Locomotion in Ctenomys talarum (Rodentia: Caviomorpha): do digging adaptations affect locomotor performance?

Abstract

Ctenomys talarum (Talas’ tuco-tuco) is a subterranean rodent from South America that inhabits sand dunes in the Atlantic coast of Buenos Aires, Argentina. Although these animals primarily conduct their activities in underground environments, surface excursions, mainly for foraging and dispersal, have been observed. The primary mode of locomotion for these subterranean rodents is walking or trotting; however, the specific gaits they employ remain poorly understood. The present study aims to describe the gaits and locomotor performance of C. talarum and to compare with that of others rodents. Five adult females (mean body mass: 109 g) were put inside a Plexiglas chamber containing a treadmill and then filmed with a high-speed camera during exercise. The following parameters were analyzed: stride duration, length and frequency (Hz); duty factor; and speed (cm/s). Speed varied between 27.08 cm/s and 94.12 cm/s. Trot was the only symmetrical gait performed. Asymmetrical patterns (16.55%) resembled a trot-like gait. Stride frequency and length were both highly correlated to speed. Preference for trotting is probably related to gain in stability since this gait was found to occur in a broad range of speeds while exhibiting very stable support patterns. The lack of aerial phase during fast locomotion–namely “groundedrunning”–is typical of small mammals, whose crouched and plantigrade posture tend to prolong the stance phase. It was found that digging adaptations influence how stride length and frequency relate to speed. C. talarum must perform a higher stride frequency to reach an equivalent speed to that of the surface-dwelling rodent Cavia porcellus. The maximum relative running speed (body length/s) observed in C. talarum was lower than the expected value for a rodent species of similar body mass. Although predominantly underground, tuco-tucos also depend on the epigeous environment, which partially explains the retention of the generalized locomotor traits shared with surface-dwelling small mammals.