Evidence for the Two-state Model of Nematode Behaviour

Abstract

A MODEL for the swimming and orientation of Panagrellus silusiae based on transitions between two behavioural states has been proposed¹. The basis of this model is that in normal, unstimulated conditions the nematode follows a more or less linear path with the anterior and posterior ends of the animal sweeping through a minimal area. This is termed the ‘normal’ behavioural state. When stimulated by chemical or physical means, the animal enters the ‘activated’ state, making rapid changes in orientation with the ends of the animal sweeping through a maximal area. In the case of a gradient of an attractant, the animal remains in the activated state until it orientates to the gradient by sensing the maximum difference in intensity of the stimulus between the posterior and anterior sensory structures, at which point the animal returns to the normal behavioural state and migrates to the source of attractant. Laser microbeam studies indicated that the copulatory spicules of the free-living P. silusiae function as the posterior receptors for orientation to mating attraction in this species¹, and a sensory function has also been found for the spicules in other species².