Control systems models for the circadian clock of the New Zealand weta, Hemideina thoracica (Orthoptera : Stenopelmatidae)

The New Zealand weta, Hemideina thoracica, is a nocturnal. orthopteran inse ct which emerges from holes in trees or from under bark soon after sunset t o forage for several hours on plant and animal material before returning to its refuge before dawn. In tests of the internal clock hypothesis it exhib its clear circadian locomotor rhythms in which the period is initially some what less than 24 h, but frequently spontaneously increases to over 25 h. T he rhythms are entrainable by Light and temperature cycles, obey Aschoff's Law and are temperature compensated. A single oscillator feedback model acc ounts for these basic properties of the weta clock, but does not explain a variety of examples of rhythm lability, such as day skipping, spontaneous c hange in period, scalloping and desynchrony typically found in the real dat a. To account for these characteristics the model is expanded into two Link ed populations of oscillators, which retain the basic properties of the sim ple model and in addition interact through their coupling to show the vario us types of free-run lability. To make these control systems models compati ble with the molecular interpretation of circadian biology, each of the com ponents in the feedback loop is matched with molecular function and structu re.