Differential control of morning and evening components in the activity rhythm of Drosophila melanogaster - Sex-specific differences suggest a different quality of activity

The rhythms of locomotor activity of male and virgin or mated female flies were compared in the Drosophila melanogaster wild-type strains CantonS, Ber lin, and Oregon(R). Under light-dark conditions, most flies showed a bimoda l activity pattern with a morning peak around lights-on and an evening peak before lights-off. For all strains, a distinct sexual dimorphism was obser ved in the phase of the morning peak. Males had a significantly earlier mor ning peak than females and consequently a larger phase angle between mornin g and evening peak (psi(m,e)). Under constant dark conditions, the morning component merged with the evening component to a unimodal activity band in about half of the flies. In those flies who maintained bimodality, the sex- specific difference in psi(m,e) disappeared. Other sex-specific differences were now apparent: Males showed a shorter free running period than females , and in two of the three strains, females were more active than males. Mor ning and evening components seem to contribute to the free-running period. Spontaneous or externally provoked change in psi(m,e) were correlated with period changes. In some flies, the morning and the evening components showe d splitting, indicating that they are the output of two different oscillato rs. The sexual dimorphism in the phase of the morning peak under LD-conditi ons suggests that the function of activity during morning and evening peak might be different, for example, during the morning peak, males are active to find females. Overall, the results underline the multioscillatory nature of Drosophila's circadian system.