Spatial Information in the Three-Dimensional Fine Structure of an Aquatic Odor Plume

Turbulent odor plumes play an important role in many chemically mediated behaviors, yet the fine scale spatial structure of plumes has not been measured in detail. With the use of a newly introduced microelectrochemical recording technique, we have measured, in some detail, the fine structure of an aquatic odor plume in the laboratory. We sampled a turbulent odor plume at 10 Hz with a spatial sampling area of 0.02 mm2, approximately that of a chemoreceptor sensillum of the lobster, Homarus americanus. A 3-min record was sampled at 63 different sites in 3 dimensions (x, y, z). As expected from time averaging models, the mean values of pulse parameters such as height and onset slope were greatest near the source. However, what cannot be described by time averaging models is the instantaneous distribution of pulses: periodically high peaks with steep concentration slopes (well above the local average and far above predictions from averaging models) can be found far away from the source. However, the probability of above-average pulse heights decreases with distance from the source in x, y, and z directions. The most intense odor fluctuations occurred along the x axis (the cross-sectional center of the plume). Odor profiles were analyzed with three different models of sensory filters; logarithmic, probability, and temporal filters. This analysis indicates that features contained within the plume structure could be used as directional cues for orienting animals. It remains to be demonstrated that animals use such sensory filters to extract biologically relevant spatial information from odor plumes.