Gender, age, and diet influence locomotor activity rhythms in the flesh fly (Sarcophaga crassipalpis)

We are using the flesh fly (Sarcophaga crassipalpis) as a model system for examining circadian behavior under various conditions. To characterize entrainment of the locomotor rhythm to light-dark cycles (LD 12:12; 25^o C), flies were divided into four different groups on the day of adult emergence (day 0): males provided liver on days 1 & 2 (ML), males provided no liver (MNL), females provided liver on days 1 & 2 (FL), and females provided no liver (FNL). At the end of day 2, the flies were placed into individual activity monitors equipped with infrared motion detectors and provisioned with water and sugar. Both males and females were predominantly diurnal with the greatest amount of activity occurring in late photophase. Females exhibited higher overall activity levels and developed a transient 3-day burst of nighttime activity (confined to early scotophase). Reflecting the influence of protein in early adulthood, the nighttime burst occurred several days earlier in the FL group compared to the FNL group. Males given protein displayed an overall increase in daytime (but not nighttime) activity. Under constant dark (DD) conditions, both sexes showed free-running rhythms including spontaneous changes in period, suggesting a multi-oscillator circadian system. Typically, the rhythm changed period around day 12 or 13 and showed a depression in activity level between days 6-11. The female nocturnal activity seen during LD entrainment did not persist during the subsequent DD free-run. Future work will focus on the physiological processes underlying these age- and nutrition-related changes.