Sensitivity of activity/rest rhythMS to temperature in populations of Drosophila melanogaster selected for divergent phases of adult emergence

Abstract

Emergence from the pupal case in holometabolous insects (eclosion) is under the regulation of the circadian clock such that maximum emergence occurs at dawn just after lights ON. Results from the lab have shown that evolution of a delayed (evening) phase of emergencies associated with the evolution of enhanced temperature-sensitive clocks. On the other hand, activity/rest in Drosophila is clearly bimodal with a morning peak around dawn and an evening peak around dusk. Previous results have also shown increased temperature sensitivity of the clock which regulates the evening bout of activity in the locomotor behaviour. By using a series of combinations of regimes where light/dark and temperature cycles were phased apart, we asked if the phase of evening peak of locomotor activity of these flies (which have been selected to emerge in the evening) more closely tracks temperature cycles rather than light/dark cycle in comparison with controls. We found that the evening bout of activity of late flies tracks temperature cycles more efficiently compared to the early and control flies, although only for a limited range of light-temperature phase relationships, i.e., for the smaller phase differences between the light and the temperature cycle. However, for larger phase differences, it can be concluded that across stocks, the clock that drives activity rhythms is strongly influenced by light cycles rather than temperature or that the clock is responding to light and temperature equally.