8 – Chemoreception and Thermoreception

Many aquatic organisms possess well-developed chemosensory systems that are adapted to monitoring changes in the chemical composition of the aqueous environment in which they live. For aquatic organisms. specific chemicals in the environment may evoke highly predictable changes in behavior. Facets of behavior known to be affected by external chemicals include those associated with feeding. avoiding predators, recognizing a suitable habitat, reproducing, migrating. and interacting with conspecific organisms. General reviews of this material are provided by Mackie and Grant ( 1974). Daloze, Braekman. and Tursch (1980). and Atema (1985).

The Molecular Nature of Chemical Stimuli in the Aquatic Environment

The physicochemical environment can strongly constrain the outcome of ecological interactions such as predation, mating, and competition. This is especially true of processes mediated by the sense of olfaction, because wind and water currents control the dispersal of odor signals and act as ancillary cues during odor plume following. In the field, we examined how variations in the physical and chemical properties of odor plumes would alter the foraging behavior of the blue crab Callinectes sapidus, a common predator/ scavenger in tidal marsh creeks in the southeastern United States. We video-recorded re- sponses of naturally foraging crabs to odor plumes of varying composition and odor release rate (characteristic of clams of differing size). During each trial we presented crabs with an experimental plume that was a mixture of fluorescein-dyed seawater and clam mantle fluid, oyster mantle fluid, or a suite of amino acids, and a control plume which consisted of dyed seawater only. In addition to manipulating the chemical composition and odor release rate of the plume, we allowed flow speed to vary naturally with the tide. We tested for effects of odor composition, odor release rate, and flow speed on the success (i.e., finding the target) and efficiency (i.e., search path direction) of blue crab foraging. Mantle fluid solutions and wounded prey items elicited active search and upstream walking, while control and amino acid solutions had no effect on crab behavior. Odors released at a low rate (either low volume flow or low concentration) elicited fewer responses from crabs, and the resulting search was less efficient and less successful than responses to odors released at higher rates. Ambient current speed also affected both search success and efficiency. There was a decline in search success when current speed in the tidal channel was below 1 cm/s; search success remained constantly high, however, when current speed was above this threshold. Search efficiency was directly proportional to ambient current speeds. Such relationships between hydrodynamic and chemical properties of the environ- ment and foraging success and efficiency suggest that variation in the physicochemical environment can influence the detectability of prey and strategies employed by foragers. These results extend beyond the foraging of marine crustaceans into other olfactory- mediated interactions and habitats.

Physical constraints on ecological processes: a field test of odor‐mediated foraging

1. Taurine sensitive receptors in the antennules of the spiny lobster, Panulirus argus, were identified electrophysiologically.2. Recordings from single receptors revealed a narrow and consistent specificity when tested with taurine, taurine analogs and derivatives, and structurally related compounds.3. Taurine was the most stimulatory compound tested. Threshold concentrations for 36 individual receptors ranged from 10-8 to 10-10 M.4. The taurine analogs, hypotaurine and β-alanine, were also very effective but the phosphonic acid analog of taurine was ineffective.5. Regarding receptor specificity, receptor stimulation was greatest with compounds having single terminal basic (amine) and acidic groups separated by two carbon atoms. Compounds having terminal basic and acidic groups separated by three to five carbon atoms were also active. However, activity decreased with the distance of separation of charged groups.6. Alpha-amino acids and compounds with terminal basic and acidic groups separated by only one...

Antennular chemosensitivity in the spiny lobster, panulirus argus: studies of taurine sensitive receptors

Chemical and live feeding stimulants of the sand fiddler crab, Uca pugilator (Bosc)☆

Antennular chemosensitivity in the spiny lobster, Panulirus argus, to extract of the pink shrimp, Penaeus duorarum is based on extract components of less than 1,000 molecular weight. Amino acids account for a major part, but not all, of the extract's capacity to stimulate antennular receptors. Taurine is the most stimulatory of the amino acids comprising P. duorarum extract, although no single amino acid accounts for the amino acid fraction's stimulatory potential.

Bruce R. Johnson

Papers

Antennular chemosensitivity in the Spiny lobster, panulirus argus: Amino acids as feeding stimuli