Modelling the circadian system of the weta,Hemideina thoracica(Orthoptera: Stenopelmatidae)

Abstract

The development of the current model of the circadian system of the nocturnal insect Hemideina thoracica is traced from a single feedback oscillator, to more complex interactions of two populations of oscillators. Each unit oscillator is based on a negative feedback system incorporating time‐delay and sensitivity to light and temperature. Individual oscillators are linked to one or more similar oscillators to form populations or networks of units. The components of each unit reflect functions which are physiologically relevant with respect to the biochemical evidence for circadian clocks. The single oscillator model accounts for many of the basic properties of the Hemideina locomotor rhythms, including temperature compensation, light and temperature entrainment and the effects of constant dim and bright light. The population concept enhances the model by explaining much of the spontaneous and induced lability of the free‐running rhythm. The single population model has been extended, and we now propose that there is more than one clock control centre in this insect. The overall pattern of temporal behaviour may result from the interaction of two major clock centres, one regulating, among other functions, the locomotor activity subsystem, and the other the control of cuticle deposition. The concept of feedback control of the clock system of this insect is based on the original circadian feedback model of Johnsson and Karlsson which they proposed for the rhythmic petal movements of the plant Kalanchoe blossfeldiana.