Sensory Detection of Water

Abstract

Although some species derive water exclusively from their food, most terrestrial animals seek out and consume water. This behaviour has three phases — location, discrimination and monitoring — and each phase may utilize distinct sensory receptors. The problem of locating water sources in the environment varies considerably with species and climate. Given that a creature knows its home range, however, locating water is probably more a cognitive than a sensory problem. Once located, assessing the quality of water is a sensory problem, presumably involving oral receptors. Monitoring the amount of fluid ingested also apparently uses sensory information, but the receptors may be different from those required for discrimination. This last assertion is based on complementary behavioural observations. At least in some species, water intake closely matches an imposed deficit, even when drinking ceases before significant absorption has taken place. If provided with an open gastric cannula, the same thirsty animal may drink to great excess (Blass and Hall 1976). Abundant other behavioural data attest to a role for both oropharyngeal and gastrointestinal afferent activity in regulating water intake (see Smith 1986 for a recent review). Direct electrophysiological evidence also exists, but it derives from far fewer experiments that can be over-interpreted.