Meeting Abstract
32.4 Friday, Jan. 4 The medium matters: tongue-flicking mechanics in air and water in the water snake (Nerodia sipedon) RYERSON, WG*; SCHWENK, K; Univ. of Connecticut william.ryerson@uconn.edu
Snakes use oscillatory tongue-flicking to sample the environment for odor molecules. In air, the oscillations set up two pairs of vortices and regions of high velocity air flow. This pattern of air movement maximizes the rate of molecular mass transfer onto the tongue tips through convection, diffusion and sorption. Water snakes tongue-flick in water as well as in air, leading us to wonder if the same patterns would be observed in the more viscous fluid. We used high speed video analysis and particle image velocimetry (PIV) in air and water to examine differences between environments in the kinematics of tongue-flicking and the patterns of air/water flow it generates around the tongue tips. In water, both the kinematics and fluid dynamics are strikingly different from air-flicks. The velocity and duration of individual oscillations is reduced, as is the number of oscillations within a tongue-flick bout. In water the tines are not kept rigid as they are during air-flicking; instead they bend in a continuous curve along with the body of the tongue and water appears to flow along the tines rather than across them. Vortex formation is similar in both environments, but the reduced number of oscillations and decrease in velocity results in the formation of only a single pair of counter-rotating vortices before the tongue is retracted. It appears that the greater viscosity of water constrains the mechanics of tongue-flicking and that water snakes are unable to exploit the fluid dynamic mechanism used in air-flicking to maximize chemical collection. It is possible that slower and shorter bouts of tongue-flicking help to prevent the dissolution of the salivary fluid covering the tongue tips—the material that physically collects odor molecules during oscillatory tongue-flicking, which trades-off with the efficiency of mass transfer.
