Hand preferences in captive non-human primates are associated with generation and stress level

Abstract

Hand-use preferences of non-human primates are affected by various factors, such as posture and task difficulty. Additionally, the degree of lateralization may be a useful indicator for evaluating the welfare of non-human primates, but more empirical studies are needed to explore the relationship between lateralization and stress levels. In this study, we compared the handedness of four groups of Callitrichids at Nanjing Hongshan Forest Zoo during two tasks, simple reaching and reaching into a feeder, as well as the handedness of subjects that repeated the simple reaching task at a one-year interval. The subjects did not display different levels of hand preference (including direction and strength of hand preference) across four groups in the two different tasks, and 26 marmosets showed a stronger hand preference (absolute handedness index [ABS-HI]) in the repeated simple reaching task one year later. Individual factors such as sex and generation significantly impacted individual hand preference; in particular, the strength of hand preference in all three tests differed significantly across generations. The results revealed that individuals with high ABS-HI have higher levels of fecal cortisol in golden-handed tamarins (Saguinus midas), implying an association between handedness and physiological stress, which suggested the potential of using handedness as an indicator for assessing physiological stress in captive non-human primates in the future, thus contributing to enhancing animal welfare.