Linking Field and Laboratory Approaches for Studying Primate Locomotor Responses to Support Orientation

Studies of primate locomotor kinematics typically focus on data ­conducted in the laboratory setting, with cameras carefully positioned to afford clear views of the focal subjects, and strict control of a range of other variables ranging from light levels, to the travel path and even locomotor velocity of the focal subject. Such studies permit the manipulation of support types, facilitating the collection of a large number of data points relating to specific aspects of animal locomotion, and detailing how an individual responds to differences in arboreal support types. Studies of primate behavior in the field setting provide a completely different window into locomotor behavior. These approaches lend insights into the choices that animals make with regard to support use, providing information on the frequencies of different locomotor behaviors on different locomotor substrates. In this study, we explore the relationship between arboreal support type and forelimb and hind limb kinematics using locomotor data gathered in both the laboratory and natural settings. In the laboratory, we test a biomechanical model generated to explain limb kinematic response to support orientation using a large number of strides obtained from Eulemur individuals negotiating simulated arboreal supports. Next, using techniques that expand laboratory analyses into the field setting, we examine limb movements in Eulemur cinereiceps at the Manombo Special Reserve in southeastern Madagascar. Results suggest that animals tend to protract forelimbs more at touchdown on declines, and retract hind limbs more at lift-off on declines, patterns that generally maintain the line of gravity between the points of contact with oblique substrates. Focal individuals flex the elbow and knee joints more at midsupport on inclined and declined branches, bringing the center of mass closer to oblique supports. Patterns observed in the natural setting accord well with strides collected in the laboratory. This study both documents the effects of support orientation upon strepsirhine primate quadrupedal locomotion and represents the first record of limb kinematics in the natural setting for the critically endangered Eulemur cinereiceps.