Circadian rhythm of locomotion and its temperature dependence in Blattella germanica.

A number of investigators have reported on the diurnal rhythm of locomotion in cockroaches, which shows a very similar picture in the different species. It is well documented that the releasing factor is a change from light to darkness (Gunn, 1940; Harker, 1956; de Roberts, i960). The rhythm persists under constant conditions, and this so-called free-running rhythm is remarkably temperature-independent, although part of the mechanism might be of a hormonal nature (Harker, 1964). Based on several years experiments on stridulation in Orthoptera Ensifera (Nielsen & Dreisig, 1970), and later confirmed by experiments on cockroaches and on lightemission of glowworms (H. Dreisig, in preparation), the hypothesis was advanced that activity in nocturnal animals is released by a reduction in illumination if the animal is in a state of specific sensitization. This state was thought to be caused by an unknown agent, a sensitizer (perhaps a hormone) produced continuously, the rate of production being dependent on the temperature. During the daytime quiescent period the sensitization grows until a level is reached at which the activity starts, the threshold of release. This threshold is solely dependent on actual environmental factors. This paper is intended to elucidate the effect of light and temperature on the threshold of release. The experiments with nocturnal insects have shown that the threshold is high in light and low in darkness and high at high temperatures and low at low temperatures. This means that there is a delay in the start of activity in constant light or if the temperature is raised just before the expected start, and that there is an advance in constant darkness or if the temperature is lowered just before the expected start of activity. This hypothesis is helpful in explaining the various phenomena connected with a diurnal rhythmic behaviour, and the experiments reported below were made to review the.circadian rhythm in a common cockroach, Blattellagermanica, in the light of the concept outlined above. Especially we wanted to test the validity of the assumption that the temperature-independence of the free-running rhythm in constant darkness could be explained by a temperature-dependent threshold of release.