| Infancy was the first stage of behavioral development after birth,and it was also an important period of infant from dependence to independence.During this period,infant behaviors had a development process from nonexistence to existence,from simpleness to complexity,from strength to skill.What’s more,infants learned the skills of predation and survival through observation,imitation,learning,trainning and social cognition.As the earliest social relationship after infant birth,mother-infant relationships played an important role in infant survival,behavioral development,social networks and later reproductive success.With the growth of age and enhancement of activity ability,infants began to break away from the restriction and protection of their mothers,then integrated into the social relationships.This process could help infants establish a stable and suitable social environment with other individuals,and laid the foundation for future survival and reproduction.In order to understand the behavioral development,main social relationships and the evolution of social cognitive gene in infant Taihangshan macaques,from June 2016 to January 2020,we conducted the study in Wulongkou area of the Taihangshan Macaque National Nature Reserve.In this study,Troop WLK-1A was the target group,we used the tracking observation,molecular biology and bioinformatics to carry out the research.Our findings were summarized below:1.Behavioral development of 0-2 years old macaquesFrom March 2018 to January 2020,we observed and recorded all the behaviors of infants aged 0-2 years.The results showed that:1)Infant macaques showed 15 behaviors from birth to 2 years old,which were resting,suckling,looking around,trying to leave,help calling,solitary play,following,social play,locomotion,feeding,submission,self-grooming,social grooming,climbing and aggression.2)The developmental process of infant behaviors could be divided into five stages,which were dependence period,exploration period,integrating period,adaptive stage and gradual independence period.3)The percentage of suckling behavior(Pearson r=0.88,P<0.001)and resting behavior(Pearson r=-0.73,P=0.01)were significant negative correlated with infant age.4)The percentage of feeding behavior(Pearson r=0.84,P=0.001)and self-grooming behavior(Pearson r=0.77,P=0.005)were significant positive correlated with infant age.5)There was no significant correlation between the percentage of following-locomotion and infant age(Pearson r=0.09,P=0.79),the same as playing behavior(Pearson r=0.25,P=0.45).2.Mother-infant relationships in Taihangshan macaquesFrom March 2018 to January 2020,the newborns and their mothers were followed and observed.The results showed that:1)The mother-infant behaviors included lactation,cradling,ventral carrying,dorsal carrying,examination,grooming,restriction,rejection and leaving.2)At population level,there was a significant right-hand maternal cradling preference(Z=-2.72,P=0.007,N=54),but the strength was not correlated with infant age(Pearson r=0.44,P=0.38).3)Mothers’ restriction behavior began at 1 weeks old and continued to 5 months old,with the highest frequency and duration at 3 months old.4)There was a significant negative correlation between the frequency of ventral carrying and infant age(Pearson r=-0.87,P=0.001),while there was no significant correlation between the frequency of dorsal carrying and infant age(Pearson r=-0.44,P=0.21).5)The frequency of mother-infant grooming showed significant difference between months,and exhibited an increase-reduce-increase trend with infant age(F=3.08,P<0.01).6)The frequency of infant-mother grooming showed significant difference between months,and exhibited a single peak pattern with infant age(F=1.96,P<0.01).3.Neonatal nipple preference in Taihangshan macaquesFrom March to September 2018,we observed and recorded the nipple contact behavior of infant macaques.The results showed that:1)Seven of nine neonates exhibited a significant left-side nipple preference during the first 12 weeks of life,whereas two of nine neonates displayed a significant right-side nipple preference.2)At population level,infant macaques showed significant left nipple preference(Z=-4.05,P<0.001,N=54),but there was no significant correlation between the strength and infant age(Pearson r=0.42,P=0.41).3)There was no significant correlation between neonatal nipple preference and infant sexes(U=9,N1=5,N2=4,P=0.99),the same as the strength(U=9,N1=5,N2=4,P=0.91).4)At population level,there was no significant correlation between neonatal nipple preference and maternal cradling bias(LBI scores:Pearson r=0.632,P=0.068;Direction:r=0.189,P=0.626),but there was a non-significant correlation between the strength of neonatal nipple preference and maternal cradling laterality(Pearson r=-0.379,P=0.314).4.Allomaternal care in Taihangshan macaquesFrom March 2018 to January 2020,the social activities of non-mothers and infants were observed and recorded using all-occurrence recording methods.The results showed that:1)Allomaternal care of Taihangshan macaques included inspection,holding,grooming and grabbing infant.2)There were significant differences at allomaternal care behaviors among infants of different ages(F=2.70,P=0.006),while there was a significant positive correlation between the allomaternal care initiate by infants and infant age(Pearson r=0.80,P=0.009).3)The allomaternal care frequency initiated by non-related individuals significantly higher than that initiated by related individuals(U=51.50,P=0.004).4)The allomaternal care frequency of nonparous was significantly higher than that of multiparous(U=53.50,P=0.005).5)The infant survival rate of caregivers was significantly higher than non-caregivers(Z=1.45,P=0.02,N=7).5.Male-infant relationships in Taihangshan macaquesFrom March 2018 to January 2020,we studied the social relationships between adult males and infant macaques.The results showed that:1)Adult males showed three kinds of allomaternal behaviors,which were cradling,tolerance and grooming.2)The frequency of male-infant caring were significant differences among different maleinfant pairs(t=6.01,df=10,P<0.01).3)There were 15 microsatellite loci selected for the parental identification,and of which 13 loci showed high polymorphism(the average PIC was 0.74).4)The total exclusion rate of cumulative non-parentage was 99.99%when seven microsatellite loci were used for paternity identification,while nine loci were 99.999%.5)The results of maternal identification using 15 microsatellite loci were consistent with the results of reproductive records observed in the field,which verified the validity of these microsatellite loci.6)The three pairs with the highest male-infant caring frequency had a clear father-infant relationship.6.Fecal cortisol and IgA levels in adult Taihangshan macaquesFrom June 2016 to March 2017,the stress hormone levels and immune levels of adults in the WLK-1A group were studied by non-invasive sampling method.The results showed that:1)There was no significant difference in fecal cortisol concentration between adult females and adult males(mating period:U=228,P=0.10;Non-mating period:U=138,P=0.09).2)In mating period,the fecal cortisol concentration of adult females and males were significantly higher than that in nonmating period(adult female:U=125,P<0.01;Adult male:U=28,P<0.01).3)In mating period,the fecal IgA concentration of adult females was significantly higher than that in non-mating period(U=73,P<0.01),while there was no significant difference in fecal IgA concentration of adult males between mating and non-mating period(U=138,P=0.14).4)There was a significant negative correlation between fecal cortisol level and IgA level during mating period(adult female:Pearson r=-0.44,df=33,P=0.01;Adult male:Pearson r=-0.57,df=19,P=0.01),while there was no significant correlation between fecal cortisol level and IgA level during non-mating period(adult females:Pearson r=0.13,df=20,P=0.60;Adult males:Pearson r=0.08,df=20,P=0.74).7.The phylogenetic evolution of DRD4 and OXTR genes in primatesBased on the sequencing results of DRD4 and OXTR genes in infant Taihangshan macaques,and the download sequences of primates,we analyzed the phylogenetic evolution of primates.The results showed that:1)The DRD4 gene of Taihangshan macaques was clustered into a branch with that of other Macaca species;2)The OXTR gene of Taihangshan macaques was clustered into a branch with that of other Macaca species,but the OXTR gene of Taihangshan macaques had the longest branch length in the phylogenetic tree,and the OXTR gene sequence of Taihangshan macaques was significantly different from that of other species.Conclusions:1)There were fifteen behaviors in the developmental process of infant Taihangshan macaques at the age of 0-2 years.The developmental process of infant behaviors could be divided into five stages,which were dependence period,exploration period,integrating period,adaptive stage and gradual independence period.The percentages of suckling behavior and resting behavior were negative correlated with infant age,while the percentages of feeding behavior and self-grooming behavior were positive correlated with infant age.2)In Taihangshan macaques,mothers’ restriction and ventral carrying behaviors were significantly negative related to infant age,and the maternal cradling behavior showed a significant right-hand preference.3)Infant Taihangshan macaques showed significant left nipple preference,and this preference was not correlated with infant sexes,age,and maternal cradling behavior.Moreover,the left-side nipple preference supported the maternal heartbeat hypothesis.4)There was allomaternal care behavior in Taihangshan macaques.The caregivers included non-related individuals and related individuals,who gained experience through allomaternal care behaviors,and improved the survival rate of offsprings.Allomaternal care in Taihangshan macaques supported the learning to mother hypothesis.5)There was male-infant caring behavior in Taihangshan macaques,and the relationship between adult males and infants was acceptance.Adult males might recognize their own offspring by increasing the frequency of paternal caring.6)The mating-related stress could increase the concentration of fecal cortisol of adult Taihangshan macaques,and that the stress-linked immunosuppression hypothesis was supported in mating period.7)The evolutionary results of DRD4 and OXTR were consistent with the results of species differentiation,but the OXTR gene of Taihangshan macaques was significantly different from that of other Macaca species,which may be subjected to the greater selection pressure in Taihangshan mcacaques than other species. |
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