LIGHT-PULSE PHASE RESPONSE CURVES FOR THE LOCOMOTOR-ACTIVITY RHYTHM IN PERIOD MUTANTS OF DROSOPHILA-MELANOGASTER

Parameters (tau, alpha and rho) of the adult locomotory rhythm, and ph ase response curves (PRCs) of this rhythm to light pulses, were examin ed in wild type and period mutants (per(S) and per(L2)) of Drosophila melanogaster. When compared to wild type, peu(S) was shown to have a s hortened active phase (a) whereas per(L2) was shown to have a lengthen ed rest phase (rho). PRCs for all three strains were shown to change f rom a 'low amplitude' Type 1 to a 'high amplitude' Type 0 with increas ed duration of the light pulse, and pers to have an apparently increas ed light 'sensitivity'. These PRCs offered good predictions for steady state entrainment (of per(S)) to 24 h light-dark cycles. The shorteni ng of circadian period in pers and its lengthening in per(L2) were sho wn to be consequences of changes in the 'time course' of the oscillati on in the late subjective day. Since the late subjective day was lengt hened in per(L2) but a was not, these two parameters are considered to be independently regulated.