Meeting Abstract
Water and land transitions often require gait changes specific to the environment. For example, on land, animals walk by supporting their body weight with their limbs, but when underwater, their body weight is at least partially supported by the surrounding fluid. Studies have shown that semi-aquatic animals use different gaits when under water, such as swimming or bottom walking. However, little is known about how size can affect gait choice while fully submerged. To address this gap in knowledge, we filmed fourteen semi-aquatic red-eared slider turtles (Trachemys scripta elegans), divided into small, medium and large size classes (mass: 6.2 – 106.8 g, carapace size: 3.0 – 9.8 cm), while moving under water. A principal components analysis revealed that 80.1% of variation in gait patterns was explained by two principal components (PC), revealing distinct clustering of three gait patterns: bottom walking, swimming and hind limb pushing (hind limbs are walking, while the front limbs are swimming). Velocity (Pearson R2=0.68) and stride length (Pearson R2=0.70) loaded high on PC1, whereas stride frequency (Pearson R2=0.74) loaded high on PC2. We used relative limb phases to characterize the onset of the stance for each leg relative to a reference leg. In synchronous gaits, diagonal limb pairs move together, resulting in a phase of zero – such as what is observed during bottom walking and swimming. This differs for hind limb pushing, where the relative limb phasing of diagonal limbs is shifted by 17 +/- 6%. However, we only observed hind limb pushing for small and medium sized turtles – large turtles exclusively swam or bottom walked. We conclude that different size turtles use three distinct locomotor modes (or gaits) to move effectively under water, with hind limb pushing reserved for smaller size classes.
