A DUAL PACEMAKER MODEL FOR THE CIRCADIAN SYSTEM OF THE INSECT HEMIDEINA-THORACICA

A dual pacemaker model is described which accounts for the variety of types of free-run lability evident in the locomotor rhythms of the insect Hemideina thoracica (Orthoptera: Stenopelmatidae). The model pacemakers, each comprising a linked population of circadian feedback oscillators, interact through unequal mutual coupling. One pacemaker (Y) directly controls the timing of locomotor activity, and the other (X) regulates other rhythms, such as the daily rhythm of cuticle deposition. The evidence on which the model is based includes spontaneous change in period, compression and decompression of active phases (scalloping), rhythm splitting, "day skipping" and arrhythmicity. The simulations of free-running activity mirror a number of features of the real data, and hence lend support to this model.