Orientation in complex chemical landscapes: Spatial arrangement of chemical sources influences crayfish food‐finding efficiency in artificial stream

Abstract

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...

Chemosensory guidance cues in a turbulent chemical odor plume

“…Although our results apply most directly to isokinetic release, the fact that the general characteristics of odor pulses produced by this method resemble that produced in situations with substantially different release properties, both in air and in water (Elkinton et al 1984;Moore and Atema 1991;Murlis et al 1992;Moore et al 1994;Finelli et al 1999;Keller et al 2001), suggests that the futility of relying on temporal sampling is a widespread phenomenon.…”

“…Moore and Atema (1991) noted that the slope of the leading edge of a high concentration peak (i.e., a rising slope) is a function of the distance from the source and suggested that an animal could use it as a tracking cue. Measurements of isokinetically released odor into field environments also indicate a systemic decrease in the rising slope away from the source (Finelli et al 1999), as do measurements of a jet source released into a cross-flow (e.g., a bivalve siphon, Moore et al 1994) and a leaky source that disrupts the flow (Keller et al 2001). However, for the slope to be a useful parameter, it must be perceptible by the animal and yield predicable patterns within the sampling period available to a searcher.…”

Slow-moving predatory gastropods track prey odors in fast and turbulent flow

“…Compared with whelk performance in slow and unobstructed flow, total search time was significantly reduced in the fastest and most turbulent conditions tested (Fig.·6), suggesting that turbulence can facilitate odor tracking by these animals. Similarly, crayfish foraging in flows of up to 5·cm·s -1 had improved search efficiency in more turbulent conditions (Moore and Grills, 1999) or when signal structure was modified by increasing spatial complexity at the location of odor release (Keller et al, 2001). In contrast, flow speed and bed-generated turbulence suppressed the ability of blue crabs to locate the source of attractive odor plumes (Weissburg and Zimmer-Faust, 1993).…”

A comparison of antennule structure in a surfaceand a cave-dwelling crayfish, genus Orconectes (Decapoda, Astacidae)

“…Cray sh have been shown to use chemical signals to nd prey (Keller et al, 2001), avoid predators (Hazlett & Schoolmaster, 1998), recognize mates (Hazlett, 1985), and assess social status (Zulandt-Schneider et al, 1999). Not only must cray sh detect and identify a diverse array of compounds, but the meaning and source of these signals must be decoded in an environment often characterized by complex mixing patterns and turbulence.…”