The fluid dynamical context of chemosensory behavior

The fluid mechanical environment provides the context in which denizens of aquatic realms, as well as terrestrial creatures, use chemoperception to se arch for objects. Our ability to understand the nature of olfactory-guided navigation rests on our proficiency at characterizing the fluid dynamic set ting and at relating properties of flow to behavioral and sensory mechanism s. This work reviews some fluid dynamical concepts that are particularly us eful in describing aspects of flow relevant to chemosensory navigation, and it considers studies of orientation in animals in light of these principle s. Comparisons across broadly different fluid environments suggest that par ticular sensory and behavioral mechanisms may be tailored to specific flow regimes and stimulus environments. This is clearly evident when examining a nimals that operate in high vs. low Reynolds number flows. In other cases, animals may converge on common solutions in given flow regimes in spite of differences in taxonomic class or size. Potential parallels may include beh avior of aquatic vs. terrestrial arthropods, and animals without fixed refe rence points in flows dominated by molecular vs. turbulent diffusion. In an effort to add further fluid dynamical underpinnings to navigational strate gies, I suggest how simple nondimensional categorization of behavior in rel ation to flow may aid in identifying the forces underlying common elements, even across animals of seemingly disparate size and scale.