Changes in biogenic amines correlate with time of day, light cycle, age, and aggressive state in the flesh fly, Sarcopaga crassipalpis

The biogenic amines serotonin (5HT), dopamine (DA), and octopamine (OA) have been indicated in the regulation of behavior in invertebrates.  Few studies have investigated how amines change in a circadian or ontogenetic fashion, and rarely have controls for these changes been employed.  The flesh fly, Sarcophaga crassipalpis, is proposed as a model system for investigating ontogenetic and circadian changes in amines and aggression.  The present study examined amine levels over a 24-hour period, using high performance liquid chromatography with electrochemical detection (HPLC-ECD).  Heads of newly emerged male flies, kept in either 12:12 or 15:9 LD, were analyzed over 4 days for amine content throughout the 24-hour period.  Both DA and OA levels varied based upon age. Light-cycle dependent differences were observed for all amines in overall levels and patterns of change throughout the day.  These are novel findings, as no study to date has examined aminergic changes in separate light cycles in such detail.  Changes between the light cycles could relate to seasonal variation that occurs in a natural habitat, and emphasizes the strong role that environmental factors play in the control of physiological changes. A behavioral assay quantified interactive and aggressive behaviors observed throughout three time points in the light period for two age groups.  The daily changes in behavioral profiles differed dependent on age.  Correlations from these data can be made between changes in amine levels and time of day, photoperiod, age, and aggressive state.  Future behavior and amine studies should consider the relationship between these factors.