How Aging Affects Grasping Behavior and Pull Strength in Captive Gray Mouse Lemurs (Microcebus murinus)

Prehension is essential for animal survival and fitness. It is involved in locomotion and feeding behavior and subject to physical and physiological constraints. Studies of prehension in primates have explored the importance of food properties and of the environment, but aging has rarely been studied although prehensile capacity may deteriorate with age in humans. To test the hypothesis that aging affects grasping abilities and to reveal possible behavioral adaptations to this, we quantified behavioral grasping strategies and pull strength in 10 young adult (2-3 yr old) and 10 aged (7-8 yr old) gray mouse lemurs (Microcebus murinus). We assessed grasping strategies in an experimental cage by quantifying grip types used to grasp static and mobile foods. We measured strength using a Kistler triaxial force platform. Our results show that 1) mobile and static foods affected individuals of different ages in similar ways; 2) older individuals used more mouth grasps than young ones; 3) aged individuals made twice as many attempts as young ones when grasping mobile food items but this difference was not significant; and 4) there were no differences in hand grip strength between age classes but young individuals showed a higher foot pull strength compared to old ones. These data suggest that the observed differences in behavior may be due to a decrease in foot grip strength, which in turn influences stability on narrow branches, forcing animals to use their hands to maintain stability and preventing them from using their hands for food-related tasks.