Abstract
Whether and how primates are able to maintain long-term affiliative relationships is still under debate. Emotional bookkeeping (EB), the partner-specific accumulation of emotional responses to earlier interactions, is a candidate mechanism that does not require high cognitive abilities. EB is difficult to study in real animals, due to the complexity of primate social life. Therefore, we developed an agent-based model based on macaque behavior, the EMO-model, that implements arousal and two emotional dimensions, anxiety-FEAR and satisfaction-LIKE, which regulate social behavior. To implement EB, model individuals assign dynamic LIKE attitudes towards their group members, integrating partner-specific emotional responses to earlier received grooming episodes. Two key parameters in the model were varied to explore their effects on long-term affiliative relationships: (1) the timeframe over which earlier affiliation is accumulated into the LIKE attitudes; and (2) the degree of partner selectivity. EB over short and long timeframes gave rise to low variation in LIKE attitudes, and grooming partner preferences were only maintained over one to two months. Only EB over intermediate-term timeframes resulted in enough variation in LIKE attitudes, which, in combination with high partner selectivity, enables individuals to differentiate between regular and incidental grooming partners. These specific settings resulted in a strong feedback between differentiated LIKE attitudes and the distribution of grooming, giving rise to strongly reciprocated partner preferences that could be maintained for longer periods, occasionally up to one or two years. Moreover, at these settings the individual’s internal, socio-emotional memory of earlier affiliative episodes (LIKE attitudes) corresponded best to observable behavior (grooming partner preferences). In sum, our model suggests that intermediate-term LIKE dynamics and high partner selectivity seem most plausible for primates relying on emotional bookkeeping to maintain their social bonds.
Highlights
Group-living animals have varied social relationships with their group members
In this paper we present the results of different settings of the EMO-model, in which individuals dynamically update their LIKE attitudes according to earlier received affiliation by specific group members and subsequently use these LIKE attitudes to choose affiliation partners
General patterns of LIKE attitudes and grooming Distribution of LIKE attitudes First, we are interested in how the pattern of developed LIKE attitudes within the group depended on the different settings in our model, i.e., the half-life of the LIKE attitudes (LHW: the LIKE-HISTORY WEIGHT explained in Fig. 1) and the selectivity of individuals when choosing affiliation partners (LPS)
Summary
Group-living animals have varied social relationships with their group members. In primates, this variation has been extensively investigated and different types of relationshipsHow to cite this article Evers et al (2016), Intermediate-term emotional bookkeeping is necessary for long-term reciprocal grooming partner preferences in an agent-based model of macaque groups. Group-living animals have varied social relationships with their group members. In primates, this variation has been extensively investigated and different types of relationships. Non-kin friendly relationships can vary as well in their quality based on high or low rates of proximity and grooming (Silk, 2002; Massen, Sterck & De Vos, 2010; Massen & Sterck, 2013). Social relationships provide a substrate for evolution, as strong bonds with kin and non-kin partners may provide fitness benefits (baboons (Silk, Alberts & Altmann, 2003; Silk et al, 2009; Silk et al, 2010a), feral horses (Cameron, Setsaas & Linklater, 2009), bottlenose dolphins (Frère et al, 2010) and rhesus macaques (Kulik et al, 2012; Massen et al, 2012)). The nature and number of relationships are important features of group living animals
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