Mechanisms of animal navigation in odor plumes

Chemical signals mediate many of life's processes. For organisms that use t hese signals to orient and navigate in their environment, where and when th ese cues are encountered is crucial in determining behavioral responses. In air and water, fluid mechanics impinge directly upon the distribution of o dorous molecules in time and space. Animals frequently employ behavioral me chanisms that allow them to take advantage of both chemical and fluid dynam ic information in order to move toward the source. In turbulent plumes, whe re odor is patchily distributed, animals are exposed to a highly intermitte nt signal. The most detailed studies that have attempted to measure fluid d ynamic conditions, odor plume structure, and resultant orientation behavior have involved moths, crabs, and lobsters. The behavioral mechanisms employ ed by these organisms are different but generally integrate some form of ch emically modulated orientation (chemotaxis) with a visual or mechanical ass essment of flow conditions in order to steer up-current or upwind (rheo- or anemo-taxis, respectively). Across-stream turns are another conspicuous fe ature of odor-modulated tracks of a variety of organisms in different fluid conditions. In some cases, turning is initiated by detection of the latera l edges of a well-defined plume (crabs), whereas in other animals turning a ppears to be steered according to an internally generated program modulated by odor contacts (moth counterturning). Other organisms such as birds and fish may use similar mechanisms, but the experimental data for these organi sms is not yet as convincing. The behavioral strategies employed by a varie ty of animals result in orientation responses that are appropriate for the dispersed, intermittent plumes dictated by the fluid-mechanical conditions in the environments that these different macroscopic organisms inhabit.