| Behavioral lateralization is the functional asymmetry caused by the asymmetry of the left and right hemispheres of the brain,which is of great significance for the adaptive survival and evolution of animals.In order to respond quickly to the environment,the right hemisphere of the brain evolved into the dominant region that controls consciousness,while the left hemisphere dominates everyday behavior that processes structured sequences of action.Both human and non-human primates show significant behavioral bias.However,unlike other primates,humans show a consistent right-handed preference for a variety of tasks,and this is true at the population level(90%).While there has been some progress in studying hand preference in non-human primates,most research has focused on only a few species.White-headed langurs are rare and endangered primates endemic to China.They all live in the environment of karst rock mountains and are semi-arboreal and semi-terrestrial.They are closely related to humans and are typical social species.In this study,we selected 27 adult monkeys from 2 groups of wild monkeys in the Banli area of Chongzuo,Guangxi,from July 2019 to August 2020.Focal sampling data were collected by camera to conduct a behavioral bias study on the spontaneous foraging and grooming behaviors of white-headed langurs.To explore the adaptation mechanism of arboreal primate white-headed langurs to the rocky mountain environment and the factors that influence the deviation of its behavior.The results are as follows:1.In the free-feeding task,all 27 individuals(adult females: 25,adult males: 2)showed hand preference at the individual level.Among them,4 individuals showed left-hand preference,9 individuals showed right-hand preference,and 14 individuals showed no preference at the population level(t=1.536,df=26,P=0.137).During grooming tasks,21 individuals(adult females: 21)showed differences in hand preference at the individual level.Among them,5 individuals showed left-hand preference,9 individuals showed right-hand preference,7 individuals showed no preference,and there was no significant preference at the population level(t=0.889,df=20,P=0.384).In the free feeding task,there were no gender differences in the direction and intensity of overhand preference at the group level(HI: U=9.500,Z=-1.436,P=0.151;ABS-HI value: U=18.500,Z=-0.602,P=0.547);There was no significant difference in the direction and intensity of hand preference between the two tasks(HI value: U=278.000,Z=-0.104,P=0.917;ABS-HI value: U=212.500,Z=-1.477,P=0.140).2.In the free feeding task,more trees were used,followed by Fujimotos,followed by shrubs,bare land and bare rock,which accounted for 43.58%,28.87%,17.25%,6.60% and4.70%.Hand preference at the individual level and not at the group level was found in the free feeding task on five kinds of supports.Trees: At the individual level,5 individuals showed left-hand preference,9 individuals showed right-hand preference,13 individuals showed no preference,and there was no significant preference at the population level(t=0.847,df=26,P=0.405).Shrubs: At the individual level,5 individuals showed left-hand preference,8 individuals showed right-hand preference,13 individuals showed no preference,and there was no significant hand preference at the population level(t=1.250,df=25,P=0.223).Fujimotos: At the individual level,3 individuals showed left-hand preference,9 individuals showed right-hand preference,9 individuals showed no preference,and there was no significant preference at the population level(t=1.565,df=20,P=0.133).Bare land: At the individual level,3 individuals showed left-hand preference,3individuals showed right-hand preference,5 individuals showed no preference,and there was no significant preference at the population level(t=-0.084,df=10,P=0.935).Bare rock:At the individual level,3 individuals showed left-hand preference,3 individuals showed right-hand preference,6 individuals showed no preference,and no obvious preference at the population level(t=0.380,df=11,P=0.711).At the population level,there was no significant correlation between the direction and intensity of hand preference and support type(HI: r=-0.016,P=0.922;ABS-HI: r=0.177,P=0.274).3.In the free feeding task,upright posture was the most used,followed by sitting posture,then prone posture and bipedal standing posture,which accounted for 55.32%,36.26%,5.94% and 2.48%.Hand preference at individual level and no hand preference at group level were found in all the four postures.At the individual level,5 individuals showed left-hand preference,10 individuals showed right-hand preference,6 individuals showed no preference,and there was no obvious preference at the group level(t=0.748,df=20,P=0.463).Sitting posture: At the individual level,6 individuals showed left-hand preference,8 individuals showed right-hand preference,12 individuals showed no preference,and there was no significant preference at the group level(t=0.099,df=25,P=0.922).Sitting posture: At the individual level,5 individuals showed left-hand preference,9 individuals showed right-hand preference,13 individuals showed no preference,and there was no significant preference at the population level(t=1.532,df=26,P=0.138).Bipedal posture: At the individual level,2 individuals showed left-handed preference,3 individuals showed right-handed preference,3 individuals showed no preference,and there was no significant preference at the population level(t=0.248,df=7,P=0.811).At the population level,there was no significant correlation between hand preference direction and hand strength and posture type(HI: r=-0129,P=0.483;ABS-HI:r=0.217,P=0.234).4.In the free feeding task,the most feeding plant parts were leaves,followed by stems,fruits and flowers,which accounted for 62.40%,19.61%,13.51% and 4.48%.There was hand preference at the individual level but no hand preference at the population level when the four plant parts were fed.Flowers: At the individual level,3 individuals showed left-handed preference,5 individuals showed right-handed preference,4 individuals showed no preference,and there was no significant preference at the population level(t=1.138,df=26,P=0.265).Leaves: At the individual level,4 individuals showed left-hand preference,9 individuals showed right-hand preference,14 individuals showed no preference,and there was no significant preference at the population level(t=1.250,df=25,P=0.223).Fruits: At the individual level,6 individuals showed left-hand preference,5individuals showed right-hand preference,10 individuals showed no preference,and there was no significant preference in the population(t=0.306,df=20,P=0.763).Stems: At the individual level,8 individuals showed left-handed preference,7 showed right-handed preference,8 showed no preference,and no significant preference at the population level(t=-0.025,df=22,P=0.981).At the population level,there was no significant correlation between the preference direction and intensity of hands and the site of feeding(HI:r=-0.248,P=0.104;ABS-HI: r=0.056,P=0.710).5.White-headed langurs in grazing and grooming task,left hand preference appears on the individual level,the right hand preference and unbiased good phenomenon,because of the white-headed langurs habitat is half to primates,as the evolution of terrestrial life style,the right hand is no longer necessary to support position,so the right hand preference,but still has the characteristic of arboreal primates left hand preference,This fits the postural origin hypothesis.In the free-feeding task,there was no significant sex difference at the population level,which was caused by the fact that the sexual dimorphism of white-headed langurs was not obvious,and the body size of adult males and females was similar,so they did not cause hand preference.In a free feeding and grooming tasks are no level of preference,while feeding and grooming tasks will also coordinate using both hands,but spontaneous feeding and grooming task is primate survival instinct of life,compared with the pipe tasks such as its low complexity,and is not easy to show the side group level behavior,conform to the task complexity theory. |
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