Meeting Abstract

17.6  Jan. 4  Small-bodied primates adapt asymmetrical gait dynamics to locomotion on arboreal substrates YOUNG, JW; Stony Brook University jwyoung@ic.sunysb.edu

Whereas the dynamics of symmetrical gaits (i.e., walking and running) in primates have been well researched, their use of asymmetrical gaits (i.e., galloping and bounding) remains understudied. Asymmetrical gaits are usually associated with greater peak vertical forces, potentially causing branch sway when traveling arboreally and therefore compromising stability. I predicted that primates would attempt to mitigate peak vertical forces during arboreal locomotion by reducing the vertical displacement of the center of mass, increasing stride length, decreasing stride frequency and using gaits that permit the limbs to remain on the substrate for a longer period of time (i.e., gallops and half-bounds rather than bounds). Two juvenile (mean body mass=180g) and two adult (mean body mass=330g) marmosets (Callithrix jacchus) were filmed traversing a 3m runway (T) or elevated pole (A) into which two force transducers were incorporated. A total of 76 complete strides over the force transducers were selected for analysis. As predicted, peak vertical forces (scaled to body weight) were significantly lower during arboreal trials, even when controlling for speed (T: 2.4bw; A: 2.0bw). Decreases in peak forces were accomplished through decreased vertical displacements of the center of mass (T: 1.7cm; A: 0.9cm) and a greater use of half-bounds and gallops (T: 53% of strides; A: 93% of strides). Contradicting my predictions, stride length decreased (T: 0.39m; A: 0.31m) and stride frequency increased (T: 4.3Hz; A: 4.9Hz) during arboreal locomotion, perhaps due to the decreased use of more powerful bounding gaits. These results may have implications for interpreting the locomotor behavior of the ancestral primate, often reconstructed as a small-bodied arboreal taxon. Supported by the L.S.B. Leakey Foundation.