Combining dissimilar senses: central processing of hydrodynamic and chemosensory inputs in aquatic crustaceans

Aquatic environments are by their nature dynamic and dominated by fluid movements driven by lunar tides, temperature and salinity density gradients, wind-driven currents, and currents generated by the earth's rotation. Accordingly, animals within the aquatic realm must be able to sense and respond to both large-scale (advection) and small-scale (eddy turbulence) fluid dynamics, for chemical signals critically important for their survival are embedded within such movements. Aquatic crustaceans possess many types of near-field fluid-flow detectors and two general classes of chemoreceptors on their body appendages: high-threshold, near-field receptors that may be somewhat equated with the sense of taste, and low-threshold far-field receptors that can be considered as olfactory. This review briefly summarizes the distribution of hydrodynamic and high-threshold chemoreceptors in aquatic crustaceans and the physiological characteristics of olfactory receptors in lobsters; it also examines recent physiological evidence for the central nervous integration of inputs from olfactory receptors and hydrodynamic detectors, two dissimilar senses that must be combined within the brain for survival. Marine crustaceans have provided valuable insights about mechanisms of primary olfactory sensory physiology; their additional sensitivity to hydrodynamic stimulation makes them a potentially useful model for examining how these two critical sensory inputs are combined within the brain to enhance foraging behavior. Multimodal sensory processing is critically important to all animals, and the principles and concepts derived from these crustacean studies may provide generalities about neuronal processing across taxa.