Persistence of eclosion rhythm in Drosophila melanogaster after 600 generations in an aperiodic environment

The ubiquity of circadian rhythms suggests that they have an intrinsic adap tive value (Ouyang et al. 1998; Ronneberg and Foster 1997). Some experiment s have shown that organisms have enhanced longevity, development time or gr owth rates when maintained in environments whose periodicity closely matche s their endogenous period (Aschoff et al. 1971; Highkin and Hanson 1954; Hi llman 1956; Pittendrigh and Minis 1972; Went 1960). So far there has been n o experimental evidence to show that circadian rhythms per se (i.e, periodi city itself, as opposed to phasing properties of a rhythm) confer a fitness advantage. We show that the circadian eclosion rhythm persists in a popula tion of the fruitfly Drosophila melanogaster maintained in constant conditi ons of light, temperature, and humidity for over 600 generations. The resul ts suggest that even in the absence of any environmental cycle there exists some intrinsic fitness value of circadian rhythms.