Interchange between grooming and infant handling in female Tibetan macaques(Macaca thibetana)

In some non-human primates, infants function as a social tool that can bridge relationships among group members. Infants are a desired commodity for group members, and mothers control access to them. The biological market theory suggests that grooming is widespread and represents a commodity that can be exchanged for infant handling. As a limited resource, however, the extent to which infants are interchanged between mothers(females with an infant) and non-mothers(potential handlers,females without an infant) remains unclear. In this study, we collected behavioral data to investigate the relationship between grooming and infant handling in free-ranging Tibetan macaques(Macaca thibetana)at Mt. Huangshan, China. Our results showed that females with infants received more grooming than females without infants. After her infant was handled,mother females received more grooming than they did during daily grooming interactions. However, with the increasing number of infants within the social group, both the grooming that mothers received and the grooming that non-mothers invested for handling infants decreased. We also found that non-mothers invested more time in grooming to gain access to younger infants than older infants. Our results provide evidence that infants are social commodities for both mother and non-mother females. Mothers use infants for obtain grooming and non-mothers use grooming to gain access to infants. The current study implies a bidirectional and complex interchange pattern between grooming and infant handling to compensate for the dyadic grooming disparity in non-human primates.

Infant attraction:why social bridging matters for female leadership in Tibetan macaques

Leadership is a key issue in the study of collective behavior in social animals.Affiliation-leadership models predict that dyadic partner preferences based on grooming relationships or allianee formation positively affect an in dividua I's decision to follow or support a con spec ific.In the case of many primate species,females without young infants are attracted to mother-infant dyads.However,the effects of mother-infant-female associations on affiliation-leadership models remain less clear.In free-rangi ng Tibeta n macaques Macaca thibetana,we used social network analysis to examine the importance of mother-inf a nt-adult female"social bridging eve nts as a predictor of who leads and who follows during group movement.Social bridging is a common behavior in Tibetan macaques and occurs whe n 2 adults,gen erally females,engage in coordinated in fa nt handling.Using eigenvector centrality coefficients of social bridging as a measure of social affiliation,we found that among lactating females,initiating bridging behavior with another female played a sign讦icant role in leadership success,with the assisting female following the mother during group movement.Among non lactati ng females,this was not the case.Our results in dicate that in fa nt attracti on can be a strong trigger in collective action and directing group movement in Tibetan macaques and provides benefits to mothers who require helpers and social support in order to ensure the safety of their infants.Our study provides new insights into the importance of the third-party effect in rethinking affiliation-leadership models in group-living animals.

Coordination and consensus:the role of compromisers in Tibetan macaques

Coordination and consensus in collective behavior have attracted a lot of research interest.Although previous studies have investigated the role of compromisers in group consensus,they provide little insight into why compromisers would allow such social arrangements to persist.In this study,the potential relationship between group movements and conflict management in Tibetan macaques in Anhui province,China,was investigated using hierarchical cluster analyses.Some members with higher social centrality or social rank often formed a front-runner cluster during group movements.They had higher leadership success than individuals outside the frontrunner cluster.Other members with lower social centrality or social rank often followed the group movements initiated by the front-runner cluster,and thus formed the compromiser cluster.Compromisers'proximity relations with front-runners increased with their following scores to front-runners.Compromisers had fewer events of being attacked when they followed group movements initiated by the front-runners.The compromising process made compromisers lose the choice of direction preference,but it could increase their individual safeties.This trade-off suggests that compromisers play a role of decision-maker in coordination and consensus scenarios among social animals.