Locomoção de Ctenomys talarum (Rodentia: Ctenomyidae): um estudo com câmera de alta velocidade

Abstract

Ctenomys talarum (tuco-tuco) is a subterranean rodent from South America that inhabits sand dunes in the Atlantic coast of Buenos Aires, Argentina. These animals perform most of their activities into the underground environment, though surface excursions also occur for brief periods in a few contexts mainly forage. Studies on the motor behavior of subterranean rodents generally concentrate on digging. On the other hand, little is known about how these animals move, particularly regarding the gaits they use. The present study aims to describe gaits and locomotor performance of C. talarum. One at a time, five adult females were put inside a Plexiglas chamber containing an improvised treadmill and then filmed with a high-speed camera (Casio Exilim EXF1) during treadmill exercise. Data on different locomotor parameters were taken from records through frame-by-frame observations of 139 strides (25-30 strides each female). The analysis was based on the following parameters: stride duration (s); stance duration (s); swing duration (s); stride frequency (Hz); stride length (cm); and speed (cm/s). In addition, limb-phase and duty factor of fore and hind limbs were taken for gait identification. Mean speed ranged from 41.7 to 85 cm/s, with maximum of 105.6 cm/s. Trot was the only symmetrical gait performed. Similarly, asymmetrical gaits (16.5 %) also resembled a trot-like pattern. Most gaits were found to happen with the touchdown of forelimbs preceding that of hind limbs, and very few have shown a true aerial phase. Stride frequency and stride length were both highly correlated to speed. In this study C. talarum surpassed maximum speeds previously estimated for locomotion in artificial burrows. Preference for trot probably mirror gain in stability since this gait was found to occur in a broad range of speeds while exhibiting very stable support patterns. On the other hand, it is very plausible that the small size of the Plexiglas chamber compromised the use of typically asymmetrical gaits, which are expected to involve vertical movements of the spine associated with the animal taking longer strides. In fact, natural burrows for this species also present a narrow inner space, so these results must reflect gait patterns performed inside subterranean galleries as well. The low frequency of aerial phase during fast locomotion namely grounded-running is typical of small mammals, whose flexed limbs and plantigrade feet tend to prolong stance phase. On the other hand, the use of a treadmill short in length may have caused gait abnormalities regarding stride length. This is the first time an approach on gaits is used to describe movements of a ctenomyid species. Like its congeners, C. talarum also depends on epigeous environment, what partially explain retention of primitive locomotor traits shared by surface-dwelling small mammals. In this sense, future studies should focus on the meaning that locomotor behavior has on the dual life of these animals