Bimanual Coordination and Right-Hand Bias in Extractive Foraging by Wild Sapajus libidinosus.

Abstract

Bimanual coordination is considered a crucial factor in the evolution of manual lateralization. Experimental tasks requiring the simultaneous and coordinated use of both hands induce hand preferences at the population level across various nonhuman primate species studied in captive environments. However, to date, research investigating laterality in bimanual coordination within natural settings remains scarce, especially with respect to platyrrhine taxa. We assessed hand preference in a bimanual coordinated extractive foraging task by wild bearded capuchin monkeys, Sapajus libidinosus, living in the Cerrado/Caatinga ecotone, Northeast Brazil. Nineteen individuals were filmed during the consumption of four different nut species for 4 months. A detailed video-coding analysis was conducted on their hand movements to extract the edible kernel(s) from the nuts. Overall, most individuals were lateralized, and as a group, capuchins significantly preferred their right-hand fingers for extracting the kernel, thus suggesting an advantage of the left hemisphere for fine finger movements. The comparison with captive capuchins previously tested with an experimental bimanual coordinated task (the tube task), revealed that the direction of the preference did not differ between wild and captive individuals, although the latter tended to use their preferred hand more consistently. Our findings are in line with a growing body of evidence suggesting that bimanual coordination might have played a major role in the evolution of limb preference for motor action in primates and indicate that the study of coordinated bimanual behaviors in natural settings provides a valuable contribution to the understanding of manual laterality.