LAMMERS, A.R.; Cleveland State Univ., Ohio: The biodynamics of quadrupedal locomotion on sloped arboreal substrates

Most small mammals regularly encounter heterogeneous terrain, including slopes, rocky debris, and vegetation. Thus they should be capable of moving on a variety of substrates. In this study, I examined gait and locomotor kinetics in gray short-tailed opossums (Monodelphis domestica) moving on horizontal, and 30 degree inclined and declined artificial branches (2cm diam., approximately 1/2 the diameter of the animal’s body). Animals were filmed with high speed video (120 Hz), and the branches were instrumented with force transducers so that vertical, craniocaudal, and mediolateral forces could be measured. Duty factor increased on the sloped branches in comparison to level. On the horizontal and upslope branches, the opossums utilized primarily trotting gaits, and some lateral-sequence (LS) trot-like gaits. On the downslope, however, they employed significantly more LS trot-like and singlefoot gaits. Patterns of vertical impulse between limbs were similar to those exhibited on a “terrestrial” sloped trackway: on the incline, both limbs generated equal vertical impulses. On the decline, the forelimbs generated about 2X the vertical impulse of the hindlimbs. Braking impulse was similar in magnitude between incline and level. On the decline, braking impulse was greater in both limb pairs (in comparison to the level), and especially greater in the forelimb. Propulsive impulse was negligible on the decline, but considerably greater on the incline (and equal between fore- and hindlimbs). Mediolateral impulses were equal between limbs and inclined & declined arboreal trackways, but greater than on the level. I conclude that 30 degree arboreal substrates may present some challenges to stability (as indicated by mediolateral impulse). There are few differences in body weight support and propulsive effort between “terrestrial” and “arboreal” sloped trackways.