Sex differences in neuronal circadian timekeeping remain relatively unexplored, despite the expanding body of research highlighting the influence of sex on the mechanisms underlying neuronal control of behavior. In mammals, steroid hormones display daily, clock-driven changes in abundance, and while these sex hormones are not required to maintain rhythms, they differentially influence the amplitude of activity behavior between the sexes. Furthermore, structural and functional sex differences have been observed in brain areas that receive direct input from the brain's circadian timekeeping center. Research in humans has also revealed significant sexual dimorphism: men tend to have lower-amplitude endogenous rhythms than women, are less resilient to nocturnal sleep disruptions, and spend less time asleep.
In Drosophila, as in other species, most of the research on how the timekeeping system in the brain controls the timing of behavioral outputs has been conducted in males, or sex has not been included as a biological variable. A critical set of circadian pacemaker neurons in Drosophila release the neuropeptide pigment-dispersing factor (PDF), which functions as a key output factor in the network with complex effects on other clock neurons. We are sudying the sexually dimorphic roles of PDF in the circadian clock network, and the extent to which the relative hierarchy of circadian oscilators is sexually dimorphic. Our results suggest that the female circadian system is more resilient to manipulations of the pacemaker nuerons and the PDF pathway, suggesting that circadian timekeeping is more distributed across the clock neuron network in females.