effect of skeleton photoperiods upon the circadian locomotor activity rhythm during development in crayfish procambarus clarkii

Abstract

This study was carried out to investigate the non-parametric effect of white light on the activity rhythm of the postembryonic stages of crayfish and to elucidate the characteristics and development of its entrainment mechanisms. Forty-five postembryonical instars of crayfish Procambarus clarkii, separated into three groups according to age and moult, were investigated. They were individually monitored with a motor activity recording system in constant photic conditions. For the three groups of animals, three trials with different skeleton photoperiod (SP) imitating LD 8:16, LD 12:12 and LD 20:4 were conducted, each followed by exposure to a period of constant darkness (DD). The locomotor activity rhythm and its entrainment ability were evaluated.-all ages showed a circadian rhythm with a capability to synchronize to the different SP increasing with age. The three groups of crayfish analysed were generally synchronized by the dusk pulse, clustering the onset of activity close to the light pulses considered as dusk. The results presented in this study suggest the involvement of extraretinal pathways in the non-parametric entrainment of crayfish.