The contralateral coordination of walking legs in the crayfish Astacus leptodactylus

Abstract

In an earlier investigation of those mechanisms which synchronize the leg movements of a multilegged animal during walking (Muller and Cruse 1991) several questions remained open. The movement of an individual leg can be described in analogy to the behaviour of a relaxation oscillator. Following this analogy the interactions between the legs can be compared with the interactions between coupled relaxation oscillators. To understand the behaviour of a system of such coupled oscillators, model calculations were performed by systematically varying the relation of the intrinsic frequencies and the character as well as the strength of the coupling influences to which each oscillator was exposed. The behaviour of several three- and four-oscillator systems was investigated. We found that prediction of the behaviour is often difficult and in some cases even counter-intuitive. It could be shown that in a four-oscillator system (which corresponds to two legs on the left and two legs on the right side of the body) diagonal neighbours can sometimes be more strongly coordinated than direct segmental neighbours, although no coupling was implemented between the diagonally neighbouring oscillators. Necessary conditions for the occurrence of this effect are described. These conditions were fulfilled in the biological experiments described in Part I. A four-oscillator model whose properties are adapted to those found in the above experiments can sufficiently describe the animal's behaviour.