Effect of different light regimes on pre-adult fitness in Drosophila melanogaster populations reared in constant light for over six hundred generations

Egg to eclosion development time and survivorship were assayed on four labo ratory populations of Drosophila melanogaster that had been reared for over 600 generations in continuous light (LL) and constant temperature. The ass ays were performed in three environments: continuous light (LL), periodical ly varying light/dark cycles (LD 12:12 hr), and continuous darkness (DD). D evelopment: time in LL was significantly less than that in LD, which, in tu rn, was significantly less than that in DD, whereas survivorship did not di ffer significantly among the three treatments. The results indicate that in dividuals from Drosophila populations routinely maintained in LL do not suf fer any deleterious effects of LL treatment on pre-adult fitness. Other stu dies on these populations have shown that free-running period (tau) of the eclosion rhythm in DD is greater than that in LD. Our results are, thus, al so consistent with the notion that development time may be a function of th e free running period.