Regulatory effects of environmental chemical signals on search behavior and foraging success

To appreciate the mechanisms governing olfactory-mediated behavior, process es of chemical signal production and transmission in fluid media lair or wa ter) must be understood. With new tools becoming available in analytical ch emistry and fluid dynamics, investigators can now quantitatively address th e processes governing chemical signals in field habitats. This study identi fies the role of amino acids as signal molecules regulating search behavior and foraging success by estuarine mud snails (Ilyanassa obsoleta). For the first time, methods are described for measuring chemical signal production , release, and transport in field habitats, over temporal and spatial scale s consistent with olfactory information processing. Rates of advection and turbulent mixing were determined, and shear velocities and roughness Reynol ds numbers were estimated to characterize bottom boundary layer hows. Nearl y instantaneous chemical measurements were made using a computerized microp robe system and conservative tracer to establish the environmental distribu tions of signal molecules at rates similar to those sampled by olfactory re ceptor neurons. In addition, we determined the dissolved free amino acid (D FAA) compositions (up to 18 amino acids), concentrations, and effluent rele ase rates for live intact and injured fiddler crabs (Uca pugilator) and har d clams (Mercenaria mercenaria), which are common prey from mud snail habit ats. The: field site populated by mud snails was found to be more conducive at broadcasting stronger chemical signals over longer distances than most other estuarine and ocean habitats. Live fiddler crabs released amino acids at very low fluxes (0.1 nmol.min(-1).g [wet tissue mass](-1)), while live intact clams took up amino acids from seawater. Once injured, hard clams an d fiddler crabs released DFAAs at 88 and 6804 nmol.min(-1).g(-1), respectiv ely. Mud snails were significantly attracted to injured clams and crabs, bu t not to intact prey, as compared with controls. Synthetic mixtures of amin o acids, simulating fluids leaking from injured prey, were also highly attr active. When we tested for effects of amino acid composition, concentration , mean volume flow rate (of chemical input), and flux, in separate experime nts, only Aux directly correlated with the number of mud snails attracted. The attraction of mud snails is thus more tightly coupled to the physical t ransport of chemical stimuli than to the molecular properties of specific a mino acids.