The olfaction in Proteus anguinus: a behavioural and cytological study

Life and development in complete darkness for a strictly cavernicolous Urodele species such as Proteus raises the problem of orientation and environmental perception. An experimental study of olfaction in Proteus anguinus was undertaken on two complementary aspects: (a) a anatomical and ultrastructural aspect (photon and electron microscopy); and (b) a behavioural aspect, by testing Proteus' sensitivity to decreasing amounts of dead prey (chironomid larvae) in a choice chamber. The results show that: (a) Proteus' olfactory epithelium clearly belonged to the general model established for all vertebrates, with a pseudo-stratified structure mainly composed of the three classical cell types (sensory cells, supporting cells and basal cells). With the unusual thickness of the epithelium common to the Proteidae, a fourth cell type is observed in Proteus; and (b) Proteus shows a well-developed olfactive sense: the sensitivity threshold occurs around 1 g of prey (in a 250 cm(3)/min water current). This relatively low detection threshold implies the use of an outstanding sense of smell probably due to the particular necessities of the subterranean environment. The experiments also emphasize the effects of environmental factors on Proteus' response to experiments, and the role of thigmotactism.