Flies, clocks and evolution

The negative feedback model for gene regulation of the circadian mechanism is described for the fruitfly, Drosophila melanogaster. The conservation of function of clock molecules is illustrated by comparison with the mammalia n circadian system, and the apparent swapping of roles between various cano nical clock gene components is highlighted. The role of clock gene duplicat ions and divergence of function is introduced via the timeless gene. The im pressive similarities in clock gene regulation between flies and mammals co uld suggest that variation between more closely related species within inse cts might be minimal. However, this is not borne out because the expression of clock molecules in the brain of the giant silk moth, Antheraea pernyi, is not easy to reconcile with the negative feedback roles of the period and timeless genes. Variation in clock gene sequences between and within fly s pecies is examined and the role of co-evolution between and clock molecules is described, particularly with reference to adaptive functions of the cir cadian phenotype.