Selection for Timing of Eclosion Results in Co-evolution of Temperature Responsiveness in Drosophila melanogaster

Circadian rhythms in adult eclosion of Drosophila are postulated to be regulated by a pair of coupled oscillators: one is the master clock that is light sensitive and temperature compensated and the other that is a slave oscillator whose period is temperature sensitive and whose phase is reflected in the overt behavior. Within this framework, we reasoned that in populations of Drosophila melanogaster that have been artificially selected for highly divergent phases of eclosion rhythm, there may be changes in this network of the master-slave oscillator system, via changes in the temperature-sensitive oscillator and/or the coupling of the light- and temperature-sensitive oscillators. We used light/dark cycles in conjunction with different constant ambient temperatures and 2 different amplitudes of temperature cycles in an overall cool or warm temperature and analyzed phases, gate width, and normalized amplitude of the rhythms in each of these conditions. We found that the populations selected for eclosion in the morning (early flies) do not vary their phases with change in temperature regimes, whereas the populations selected for eclosion in the evening (late flies) show phase lability of up to ~5 h. Our results imply a genetic correlation between timing of behavior and temperature sensitivity of the circadian clock.