A Role of Histone Acetylation in the Regulation of Circadian Rhythm in Ants

Abstract

Circadian rhythms and associated oscillating gene expression patterns are controlled in many organisms by post-translational modifications of histone proteins. Although epigenetic mechanisms have been suggested to influence key aspects of insect societies, the role of histone modifications in regulating their circadian rhythm has never been studied. Here we ask whether histone acetylation plays a role in adjusting the circadian rhythm in colonies of the ant Temnothorax longispinosus. First, we characterized the circadian activity of 20 colonies by recording the proportion of active ants inside and outside the nest every hour over four days under a 12h:12h light:dark regime. Our analyses revealed that T. longispinosus ants are diurnal and show a clear circadian rhythm in colony-level activity. Second, we tested circadian rhythmicity after shifting the light regime six hours forward to find that the peak activity also moved six hours forward, revealing that colonies rapidly adjust to changes in the light regime. Finally, we investigated whether histone acetylation regulates rhythmicity and its adjustment to light by feeding T. longispinosus colonies with C646, a chemical inhibitor of histone acetyltransferases. Treated colonies lost their circadian rhythmicity, and failed to adjust their activity to the new light regime. These findings suggest a role for histone acetylation in underlying rhythmicity and synchronization of the periodic activity to external cues in T. longispinosus, and implicate epigenetic processes in the regulation of circadian rhythm in a social context.