Two types of hand withdraw movement to place food in the mouth mediated by somatosensation in 22-species of strepsirrhines
The evolution of visual control of the hand to assist feeding by primates is uncertain but in anthropoid primates vision contributes not only to reaching for food and grasping it but also to the withdraw movement that brings food to the mouth. The strepsirrhines are a relatively large monophyletic group of Euarchontoglires near the base of the primate cladogram that are described as using vision to reach for food, but it is not known whether they use vision to assist the withdraw movement. The present study answere this question in 22 species of captive strepsirrhines from 6 of the seven strepsirrhine families, Daubentoniidae, Cheirogaleidae, Indriidae, Lemuridae, Lorisidae and Galagidae. Animals were videorecorded as they ate their normal food provisions. Dependent measures for analyses were ground withdraw movements, bringing grasped food to the mouth, and inhand withdraw movements, brining food held in the hand to the mouth, as well as the posture and head movements associated with each type of withdraw. Frame-by-frame scores from the video record showed that there were large differences between and within strepsirrhine families in these movements. Nevertheless, for all species, the withdraw movement was mediated by somatosensation, with mouth reaching and perioral contact with food determining how food was eventually eaten. Nonvisual behavior also contributed to food grasping as many species sniffed food before or during grasping. Even amongst species that made most use of the hand for their withdraws, the insectivores Loris lydekkerianus and Galago senegalensis, and herbivores, Hapalemur simus and Eulemur flavifrons, perioral contact was used to orient food for biting. The use of somatosensation and the absence of vision in mediating getting food in strepsirrhines suggests that visual mediation of the withdraw is an anthropoid innovation.