| Summary: | 碩士 === 國立中興大學 === 物理學系所 === 100 === Olfaction relies on direct contact of odorants and the receptors, which can be facilitated by fluid motion and animal behaviors. This study examined the kinematics and fluid dynamic consequences of antennular flicking in marine hermit crabs, and further examined the biophysical mechanisms of odorant sampling. Marine hermit crabs sniff by flicking their antennules in three phases: downwards refresh stroke, stationary catch stroke, and translational motion. During the refresh stroke, Dardanus megistos had flicking speed of 189±27.68 mm/s, similar to 169.27±48.41 mm/s in Dardanus deformis; in this phase, sensory hairs on the antennules deform to increase the fluid volume housed by the hairs up to about 6 times its original volume. During the catch stroke, D. megistos had flicking speed of 104.8014±29.4868 mm/s, also similar to 116.2894±34.0268 mm/s in D. deformis; in this phase, both antennules and sensory hairs deform to contract the fluid housed by the hairs. Therefore, in marine hermit crabs, the flicking velocities of both strokes are similar, which is different from the velocity asymmetry reported previously in stomatopods and lobsters. The boundary layer thickness caused by the antennules, estimated during either flicking or translational motion, is about 0.7 mm and smaller than the hair length of 1.1 mm; hence while the hair base lies within the boundary layer, hair tips are exposed to the environments. When considering the effects of the hairs, at the antennule base, only when flicking velocity reaches maximum during refresh stroke would 20% hair length at the hair tips extend outside the boundary layer to make the hairs “leaky” so the external odorant plume could enter the inter-hair space to replace and refresh the old fluids. When the antennule and hairs contract, some odorants would stay within the hairs to diffuse to the receptors. Antennular flicking also induced surrounding fluids to generate vortex to disrupt and flush the sampled odorant plume, preventing re-sampling. In conclusion, I propose that marine hermit crabs sniff by flicking antennules with “Search-Refresh-Catch” modes mainly by deforming hairs and antennules to change inter-hair spacing for different leakiness. The induced vortex behind the antennules serves to prevent re-sampling.
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