Gait kinematics during forward and backward locomotion in the Ansell’s mole-rat (Fukomys anselli)

Subterranean mammals have often been reported to habitually walk backwards both in the wild and in captivity. However, quantitative studies on this unusual behavior are sparse. For the present work, we collected video footage of spontaneous and induced forward and backward locomotion in captive Ansell’s mole-rats (Fukomys anselli; family Bathyergidae). Based on that, analyses of spatio-temporal gait parameters (speed, stride length and duration, duty factor, footfall pattern and foot posture) were performed and subsequently compared between forward and backward locomotion. Foot posture was quantified by aid of the deep learning-based pose estimation software DeepLabCut. When startled by a pump-induced air flow in a tunnel, the mole-rats reached an average maximum speed of 0.58 ± 0.13 m/s SD while walking backwards which was approximately 1.5 times faster than while walking forwards (0.39 ± 0.11 m/s SD). Whereas a similar or even higher speed was maintained during backward compared to forward locomotion, stride length and stride duration decreased significantly. This was compensated for by a higher stride frequency. The angle between the hind foot and the ground was significantly lower while locomoting backwards. The footfall pattern of Ansell’s mole-rats is lateral while locomoting forwards and diagonal while locomoting backwards. The decreased angle of the hind feet and the decreased stride length and stride duration while locomoting backwards might provide the mole-rats with more gait stability and control. Fast backward locomotion in mole-rats and other subterranean mammals probably represents an adaptation to life underground, since it facilitates swift movement, food transport, and predator evasion in greatly confined space.