Meeting Abstract

60.2  Friday, Jan. 6  Burrowing of the ocellated skink (Chalcides ocellatus) in wet and dry granular media SHARPE, S.S.*; JUDY, K.N.; DAFFON, K.; GOLDMAN, D.I.; Georgia Tech; Georgia Tech; Georgia Tech; Georgia Tech

Many terrestrial animals locomote on and within soil in which water content can vary depending on rainfall, geographical location, and time of day. Empirical drag measurements in a wetted granular medium (GM) of 0.3 mm glass particles prepared into a loosely packed state revealed that resistance force increased by a factor of two as water content (W, the mass of water/mass of GM) increased to 3%, after which force became approximately independent of W. We tested if subsurface locomotion was affected by W using the ocellated skink (Chalcides ocellatus) (N=6 animals), a generalist burrower. We used high speed x-ray imaging to measure head, body and limb kinematics of the lizard during burial in loosely packed dry and wet (W=3%) GM. No gross differences in locomotor kinematics were observed; in both substrates during burial the body was maintained in a curved posture and the animal moved using a start-stop motion. During movement, the head oscillated and the fore limb on the convex side of the body was used to push the animal forward. Once the lizard was fully submerged, the hind limbs remained alongside the body. All body points posterior to the pectoral girdle followed the same trajectory indicating that the material surrounding the body remained solid during forward locomotion. We hypothesized that the head oscillation is used to decrease resistive force felt by the animal in the forward direction. We performed a test in which a rod, comparable in size to the diameter of the animal, was rotated back and forth by 30° then moved forward by 2.5 cm. In the dry GM the drag forces were independent of the oscillation, but in the 3% W GM forces were reduced by 16 ± 6%. This implies that head undulation can enhance locomotor performance in cohesive soils.