Experimental rank reversals among peers in Macaca fuscata: Rank is maintained after the removal of kin support

In many species of cercopithecines female rank is inherited matrilineally so that maternal kin occupy adjacent ranks. A female is said to have acquired her matrilineal rank in relation to a given subordinate female when the submission she receives from that female and the aggression she directs to her are both unidirectional. Kin support appears to be important in that process (rank acquisition). Matrilineally dominant females also appear to need kin support for maintaining their rank once they have acquired it. This is inferred from observations indicating that subordinates can form kin-based coalitions and outrank single dominant females. Therefore, if subordinates did not, or could not, form coalitions, the maintenance of rank among similar-sized females might be independent of kin support. One test of this hypothesis would be to remove all kin support shortly after rank acquisition has taken place. We report such a test performed in a group of captive Macaca fuscata composed of three families with similar age-sex compositions. Experimental subgroups were formed by placing together peers from different families and a single kin (ally) of one subordinate peer (mother or older sister). These experiments induced a series of rank reversals whereby the subordinate peer, whose ally was present, outranked the dominant peers. Following the rank reversals, the ally of the newly dominant peer was removed and the peers left together. All five experimentally inverted rank orders of peers remained stable. The finding that experimentally subordinate individuals abstained from challenging experimentally dominant peers despite their long ontogenetic experience of reversed dominance roles suggests (1) that matrilineal rank acquisition is a punctuate (versus ontogenetically cumulative) process, (2) that the maintenance of rank among peers does not necessitate kin support if subordinates cannot form coalitions, and (3) that the "minimal risk constraint on competition" helps account for the stability of matrilineal hierarchies.