LAMMERS, A.R.: Stability on arboreal substrates: the interaction between branch diameter and limb kinematics

Arboreal and terrestrial locomotion differ in several important ways; for example, proficient climbers must remain stable while branch diameter and incline changes. Climbing animals can increase stability on arboreal substrates by adjusting their gait, duty factor, and limb angles. Non-arboreal specialists may provide a better view of the constraints on arboreal locomotion. To this end, terrestrial Monodelphis domestica (gray short-tailed opossum) was used to assess climbing ability and limb kinematics across different branch diameters. Animals were encouraged to locomote on artificial branches of varying diameters (ranging from body diameter to one-eighth body diameter) at 0, 45, and 90 degrees (incline and decline). Two digital video cameras (recording at 120 Hz) captured the three-dimensional coordinates of the limb joints, as well as the footfall timing. Limb surface landmarks were then digitized using APAS. Preliminary results suggest that the animals use kinematically walking trots (no aerial phase) on low inclines where branch diameter approximates body diameter, and that they switch to slow, lateral sequence singlefoot walks on higher inclines. Narrower branches may limit the ability of M. domestica to use trots.