Temperature pulses synchronise the crayfish locomotor activity rhythm

Unrestrained crayfish maintained in the dark exhibit a unimodal circadian activity that freely runs with a period of approximately 24 h rhythm that is able to entrain light–dark cycles. Although the activity rhythm has been shown to compensate for temperature, its potential for temperature synchronisation is unknown. In this work, we analysed the effects of cold-water pulses on crayfish locomotor activity. The crayfish were maintained under a 12:12 light–dark (LD) cycle and 30-min cold (5°C) water pulses were applied at three different circadian times (CTs). The crayfish were subsequently kept in darkness. Cold-water pulses applied at the beginning of the subjective night produced phase advances whereas pulses applied at the end of the subjective night produced phase delays. The magnitudes of the phase shifts were similar to those produced by light pulses but the direction was a mirror image. These findings suggest that the temperature- and light-synchronising pathways differ in crayfish.