Odor Plumes and Orientation
The basis of all ecological interactions ultimately depends upon an organism’s ability to detect and extract relevant information about their environment. For many organisms chemical stimuli have particularly fundamental implications for survival, growth, and reproduction. Our lab, in particular, has been involved in the quantification of environmental stimulus patterns and the orientation behavior evoked by these stimulus patterns. Our research in this area and be broken down into two main themes: 1.) the role of hydrodynamics in distributing chemical signals at various temporal and spatial scales, and 2.) Orientation behavior under different stimulus patterns.

As with all of our work, we have taken a multi-organism and interdisciplinary approach to this research. Our research has shown that the hydrodynamics of a specific environment determines the types of information that are available to an organism for decision making. For example, one recent study (Moore et al., 1999) has shown that copepods with different feeding currents will have different types of chemosensory information available to them. A deep-water omnivorous copepod (Pleuromamma xiphias) has a feeding current with high shear zones. Because of these high shear zones, chemicals entrained in the feeding current give the copepod an advanced warning of approaching algal cells. Conversely, a shallow water predatory copepod (Euchaeta rimana) has a feeding current with relatively low shear zones which does not give this animal the same advantage as P. xiphias. We have also quantified the types of chemosensory information in flowing water using both flumes and artificially constructed streams. From these measurements, we know that chemical signals are very patchy in space and time and animals must use sophisticated sampling techniques to extract relevant information. Also the types of information available to the animals is dependent upon subtle changes in the hydrodynamics of the habitat.

Spatial and temporal heterogeneity of chemical plumes has potentially important implications for organisms. Since transport determines signals availability, changes in flow direction, stimulus concentration, or exposure to degradative processes can constrain an organism’s ability to effectively recognize and use chemical signals. Plume characteristics could provide additional information for organisms. For distances shorter than 2 m, the fine-scale filaments in plumes change predictably with distance from a source (Moore and Atema 1991). Organisms that detect temporal/spatial patterns in plume structure may locate distant chemical sources using this information. Studies examining the chemosensory information in plumes have demonstrated the importance of hydrodynamics in altering animal behavior
Recognition of chemical signals as a potential guidepost for orientation has generated a considerable body of literature. In an effort to simplify chemosensory information, studies often examine animal orientation using a single chemical source. Studies using multiple chemical stimuli have focused on behavioral integration rather than within plume signal structure. In nature chemical landscapes are complex composed of the interacting spatio-temporal dynamics of multiple odor sources. Sources such as pheromone-releasing females, actively searching predators, or as in this study, multiple carrion sources can perfuse the sensory horizon of organisms. Organisms using chemosensory-mediated search strategies are faced with difficult challenges in natural environments. They must detect, filter, and process the multitude of chemical information that exists in temporally and spatially dynamic stimuli. Given the evolutionary importance of these signals (e.g., survival, growth, and reproduction), organisms may have evolved sensory mechanisms that allow them to extract and respond to ecologically relevant information. Our more recent work has begun to investigate how multiple odor sources and increases in complexity alter orientation behavior.

We have begin to characterize plume structure, fluid dynamics, and orientation behavior of the crayfish, Orconectes virilis and Orconectes rusticus, to address this important issue in sensory ecology. This study was designed to answer two fundamental questions in chemical orientation. First, how do organisms in general and crayfish in particular respond behaviorally to changes in chemosensory information? Second, how does spatial arrangement of odor sources alter hydrodynamics and fine-scale chemical signal structure?