Meeting Abstract
41.7 Sunday, Jan. 5 11:45 The effect of body length and slenderness on sand-swimming: comparing the performance of the sandfish lizard and the shovel-nosed snake SHARPE, S.S.; KUCKUK, R.M.; KOEHLER, S.A.; GOLDMAN, D.I.*; Georgia Tech; Georgia Tech; Harvard; Georgia Tech ssharpe@gatech.edu
A few desert dwelling animals possess the ability to swim subsurface in sand and move by propagating anterior-to-posterior waves down their body. To investigate how body morphology affects swimming performance, we compare the movement strategies of two desert dwelling sand-swimmers exhibiting disparate body forms: the long-slender limbless shovel-nosed snake (Chionactis occipitalis) and the relatively shorter limbed sandfish lizard (Scincus scincus). The snake has an average body radius to length ratio (r/L) of 0.02 compared to the sandfish which has a r/L of 0.05. We hypothesize that a long slender body improves swimming performance. X-ray imaging of subsurface kinematics revealed that the snake operated with a lower slip factor (S = 6.0 ± 1.6°, defined as the average angle between velocity and tangent vectors along the body) compared to the sandfish (S = 21.6 ± 3.7°, P <0.01); this implies that both animals caused local flow of the surrounding media but that the snake yielded the material less. The snake also used a higher number of waves along the body (ξ = 3.5 ± 0.7) compared to the sandfish (ξ =1 ± 0.1, P <0.01). We use a previously developed frictional fluid model (granular resistive force theory) to predict how r/L, ξ, and the curvature (κλ, local curvature at a bend multiplied by the arc length of the wave averaged over all visible undulations) affect S for the two animals. The model predicts that r/L affects S differently depending on κλ and ξ, but for the range that the sandfish and snake operate, surprisingly, r/L alone has little effect. The model shows that having a larger κλ or ξ results in a lower S. Therefore, the snake’s long body may offer a functional advantage for low slip locomotion by allowing the snake to use a large ξ while maintaining a swimming waveform with higher κλ.
