RIGHT OR LEFT, HAND OR MOUTH: GENERA-SPECIFIC PREFERENCES IN MARMOSETS AND TAMARINS

Hand use was compared in 45 individuals of three genera of the Callitrichinae (Callithrix, Saguinus, Leontopithecus) which differ concerning their postural and manipulative behaviour. The Postural Origins theory of MacNeilage et al. (1987) predicts left-hand preference for visually guided reaching, especially when performed from a vertical clinging posture (as mainly seen in Callithrix) and right-hand preference for manipulative acts (as shown by Leontopithecus). Five tasks were carried out, differing in sensory modality (visual/tactile), postural requirements (vertical/quadrupedal) and task demands (accessibility to food-items). Data on successful left and right-hand reaching and mouth pick-ups were collected using all occurrences sampling. Statistical analysis comprised calculation of binominal z-score, application of unbalanced repeated measures models with structured covariance matrices and analysis of covariance. All individuals displayed hand preferences not influenced by task design. The genera differed in the hand preferred: Leontopithecus showed a greater proportion of right-hand preferences, whereas Callithrix tended to prefer the left hand. Saguinus was intermediate between these two genera. The results point out that genus-specific foraging strategies determine population-level hand preferences rather than task-specific demands. The differences in foraging strategy and hand preference among the three genera correspond to the Postural Origins theory (MacNeilage et al., 1987). When feeding on freely accessible, non-mobile food items, most individuals showed a clear preference in picking-up with the mouth or with one hand. Callithrix took objects predominantly with the mouth, Leontopithecus preferred the hand and Saguinus favoured neither mouth nor hand. Mouth-hand preferences can also be linked to genera differences on hand function in foraging behaviour.