Reconciling conflicts in a one-male society: the case of geladas (Theropithecus gelada)

Abstract

Animals derive benefits from living in social groups but sociality also has its costs in that animals must compete with others for resources and mating opportunities. To cope with the conflict aftermath and social damage caused by competitive aggression, several group-living species use a variety of peace-keeping strategies. The affinitive post-conflict reunion of former opponents, defined as reconciliation, is the primary peace-keeping mechanism. In this study, we provide evidence for the occurrence of reconciliation and test some hypotheses on this post-conflict mechanism in geladas (Theropithecus gelada), a species often neglected in the study of post-conflict dynamics. The conciliatory contacts were uniformly distributed across the different sex–class combinations. Different from baboons, geladas did not show any particular kind of affinitive reconciliation behaviour. Notwithstanding the presence of a linear hierarchy, the dominance relationships did not affect the reconciliation dynamics. According to the valuable relationship hypothesis, coalitionary support seems to be a good predictor for a high level of conciliatory contacts. Finally, at an immediate level reconciliation plays a role in reducing renewed attacks by aggressors, which sought conciliatory contact more frequently than victims. In conclusion, even though the study of post-conflict behaviour in geladas needs to be continued, the patchy nature of their social network is a good model for testing some of the theoretical assumptions about primate conflict resolution.

Introduction

Understanding the evolution of complex sociality is a central issue in ecology and evolutionary biology. In theory (Maynard Smith and Szmathmáry 1995), sociality evolves when the net benefits of association with conspecifics exceed the costs (Silk 2007a). Sociality may provide protection from predators (Bertram 1978), may enhance success in locating resources (Giraldeau and Beauchamp 1999), and may improve mating opportunities (Norscia et al. 2009). The nature and the relative amount of benefits are expected to vary across species and their social environment. Costs mainly result from a high probability of parasitic infection, disease transmission, and competition for limited resources (e.g. food) (Krause and Ruxton 2002). In stable social groups, an increase in conflicts of interest may cause aggression and jeopardize future cooperation (de Waal 1986; van Hooff 2001).

A growing body of evidence from an increasing range of taxa (birds, and primate and non-primate mammals) indicates that evolution has provided animals with behavioural tools to prevent and resolve conflicts. Specifically, to cope with the conflict aftermath and social damage caused by aggressions, several group-living species use a variety of peace-keeping strategies (Aureli et al. 2002; Silk 2007b). Such peaceful mechanisms include reconciliation, triadic contacts (directed from third-parties to one of the former opponents), and quadratic affiliation (previous aggression may increase post-conflict affiliation between bystanders) (de Waal and van Roosmalen 1979; Palagi et al. 2004, 2006, 2008a; Judge and Mullen 2005; Cordoni et al. 2006; Koski and Sterck 2007, Palagi and Cordoni 2009).

Reconciliation, defined as the peaceful post-conflict reunion of former opponents (de Waal and van Roosmalen 1979), is the primary mechanism used by animals to avoid relationship disruption after a previous conflict. Reconciliation has been demonstrated in many primate (Aureli and de Waal 2000; Koyama and Palagi 2006; Thierry et al. 2008; Palagi et al. 2008b) and non-primate species (e.g. domestic goats, Capra hircus: Schino 1998; spotted hyaenas, Crocuta crocuta: Wahaj et al. 2001; bottlenose dolphins, Tursiops truncatus: Weaver 2003; domestic dogs, Canis familiaris: Cools et al. 2008; wolves, Canis lupus: Cordoni and Palagi 2008). Although reconciling conflicts is a common behavioural option for group-living animals, reconciliation does not necessarily occur after all cases of aggression and its occurrence rates show inter-species, intra-species, and within-group variation (Arnold and Aureli 2007). After a first descriptive and observational approach, in the last few years the field of conflict management has focussed on theoretical development and hypothesis testing and, specifically, efforts have been made to develop hypotheses to explain the functions of reconciliation at both proximate and ultimate levels (Koyama and Palagi 2006).

Geladas live in multi-level societies (Kawai et al. 1983) in which the basic level consists of one-male units (OMUs) which normally comprise a reproductive male, his females (ranging from 6 to 8), and their offspring. An OMU is stable in time and in the terms of the individuals which form it. Several OMUs naturally live closely together forming a social set of upper levels named “teams” (two or more OMUs that regularly associate) and “bands” several OMUs or teams that associate often, but somewhat less regularly (Kawai 1979; Mori 1979a; Dunbar 1984). Typically, males dominate females and the OMU leaders avoid interactions with the females belonging to other OMUs (Smuts 1987; Dunbar 1988).

Geladas are characterised by female philopatry and male dispersal. The social relationships within the OMU centre primarily round the females, and most of the male’s friendly interactions are generally with few of them (Dunbar 1983a). Different from hamadryads, which maintain group integrity by aggressive herding by the males, the social cohesion of the gelada unit is a result of strong bonds among group members (Bramblett 1970). The relationships are determined primarily by use of protected threats and coalitions and there is a preference for social partners, especially among the females (Mori et al. 2003; Palagi et al. 2009).

Although, in the last two decades, many efforts have been made to clarify reconciliation dynamics in many primate species, geladas have often been neglected in the study of post-conflict social dynamics. The only paper published on gelada post-conflict behaviour is that by Swedell (1997), who showed that this species reconciles.

The objectives of our study are to describe modalities (occurrence, quantification, and timing of the phenomenon and patterns used to reconcile), to evaluate the effect of sex and hierarchy, and to investigate some potential roles of reconciliation in geladas (Theropithecus gelada).

The closeness of a social relationship affects reconciliation levels (the friendship hypothesis: de Waal and Yoshihara 1983; Cords 1997; Preuschoft et al. 2002). In addition, according to the valuable relationship hypothesis, animals tend to reconcile more with fellows whom they need for agonistic support (Cords and Aureli 1993; Cords and Thurnheer 1993; Cords 1997). During agonistic support, an animal intervenes in an ongoing conflict risking injury, while the recipient clearly benefits from the help (Schino et al. 2007). Aiding is often considered a prime example of cooperational behaviour (Noë and Hammerstein 1994) and is expected to be a good indicator of partner value (van Schaik and Aureli 2000). Dunbar’s work (1975, 1983b) showed that not all group members in the same OMU are valuable partners at least not when it comes to grooming and competition within units. Via direct measures of relationship characteristics, we try to verify whether adults (the core of the gelada OMUs) with higher-quality relationships (e.g. high rates of affinitive interactions and/or “aiding” events) show higher levels of conciliatory tendency than those characterized by lower-quality relationships (e.g. less affinitive bonds or “aiding” events) as predicted by the friendship (de Waal and Aureli 1996; Aureli et al. 1997) and valuable relationship hypotheses (van Schaik and Aureli 2000; Aureli et al. 2002).

Because aggressive interactions have a clear beginning but, generally, a quite ambiguous ending, reconciliation may function at an immediate level “like a cease fire” (Silk 2007b, p. R50). In this perspective, the conciliatory act can be viewed as a predictive gesture which indicates that the aggressor does not intend to resume the conflict. In this view, we predict that aggressors would be more likely to approach victims which, in turn, will accept interaction with their former opponents.

Generally, conciliatory contacts may reduce the probability of further aggressive events which typically increase after a previous fight (Aureli and van Schaik 1991; Cords 1992; Watts 1995; Castles and Whiten 1998; Palagi et al. 2008b). If, in geladas, reconciliation ratifies the definitive conclusion of the conflict, we predict that the probability of further attacks by the aggressor (renewed aggression) would be significantly reduced by post-conflict reunions.

Methods

Animals and data collection

We collected behavioural data on a colony of Theropithecus gelada hosted at the NaturZoo (Rheine, Germany). The gelada baboon colony was made up of two OMUs (1 and 2) and was composed of 2 adult males, 8 adult females, and 11 immature subjects (Table 1).

Table 1 The group of gelada baboons (Theropithecus gelada) housed in the NaturZoo (Rheine, Germany)

The colony was housed in an enclosure with both indoor (a room of about 36 m2) and outdoor (an island of about 2,700 m2 surrounded by a boundary ditch) facilities. The environments were equipped with everything necessary to allow the geladas to move freely in all three dimensions. Specifically, the outside enclosure was located in a naturally hilly area equipped with trees, branches, ropes, and dens.

The animals were fed with grass, vegetables, and pellets, which were scattered on the ground three times per day. Water was available ad libitum. No stereotypic or aberrant behaviours characterized the study group.

We collected behavioural data during a period of 6 months (June–November 2007) on all the subjects of the colony. Before starting systematic data collection, the three observers underwent a training period (about 90 h). We used, concurrently, two methods of observation: all-occurrences sampling and focal-animal sampling (Altmann 1974). During the training period, the same focal animal was followed by the observers simultaneously and the data were then compared and discussed. Training (about 90 h) was over when the observations matched in 95% of cases (Martin and Bateson 1986). The observations took place daily over 6-h periods, that spanned morning (6.00 a.m.) and evening (10.00 p.m.).

We recorded all agonistic events among the geladas by use of an all occurrences sampling method (633 h of observation) (Altmann 1974). For each aggressive encounter we recorded:

  1. 1.

    the opponents,

  2. 2.

    context (circumstance in which the aggression took place, e.g. “feeding”),

  3. 3.

    the outcome of the conflict (decided or undecided),

  4. 4.

    aggressive behavioural patterns, and

  5. 5.

    the winner and loser supporters.

Decided conflicts were those in which we could clearly distinguish winners and losers.

After the last aggressive act (Table 2) of any given agonistic event, we followed the victim as the focal individual for a 10-min post-conflict period (PC).

Table 2 Gelada behavioural patterns recorded during the observation period

Control observations (MCs) took place on the next possible day at the same time as the original PC, on the same focal animal, in the absence of agonistic interactions during the 10 min before the beginning of MC and when the opponents had the opportunity to interact (de Waal and Yoshihara 1983). Both for PCs and MCs we recorded:

  1. 1.

    starting time (min),

  2. 2.

    type of first affinitive interaction (Table 2),

  3. 3.

    the minute of first affinitive behaviour,

  4. 4.

    initiator of the affinitive behaviour, and

  5. 5.

    partner identity.

Because, during the training period (about 90 h), we never observed any kind of affinitive patterns (Table 2) between the adults belonging to the two OMUs, we decided to collect PCs–MCs for intra-unit dyads only.

We also extracted background information on the relationship quality among individuals using:

  1. 1.

    grooming interactions (see Table 2 for definition) collected via focal animal sampling (Altmann 1974), and

  2. 2.

    agonistic support (defined as the number of occasions on which the individual A supports individual B divided by the number of conflicts in which B is involved minus the number of agonistic encounters involving the dyad A–B).

The mean number of conflict in which an individual was involved was 209.29 ± 44.16 SE.

Data analysis

Reconciliation analysis was carried out at the individual level. In the case of reconciliation for each animal we determined the number of attracted (A), dispersed (D), and neutral (N) pairs over all PC–MC pairs (Table 1).

In attracted pairs, affinitive contacts occur earlier in the PC than in the MC (or in the PC, but not in the MC), whereas in dispersed pairs affinitive contacts occur earlier in the MC than in the PC (or they did not occur at all in the PC). In neutral pairs, affinitive contacts occur during the same minute in the PC and the MC, or no contact occurs in either the PC or the MC. To avoid coding the same incident twice, for each individual we used only PC–MC pairs in which that individual was the focal animal, and entered them under its name. The overall minimum number of PC–MC pairs per focal animal was four (Table 1). To evaluate individual reconciliation, we used Veenema et al.’s (1994) measure of conciliatory tendency (CCT), defined as “attracted minus dispersed pairs divided by the total number of PC–MC pairs”. Individual CCTs were used to determine the mean group CCT.

To investigate the effect of relationship quality on reconciliation we took into account grooming interactions and agonistic support levels, separately. For each individual we first calculated the mean value of the grooming rates and agonistic support levels for dyads in which that selected individual was involved. Second, for each individual we divided dyads involving it into two quality classes (weak and close) by the following procedure: dyads showing grooming frequencies higher than the mean value for the selected individual were assigned to the close class; alternatively, dyads showing grooming frequencies lower than the mean value for the selected individual were assigned to the weak class. Afterwards, we calculated the mean CCT value that each subject showed with its partners belonging to close and weak relationship quality classes. The same procedure was applied for the influence of agonistic support on the distribution of CCT values.

To define the hierarchy, we analysed all dyadic, decided dominance interactions (comprising one-on-one encounters). We produced a dominance interaction matrix, and performed the subsequent analysis via the improved index of linearity h′ (de Vries 1995), with the aid of the software package MatMan 1.0 by Noldus (with 10,000 permutations). The directional consistency index (DC) was calculated across all dyads as the total number of times the behaviour was performed in the main direction within each dyad, minus the number of times the behaviour occurred in the less frequent direction within each dyad, divided by the total number of times the behaviour was performed by all individuals. This index ranges from 0 (completely equal exchange) to 1 (complete unidirectionality) (van Hooff and Wensing 1987).

Because of the small sample size and the deviation from normality (Kolmogorov–Smirnov test P < 0.05), nonparametric statistics were applied (Siegel and Castellan 1988).

The Wilcoxon matched-pair signed-ranks test was used to assess difference between attracted and dispersed pairs. In order to identify a time-window during which the conciliatory contacts actually took place, we compared the frequency of first affinitive interactions recorded during PCs and MCs within each minute of focal sampling.

We used the same test to evaluate:

  1. 1.

    possible differences between aggressors and victims in initiating post-conflict reunions, and

  2. 2.

    whether the presence of conciliatory contacts affects the probability of renewed attacks by one of the two opponents.

In order to test for possible differences in the affinitive pattern distribution used to reconcile we used Friedman’s 2-way ANOVA.

The Spearman test was used to check for possible correlation between CCTs and rank.

We made use of exact tests according to the threshold values suggested by Mundry and Fischer (1998). Nonparametric statistical analysis was performed by using SPSS 12.0.

Results

We were able to collect 319 PC–MC pairs (Table 1). At team level (OMU 1 and OMU 2), friendly interactions between former opponents were more likely to occur after a conflict than during control periods (Wilcoxon’s T = 0, ties = 0, n = 18, P = 0.0001). The mean CCT of all focal individuals was 23.18% ± 3.18 SE. When we analysed data for adults and juveniles separately, we found a significant difference between attracted and dispersed pairs both considering only adults (attracted pairs > dispersed pairs: Wilcoxon’s T = 0, ties = 0, n = 12, P = 0.0001; mean CCTad = 22.86% ± 3.70 SE) and juveniles (Wilcoxon’s T = 0, ties = 0, n = 6, P = 0.031; mean CCTj = 23.83% ± 6.53 SE).

Victims and aggressors affiliated more often in the first minute of the PCs than in the first minute of the MCs (Wilcoxon’s T 1min = 0, ties = 0, n = 18, P = 0.0001; Fig. 1), whereas no difference in the frequency of affiliation was found between PCs and MCs from the second to the tenth minute (see the legend of the Fig. 1 for the statistical results). The CCT value calculated on the basis of the post-conflict affinitive contacts which occurred within the first minute was 28.69% ± 4.82 SE.

Fig. 1
figure1

Temporal distribution of first affinitive contact in PCs (black squares) and MCs (white squares, dotted line) for reconciliation. Frequencies of first affinitive contact during both PCs and MCs are depicted on the Y axis. Only statistically significant values are reported on the figure (T 2min = 10.50, ties = 12, n = 18, P = 1; T 3min = 13.50, ties = 9, n = 18, P = 0.398; T 4min = 10.50, ties = 12, n = 18, P = 1; T 5min = 9, ties = 12, n = 18, P = 1; T 6min = 6, ties = 13, n = 18, P = 1; T 7min = 2, ties = 15, n = 18, P = 1; T 8min = 7, ties = 12, n = 18, P = 0.688; T 9min = 0, ties = 18, n = 18, P = 1; T 10min = 0, ties = 17, n = 18, P = 1)

Given these results, we restricted subsequent analysis to the time-window in which reconciliation occurred (within the first minute).

The first affinitive patterns used to reconcile conflicts between adults were contact sitting (23.96%), grooming (16.67%), touching (16.67%), sexual interactions (6.25%), play (8.33%), lip-smacking (14.58%) and vocalizations (grunting and moan) (13.54%). Geladas did not show any preference in the use of first affinitive pattern to reconcile (exact Friedman’s χ 2 = 10.87; n = 12, df = 6, P = 0.1). When a juvenile was involved in the aggressive encounter the percentages of first affinitive patterns used to reconcile were: contact sitting (44.44%), grooming (11.12%), touching (29.63%), sexual interactions (0.00%), play (14.81%), lip-smacking (0.00%) and vocalizations (grunting and moan) (0.00%). In this case, the two-way analysis of variance revealed a statistical significance in the use of conciliatory patterns (exact Friedman’s χ 2 = 19.49; n = 6, df = 6, P = 0.001). However, such significance is probably because animals never used sexual interactions, lip-smacking, and vocalizations to reconcile.

We did not find any significant difference between individual CCT levels according to the sex of the opponents involved (F–F vs. F–M, Wilcoxon’s T = 7, ties = 0, n = 6, P = 0.562). We were able to compare just six females because three of them were never victims of other females.

We found a linear hierarchy among adults (the male and the eight reproductive females) of the OMU 1 (h′ = 0.92, P = 0.0031, n = 9). The directional consistency index (the frequency in the relative direction of aggression) was 0.62. The significance remained also when we checked for linearity among the eight reproductive females (h′ = 0.73, P = 0.033, n = 8). In this case, the directional consistency index was 0.63. It was not possible to test for the linearity of hierarchy on the OMU 2 because of the small sample size (n = 4).

We did not find any significant correlation between female CCTs and rank (Spearman r s = −0.429, n = 7, P = 0.337).

A statistical significance was found in the distribution of CCTs according to the quality of relationships (weak and close) calculated by use of the coalitionary support frequency on all reproductive adults of OMU 1 (mean CCTweak = −1.9% ± 4.60 SE; mean CCTclose = 14.00% ± 4.64 SE: Wilcoxon’s T = 0; ties = 1; n = 8; P = 0.015) (Fig. 2). In contrast, no difference was found in the distribution of CCTs in relation to the quality of affinitive relationships calculated by grooming frequency (mean CCTweak = 4.00% ± 3.61 SE; mean CCTclose = 8.03% ± 8.39 SE: Wilcoxon’s T = 13, ties = 1, n = 8, P = 0.938) (Fig. 2).

Fig. 2
figure2

CCT levels as a function of relationship quality: weak and close relationships measured by agonistic support and weak and close relationships measured by grooming. CCTs% per animal are depicted on the Y axis. Solid horizontal lines indicate medians; length of the boxes corresponds to inter-quartile range; thin horizontal lines indicate range of observed values. Only statistical significant values are reported on the figure

Considering conflicts between adults, winners initiated post-conflict reunions more frequently than victims did (Wilcoxon’s T = 8, ties = 2, n = 12, P = 0.045); we did not find any significant difference when a juvenile was involved in the previous conflict (Wilcoxon’s T = 7.5, ties = 1, n = 6, P = 1).

The probability of further aggression directed by a third party at the victim was not significantly affected by the presence of the previous conciliatory contact between the opponents (Wilcoxon’s T = 23.50, ties = 8, n = 18, P = 0.71). On the other hand, the presence of reconciliation reduced the probability of further attacks directed by the previous aggressor at both victims and third parties (Wilcoxon’s T = 3, ties = 6, n = 18, P = 0.002) (Fig. 3).

Fig. 3
figure3

Probability of further attacks directed by previous aggressors towards third parties both in the presence and in absence of reconciliation. Solid horizontal lines indicate medians; length of the boxes corresponds to inter-quartile range; thin horizontal lines indicate range of observed values. Only statistical significant values are reported on the figure

Discussion

In this study, we provide evidence for the occurrence of reconciliation in geladas. We verified that conciliatory contacts occur immediately after the end of conflicts (within the first minute of the PC). Geladas did not show any particular kind of affinitive behaviour to reconcile. Neither dominance rank nor sex of the individuals seem to affect the distribution of conciliatory contacts (adult females reconciled equally often with the adult male and with each other). The amount of coalitionary support was a good predictor of the level of conciliatory contacts; conversely, friendship (measured by grooming rates) did not affect the distribution of reconciliation. Aggressors sought conciliatory contact more frequently than victims. Moreover, reconciliation did not reduce the probability of further attacks directed by third parties at victims, although it significantly reduced the motivation of the aggressor to renew the attack on both victims and third parties.

Reconciliation in gelada baboons was reported in 1997 by Swedell, who recorded 47 aggressive interactions in the Bronx Zoo gelada colony. The CCT levels recorded in our study (28.69%) are similar to those (30%) obtained by Swedell (1997). Despite the differences in sample size/group composition and the intra-specific variability present in conflict resolution mechanisms (Castles et al. 1996), the two studies seem to converge in terms of occurrence and quantification of the phenomenon.

In contrast with other species characterized by one-male society, gelada females reconciled with the adult male and other females to the same extent. For instance, in mountain (Gorilla beringei Watts 1995) and lowland (Gorilla gorilla Cordoni et al. 2006) gorillas reconciliation occurs only in dyads with valuable social bonds, i.e., adult male–female pairs (Watts 1995; Cords and Aureli 2000). Gorilla females maintain high proximity levels with the adult male to obtain his protection and show weak social relationships with other females (Watts et al. 2000). As for gorillas, in Papio hamadryas cross-sex bonds are generally stronger than intrasexual bonds (Kummer 1995).

In contrast with geladas (Mancini and Palagi 2009), in hamadryas Colmenares (2004) found that grooming was more frequent in female–male than in female–female dyads and, more recently, Romero et al. (2008) showed that the highest rate of reconciliation occurred between leader males and their females. The absence of any sex-trend bias in gelada reconciliation can be interpreted in light of the female social network which characterizes the species. The tendency for females to form strong bonds and coalitions with each other is at the basis of the cohesion and stability typical of gelada OMUs. As has been reported, in some cases, the strength of female positive bonds is sufficient to maintain the unit’s integrity despite the absence of the male (Dunbar and Dunbar 1975).

Although gelada females are characterized by a stable and linear hierarchy (this work; Dunbar 1979; Mori 1979b), it seems that dominance relationships do not affect the distribution of reconciliation rates. Our finding is in agreement with those from Bernstein (1970) and Spivak (1971) who failed to find any significant correlation between dominance (defined by wins in agonistic encounters) and other kinds of social behaviour among gelada females. A similar finding has also been reported for some non-primate species (Crocuta crocuta, Holekamp et al. 1997; Boydston et al. 2001; Canis lupus, Cordoni and Palagi 2008) in which group members cooperate to acquire and defend resources despite their highly structured hierarchical relationships. Vehrencamp (1983) stated that when the cooperation of all group members is indispensable dominance may be relaxed, because any subject of the group can exert leverage power by withholding coalition and support; in such cases, conflict resolution mechanisms may be favoured independently of hierarchical rules.

In geladas, the agonistic alliances (more than grooming) seem to be the key factor affecting the distribution of conciliatory contacts, thus providing support for the valuable relationship hypothesis. Although agonistic alliances are beneficial, their effect on CCT has been difficult to demonstrate (Kappeler and van Schaik 1992; Cords and Aureli 1993; Preuschoft et al. 2002). To our knowledge, only three studies report evidence supporting the coalitionary hypothesis, two of them focussed on primates (wild Macaca assamensis, Cooper et al. 2005; captive Papio hamadryas, Romero et al. 2008) and the third on captive wolves (Cordoni and Palagi 2008). Whatever the taxa studied, all the authors interpreted their findings on reconciliation and coalitionary support in the light of the cooperational behaviour exhibited by the different species (Palagi and Cordoni 2009).

In agreement with previous reports for other reconciling species (Aureli et al. 2002), in geladas the first affinitive contact between aggressors and victims took place within the first minute of the PC. This finding suggests the strong motivation of the former opponents to settle the conflict and restore affiliation swiftly, thus indicating that reconciliation may have important consequences at an immediate level. Different from baboons (Papio sp.) in which conciliatory behaviour must be accompanied by grunts to occur (Silk et al. 1996), in geladas only 13.54% of the post-conflict reunions occurred after a vocalized approach (grunt/moan, Dunbar and Dunbar 1975), thus suggesting that vocalizations are not a necessary precursor to post-conflict affiliation. However, similar to baboons, most of the conciliatory grunts were emitted by high-ranking individuals (the adult male and the alpha female). Without any peaceful signal by one of the opponents, after the first episode of aggression a conflict may continue and/or even escalate to a more dangerous level. Such an ambiguous situation makes the period following the conflict stressful for both aggressors and victims (Aureli et al. 1989, Aureli and van Schaik 1991). Probably, when the aggressor does not intend to continue fighting, he/she gives the victim a clear signal which, if truthful, may ratify the end of hostilities, thus being beneficial both for aggressors and victims. Our finding supports such an assumption; in fact, even though our study could not disentangle the cause–effect relationship between reconciliation and subsequent aggression, one of the immediate consequences of the conciliatory gesture could be the reduction of the renewed attacks by the former aggressor, which also initiates most of the conciliatory contacts.

In conclusion, the comparable levels of male-female and female–female reconciliation, the effect of valuable more than dominance relationships on post-conflict affiliation, and the absence of any specific pattern used to reconcile seem to reflect the peculiar nature of gelada social dynamics (female bonding, high level of protected threats and coalitions, preference for a social partner, Mori et al. 2003; Palagi et al. 2009). Although study of post-conflict behaviour in geladas warrants further investigation of both captive and wild OMUs, they are a good model species to test some of the theoretical assumptions about primate conflict resolution.

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Acknowledgments

Thanks are due to the RheineZoo, Rheine (Germany): the director, Achim Joahnn, and the gelada keepers for allowing and facilitating this work; Giada Mancini and Michele Mignini for collaboration with data collection; Ivan Norscia for his invaluable comments on the manuscript; Cecilia Ragaini for language revision; and Grignolino for his important clarifying input in discussing results. This research was supported by private funding and it complies with current laws of Italy and Germany.

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Correspondence to Elisabetta Palagi.

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Leone, A., Palagi, E. Reconciling conflicts in a one-male society: the case of geladas (Theropithecus gelada). Primates 51, 203–212 (2010). https://doi.org/10.1007/s10329-010-0188-4

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Keywords

  • Peace-keeping mechanisms
  • Female social cohesion
  • Valuable relationship hypothesis
  • Coalitionary support
  • Theropithecus gelada