Biodynamics of climbing: effects of substrate orientation on the locomotion of a highly arboreal lizard (<i>Chamaeleo calyptratus</i>)

Vertical climbing is an essential behavior for arboreal animals, yet limb mechanics during climbing are poorly understood and rarely compared with those observed during horizontal walking. Primates commonly engage in both arboreal walking and vertical climbing, and this makes them an ideal taxa in which to compare these locomotor forms. Additionally, primates exhibit unusual limb mechanics compared with most other quadrupeds, with weight distribution biased towards the hindlimbs, a pattern that is argued to have evolved in response to the challenges of arboreal walking. Here we test an alternative hypothesis that functional differentiation between the limbs evolved initially as a response to climbing. Eight primate species were recorded locomoting on instrumented vertical and horizontal simulated arboreal runways. Forces along the axis of, and normal to, the support were recorded. During walking, all primates displayed forelimbs that were net braking, and hindlimbs that were net propulsive. In contrast, both limbs served a propulsive role during climbing. In all species, except the lorisids, the hindlimbs produced greater propulsive forces than the forelimbs during climbing. During climbing, the hindlimbs tends to support compressive loads, while the forelimb forces tend to be primarily tensile. This functional disparity appears to be body-size dependent. The tensile loading of the forelimbs versus the compressive loading of the hindlimbs observed during climbing may have important evolutionary implications for primates, and it may be the case that hindlimb-biased weight support exhibited during quadrupedal walking in primates may be derived from their basal condition of climbing thin branches.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The evolution of vertical climbing in primates: evidence from reaction forces

Hanna

Granatosky

Rana

et al. 2017

“…The changes in limb posture suggest weight transfer towards the hindlimbs (Lee et al, 2004;Krause and Fischer, 2013), although why that might occur as a consequence of tail loss remains unclear. Electromyography could reveal whether such a postural shift permits the lizard to engage larger muscle groups for stabilization or facilitating greater running speeds.…”

Section: Kinematic Changes Associated With Tail Lossmentioning

confidence: 99%

Tail loss and narrow surfaces decrease locomotor stability in the arboreal green anole lizard (Anolis carolinensis)

Hsieh

2015

Tails play an important role in dynamic stabilization during falling and jumping in lizards. Yet tail autotomy (the voluntary loss of an appendage) is a common mechanism used for predator evasion in these animals. How tail autotomy has an impact on locomotor performance and stability remains poorly understood. The goal of this study was to determine how tail loss affects running kinematics and performance in the arboreal green anole lizard, Anolis carolinensis. Lizards were run along four surface widths (9.5 mm, 15.9 mm, 19.0 mm and flat), before and following 75% tail autotomy. Results indicate that when perturbed with changes in surface breadth and tail condition, surface breadth tends to have greater impacts on locomotor performance than tail loss. Furthermore, while tail loss does have a destabilizing effect during regular running in these lizards, its function during steady locomotion is minimal. Instead, the tail probably plays a more active role during dynamic maneuvers that require dramatic changes in whole body orientation or center of mass trajectories.

“…It is unclear what role this suggests, but this could imply that the gastrocnemius simply is not recruited as much during stance to propel the relatively slowmoving leopard geckos. Although chameleons are also quite slow, they are arboreal and may exhibit muscle recruitment patterns related to the specialized grasping and propulsive mechanics (Higham and Jayne, 2004a;Higham and Anderson, 2013;Fischer et al, 2010;Krause and Fischer, 2013;Peterson, 1984). Future work should investigate the activation patterns of the gastrocnemius in other geckos, including arboreal and terrestrial species.…”

Section: Comparisons With Other Lizardsmentioning

confidence: 99%

Neuromuscular control of locomotion is altered by tail autotomy in geckos

Jagnandan

Higham

2018

Animal locomotion is driven by underlying axial and appendicular musculature. In order for locomotion to be effective, these muscles must be able to rapidly respond to changes in environmental and physiological demands. Although virtually unstudied, muscles must also respond to morphological changes, such as those that occur with tail autotomy in lizards. Tail autotomy in leopard geckos () results in a 25% loss of caudal mass and significant kinematic alterations to maintain stability. To elucidate how motor control of the locomotor muscles is modulated with these shifts, we used electromyography (EMG) to quantify patterns of muscle activity in forelimb and hindlimb muscles before and after autotomy. Forelimb muscles (biceps brachii and triceps brachii) exhibited no changes in motor recruitment, consistent with unaltered kinematics after autotomy. The amplitude of activity of propulsive muscles of the hindlimbs (caudofemoralis and gastrocnemius) was significantly reduced and coincided with decreases in the propulsive phases of femur retraction and ankle extension, respectively. The puboischiotibialis did not exhibit these changes, despite significant reductions in femur depression and knee angle, suggesting that the reduction in mass and vertical ground-reaction force by autotomy allows for the maintenance of a more sprawled and stable posture without increasing motor recruitment of the support muscles. These results highlight the significant neuromuscular shifts that occur to accommodate dramatic changes in body size and mass distribution, and illuminate the utility of tail autotomy as a system for studying the neuromuscular control of locomotion.