Aggression & Postconflict Affiliation in Hamadryas Baboons

Running head: RELATIONSHIP QUALITY & AGGRESSION ON POST-CONFLICT

The Influence of Relationship Quality and Severity of Aggression on Post-Conflict Affiliation in Hamadryas Baboons (Papio hamadryas hamadryas) Tan Mavis (Neo Chern Ee Frederick & Lau Weng Yi) Michael D. Gumert

Graduation Project submitted to the School of Humanities and Social Sciences, Nanyang Technological University in partial fulfillment for the degree of Bachelor of Arts (Hons) in Psychology.

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Abstract This paper explores the influence of relationship quality and level of aggression on postconflict affiliation in 16 captive hamadryas baboons (Papio hamadryas hamadryas) at the Singapore Zoo. Focal sampling was used to record baseline affiliation rates and relationship quality between dyads, and 3 levels of aggression were categorized based on intensity.

Amount of post-conflict affiliation was measured using post-conflict (PC) and matchedcontrol (MC) samples. In line with previous studies, the results demonstrate that relationship quality is highly correlated to reconciliation but not third party consolation (TPC), and level of aggression did not significantly influence reconciliation and TPC. Changes could be made to traditional methods which may improve the reliability of results in future studies on primates.

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The Influence of Relationship Quality and Severity of Aggression on Post-Conflict Affiliation in Hamadryas Baboons (Papio hamadryas hamadryas) Social interaction in non-human primate societies involves both affiliation and agonistic interaction, and these forms of social behaviour underlie the basic social organization, structure, and relationships found in societies (Alexander, 1974; de Waal, 1986; Higley, 2003; Hinde, 1983; Kummer, 1968; Sussman, Garber, & Cheverud, 2005; Terborgh & Janson, 1986). Most anthropoid primates live in social groups, and this requires them to cooperate and compete, and form relationships with individuals in a social environment (Hinde, 1983; Kummer, 1968). When conflict occurs between individuals, relationships may be disrupted; therefore forms of affiliative post-conflict interaction may take place to ameliorate stressed relationships (de Waal & van Roosmalen, 1979) and restore a peaceful social situation (Judge & Mullen, 2005).

Aggression in non-human primates may occur as a result of competition for food (Janson, 1985; Janson 1988; Su & Birky, 2007), access to mating partners (Slater, Schaffner, & Aureli, 2009), and to protect the physical well-being of self and kin (Higley, 2003). In addition, aggression can be used to punish inappropriate behaviours (Clutton-Brock & Parker, 1995; Kummer, 1995). Overall, aggressive interaction seems to enforce social norms and rules (de Waal, 1986; Higley, 2003), preserve social power of dominants, and maintain patterns of social interaction (Janson, 1985; Silk, 2002; Sterck, Watts, & van Schaik, 1997).

In most despotic societies, aggression between dominant and subordinate conspecifics is more asymmetrical, which may be associated with more frequent but less severe aggression (Higley, 2003; Sapolsky, 2005; Thiery, 1985). Dominant individuals which attack and threaten subordinates rarely cause serious injuries on their victims because low severity aggression is sufficient to reinforce the dominant individual’s social status (Silk, 2002). In Old World monkeys, adult males are more aggressive than females and are more capable of

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inflicting physical injuries although they seldom engage in contact aggression (Berstein, Williams, & Ramsay, 1983). However, the scars and wounds observed on Old World monkeys show that individuals do at times have aggressive encounters which results in serious injuries (Higley, 2003).

Post-conflict affiliation between individuals may be influenced by relationship quality and aggression intensity. Reconciliation is the post-conflict affiliative interaction between opponents (de Waal & van Roosmalen, 1979), and is expected to play a role in mending the damaged relationship and reducing tension between the pair (Judge & Mullen, 2005; de Waal & van Roosmalen, 1979). Restoring disrupted relationships may be important because social partners need to cooperate in terms of protection (Higley, 2003; Mitani & Watts, 2005), gaining access to food (Janson 1985; Janson, 1988; Su & Birky, 2007) and agonistic support (Setchell, Knapp, & Wickings, 2006; Watts, 2002). In addition, reconciliation may decrease the possibility of renewed aggression, decrease post-conflict anxiety of opponents, and restore baseline levels of tolerance and affiliative interaction (Aureli, Cords, & van Schaik, 2002; Aureli & van Schaik, 1991; Cords, 1992; Silk, 1997).

Relationship strength and quality varies, and some relationships may be stronger than others. High relationship quality (i.e, a valuable relationship) is characterized by frequent baseline levels of affiliation and relatively infrequent levels of aggression (Cords & Aureli, 2000; Judge, 2003). Kinship is one type of valuable relationship, and individuals seem to prioritize kin over non-kin social partners during affiliative social exchanges (Roney & Maestripieri, 2003; Silk, 2002). According to Hamilton’s (1964) inclusive fitness theory, an individual tends to select kin as preferred recipients of beneficial behaviour such as allogrooming and food sharing, which may indirectly increase its inclusive fitness (as cited in Chapais, 2002, p. 204). In macaque (Macaca spp.) societies, female grooming is more kinoriented than male grooming because of the matrilineal kinship systems due to female

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philopatry (as cited in Roney & Maestripieri, 2003, p. 189). Restoring quality of relationship with kin may be important because a disrupted tie with kin could result in a loss of reproductive success.

Besides kinship, close relationships with non-kin social partners may also benefit individuals. High-ranking individuals groom others less and receive more grooming compared to low-ranking individuals, which may be related to the protection that these individuals can offer to low-ranking individuals (Seyfarth, 1977; Silk, 1992). In order to gain access to mating partners during mating seasons, grooming increased between adult males and females, and adult males groomed estrous females more than they were groomed by the estrous females (Roney & Maestripieri, 2003). Also, males groomed females longer when sexual activity was involved, and male-to-female grooming promoted sexual activity during or after the grooming bout (Gumert, 2007b). Moreover, females groomed mothers with infants more, and grooming facilitated infant handling (Gumert, 2007a; Henzi & Barrett, 2002).

Overall, individuals derive benefits from their relationships and some are more valuable than others. In order to minimize losses incurred from a disrupted relationship, reconciliation may be important, especially to more valuable ties. Studies have found that aggressors and victims may experience post-conflict anxiety due to the disrupted tie because it may prevent future cooperative interaction (Aureli & van Schaik, 1991; Castles & Whiten, 1998b, Das et al., 1998; Koski & Sterck, 2007; Romero, Colmenares, & Aureli, 2009; Sapolsky, 2005). Opponents with high relationship quality tend to reconcile more frequently than others (Cords & Aureli, 2000), as observed in chimpanzees (Pan troglodytes) (Arnold & Whiten, 2001; de Waal & Yoshihara, 1983), macaques (Aureli, van Schaik, & van Hooff, 1989; Castles, Aureli, & de Waal, 1996) and baboons (Papio spp.) (Castles & Whiten, 1998a; Das, Penke, & van Hooff, 1998; Romero, Colmenares, & Aureli, 2008). Tolerance, which

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could be exhibited as a dominant permitting subordinates to feed near it (Yamada, 1963), is higher between opponents with high relationship quality, which may facilitate post-conflict proximity and reconciliation (Aureli et al. 2002; Cords, 1992). In contrast, opponents with weak relationship quality may not reconcile as frequently because they may benefit less from restoring an already weak relationship (Aureli et al., 2002; Silk, 1997). In addition, low tolerance and high chances of renewed aggression after a highly aggressive conflict may be too dangerous for these opponents to reconcile (Aureli et al., 2002).

Post-conflict affiliation may not only involve the opponents, but can involve bystanders as well. For example, triadic post-conflict affiliation is the affiliative interaction between opponents and uninvolved third parties (Koski & Sterck, 2007). Triadic post-conflict affiliation functions differently depending on the relationship between the third party and the aggressor or victim (Das, 2000). Consolation is a form of triadic post-conflict affiliation between victims and third parties (de Waal & van Roosemalen, 1979), and more specifically, a form of post conflict affiliation initiated by an uninvolved third party towards the victim (Cordoni, Palagi & Borgognini Tarli, 2006).

For our study, however, we are interested in post-conflict affiliation between third parties and both conflict opponents. Therefore, with reference to Koski & Sterck (2007), we described all third-party affiliation with aggressor and victim using the term ‘third- party consolation’ or TPC. Third-party consolation has been observed following aggressive outbreaks in several non-human primates (Koyama & Palagi, 2006) such as long-tailed macaques (Macaca fascicularis) (Das et al., 1998), gorillas (Gorilla gorilla) (Cordoni et al., 2006), chimpanzees (de Waal & van Roosmalen, 1979; Koski & Sterck, 2007; Palagi, Cordoni, & Borgognini Tarli, 2006, Wittig & Boesch, 2003), bonobos (Pan paniscus) (Palagi, Paoli, & Borgognini Tarli, 2004), and hamadryas baboons (Papio hamadryas hamadryas) (Judge & Mullen, 2005). Palagi et al. (2006) found that consolation in bonobos

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took place more frequently than reconciliation after a conflict of high aggression intensity, and consolation took place more frequently in the absence of reconciliation. Also, consolation seems to decrease post-conflict anxiety in the victim, and restore a peaceful social situation (Wittig & Boesch, 2003). In contrast, Koski and Sterck (2007) found no decrease in postconflict anxiety levels when consolation took place, which suggests that consolation may not be a substitute for reconciliation.

Aggressors, like victims, may experience post-conflict anxiety as well (Castles & Whiten, 1998b, Das et al., 1998; Romero et al., 2009; Sapolsky, 2005). This may occur because the valuable relationship with the victim is disrupted (Aureli & van Schaik, 1991; Koski & Sterck, 2007), or aggressors are potential targets of post-conflict aggression by retaliators defending the victim. A recent study on hamadryas baboons found that postconflict anxiety levels in aggressors were higher than baseline levels, and aggressors were also more likely to be targets of post-conflict aggression initiated by uninvolved third parties (Romero et al., 2009). Triadic post-conflict affiliation between aggressors and uninvolved parties may have a calming or appeasing effect on the aggressor, which seem to decrease post-conflict anxiety (Romero et al., 2009). In other words, the triadic post-conflict affiliation between aggressors and third parties may function similarly to ‘consolation’.

A few studies have investigated aggression and post-conflict behaviour in hamadryas baboons (Judge, Griffaton, & Fincke, 2006; Judge & Mullen, 2005; Romero et. al., 2009), however, the relationship between reconciliation and consolation with relationship quality and severity of aggression has not been well studied in this species. Therefore to better understand the post-conflict affiliation in hamadryas baboons, we studied reconciliation and consolation in hamadryas baboons and investigated whether post-conflict affiliation relates to a dyad’s relationship quality and the severity of aggression.

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We examined how the intensity of aggression between two individuals might influence affiliative behaviour following aggression. We expected that in both high and low aggression levels, reconciliation would occur less frequently and for shorter time intervals compared to moderate aggression levels. Under this model, we hypothesized that (1) reconciliation should occur for a longer duration following moderate levels of aggression.

Also, we hypothesized that (2) high aggression intensity will lead to longer bouts of TPC between aggressors and third parties, and (3) high aggression intensity will lead to longer bouts of TPC between victims and third parties.

Also, we studied the relationship between relationship quality (i.e., measured as baseline affiliation rates) between dyads and the type of affiliative behaviour observed following episodes of aggression. In order to mend important relationships after aggression and decrease post-conflict anxiety, we hypothesized that (4) reconciliation is should occur for a longer duration in pairs with higher rates of base line affiliation, than those with lower rates, and (5) TPC should occur for a longer duration when the pair in conflict exhibits low base line rates of affiliation, compared to pairs with higher rates.

Method Subjects and Housing The subjects of our study belonged to a group of hamadryas baboons housed in the Singapore Zoo. The outdoor enclosure was 860m2, which was designed to imitate the natural arid desert habitat of hamadryas baboons and included structures such as cliffs, caves and waterfalls. The colony consisted of 86 individuals (23 males, 26 females, and 34 of unknown sex) organized into 8 one-male units which varied in size (1-9 females in each unit), and 1 all-male unit. Our study focused on 16 adults (5 males and 11 females) of 3 one-male units, and 2 males. In order to identify subjects, we used photography, videography, and/or

Relationship Quality & Aggression on Post-conflict 10 recorded their physical features. Adults in other units, adolescents, juveniles and infants were not included in this study because they could not be not clearly identified.

Data Collection Before conducting data collection, we ensured that our method and procedure had been approved by the Singapore Zoo, which is monitored by the Wildlife Reserves Singapore Animal Welfare & Ethics Committee (WRS AWEC). In order to ensure high inter-observer reliability, there was a two week on-site training where observers conducted practice observations and recordings before proceeding with formal observations.

We collected data from June 2008 – January 2009. Observations were conducted on an average of twice every week on any weekday, and for an average of 3 hours continuously during any time between 09.30 hr and 17.00 hr. All observations were recorded using audio recorders. We conducted a 10-minute focal sample observation (Altmann, 1974) on each subject at a time for an average of 70 minutes per subject, and collected 1130 minutes of focal samples in total. Subjects were selected for focal sampling based on a randomized list.

Proximity (i.e., positioned < 1m from a partner) and allo-grooming were measured as states, while lip-smacking, touching, inspection, presentation and mounting were recorded as events.

Focal sample observations would stop when an aggressive interaction occurred in the group because focal samples were intended to reflect the behaviour of subjects in nonaggressive circumstances. When either of the conflict opponents was identified as our subjects, we recorded details of the aggressive interaction, such as the identity of the aggressor, victim, third parties which are involved, bystanders, and the type and level of aggression. We proceeded with a 10-minute post-conflict focal observation (PC) (PC-MC method, de Waal & Yoshihara, 1983) on the aggressor and victim immediately after the aggressive exchange stopped. If there were more than one aggressor, a PC was conducted on the initial aggressor. We recorded all affiliative and aggressive gestures during the PC. We

Relationship Quality & Aggression on Post-conflict 11 did not restart a PC when an aggressive behaviour took place during the PC sample; instead we recorded aggressive behaviour in PC as post-conflict aggression.

In order to generate a control sample to compare PC samples to, we conducted matchedcontrol observations (MC) on the next data collection day after a conflict where a PC was collected. These MC samples were then paired with their comparable PC sample. MC samples were focal samples on former opponents under comparable conditions to the PC it was matched with. We controlled MC samples so that the only difference was that there was no aggression between the pair prior to the MC sample. This allowed us to fully test the effects of aggression on subsequent behaviour in PC samples. MC samples were collected on the next data collection day after the conflict. We chose to start a MC when the former opponents of the PC were first seen in proximity with each other. All focal sampling would stop at the time proximity was observed and a MC sample was started.

We controlled for proximity in MC samples to account for bias due to proximity. There may be a bias because in PC samples there was no control over proximity; the pair in conflict must be in proximity to aggress and/or affiliate. However, in MC the pair in conflict may or may not be in proximity. Any increase in amount of interaction between the pair in conflict during PC could simply be a function of proximity. This method seems to be better compared to the traditional PC-MC method (de Waal & Yoshihara, 1983) when used to assess if a pair was more likely to affiliate (i.e., reconcile) during PC compared to MC. Data Analysis We recorded 29 PC samples and 21 MC samples, with 21 PC-MC pairs. MC sampling was not carried out on 8 pairs of PC samples because either opponent in those conflict pairs were not among our individually identified subjects. When former opponents made affiliative contact during the PC sampling, they were labelled as having displayed “reconciliation”.

When aggressors or victims had affiliative interaction with third parties during the PC

Relationship Quality & Aggression on Post-conflict 12 sampling, the behaviour was labelled as “third-party consolation”. Within the 29 PC samples, 16 pairs showed both reconciliation and third party consolation, and 13 pairs showed only third party consolation. Time spent in proximity and on grooming were converted to seconds, and used for data analysis.

Affiliative instances recorded as events were excluded from data analysis because the amount of affiliative instances during PC-MC sampling was infrequent, and may not contribute meaningfully to the statistical analysis. Therefore, only grooming and proximity were included in the data analysis.

A Shapiro-Wilk test of normality was carried out on the PC and MC data. We did not expect it to be normal because of the nature of PC-MC data and the small sample size.

Therefore, we used non-parametric tests for this study using SPSS 14.0. In order to show that PC affiliation may be meaningful and different from MC affiliation, a Wilcoxon test was conducted to evaluate if time spent on PC affiliation (i.e., grooming and proximity) was greater than time spent on MC affiliation.

To compare time spent on PC affiliation to levels of aggression, we categorized aggressive acts into 3 levels based on intensity: Low (eyebrow raise, open mouth display, and stamp/charge one or two steps), Moderate (chase, and physical contact) and High (biting, and injurious attack). Kruskal-Wallis tests were carried out to compare time spent on PC grooming and PC proximity with the three levels of aggression. Time spent on PC grooming and PC proximity were dependent variables, and level of aggression was the independent variable. A Mann-Whitney post hoc test was used if the Kruskal-Wallis tests showed significant differences across the three levels of aggression.

Focal samples were used for analysing baseline affiliation. To measure baseline affiliation between dyads, interaction matrices were created for each variable of proximity, grooming, and instances of affiliative gestures. In each matrix, a subject’s interactions with

Relationship Quality & Aggression on Post-conflict 13 all other subjects were represented. Taking into account the non-independence of dyads, values in the matrices were normalized, and correlations between the three variables (proximity, grooming, and instances of affiliative gestures) were calculated using the Mantel R-test on Matman 1.1. The significance of the correlation is tested using 10,000 permutations.

To evaluate the relationship between time spent on PC affiliation (i.e., grooming and proximity) and relationship quality, we used a Spearman’s rho correlation test. Correlation tests were performed using time spent on PC grooming and PC proximity, with baseline affiliation rates.

In addition, we performed a Mann-Whitney’s U test to evaluate the differences in time spent on TPC (i.e., grooming and proximity) between uninvolved third parties and aggressors, and between uninvolved third parties and victims. Although this test may not be directly related to our hypotheses, we were interested in possible differences in TPC with regard to aggressors and victims.

Results Shapiro-Wilk test for normality showed that the PC and MC data was not normally distributed, p < .05. This result was expected due to the nature of PC-MC data and the small sample size; therefore we proceeded with non-parametric tests on our data.

A Wilcoxon-T test was conducted to evaluate if amount of PC affiliation (i.e., grooming and proximity) was greater than amount of MC affiliation. The results showed that PC grooming (M=211.04s, SD=234.49s) was significantly greater than MC grooming (M=46.10s, SD=75.19s), T = 0.00, N = 14, p < .01. PC proximity (M = 297.34s, SD = 267.93s) did not differ significantly from MC proximity (M = 417.81s, SD = 226.32s), T = 54.00, N = 18, p = .17.

Relationship Quality & Aggression on Post-conflict 14 A Kruskal-Wallis test was conducted to evaluate differences among the three levels of aggression (Low, Moderate, and High) on reconciliation (i.e., grooming and proximity) between former opponents. The test was not significant for grooming χ2(2, N = 29) = .45, p = .81, and was not significant for proximity χ2(2, N = 29) = 2.12, p = .35. In opponents which reconciled, differences among the three levels of aggression was not significant for grooming χ2(2, N = 16) = 4.38, p = .11, but was significant for proximity χ2(2, N = 16) = 7.49, p = .02 (see Figure 1). Post-hoc comparisons were done to evaluate pair-wise differences between these three groups by using Mann-Whitney's test. Correction using the Bonferroni approach was done to control for Type I error. Results showed that the significant difference found in the Kruskal-Wallis test was between low level of aggression and high level of aggression, U = 4.50 , p = .01.

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Figure 1. Amount of PC proximity and PC grooming between conflict pairs which reconciled, across three levels of aggression.

Relationship Quality & Aggression on Post-conflict 15 Kruskal-Wallis tests were conducted to evaluate differences among the three levels of aggression (Low, Moderate, and High) on TPC (i.e., grooming and proximity) towards aggressor and towards victim. Differences in TPC across all levels with aggressor was not found to be significant for grooming χ2(2, N = 18) = 1.06, p = .59, but was significantly different across all levels for proximity χ2(2, N = 18) = 6.38, p = .04. Post-hoc comparisons were done to evaluate pair-wise differences between these three levels of aggression using Mann-Whitney's test. Correction using the Bonferroni approach was done to control for Type I error. Results indicated that time spent in proximity was significantly higher when the level of aggression was moderate than when the level of aggression was high, U = 0.00, p = .01 (see Figure 2). TPC with victims was not significant for grooming χ2(2, N = 11) = 2.67, p = .

26, and was not significant for proximity χ2(2, N = 11) = 1.39, p = .50.

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Figure 2. Amount of TPC proximity between third parties and aggressors, across three levels of aggression.

Relationship Quality & Aggression on Post-conflict 16 A Mantel-R test was used to evaluate the relationship between the three types of affiliative behaviour (i.e. proximity, grooming, and instances). There were significant positive correlations between proximity and grooming (r = 0.72, p < 0.01), proximity and instances (r = 0.51, p < 0.01), and grooming and instances (r = 0.48, p < 0.01). Since these variables were correlated, we used proximity as a measure for baseline affiliation and relationship quality because there were zero values present in grooming and instances.

A Spearman’s rho correlation was used to evaluate the relationship between the reconciliation and relationship quality (M = 75.54s, SD = 43.03s), and the relationship between amount of TPC (proximity, M = 330.34s, SD = 254.37s); (grooming, M = 188.72s, SD = 202.19s) and relationship quality. The correlation between reconciliation and relationship quality was found to be statistically significant; for proximity, rs(19) = .72, p < .

01 (see Figure 3), and for grooming, rs(19) = .76, p < .01 (see Figure 4). The correlation between TPC and relationship quality between the conflicting pair was found to be negatively correlated but statistically non-significant; for proximity rs(19) = - .38, p > .01, and for grooming, rs(19) = -.31, p > .01. This indicates that amount of reconciliation and relationship quality is positively related, and that amount of TPC and relationship quality does not appear to be significantly related.

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R Sq Linear = 0.592

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Figure 3. Correlation between amount of PC proximity and relationship quality of conflict pairs.

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Figure 4. Correlation between amount of PC grooming and relationship quality of conflict pairs.

Relationship Quality & Aggression on Post-conflict 18 A Mann-Whitney U test was conducted to evaluate if amount of TPC (i.e., grooming and proximity) with an aggressor differed from the amount of TPC with a victim. The results did not indicate a significant difference in proximity with aggressor (M=381.39s, SD=231.08s) and proximity with victim (M=246.82s, SD=279.35s), U = 69.50, p > .05.

However, TPC-grooming was found to be significantly higher for aggressors (M=248.22s, SD=200.93s) than for victims (M=91.36s, SD=170.37s), U = 55.00, p < .05).

Discussion In our study, we predicted that reconciliation should occur for longer periods following moderate level aggression because high level aggression results in a high chance for re-aggression (Aureli et al., 2002), while low level aggression may be a form of reinforcing dominance status and pose little threat to relationship quality (Silk, 2002). This prediction was not supported; we did not find grooming and proximity to differ significantly across all levels of aggression. However, in dyads which reconciled, proximity was significantly higher after conflicts of high level aggression. Also, our results did not show support for high level aggression to lead to longer bouts of consolation between aggressors and third parties, and between victims and third parties; level of aggression did not seem to affect third party consolation. Previous studies have found reconciliation to be positively correlated to relationship quality (Castles & Whiten, 1998a; Das et al., 1998; Romero et al., 2008). In line with these studies, our results demonstrate that reconciliation occurred for longer periods in conflict pairs with higher rates of baseline affiliation, than those with lower rates. We did not find TPC to occur for longer periods in conflict pairs with lower baseline affiliation rates, than those with higher affiliation rates. In addition, we found that third party consolation was significantly higher for aggressors than victims; aggressors engaged in TPC more than victims.

Relationship Quality and Level of Aggression

Relationship Quality & Aggression on Post-conflict 19 Our results suggest that in hamadryas baboons, relationship quality may play a more important role than level of aggression in influencing post-conflict affiliative behaviour.

Studies have found that aggressors and victims may experience post-conflict anxiety due to damage to a valuable relationship and uncertainty on the likelihood of subsequent attack (Aureli & van Schaik, 1991; Castles & Whiten, 1998b, Das et al., 1998; Koski & Sterck, 2007; Romero, Colmenares, & Aureli, 2009; Sapolsky, 2005), and engage in post-conflict affiliation to restore the relationship and lower tension levels to restore the situation to a homeostatic level. According to Romero et al. (2009), level of aggression did not seem to affect post-conflict anxiety in hamadryas baboons. It could be possible that in despotic societies with strict hierarchical systems, such as in hamadryas baboons’ societies, factors such as dominance ranks, kinship, and social exchange may have a greater impact on postconflict affiliation.

In our study, many of the dyads in conflict were individuals of the same one-male unit (OMU). An OMU is a stable social unit in hamadryas baboons’ social system, and individuals of an OMU usually engage in social activities in proximity (Kummer, 1968); therefore proximity could be expected even after a conflict. It should be noted that although staying in proximity may not be an affiliative interaction (i.e. grooming), staying in proximity after a conflict may suggest that tolerance is restored between the dyads (Aureli et al. 2002; Cords, 1992).

Based on our observations, dominant males and their females could engage in conflicts of high-level aggression. As mentioned before, level of aggression may not play as important a role as relationship quality in the expression of post-conflict affiliation. It is possible that despite potential danger of subsequent post-conflict aggression, the high relationship quality between females and their dominant males increases the rates of reconciliation. Hamadryas baboon females tend to groom their dominant males more than

Relationship Quality & Aggression on Post-conflict 20 other females, which may suggest that hamadryas females have a higher relationship quality with their dominant males than with others females within the unit (Kummer, 1968). In our study, third-party females initiated affiliative contact with their dominant males which aggressed. This form of TPC may take place due to a high relationship quality between a dominant male and its females, and serve as a way to appease the dominant male.

Our study found that females may develop close relationships as well, such as having high baseline affiliation rates, and after low-level aggression female opponents engage in post-conflict grooming. It may be possible that females in hamadryas baboons establish close bonds for coalition support (Seyfarth, 1977). In addition, our results showed that female aggressors tend to initiate contact with their dominant males after the aggressive bout.

Hamadryas baboon males seem to have low tolerance over disruptive behaviour in the OMU, and may attack females which aggress within the OMU. Therefore, females may reconcile, or engage in TPC with the dominant male as a form of appeasement.

Social Organization and Cognition In our study, we observed that victims initiated affiliative contact with third parties.

However, we did not observe third parties initiating affiliative contact towards victims. In chimpanzees (de Waal & van Roosmalen, 1979; Koski & Sterck, 2007; Palagi et al., 2006; Wittig & Boesch, 2003), bonobos (Palagi et al, 2004), and gorillas (Cordoni et al., 2006), third parties have been shown to initiate post-conflict affiliation with victims. The ability to offer consolation may have been a result of learning and modeling during developmental stages, or as a result of social organization complexity, which positively correlates with cognitive abilities (de Waal & Aureli, 1996). Hamadryas baboons live in socially complex hierarchical systems, and may be pressurized to acquire or possess cognitive strategies such as recognizing dominance relationships, learning social norms and rules, and detecting cheaters (Cummins, 2000). Also, Judge and Mullen (2003) suggest that hamadryas baboons

Relationship Quality & Aggression on Post-conflict 21 may possess cognitive abilities required for quadratic post-conflict affiliation. Our small sample size and limited number of post-conflict data may have resulted in the lack of observations of consoling behaviour in hamadryas baboons.

Evaluation of Method The traditional PC-MC method was designed to collect a MC sample on the following day at the same time of day that the previous conflict occurred (de Waal & Yoshihara, 1983).

We did not use this method in our study in order to avoid bias due to proximity. Also, aggression outbreaks are most likely to be related to social events, and not time of day.

Therefore, we used a socially-based criterion for selecting MC sampling times to provide a better control, as both the MC and PC samples would involve times where the former opponents socially interacted.

We used one meter or less as a measure of proximity in our study. However, it may not be the most suitable measure for primates in captivity. The large population and enclosed area may increase the proximity between animals compared to living in the natural habitat.

Therefore, we suggest that for studies on captive primates, the measure for proximity be decreased to an arm’s length apart, depending on the size and type of primate observed in a study. We could also measure proximity in varying degrees; for example, as being apart at an arm’s length, one meter, and three meters. This method may be useful for studying the function of social distances between dyads and groups, and in relation to other variables of interest such as relationship quality and dominance ranks.

Conclusion Post-conflict affiliation is an important process in restoring a disrupted relationship after an aggressive bout by increasing tolerance levels and decreasing anxiety due to uncertainty. In our study on hamadryas baboons, relationship quality seems to play a more important role in post-conflict affiliation compared to level of aggression. Our results may

Relationship Quality & Aggression on Post-conflict 22 not be similar to findings in other baboon species or primate species because the function of post-conflict behaviour may vary according to the type of social system, social interaction patterns and cognitive ability. Future studies on captive primates could design study methods taking into consideration the possibility of biases and the average proximity between individuals.

References Alexander, R. D. (1974). The evolution of social behavior. Annual Review of Ecology & Systematics, 5, 325-383.

Altmann, J. (1974). Observational study of behavior: sampling methods. Behaviour, 49, 227267.

Arnold, K., & Whiten, A. (2001). Post-conflict behaviour of wild chimpanzees (Pan troglodytes schweinfurthii) in the Budongo forest, Uganda. Behaviour, 138, 649–690.

Aureli, F., Cords, M., & van Schaik, C. P. (2002). Conflict resolution following aggression in gregarious animals: a predictive framework. Animal Behaviour, 64, 325–343.

Aureli, F., & van Schaik, C. P. (1991). Post-conflict behaviour in longtailed macaques (Macaca fascicularis): II coping with the uncertainty. Ethology, 89, 101–114.

Aureli, F., van Schaik, C. P., & van Hooff, J. A. R. A. M. (1989). Functional aspects of reconciliation among captive long-tailed macaques (Macaca fascicularis). American Journal of Primatology, 19, 39–51.

Relationship Quality & Aggression on Post-conflict 23 Bernstein, I., Williams, L., & Ramsay, M. (1983). The expression of aggression in old world monkeys. International Journal of Primatology, 4, 113-125.

Castles, D. L., Aureli, F., & de Waal, F. B. M. (1996). Variation in conciliatory tendency and relationship quality across groups of pigtail macaques. Animal Behaviour, 52, 389403.

Castles, D. L., & Whiten A. (1998a). Post-conflict behaviour of wild olive baboons. I. Reconciliation, redirection and consolation. Ethology, 104, 126–147.

Castles, D. L., & Whiten, A. (1998b). Post-conflict behaviour of wild olive baboons. II. Stress and self-directed behaviour. Ethology, 104, 148–160.

Chapais, B. (2001). Primate nepotism: what is the explanatory value of kin selection?

International Journal of Primatology, 22, 203-229.

Clutton-Brock, T. H., & Parker, G. (1995). Punishment in animal societies. Nature, 373, 209– 216.

Cordoni, G., Palagi, E., & Borgognini Tarli, S. (2006). Reconciliation and consolation in captive western gorillas. International Journal of Primatology, 27, 1365–1382.

Cords, M. (1992). Post-conflict reunions and reconciliation in longtailed macaques. Animal Behaviour, 44, 57–61.

Cords, M. & Aureli, F. (2000). Reconciliation and relationship qualities. In Aureli, F., & de Waal, F. B. M. (Eds.), Natural conflict resolution (pp. 177-198). Berkeley, California: University of California Press.

Das, M. (2000). Conflict management via third parties. In Aureli, F., & de Waal, F. B. M. (Eds.), Natural conflict resolution (pp. 263-280). Berkeley, California: University of California Press.

Relationship Quality & Aggression on Post-conflict 24 Das, M., Penke, Z., & van Hooff, J. A. R. A. M. (1998). Postconflict affiliation and stressrelated behavior of long-tailed macaque aggressors. International Journal of Primatology, 19, 53-71. de Waal, F. B. M. (1986). Integration of dominance and social bonding in primates. The Quarterly Review of Biology, 61, 459–479. de Waal, F. B. M., & Aureli, F. (1996). Consolation, reconciliation, and a possible cognitive difference between macaques and chimpanzees. In Russon, A. E., Bard, K. A., & Parker S. T. (Eds.), Reaching into thought: The mind of the great apes (pp. 80-110).

UK: Cambridge University Press. de Waal, F. B. M., & van Roosmalen, A. (1979). Reconciliation and consolation among chimpanzees. Behavioral Ecology and Sociobiology, 5, 55-66. de Waal, F. B.M., & Yoshihara, D. (1983). Reconciliation and re-directed affection in rhesus monkeys. Behaviour, 85, 224–241.

Gumert, M. D. (2007a). Grooming and infant handling interchange in long-tailed macaques (Macaca fascicularis): the relationship between infant supply and grooming payment.

International Journal of Primatology, 28, 1059-1074.

Gumert, M. D. (2007b) Payment for sex in a macaque mating market. Animal Behaviour, 74, 1655-1667.

Hamilton, W. D. (1964). The genetical evolution of social behaviour. Journal of Theoretical Biology, 7, 1-16.

Henzi, S. P., & Barrett, L. (2002). Infants as commodity in a baboon market. Animal Behaviour, 63, 915-921.

Higley, J. D. (2003). Aggression. In Maestripieri, D. (Ed.), Primate psychology (pp. 17-40).

London: Harvard University Press.

Relationship Quality & Aggression on Post-conflict 25 Hinde, R. A. (1983). Primate social relationships: An integrated approach. Sunderland, Mass: Sinauer.

Janson, C. H. (1985). Aggressive competition and individual food consumption in wild brown capuchin monkeys (Cebus apella). Behavioral Ecology and Sociobiology, 18, 125-138.

Janson, C. H. (1988). Food competition in brown capuchin monkeys (Cebus apella): quantitative effects of group size and tree productivity. Behaviour, 105, 53-76.

Judge, P. G. (2003). Conflict resolution. In Maestripieri, D. (Ed.), Primate psychology (pp.

41-68). London: Harvard University Press.

Judge, P. G., & Mullen, S. H. (2005). Quadratic postconflict affiliation among bystanders in a hamadryas baboon group. Animal Behaviour, 69, 1345–1355.

Judge, P. G., Griffaton, N. S., & Fincke, A. M. (2006). Conflict management by hamadryas baboons (Papio hamadryas hamadryas) during crowding: a tension-reduction strategy. American Journal of Primatology, 68, 993-1006.

Koski, S. E., & Sterck, E. H. M. (2007). Triadic postconflict affiliation in captive chimpanzees: does consolation console? Animal Behaviour, 73, 133–142.

Koyama, N., & Palagi, E. (2006). Managing Conflict: Evidence from wild and captive primates. International Journal of Primatology, 27, 1235-1240.

Kummer, H. (1995). In quest of the sacred baboon: A scientist’s journey. New Jersey, USA: Princeton University Press.

Kummer, H. (1968). Social organization of hamadryas baboons: A field study. Chicago: University of Chicago Press.

Mitani, J., & Watts, D. (2005). Correlates of territorial boundary patrol behaviour in wild chimpanzees. Animal Behaviour, 70, 1079–1086.

Relationship Quality & Aggression on Post-conflict 26 Palagi, E., Cordoni, G., & Borgognini Tarli, S. (2006). Possible roles of consolation in captive chimpanzees (Pan troglodytes). American Journal of Physical Anthropology, 129, 105–111.

Palagi, E., Paoli, T., Borgognini Tarli, S. (2004). Reconciliation and consolation in captive bonobos (Pan paniscus). American Journal of Primatology, 62, 15–30.

Romero, T., Colmenares, F., & Aureli, F. (2008). Testing the function of reconciliation and third-party affiliation for aggressors in hamadryas baboons (Papio hamadryas hamadryas). American Journal of Primatology, 70, 1–10.

Roney, J. R., & Maestripieri, D. (2003). Social development and affiliation. In Maestripieri, D. (Ed.), Primate psychology (pp. 171-204). London: Harvard University Press.

Sapolsky, R. M. (2005). The influence of social hierarchy on primate health. Science, 308, 648-652.

Setchell, J. M., Knapp, L. A., & Wickings, E. J. (2006) Violent coalitionary attack by female mandrills against an injured alpha male. American Journal of Primatology, 68, 411418.

Seyfarth, R. M. (1977) A model of social grooming among adult female monkeys. Journal of Theoretical Biology, 65, 671-698.

Silk, J. B. (1992). The patterning of intervention among male bonnet macaques: reciprocity, revenge, and loyalty. Current Anthropology, 33, 318-325.

Silk, J. B. (1997). The function of peaceful post-conflict contacts among primates. Primates, 38, 265-279.

Silk, J. B. (2002). Kin selection in primate groups. International Journal of Primatology, 23, 849-875.

Silk, J. B. (2002). Practice random acts of aggression and senseless acts of intimidation: the logic of status contests in social groups. Evolutionary Anthropology, 11, 221–225.

Relationship Quality & Aggression on Post-conflict 27 Slater, K. Y., Schaffner, C. M., & Aureli, F. (2009). Sex differences in the social behavior of wild spider monkeys (Ateles geoffroyi yucatanensis). American Journal of Primatology, 71, 21-29.

Sterck, E. H. M., Watts, D. P., & van Schaik, C. P. (1997). The evolution of female social relationships in nonhuman primates. Behavioral Ecology and Sociobiology, 41, 291– 309.

Su, H., & Birky, W. A. (2007). Within-group female-female agonistic interactions in Taiwanese macaques (Macaca cyclopis). American Journal of Primatology, 69, 199211.

Sussman, R. W., Garber, P. A., & Cheverud, J. M. (2005). Importance of cooperation and affiliation in the evolution of primate sociality. American Journal of Primatology, 128, 84-97.

Terborgh, J., & Janson, C. H. (1986). The socioecology of primate groups. Annual Review of Ecology & Systematics, 17, 111-135.

Thierry, B. (1985). Pattern of agonistic interactions in three species of macaque (Macaca mulatta, M. fascicularis, M. tonkeana). Aggressive Behavior, 11, 223-233.

Watts, D. P. (2002). Reciprocity and interchange in the social relationships of wild male chimpanzees. Behaviour, 139, 343-370.

Wittig, R., & Boesch, C. (2003). The choice of post-conflict interactions in wild chimpanzees (Pan troglodytes). Behaviour, 140, 1527–1560.

Yamada, M. (1963). A study of blood-relationship in the natural society of the Japanese macaque—an analysis of co-feeding, grooming, and playmate relationships in MinooB-troop. Primates, 4, 43-65.