Ontogenetic development of locomotion in small mammals - a kinematic study

Abstract

SUMMARY Comparative studies of locomotion indicate that limb design and performance are very similar in adult mammals of small to medium size. The present study was undertaken to test whether basic therian limb pattern is present during postnatal development. Kinematic data were collected from juveniles of two eutherian species in a cross-sectional study, using cinevideography. The tree shrew Tupaia glis and the cui Galea musteloides were selected because of their different reproductive strategies, which could result in differences in the development of locomotor abilities. The aims of this study were to describe the process by which young animals develop the adult pattern of locomotion and the extent to which this process varies in two species with very different postnatal ontogenies. Despite their different life histories, the development of kinematic parameters in the altricial tree shrew and the precocial cui are surprisingly similar. General limb design, performance, and timing of segment and joint movements in the young animals were similar to adults in both species, even from the first steps. Touch-down of the forelimb occurred at the position below the eye in all individuals and limb position was highly standardized at touch-down; no major changes in segment and joint angles were observed. Significant changes occurred at lift-off. With increasing body mass, limb segments rotated more caudally, which resulted in larger limb excursions and relatively longer steps. Developmental changes in locomotor abilities were similar in both species; only the time necessary to reach the adult performance was different. Despite the widely assumed maturity of locomotor abilities in precocial young, the first steps of the cui juveniles were not similar to the movements of adults. The adult locomotor pattern was reached within the first postnatal week in the cui and by the time they leave the nest in the tree shrew (39 days after birth; individual P39). These results suggest that during the evolution of precocial development only processes independent of exercise or gravity can be shifted into the intrauterine period. However, development of locomotor ability dependents on exercise, and adjustments and training occur during growth. Therefore, only the time necessary to reach maturity was clearly shortened in the precocial juvenile relative to the ancestral altricial condition.

The kinematic consequences of locomotion on sloped arboreal substrates in a generalized (Rattus norvegicus) and a specialized (Sciurus vulgaris) rodent

“…Moreover, placing the limbs more laterally should increase the risk of sliding down the branch and thus increase the muscle effort required to generate mediolateral pressure to prevent toppling down. A highly standardized touch-down position during terrestrial locomotion has also been argued to be a mechanism for maintaining dynamic stability Schilling, 2005;Daley and Biewener, 2006;Fischer and Blickhan, 2006;Blickhan et al, 2007).…”

Ontogeny of joint mechanics in squirrel monkeys (Saimiri boliviensis): functional implications for mammalian limb growth and locomotor development

“…Moreover, because of the precocial nature of squirrel monkey behavioral development (Elias, 1977;Hartwig, 1995), size should have a stronger effect on locomotor mechanics than age per se (cf. Schilling, 2005).…”

Asymmetric interjoint feedback contributes to postural control of redundant multi-link systems

“…Each link of the model is a thin rod of length L and mass m. The nominal joint configuration for simulations was chosen to mimic feline stance posture (θ 1 = −51°, θ 2 = −86°, θ 3 = 35°) based on experimental data (Torres-Oviedo, Macpherson & Ting, 2006). Additional simulations were performed with tree shrew posture (θ 1 = −150°, θ 2 = 120°, θ 3 = −117°) (Schilling, 2005), which is more compact. The equations of motion for the system, expressed in the generalized coordinate system, θ ⃑ = [θ 1 , θ 2 , θ 3 ] T , are (1) where M is the inertia matrix, v⃑ is the centrifugal and Coriolis forces, T ⃑ is the control joint torques, J is the Jacobian, and F ⃑ END is an applied force at the endpoint.…”

“…To test whether the asymmetry was a coincidental result of the joint configuration, the optimization was repeated for an additional posture (θ 1 = −150°, θ 2 = 120°, θ 3 = −117°) based on the stance phase of locomotion of the tree shrew Tuapaia glis (Schilling, 2005). At the new posture, the equations were re-linearized so that the new optimization represents the optimal behavior of the limb locally at the new posture and is not an extrapolation of the optimization at the previous posture.…”