Sound Perception in Aquatic Crustaceans

Abstract

In order to understand the function of the crustacean brain, it is necessary to know what kind of stimuli the animals filter from their natural environment. In crustaceans the classical five senses cannot be identified easily. Only the sense of vision can be attributed to a specific prominent structure, the eye. However, for the vertebrate senses olfaction, gustation and audition we do not have discrete and prominent counterparts in crustaceans (for a discussion of olfactory abilities see Derby, this Vol.). With respect to audition in crustaceans (and other aquatic invertebrates), we face the additional problem that there are no obvious reactions of crustaceans to sound stimuli. In the past there was a debate about hearing abilities of aquatic invertebrates (Moynihan 1985; Hanlon and Budelmann 1987; Packard et al. 1990; Budelmann 1992b). In contrast to fish and aquatic mammals, no structures have been discovered in the aquatic invertebrates (with the exception of aquatic insects) that could be stimulated by the pressure component of sound. However, sound waves not only consist of pressure oscillations but also contain medium vibrations. Aquatic crustaceans are known to be sensitive to water vibrations (see Breithaupt and Tautz 1990). Does this mean that they can hear? Various definitions of hearing exist; some are based on the presence of a tympanic hearing organ, others on the reception of the pressure component of sound, while other definitions include just the perception of water vibrations (see Budelmann 1992b, for review).