The Impact of Substrate Properties on the Kinematics of Locomotion in a Limb-Reduced Skink, Ablepharus kitaibelii (Squamata: Scincidae).

The environment through which animals move is rarely homogenous and requires animals to change their kinematics. Especially for small animals, even seemingly minor variations in substrate characteristics may have strong impacts on their locomotor speed and kinematics. In most quadrupedal animals, obstacles are avoided by adapting the movements of the limbs and body, allowing animals to effectively negotiate a diversity of terrains. However, how limb-reduced animals change their kinematics in function of variation in locomotor substrates remains poorly known. Here we study the limb-reduced skink Ablepharus kitaibelii moving on two different substrates (sand and bitumen) across a range of speeds. Our results show an effect of speed as well as significant differences between substrates in most spatio-temporal gait parameters studied. Moreover, speed modulation differed between the two substrates, suggesting that the kinematic and motor control strategies used by this species are substrate-dependent. Axial movements were strong determinants of overall locomotor speed in A. kitaibelii, suggesting that in limb-reduced species, the axial system drives variation in locomotor speed. Our data provide a baseline for future studies on other limb-reduced and non-limb-reduced species.