Aggression within a social group may affect
bystanders' affinitive behaviour with other
bystanders. After a conflict such affiliations,
termed 'quadratic', may serve to reduce tension.
This particular kind of conflict management has
been found in hamadryas baboons. Following the
classical and well-established approach for
studying post-conflict behaviour
[post-conflict/matched control method
(PC/MC)], we collected behavioural data on a
group of geladas (Theropithecus gelada) in order
to check for the presence of quadratic
affiliations. A total of 192 PC/MC pairs were
collected on both adults and immature
individuals. We did not find any increase of
affiliation levels between bystanders during PC
compared with MC condition. The distribution of
affinitive quadratic interactions was not
affected by either kinship or relationship
quality of bystanders. Moreover, comparison of
yawning and self-scratching behaviours (two of
the typical non-primate displacement activities
under stressful situations) recorded during PCs
and MCs did not show any variation in the two
conditions. Probably, due to the male tolerance
and social cohesiveness in geladas, witnessing a
fight does not necessarily induce a sufficient
increase of tension in bystanders to be reduced
by quadratic affiliation.
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Introduction
Social animals possess behavioural tools to
settle conflicts and offset the costs of
competition within a group (Aureli et al. 2002).
Specifically, to cope with the conflict
aftermath and social damage caused by
aggressions, groupliving species use a variety
of peace-keeping tactics (Aureli et al. 2002;
Silk 2007). Such peaceful mechanisms include
reconciliation (post-conflict reunion of former
opponents) and triadic contacts (affinitive
patterns directed by bystanders towards one of
the former opponents and vice versa) (de Waal
and van Roosmalen 1979; Palagi et al. 2004,
2006, 2008a, b; Cordoni et al. 2006; Koski and
Sterck 2007, Palagi and Cordoni 2009; Leone and
Palagi 2010). However, a further post-conflict
mechanism has been ascertained in non-human
primates. Bystanders can increase their
affiliation levels after witnessing an
aggressive act between other group members,
especially kin (chimpanzees, de Waal 1982;
vervet monkeys, Cheney and Seyfarth 1989;
hamadryas baboons, Judge and Mullen 2005). Such
'quadratic' post-conflict affiliation might
reduce social tension generated by the previous
aggression.
Here, we aimed to verify the occurrence of
quadratic post-conflict affiliation in geladas
(Theropithecus gelada). Geladas live in
multi-level societies in which the basic level
consists of one-male units (OMU5) (Kawai 1979;
Mori 1979; Kawai et al. 1983; Dunbar 1984). The
species is characterized by male dispersal and
female philopatry, with social relationships
which centre primarily round the females (Dunbar
and Dunbar 1975; Mancini and Palagi 2009). Most
of the male's friendly interactions are with
adult females, even though the adult male shows
a preference for a few of them (Dunbar 1983).
Different from hamadryas baboons, which maintain
group integrity by aggressive herding by the
males, the social cohesion of the gelada unit is
the result of strong bonds among companions
(Bramblett 1970). The relationships are
determined primarily by the use of protected
threats and coalitions (Leone and Palagi 2010),
and there is a preference for social partners,
also among the females (Mon et al. 2003; Palagi
et al. 2009). In geladas, reconciliation has
recently been found and quantified (Leone and
Palagi 2010). Moreover, Leone and Palagi (2010)
found that valuable relationships were
predictive of high levels of conciliatory
contacts. In this view, geladas are a good model
species to examine all possible mechanisms at
the basis of natural conflict resolution.
Therefore, we focussed our attention on
quadratic post-conflict affiliation and on some
potential factors (kinship and relationship
quality) that could affect this kind of conflict
management.
Discussion
Intra-group aggression may have consequences
for the relationship not only between opponents
but also between bystanders (de Waal 1982). For
example, several studies indicated that the
relatives of two animals involved in a fight
were generally more likely to affiliate in the
minutes following the aggression (Cheney and
Seyfarth 1989; Judge and Mullen 2005). After
witnessing a fight, both adult and immature
geladas did not search for affinitive contact
with other group members. Moreover,
post-conflict affiliation was not positively
affected by either kinship or friendship of the
two bystanders.
In primates, self-directed behaviours (SDB)
or displacement activities are good indicators
of anxiety (Maestripieri et al. 1992; Kutsukake
and Castles 2001). In geladas, bystanders'
displacement activities were not significantly
higher during post-conflict intervals (PCs)
compared with baseline intervals (MCs) (Fig. 3).
Apparently, witnessing aggression did not seem
to increase tension or anxiety in the observer.
This could explain why bystanders did not
approach and affiliate each other in
post-conflict (PCs) more than in control
condition (MCs). L Probably, most of the
intra-group aggressions did not L have an
aftermath at group level since conflict
escalation is rare (Leone and Palagi 2010).
However, it seems that some animals adopt an
alternative tactic. Those subjects sharing weak
relationships tended to keep away from each
other (dispersed pairs were more frequent than
attracted pairs) after witnessing a fight. Even
though the result has to be taken with caution
(due to the possibility
of a type I error), this finding seems to
suggest that quadratic affiliation implied a
certain amount of risk for the interactants,
which resulted in a conflict-avoidance strategy.
In hamadryas baboons, quadratic affiliation
mechanism was present and occurred mainly
between preferred nonkin partners rather than
kin. The analysis of SDB in this species
revealed that the presence of intra-group
aggression caused a stressful emotional state in
the observers (Judge and Mullen 2005). Why are
there so strikingly different results in two
species (Theropithecus gelada and Papio
hamadryas) showing similar social structures
(one-male unit)?
Judge and Mullen (2005) interpreted their
findings in the light of male despotic presence
(Kummer 1968; Gore 1994). In fact, the male
leader was perceived as a powerful threat by
group members even though he was not directly
involved in the previous conflict. Romero and
Castellanos (2010) underlined the importance of
hamadryas male agonistic ability (expressed in
dominance indexes) in the process of female
acquisition and group control. In this view,
after a fight, hamadryas bystanders were
probably highly motivated to reduce arousal and
social tension. To reduce post-conflict stress,
hamadryas engaged in affiliation with non-kin
partners. The authors emphasized the
tension-reduction function of quadratic
affinitive interactions; if overall tension was
successfully reduced in the group, then the
response might have some generalized influence
on aggressive potential (Judge and Mullen
2005).
Notwithstanding the similarity with
hamadryas social organization, geladas show some
peculiarities in the nature of their social
dynamics. In contrast to 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 that characterizes the
species (Leone and Palagi 2010). The
relationships within the typical gelada one-male
unit revolve around females (Palagi et al.
2009), who form the core of the cohesion and
stability typical of OMUs. Different from
hamadryas, the strength of gelada female bonds
suffices to maintain OMU integrity despite the
absence of the male (Dunbar and Dunbar 1975;
Moth et al. 2003). In this view, the female
social network characteristic of this species
weakens the power of the male, thus contributing
to a less despotic social environment. Probably,
this more relaxed social setting contributes to
limit post-conflict anxiety experienced by
bystanders.
