Social Relationships Among Captive Male Golden Snub-nosed Monkeys (Rhinopithecus Roxellana)

In non-human primates,the all-male group is composed of immature individuals and adults who have no reproductive opportunities,which can be found in matrilineal polygynous or multimale-multifemale societies.Golden snub-nosed monkeys(Rhinopithecus roxellana)live in male-dispersing multi-level societies and the all-male band is an incompact social organization with low stability in which individuals emigrate or immigrate with groupmates frequently.In decades,there are lots of breakthroughs in studies on breeding bands and only a few studies have been focused on relationships between breeding band and all-male band in the wild troop.However,we know little about the dynamics of social relationship in the all-male band.In this study,I conducted behavioral observation on male sociality in a captive group of golden snub-nosed monkeys in Shanghai Wild Animal Park,China,which was composed of a one-male unit(OMU,n=7)and an all-male unit(AMU,n=7 or8).Using data collected for eight months,during which there was a demographic change in the AMU and this social upheaval led to distinct changes in males'sociality.To explore the characteristics of sociality among males and social stabilization mechanism of the AMU,I described the dominance hierarchy and potential relationships with two main non-aggressive behaviors,same-sex mounting and grooming,in which grooming was considered as an affiliative behavior.I also reported the changes in sociality resulted by the social upheaval.The main findings are below.1.I assessed the dyadic dominance relationships in the AMU based on displacements,which were extracted by behavioral sampling from the whole feeding processes.I found that the frequency of dominance reversals against the rank hierarchies per month was only 2.35±SD 0.94%and the modified Landau's linearity indices h'were 1.00±SD 0.00 pre-upheaval and 0.95±SD 0.05 post-upheaval,respectively.The results revealed that distinctly linear dominance relationships existed among individuals in the AMU.However,after the demographic change,there was a series of rank fluctuations among mature males.The ordinal ranks of three juveniles remained subordinately stable,while the rank of the other juvenile went up distinctively with his NDS values increased.2.By means of focal animal sampling and all-occurrence recording,I recorded the grooming bouts conducted by AMU individuals.The results revealed that grooming took up 4.03±SD 0.95%of individual daily activity.There were 178(38.20%of 466)reciprocated and 288(61.80%of 466)unreciprocated grooming bouts collected.Within a grooming bout where the subordinate initiated,the frequency of reciprocated bouts was significantly less than that of the unreciprocated bouts(Binomial test:P<0.001).That is to say,when the initiator was the lower-ranking one,it was less likely to receive grooming return than vice versa.The reciprocity index of the reciprocated grooming bouts was 0.07±SD 0.43 and the duration of time that partners groomed each other tended to be positively correlated(r_s=0.42,P<0.001).Within a reciprocated grooming dyad,whether the lower-ranking one invested more grooming than the higher-ranking one depended on the relative rank of the initiator.The result showed that only when it was the lower-ranking one who initiated a grooming bout,the initiator gave more grooming to the recipient than vice versa(Binomial test:P<0.01).However,when the reciprocated grooming was directed by higher-to lower-ranking individuals,higher-ranking ones groomed lower-ranking ones at a longer non-significant duration.3.Behavioral observations by methods of behavior sampling and all-occurrence recording were conducted with a total of 1,855 mounts recorded during the study period.In support to the dominance assertion hypothesis,I found that during the entire study period,whether the higher-ranking male was more likely to be the mounter than the lower-ranking one could be influenced by the ages of participants(Pre-upheaval:GLMM,Estimates?SE=9.57?2.28,Z=4.20,P<0.001;post-upheaval:Chi-squared test,?~2=572.58,P<0.001).Through post-hoc analysis,I found that except the mounts that happened among juveniles in non-aggressive social contexts,the higher-ranking male was more likely to be the mounter than the lower-ranking one.The results indicated that same-sex mount was quite a vital and practical method for members to express their social status.Dominant ones expressed their dominance through mounting others and subordinate ones expressed their subordination through being mounted to defuse agonistic behaviors from dominants.However,I suggested that same-sex mounts might have other different functions among juveniles and be multifunctional in a species.4.I also recorded the nearest neighbors and all high-intensity contact aggression by scan sampling and behavior sampling on all individuals of the targeted group,aiming to compare the potential social changes in both intra-and inter-unit interactions before and after the social upheaval.Except the dramatic change in social ranks,I also found elevated aggression in the AMU following this demographic change(Mann-Whitney U test,Z=-4.92,P<0.001).Social network analysis revealed that members did not associate randomly any more but formed differentiated relationships post-upheaval based on proximity data,resulting in three distinct sub-units in the AMU.In terms of inter-unit interactions,significant changes were found in the affiliations between the male juvenile of OMU and AMU individuals.He interacted with AMU individuals randomly and frequently pre-upheaval,but cut down his affiliations(Mann-Whitney U Test:Z=-5.95,P<0.001)and preferred a partner post-upheaval,121,who was a member of the dominant male's sub-unit,971-117-121.These findings suggested that social networks in the dispersing sex were dynamic structures and could vary with some demographic changes in the studied species.I also put forward the possible criterion(dominance)of the male juvenile when he chose a partner before immigrating into the AMU.In conclusion,the distinctly linear dominance hierarchy,high tolerance of the higher-ranking individuals towards the lowering-ranking ones in grooming,and low-intensity aggressive same-sex mounts for dominance assertion,all these behaviors contribute to the development of males'sociality and social stability in the AMU of golden snub-nosed monkeys.Even though the social relationships could be influenced by demographic changes,the high level of behavioral flexibility enables individuals to make strategic decisions and adjust themselves to the socioecological variations.