Genetic and behavioural adaptations of drosophila melanogaster to circadian and seasonal selection pressures

The changing of the seasons results in predictable environmental changes that exert strong seasonal selection pressures on all organisms. The most predictable is the daily oscillation of light (photoperiod) and temperature (thermoperiod). To survive the oncoming winter, Drosophila melanogaster enters a type of dormancy called diapause, characterized by an arrest in ovary development. In the long hot summer months, D. melanogaster alter their activity so that it is more diurnal with the emergence of the Afternoon (A) component.

This thesis further investigates D. melanogaster’ response to the changing seasons through genetic and behavioural dissection. In doing so, two novel regulators for diapause were discovered. The first is a role for the microRNA (miRNA) miR-276, particularly the miR-276b paralogue, which inhibits timeless and thus promotes diapause. This finding represents the first evidence of a miRNA-mRNA interaction experimentally proven to regulate diapause in D. melanogaster. The second is an inhibitory role of the long forgotten 0.9 gene which, unlike at higher temperatures, acts independently of PERIOD.

The role of temperature and light under simulated natural environmental conditions was also found to act in an unexpected way to regulate diapause. Under these conditions, the gradual changes rather than absolute or sudden changes in light and temperature must be synchronize. Only if they are in synch will the fly enter diapause. A similar relationship was also discovered in the study of the A component. Gradual changes in temperature were found to be the overriding regulator of the A component via TrpA1, in a promoter and isoform specific manner. However, light is important in the timing of the A component through the action of the Rhodopsins Rh3 and Rh6.