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

Abstract

Locomotion is precarious in an arboreal habitat, where supports can vary in both diameter and level of compliance. Several previous studies have evaluated the influence of substrate diameter on the locomotor performance of arboreal quadrupeds. The influence of substrate compliance, however, has been mostly unexamined. Here, we used a multifactorial experimental design to investigate how perturbations in both diameter and compliance affect the gait kinematics of marmosets (Callithrix jacchus; N=2) moving over simulated arboreal substrates. We used 3D-calibrated video to quantify marmoset locomotion over a horizontal trackway consisting of variably sized poles (5, 2.5 and 1.25 cm in diameter), analyzing a total of 120 strides. The central portion of the trackway was either immobile or mounted on compliant foam blocks, depending on condition. We found that narrowing diameter and increasing compliance were both associated with relatively longer substrate contact durations, though adjustments to diameter were often inconsistent relative to compliance-related adjustments. Marmosets also responded to narrowing diameter by reducing speed, flattening center of mass (CoM) movements and dampening support displacement on the compliant substrate. For the subset of strides on the compliant support, we found that speed, contact duration and CoM amplitude explained >60% of the variation in substrate displacement over a stride, suggesting a direct performance advantage to these kinematic adjustments. Overall, our results show that compliant substrates can exert a significant influence on gait kinematics. Substrate compliance, and not just support diameter, should be considered a critical environmental variable when evaluating locomotor performance in arboreal quadrupeds.

A user's guide for the quantitative analysis of substrate characteristics and locomotor kinematics in free‐ranging primates

“…Relative to the breadth of research on the effects of substrate diameter and substrate inclination, studies of how substrate compliance affects quadrupedal gait mechanics are comparatively rare (but see Gosselin‐Ildari, ; Stevens, ; Stevens, Demes, & Larson, ; Young, Stricklen, & Chadwell, ). However, previous research has shown that increasing substrate compliance significantly compromises the locomotor performance of leaping primates (Channon et al, ; Crompton, Sellers, & Gunther, ; Demes, Jungers, Gross, & Fleagle, ; Walker, ; Warren & Crompton, ) and necessitates postural and locomotor adjustments in orangutans (Myatt & Thorpe, ; Thorpe, Holder, & Crompton, ).…”

“…However, previous research has shown that increasing substrate compliance significantly compromises the locomotor performance of leaping primates (Channon et al, ; Crompton, Sellers, & Gunther, ; Demes, Jungers, Gross, & Fleagle, ; Walker, ; Warren & Crompton, ) and necessitates postural and locomotor adjustments in orangutans (Myatt & Thorpe, ; Thorpe, Holder, & Crompton, ). Additionally, field researchers have long identified that primates often move on branches that sway under their weight (Morbeck, ; Thorpe, Crompton, & Alexander, ; Thorpe, Holder, & Crompton, ; Thorpe et al, ) and laboratory researchers have argued that changes in substrate compliance should and do elicit significant changes in kinematics as mechanical energy needed to move the center of mass is lost to the deforming substrate (Alexander, ; Bonser, ; Young et al, ). We showed that substrate compliance can be quantified in the field using a force gauge apparatus and stiff rope.…”

Developments in development: What have we learned from primate locomotor ontogeny?

“…A third benefit that has been identified for DSDC gait (tested in a non‐primate arboreal mammal, the kinkajou) is that it increases not only the duration of support by diagonal limb pairs, but the linear distance between them, further enhancing stability (Lemelin & Cartmill, ). It is important to note that although the spatiotemporal features of diagonal sequence, diagonal couplets gait are often presumed to have evolved in response to relatively small‐diameter substrates, they are not strictly necessary for navigating small‐diameter supports (Karantanis et al, , , ; Schmidt & Fischer, ; Shapiro & Young, ; Shapiro et al, ), and changes in substrate orientation or compliance tend to have a more significant effect on gait parameters than substrate diameter per se (Shapiro & Young, ; Shapiro et al, ; Young, Stricklen, & Chadwell, ).…”

“…Alternatively, if the body's center of mass lies behind the line connecting the supporting diagonal limb pair (as it theoretically would be in a primate with a caudally positioned center of mass), the hindlimb of the diagonal swinging limb pair should land first, encompassing the center of gravity vector within the supporting three limbs, preventing backward pitch, and resulting in a DS gait. This explanation, known as the “Support Polygon Model” (Cartmill et al, ; Gray, ; Hildebrand, ; Tomita, ; Young, ), is problematic for the following reasons: 1) the position of the whole body center of mass of primates is not particularly caudal—in the few primate species in which whole body COM has been measured, it appears to be located relatively close to the craniocaudal midline (Crompton, Li, Alexander, Wang, & Günther, ; Druelle et al, ; Grand, ; Raichlen, Pontzer, Shapiro, & Sockol, ; Reynolds, ; Turnquist & Wells, ; Vilensky, ; Wells & DeMenthon, ; Young, ); 2) experimental manipulations of body COM in primates, or comparisons of primates with COM shifts due to tail fattening, do not result in predicted changes of footfall sequences (Young, Patel, & Stevens, ); 3) regardless of the position of the body's center of mass, primates readily switch from DS to LS gaits under certain conditions (e.g., when moving from a narrow pole to the flat ground: Hesse, Nyakatura, Fischer, & Schmidt, ; Prost & Sussman, ; Shapiro, Young, & Souther, ; Stevens, ; Vilensky & Larson, ; Vilensky & Patrick, ; Vilensky et al, ; Wallace & Demes, ) 4) in DS gaits, the landing hindlimb of a diagonal pair is not necessarily in a position to prevent backward pitch, and at that moment the direction of pitch is likely forward anyway (Cartmill et al, ); 5) the Support Polygon Model is based on static stability, and primates most likely rely more often on dynamic stability when travelling at any appreciable speed (Chadwell & Young, ; Lammers & Zurcher, ; Larson & Stern, ; Vilensky & Larson, ; Young et al, ; Young, Russo, Fellmann, Thatikunta, & Chadwell, ); and 6) the idea that primates have a more caudal COM has been conflated with the hindlimb “dominance” of primates compared to other mammals (i.e., higher substrate reaction forces on hind compared to forelimbs). Yet limb force distribution does not necessarily equate to center of mass position; greater weight support on primate hindlimbs may stem from the location of the body COM relative to the limbs, the kinematic positioning of the hands and feet relative to the COM (regardless of the latter's fore‐aft position), or an active shift to ...…”

Do Common Marmosets (Callithrix jacchus) Use Scent to Communicate Information about Food Resources?

“…Water was available ad libitum. Animals were primarily housed for a separate study on locomotion [Young et al, 2016], limiting our subject pool to two animals. The primary study had no discernable influence on animals' behavior in this study.…”