Posturally related variations in the hand preferences of the ruffed lemur (Varecia variegata variegata)

The hand preferences of 5 semi-free-ranging black-and-white ruffed lemurs were assessed by using three distinct testing procedures. Testing conditions varied in the extent to which they required animals to make a whole body postural adjustment prior to making a reach. Minimal bodily adjustment was necessary for free foraging, whereas discrete food presentations on land (DFP-land) and in a moat (DFP-moat) promoted a gross reorientation of the animal's entire body. In the DFP-moat condition 4 animals exhibited exclusive use of the left hand, and only 1 of 515 reaches was made with the right hand. Similarly, all 5 animals showed a pronounced left hand preference in the DFP-land condition. The free-foraging condition revealed a hand preference for only 1 of the 5 subjects, and that preference was weak in comparison with those measured in the other two test conditions. These findings indicate that whole body postural adjustments critically influenced the expression of hand preference and should be taken into consideration in future studies of primate hand preferences.