Fluid dynamics has been shown to alter ecologically important behaviors of aquatic organisms orienting to distant chemical sources. Because the fluid dynamics and chemical plumes change across hydraulic environments, it is unclear which of these factors influence orientation behavior more. This study examined how alterations in chemical signal structure, through changes in source spatial arrangement, affect chemically mediated search behavior. Microelectrochemical measurements of tracer molecules revealed that source arrangement significantly alters the downstream fine-scale structure of chemical plumes. Flume hydrodynamic characterizations (as measured with laser Doppler velocimetry) also differed among source arrangements; however, differences were minor and existed only at select upstream regions of the flume. Crayfish (Orconectes virilis) found the source faster and spent less time in refuges when sources were separated, compared with sources together. Similar numbers of crayfish found the source regardless of source arrangement. Crayfish searched more efficiently with increased spatial complexity at the source. These results supported the hypothesis that spatial and temporal dynamics of chemicals within plumes contain important information that organisms use during olfactory-mediated orientation in streams.The basis of all ecological interactions ultimately depends on an organism's ability to detect and extract relevant information about their environment. Because environmental signals have various physical properties, organisms have evolved various sensory mechanisms to extract ecological information (Dusenbery 1992). Among these systems, chemical senses are sources of ecological information for a variety of terrestrial and aquatic organisms (Bell and Cardé 1984;Atema 1988). Chemical cues can signal the presence of predators (Mathis and Smith 1993;Covich et al. 1994; De Meester and Cousyn 1997), availability of food resources (McLeese 1973), and status of mates (Atema and Engström 1971;Gleeson et al. 1984;Yen and Strickler 1996). For many organisms, chemical stimuli have particularly fundamental implications for survival, growth, and reproduction (reviewed in Dodson et al. 1994).Transport of chemicals by the fluid environment structures the distribution of concentration spatially and temporally. At macroscopic scales (considerably larger than 1 mm), advection (i.e., bulk flow), and eddy diffusion (i.e., mixing) disperse chemical signals. The complex interaction between odor and fluid dynamics is dependent on plume width relative to the dominant mixing length scale (Davidson et al. 1 Corresponding author (troy.keller@biology.gatech.edu). Present address: School of Biology, Georgia Institute of Technology, Atlanta, Georgia 30332-0230.2 Present address: Department of Biological Sciences, Auburn University, Auburn, Alabama 36849-5407.
AcknowledgmentsThe manuscript benefited from discussions and assistance from Alan Covich, Lakshmi Prasad Dasi, David M. Fields, Don Giddens, Eric Giddens, Shikha Rahman...
