Interaction between sexes and between different circadian phenotypes affects lifespan in the fruit fly Drosophila melanogaster

Circadian clocks regulate the daily temporal structure of physiological and behavioural functions. In the fruit fly Drosophila melanogaster Meigen, disruption of daily rhythms is suggested to reduce the fly's lifespan. In the present study, because pairs of mixed-sex flies are known to show an activity pattern different from that of individual flies, this hypothesis is tested by measuring the lifespan of flies housed same-sexually or mixed-sexually under an LD 12 : 12 h photocycle at a constant temperature of 25 degrees C. The effect of housing wild-type (Canton-S) flies with period (per) circadian clock mutant flies is also examined because the mutant flies have different daily activity patterns. When males and females of wild-type flies are housed together, their lifespan is substantially lengthened (males) or shortened (females) compared with same-sex housed flies. The shortening of the lifespan in females is significantly enhanced when mated with per mutant males. The shortening effects are significantly reduced when the mixed-sex interaction is limited for the first 5 days after emergence. A slight elongation in lifespan, rather than a reduction, occurs when wild-type females are housed same-sexually with per(0) or per(L) mutant flies. In male flies, the elongation of lifespan occurs not only when wild-type males are housed with wild-type, per(0) or per(L) females, but also when housed with per(0) or per(S) mutant males. Mixed-sex couples always show altered daily locomotor rhythms with an enhanced night-time activity, whereas same-sex couples show daily behavioural profiles slightly altered but essentially similar to a sum of the respective two flies. No significant correlation is found between the lifespan and reproductive capacity. These results suggest that the alteration of daily activity rhythms and sexual interaction may have significant impact on the fly's lifespan.