KOEHL, M. A. R.; KOSEFF, J. R.; CRIMALDI, J. P.; WILEY, M. B.; Univ. of California, Berkeley; Stanford Univ.; Univ. of Colorado; City College of New York: Hydrodynamics of Sniffing by Lobsters

Many animals use chemical cues in the water or air around them to detect mates, competitors, food, predators, and suitable habitats. The first step in processing olfactory information, before neural filtering, is physical capture of odor molecules from the surrounding fluid. Many crustaceans capture scents by flicking antennules that bear arrays of chemosensory hairs. We studied the hydrodynamics of odor interception by flicking antennules of the lobster, Panulirus argus. We used dynamically-scaled physical models to determine how flicking affects water flow into the array of chemosensory hairs, and planar-laser-induced fluorescence to reveal how flicking antennules interact with the spatial and temporal patterns of concentration of odors as they are dispersed by turbulent ambient water currents. On the scale of an antennule, an odor plume is not a diffuse cloud, but rather is a series of fine filaments of scent swirling in odor-free water. The spatial pattern of these filaments depends on distance from the odor source. Water penetrates the chemosensory hair array during the fast downstroke of an antennule, carrying these fine-scale patterns of concentration into the receptor area. This spatial pattern, blurred by flow along the antennule during the downstroke, is retained during the slower return stroke and not shed until the next flick. Because P. argus flick their antennules in the velocity range in which the penetration of water into the array of chemosensory hairs is sensitive to changes in speed, they take samples of plume structure that are discrete in space and time. They sniff.