Interaction between light and temperature in synchronizing the circadian rhythm of locomotory activity in Thermophilum duodecimguttatum (Coleoptera: Carabidae) from Kuwait

Abstract

Both light and temperature can entrain the circadian rhythm of locomotory activity of T. duodecimguttatum. At constant temperatures, the beetles are predominantly nocturnal but, when high temperatures coincide with the light phase of a LD cycle, activity takes place mainly during the second half of the light period. When the beginning of the period of higher temperature is shifted progressively further into the light phase, the timing of locomotory activity moves further and further into the dark period – until the phase shift of temperature has reached about 12 h or 180°, after which the onset of the transient cycles of activity tends to begin earlier. The fact that light and temperature cycles interact to entrain the rhythm, and that phase splitting occurs, suggests that the circadian system consists of at least two weakly coupled oscillators. It is argued that the conspicuous colouration of this species has an aposematic function and is effective both during the day and at night. It does not therefore imply day-time or nocturnal activity.