Angular momentum and arboreal stability in common marmosets (Callithrixjacchus)

Abstract

Despite the importance that concepts of arboreal stability have in theories of primate locomotor evolution, we currently lack measures of balance performance during primate locomotion. We provide the first quantitative data on locomotor stability in an arboreal primate, the common marmoset (Callithrix jacchus), predicting that primates should maximize arboreal stability by minimizing side-to-side angular momentum about the support (i.e., Lsup ). If net Lsup becomes excessive, the animal will be unable to arrest its angular movement and will fall. Using a novel, highly integrative experimental procedure we directly measured whole-body Lsup in two adult marmosets moving along narrow (2.5 cm diameter) and broad (5 cm diameter) poles. Marmosets showed a strong preference for asymmetrical gaits (e.g., gallops and bounds) over symmetrical gaits (e.g., walks and runs), with asymmetrical gaits representing >90% of all strides. Movement on the narrow support was associated with an increase in more "grounded" gaits (i.e., lacking an aerial phase) and a more even distribution of torque production between the fore- and hind limbs. These adjustments in gait dynamics significantly reduced net Lsup on the narrow support relative to the broad support. Despite their lack of a well-developed grasping apparatus, marmosets proved adept at producing muscular "grasping" torques about the support, particularly with the hind limbs. We contend that asymmetrical gaits permit small-bodied arboreal mammals, including primates, to expand "effective grasp" by gripping the substrate between left and right limbs of a girdle. This model of arboreal stability may hold important implications for understanding primate locomotor evolution.

Effects of support diameter and compliance on common marmoset (Callithrix jacchus) gait kinematics

“…We measured compliance at the two ends of the platform to better model the material properties the marmosets experienced during their initial contact with the compliant platform at the start of each stride (see Movie 1 for an exemplar stride). We used existing data on marmoset locomotor kinetics (Chadwell and Young, 2015) to select biologically reasonable control parameters, loading the platform linearly at a rate of 3 mm s −1 to a maximum force of 11 N. Loading and displacement were linearly related (R 2 ≥0.999). Average compliance of the platform ends over 10 repetitions was 1.39 mm N −1 (Table 1), with some variation between the two ends (1.31 versus 1.46 mm N −1 ).…”

“…To quantify the 3D displacement of the animal and the compliant substrate during locomotion, we calibrated the synchronized video images from the four cameras to the same 3D coordinate system using published methods (Standen and Lauder, 2005;Chadwell and Young, 2015). In our final coordinate system, the x-axis was set to be coincident with the long axis of the pole substrate (i.e.…”

“…We estimated pCoM empirically for each animal using the reaction board method (Lammers et al, 2006;Larson and Demes, 2011;Young, 2012a,b;Chadwell and Young, 2015). In this procedure, a rigid lightweight board is supported by two nails resting on a platform at one end and a single nail resting on a scale at the other.…”

“…Marmoset gait patterns are also atypical among primates. Though marmosets most frequently use asymmetrical galloping/ bounding gaits (Young, 2009;Chadwell and Young, 2015), when walking they often use trotting or lateral sequence patterns of coordination (Schmitt, 2003b), versus the diagonal sequence patterns that are typical of most other primates (Hildebrand, 1967). Nevertheless, despite their uniqueness among primates, marmosets and other callitrichines have converged on the general morphotype thought to characterize early euprimate evolution (i.e.…”

Accelerated pseudogenization of trace amine‐associated receptor genes in primates

“…69 The degeneration of TAAR gene repertoires likely began in the common ancestor of Euarchonta and is highly likely to be related to arboreal living. 20,70,71 Living in trees significantly reduces exposure to predators and facilitates escape from ground-living predators. They have already lost TAAR1 and TAAR7.…”