Many aspects of the life cycle in Drosophila are known to be either under circadian control or affected by the circadian clock. The present investigations were made to understand whether changes in the rhythm can affect fitness of Drosophila melanogaster. Fitness such as fecundity, male lifetime fertility, female lifetime fertility, male longevity, and female longevity was assessed in light/dark (LD), continuous light (LL), and continuous dark (DD) for 15th and 30th generations. D. melanogaster showed greater fitness in LD than the other two light regimes. This might be due to failure to synchronize the reproductive events properly in LL and DD. LL and DD regimes might have created a stressful environment for Drosophila which has been observed by the reduction in the reproductive success of the individuals. Longevity was more in LD and DD when compared to LL. This shows that D. melanogaster is more adaptive to a LD regime than the other two groups.

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An endogenous control of timing of many events like oviposition, eclosion, and hatching occurs at a particular time of the day, which enhances the survival of an organism. The present study is an attempt to understand the effect of different light regimes on eclosion rhythm of Drosophila agumbensis and Drosophila nagarholensis. The eclosion rhythm of the two species were analyzed under constant conditions such as continuous light (LL), continuous dark (DD), and 12-h light and 12-h dark condition. Eclosion occurred only during morning period. The peak of eclosion was observed during 10 h in the morning in all the three light regimes of both the species in 10th and 20th generation. Analysis of variance revealed that there is a significant difference in the eclosion between light/dark, DD, and LL condition and Student t test revealed that there is no significant difference between the two species.

Circadian rhythm has been identified in every organism studied, from unicellular marine algae to man, and in virtually all physiological and biochemical functions. The endogenous circadian system functions to organize behaviour and physiology to adapt to and anticipate environment changes in light and temperature. The present study is an attempt to understand enzyme profiles (alpha and beta esterases) of Drosophila melanogaster (Oregon-K strain), Drosophila gangotrii and Drosophila jambulina under light/dark (LD), continuous light (LL) and continuous dark (DD) conditions over 30 generations. A polyacrylamide gel electrophoresis (7.5% -native gel) was used to study the esterase isozyme banding patterns in three species of Drosophila. It has been noticed that there were three alpha esterase loci in Drosophila species which were designated as α-est 1, α-est 2 and α-est 3. Similarly there were three beta esterase loci which were designated as β-est 1, β-est 2 and β-est 3. Flies maintained in different light regimes showed differences in their allelic patterns with respect to alpha and beta esterases. It was observed that there was expression of some bands at a given light regime and the absence of the same in another regime. This shows that the different light regimes affect the expression of esterase isozymes.