominants' aggression levels: blocking the V1a AVT receptor induced a significant decrease in dominants' attack rate. AVT administered to subordinates enhanced the expression of the electric signals of submission, without affecting subordinates' locomotor displays. This study contributes a clear example of status-dependent AVT modulation of agonistic behavior in teleosts, and reveals distinctive activation patterns of the AVT system between dominants and subordinates.

Vervet monkeys greet adult males during high-risk situations

Many animal species produce ritualized signals during dyadic encounters but the functions of such ‘greeting’ behaviour vary considerably, or are often unknown. One established function is to acknowledge existing dominance relationships. At the same time, call rates often increase during social tension, suggesting additional functions, such as to appease higher-ranking individuals, or to maintain spatial proximity and friendly relations. For vervet monkeys, Chlorocebus pygerythrus , vocal behaviour has been studied extensively, but little research has been devoted to calls given during encounters between two individuals, i.e. grunts. Here, we examined how individual and relationship features affected the vocal greeting behaviour of wild vervet monkeys in different ecological and social situations. We used an information theory approach to investigate the functional hypotheses of vervet monkeys' vocal greeting signals. We found little support for the main functions proposed in the literature, that is, to signal submission, to avoid conflicts, to test social bonds or to coordinate group activity. Results supported the use of grunts to signal benign intent, and we found that grunts were mostly given to closely bonded males near rivers, suggesting that vervet monkeys use vocal greeting signals to recruit individuals in situations of danger to reduce predation risk.

Tail flicking in the black redstart (Phoenicurus ochruros) and distance to cover

Tail flicking is a common behavior in many bird species, but its function is often unknown. Apart from intraspecific communication, tail flicking could be used during predator–prey communication, e.g., as a signal of prey vigilance or quality. We studied this behavior in the black redstart (Phoenicurus ochruros), a species that frequently shows tail flicking and is prone to attacks by ambushing predators that hide in cover. Hence, cover might be perceived as dangerous by this species. We hypothesized that flicking should increase with decreasing distance to cover. We counted the number of tail flicks of individuals and measured their distance to the nearest cover for an ambushing predator. We found that distance to cover had a significant effect on tail flicking behavior, as flicking increased with decreasing distance, but found no difference in flicking frequency between adults and juveniles or between sexes. Consequently, tail flicking is unlikely to signal submission or to be sexually selected in the black redstart. Since tail flicking also occurred in the absence of predators, we consider tail flicking in black redstarts to display vigilance and to be directed towards ambushing predators.

Higher levels of submissive behaviors at the onset of the pairing process of rhesus macaques (Macaca mulatta) are associated with lower risk of wounding following introduction.

Social housing of rhesus macaques (Macaca mulatta) is considered to be the cornerstone of behavioral management programs in biomedical facilities. However, it also involves the risk of socially inflicted trauma. The ability to avoid such trauma would contribute to the animals' well-being and alleviate staff's concerns, thus paving the path for more introductions. Here, we sought to address the conflict between the need to socially house rhesus macaques and the need to bring social wounding to a minimum by identifying behaviors expressed early in social introductions, that may serve as predictors of later wounding events. We employed logistic regression analysis to predict the occurrence of wounding for 39 iso-sexual, adult pairs in the 30 days following the introduction into full contact using the levels of behaviors that were observed at the onset of the introduction. The results show that the levels of submissive behaviors were the only significant predictor to later stage wounding. Higher levels of submissive behaviors expressed during the early phases of the introduction were associated with a decreased likelihood of wounding. Interestingly, levels of affiliative behaviors have not added any power to the predictability of the statistical model. Therefore, it may be suggested that the exchange of submissive signals at the earliest stages of the introduction is critical in the determination of relative rank and preclude the need to establish dominance via aggression when allowed full contact. While the observation of clear-cut dominance relationships is commonly considered a harbinger of success, our findings suggest that it is the acknowledgment of subordination, rather than the expression of dominance that underlies this observed pattern. The value of our findings for guiding social housing decision-making may be strongest in situations in which the composition of potential partners is constrained, and therefore requiring that wise decisions be relied upon early behaviors.

Appeasement signals used by dogs during dog–human communication

Abstract The aim of this study was to examine the occurrence of the appeasement signals away and of shown by healthy dogs toward strangers in a standardized behavioral test. The 116 participating dogs were aged at least 13 months and could be any breed. Dogs were guided by their owners through the behavioral test which included a variety of test situations. The people conducting the test were previously unknown to the dogs and behaved in a neutral, friendly, or threatening way depending on the test situation. This design allowed us to investigate interspecific communication with a focus on the chosen appeasement signals in different contexts. The expressive behavior of the tested dogs was evaluated based on video. We found that both signals, licking of lips and looking away, may serve as appeasement signals in dog–human communication. These signals were directed more often toward those conducting the test by dogs in threatening and conflict-ridden test situations. However, our results also show that the dogs responded with significantly fewer appeasement signals in the face of a major threat than in less threatening situations. A possible explanation may be that in the case of a major threat, these appeasement signals are no longer expedient, and the dogs select more promising behavioral strategies, such as clearly behavior or escape. Furthermore, we found that licking of lips was a common component of the greeting behavior of dogs toward humans. This signal was observed significantly more often during active submission (i.e., friendly approach with submissive signals) than during sociopositive approaches. For this reason, lip licking may play the same role as in the intraspecific communication: as appeasement signal occurring with reduced interindividual distance and sent in advance to express peaceful intentions.

The fear gasping face as a threat display in a Melanesian society

Theory and research show that humans attribute both emotions and intentions to others on the basis of facial behavior: A gasping face can be seen as showing "fear" and intent to submit. The assumption that such interpretations are pancultural derives largely from Western societies. Here, we report two studies conducted in an indigenous, small-scale Melanesian society with considerable cultural and visual isolation from the West: the Trobrianders of Papua New Guinea. Our multidisciplinary research team spoke the vernacular and had extensive prior fieldwork experience. In study 1, Trobriand adolescents were asked to attribute emotions, social motives, or both to a set of facial displays. Trobrianders showed a mixed and variable attribution pattern, although with much lower agreement than studies of Western samples. Remarkably, the gasping face (traditionally considered a display of fear and submission in the West) was consistently matched to two unpredicted categories: anger and threat. In study 2, adolescents were asked to select the face that was threatening; Trobrianders chose the "fear" gasping face whereas Spaniards chose an "angry" scowling face. Our findings, consistent with functional approaches to animal communication and observations made on threat displays in small-scale societies, challenge the Western assumption that "fear" gasping faces uniformly express fear or signal submission across cultures.

Adolescent male chimpanzees do not form a dominance hierarchy with their peers.

Dominance hierarchies are a prominent feature of the lives of many primate species. These hierarchies have important fitness consequences, as high rank is often positively correlated with reproduction. Although adult male chimpanzees strive for status to gain fitness benefits, the development of dominance relationships is not well understood. While two prior studies found that adolescent males do not display dominance relationships with peers, additional research at Ngogo in Kibale National Park, Uganda, indicates that adolescents there form a linear dominance hierarchy. These conflicting findings could reflect different patterns of rank acquisition across sites. An alternate possibility arises from a recent re-evaluation of age estimates at Ngogo and suggests that the report describing decided dominance relationships between adolescent males may have been due to the accidental inclusion of young adult males in the sample. To investigate these issues, we conducted a study of 23 adolescent male chimpanzees of known age during 12months at Ngogo. Adolescent male chimpanzees exchanged pant grunts, a formal signal of submission, only 21 times. Recipients of pant grunts were late adolescent males, ranging between 14 and 16years old. In contrast, younger adolescent males never received pant grunts from other males. Aggression between adolescent males was also rare. Analysis of pant grunts and aggressive interactions did not produce a linear dominance hierarchy among adolescent males. These data indicate that adolescent male chimpanzees do not form decided dominance relationships with their peers and are consistent with the hypothesis that the hierarchy described previously at Ngogo resulted from inaccurate age estimates of male chimpanzees. Because dominance relationships develop before adulthood in other primates, our finding that adolescent male chimpanzees do not do so is surprising. We offer possible explanations for why this is the case and suggest future studies that may help clarify the matter.