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 search for objects. Our ability to understand the nature of olfactory-guided navigation rests on our proficiency at characterizing the fluid dynamic setting and at relating properties of flow to behavioral and sensory mechanisms. This work reviews some fluid dynamical concepts that are particularly useful in describing aspects of flow relevant to chemosensory navigation, and it considers studies of orientation in animals in light of these principles. Comparisons across broadly different fluid environments suggest that particular sensory and behavioral mechanisms may be tailored to specific flow regimes and stimulus environments. This is clearly evident when examining animals 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 behavior of aquatic vs. terrestrial arthropods, and animals without fixed reference points in flows dominated by molecular vs. turbulent diffusion. In an effort to add further fluid dynamical underpinnings to navigational strategies, I suggest how simple nondimensional categorization of behavior in relation to flow may aid in identifying the forces underlying common elements, even across animals of seemingly disparate size and scale.