I use the olfactory system of the lobster, Panulirus argus as a model system to study how organisms detect and track sources of odor, i.e. their prey. Many organisms use their sense of smell to find food, identify mates and predators and locate suitable habitats. Recent behavioral research suggests that temporal variations in odorant concentration encountered by animals are important in tracking an odor plume to its source, while neurobiological studies are showing the importance of the intermittency of the odor signal to neural processing. There are usually two sources of this intermittency. The first is the intermittent structure of the odor concentration in the fluid (usually air or water) due to the stirring and mixing mechanisms inherent in turbulent flow. The second cause of intermittency is "sniffing" by the animal (i.e. taking discrete samples of fluid). To understand the physical mechanisms of odor interception, an understanding of the patterns of odorant dispersion on various scales is necessary. At large scales, the structure of the odor plume is dominated by complex filamentous regions in the flow containing high odor concentrations surrounded by regions of little to no odor. These structures evolve with distance from the source and their characteristics vary depending upon mean and turbulent dynamics of the flow field. When an olfactory organ "sniffs", small-scale fluid dynamics near the surface of the olfactory organ, combined with molecular diffusion, determine the time-course of odor arrival at receptors.
The olfactory organs of P. argus are the lateral filaments of its antennules; the lobster "sniffs" by flicking the antennule. For my experiments, I place a lobster in a laboratory flume that is capable of replicating typical coastal flow habitats. With an odor source positioned upstream of the lobster, I track how the flicking motion of the antennule interacts with the odorant concentration moving downstream. I measure water velocities with a laser Doppler anemometer while the structure of the odorant field surrounding the antennule is imaged using Planar Laser Induced Fluorescence (PLIF). Simultaneous to the PLIF measurements, neurobiologists Dr. Barry Ache and Dr. Juan Aggio from the University of Florida record activity in the olfactory lobe of the lobster. This information will allow us to determine what information the lobster is processing from the odorant signal to determine the location of its prey.
Concurrent to this project, I am also studying fluid flow through a dynamically scaled model of the P. argus antennule using particle image velocimetry. In this technique, the scaled model is towed through a highly viscous fluid such that the Reynolds number, and thus the flow properties, is the same as that of the actual antennule flicking in seawater. I add particles to the viscous fluid and digitally image the motions of the particles to calculate velocities along a 2-D plane. Ultimately, odorant structure around the living lobster antennule, combined with velocity data around the scaled model, will be used in an advection/diffusion model to calculate the temporal patterns of the flux of odor molecules to receptor neurons.
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