Substrate Diameter and Orientation in the Context of Food Type in the Gray Mouse Lemur, Microcebus murinus: Implications for the Origins of Grasping in Primates

Abstract

Grasping is a widespread behavior among tetrapod vertebrates. In primates, the hands and feet are involved in many tasks including arboreal locomotion and food acquisition. Yet, the origin and the evolution of prehensile capacities, which are highly diversified across this group, remain open for inquiry. Some researchers suggest that grasping evolved in an arboreal habitat consisting of fine branches associated with insect predation and/or fruit and flower exploitation. However, few studies have tested the importance of arboreal conditions and diet, e.g., frugivorous, omnivorous, on the use of the hands in food grasping. The aim of this study was to link substrate use and food grasping strategies quantitatively to test hypotheses concerning primate grasping origins. We studied a species often described as a good ecological model to study the origin of grasping in primates, Microcebus murinus, and quantified its spontaneous substrate use (diameter and orientation) in an unconstrained environment while presenting them with different food types (static and mobile). We show that 1) Microcebus murinus appears to be an opportunistic rather than a specialist user of fine branches as suggested previously, at least under laboratory conditions; and 2) food properties had an impact on the use of the hands vs. the mouth, with the hands being used more for the grasping of mobile prey. Our results are consistent with hypotheses for primate origins that propose adaptations to both a narrow branch environment and visually directed prey capture with the hands. However, additional studies in the wild are needed to understand better the origin and increased use of the hands in primates grasping and manipulation.