Juveniles Outrank Higher-Born Females in Groups of Long-Tailed Macaques with Minimal Kinship

Abstract

In a typical matrilineal or nepotistic hierarchy a mother's rank sets both her daughter's lowest rank (above lower-born females), and her daughter's highest rank (below the mother and higher-born females). Long-tailed macaques (Macaca fascicularis) form typical matrilineal dominance orders. We report a variant of this system that we observed in 4 groups of captive long-tailed macaques characterized by an unusual kinship structure. Each group was composed of the smallest possible matrilineages (mother-offspring pairs), the mothers being unrelated to each other. In each group, juveniles ranked above all the females subordinate to their mother, as this is the case in a typical matrilineal hierarchy, but a majority of juveniles of both sexes outranked their own mothers and/or several higher-born females and their offspring. Adult females resisted the juveniles and were ≥2.5 times heavier than the latter. The patterning of interventions in conflicts suggests that this unusual ranking pattern resulted from the existence of bridging alliances between the juveniles and individuals ranking above the juveniles' targets. The results indicate that the sole presence of the mother is sufficient for a daughter to outrank the females subordinate to her mother, but it is not sufficient to prevent the daughter from ascending the rank order. Our data suggest that in the absence of extensive alliances among kin, which normally stabilize the rank order, juveniles were able to benefit from infrequent, opportunistic interventions by high-ranking nonkin individuals.