Tactic components in orientation.

In the first half of this century, taxes were considered the best models for working out the rules of stimulus-response systems. The interest for tactic behaviours suddenly disappeared in the mid-1960s, out of reasons specified in the present review. However, results of several recent studies reviewed in the present article suggest that tactic behaviours constitute, from an ontogenetic as well as phylogenetic point of view, a first step towards more complex oriented behaviours that have received much attention in recent years. The aim of this chapter is to update the implications of tactic responses in complex oriented behaviours. We argue that taxes are basic in the process of acquiring most, if not all of these behaviours, and that they often constitute the first steps in the ontogeny of orientation. Taxes are determined by a flexible balance between genetic and epigenetic factors. Their main function is to assist the ecological adaptation of the animal to the constraints of its environment. Finally, we plead for a revival of the studies of taxes in the light of a theory on the development of behaviour, based upon self-organization of autonomous living systems.