Ant circadian activity rhythms vary with social context and age
Haruna Fujioka, Haruna Fujioka , Masato S. Abe , Yasukazu Okada
University of Tokyo, Tokyo, Japan; University of Tokyo, Tokyo, Japan ; RIKEN API, Japan ; University of Tokyo, Tokyo, Japan
Social insect colonies are highly organized systems where communications among nestmates have pivotal functions for colonial organization. In order better to understand social organization, their chronobiological pattern, particularly the circadian activity rhythm, has recently attracted much attention. Circadian activity rhythm is a periodic activity of approximately 24 hours. In ant colonies, workers should coordinate their own circadian behaviours by integrating information from various social and environmental factors. An increasing number of studies show that workers in insect colonies exhibit different activity patterns between solitary and social conditions; however, how individual activity rhythms are governed in various social contexts remains largely unknown. In this study, we investigate the effects of nurse-brood interactions and worker-worker interactions on circadian activity rhythms using the monomorphic ant species Diacamma sp. from Japan. We used the automatic tracking system and collected long-term time series data on the movement of each individual ant. Firstly, we demonstrated that the brood stages (egg, larva, pupa) have different effects on nurse activities. Nurses showed around-the-clock activity only in the presence of vulnerable eggs and larva, but not of cocooned pupa. Such brood-type specific changes in circadian activity rhythms are considered to stem from the differences between caretaking demands. Secondly, we found that workers exhibited around-the-clock activity that was highly dependent on how old they are and whom they interact with. We discussed the potential roles of worker-worker interactions on the chronobiological organization of the ant society. Our study provides the first evidence, to our knowledge, that nurse-brood and worker-worker interactions can function as context-dependent cues inducing around-the-clock activities in social insects.