Evolution and the effects of temperature on the Drosophila period gene

The Thr-Gly repeat region of the Drosophila period gene is highly variable within and between species. It is thought to be involved in the ability of the circadian system to maintain a 24 h period throughout the natural physiological temperature range. Inter-specific sequence analyses of the region have suggested that there are coevolving blocks of DNA that contribute to this phenotype. If these sequences are disrupted aberrations in the circadian locomotory behaviour occur and the ability of the clock to maintain its period length with increases in temperature may diminish. In this thesis the coevolution of the Thr-Gly repeat is investigated in populations of Drosophila simulans from separate locations in France. Within each population the shorter Thr-Gly repeat length alleles show better temperature compensation.;Transgenic mutants with varying amounts of the Thr-Gly repeat region deleted, were examined, both biochemically and behaviourally. The behavioural investigation of these mutants involved the construction of heat pulse phase response curves, and a detailed analysis of the recording of phase shifts led to the design of a new measurement method. To complement the behavioural analysis, a biochemical approach examined the response of PER and TIM to heat pulses throughout the circadian cycle by Western blotting. This revealed that PER and TIM visibly decline after a heat pulse, but recover in around 2 h. It is proposed that the behavioural PRC's and apparent protein effects can be explained by a transitory interaction of clock proteins with heat shock proteins, which is relinquished after the pulse ends.;The analysis of natural Drosophila populations from Africa revealed a new clock mutation in Drosophila simulans. After extensive investigations it is proposed that this line has a per mutation, but also carries a complementary autosomal mutation.