Articles | Volume 4, issue 1
Research article
26 Jan 2017
Research article |  | 26 Jan 2017

Age-dependent change of coalitionary strategy in male Barbary macaques

Eva-Maria Rathke, Andreas Berghänel, Annie Bissonnette, Julia Ostner, and Oliver Schülke

Abstract. Inter- and intra-specific variation in the propensity to form coalitions has been explained by variation in the availability of suitable partners, distribution of fighting ability, coalition profitability, and costs of coordination. Male coalition formation can be an alternative reproductive strategy to one-on-one competition to maximize male reproductive success. Here we focus on age as a state variable to explain within-group variation in individual propensity to form coalitions against other group members. We specifically test the prediction that males conditionally switch from a solo strategy for achievement of high mating success to a cooperative strategy after reaching post-prime age in male Barbary macaques (Macaca sylvanus). We combined new observations with data collected in 2006 and 2008 on the same individuals from one captive group living in semi-natural conditions at Affenberg Salem, Germany, and found that in all years males between 5 and 13 years formed significantly fewer coalitions than males 14 years and older (post-prime). More importantly, we found those males that aged into the post-prime phase to have switched their reproductive strategy and to form significantly more coalitions in 2014 compared to 2008. These first longitudinal data together with earlier cross-sectional analyses in this and other primate species suggest that group-level measures of coalition propensity may be strongly affected by the age composition of groups and that male coalition formation can be a conditional reproductive strategy.

Short summary
Coalitions are a specific case of cooperative competition and have been explained by various factors like partner availability, distribution of fighting ability, or cost of coordination. We investigated if age is an important factor influencing coalition formation and, specifically, if males switch from a solo strategy to a cooperative one after reaching post-prime age. We found that older males formed more coalitions than younger ones, stressing the importance of age in cooperative competition.