Ant activity-rest rhythms vary with age and interaction frequencies of workers
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Social insect colonies are highly organized systems, where communication among nestmates (i.e., social interactions) has a pivotal function for colonial organization. In order to further the understanding of social organization, the chronobiological system of social insect species, particularly their circadian rhythm, has recently attracted much attention. However, gaps still remain in our understanding of how individual active/rest rhythms are governed in various social contexts. In this study, we investigate the effects of worker-worker interactions on circadian activity rhythms, using the monomorphic ant, Diacamma sp. Continuous tracking of solitary ants elucidated circadian activity rhythms, both in young and old workers (< 30 days and > 70 days after eclosion, respectively). The color tag–based automatic tracking of multiple workers revealed that young-old interactions reduced circadian rhythmic activities in both young and old workers, whereas young workers retained active/rest rhythms under young-young worker interactions. Together with the analyses of worker-worker interaction frequencies, we conclude that interactions between workers in different age groups (i.e., workers with different tasks) function as different cues to alter worker active/rest patterns. We discuss the potential roles of worker-worker interactions on the chronobiological organization of the ant society.
In social animals, how individual behavioral rhythms are governed by social interactions is a fundamental question towards the mechanistic understanding of complex biological systems. Using an image-based tracking system, we composed artificial ant worker groups consisting of different functions (i.e., young nurses and old foragers) and investigated whether the age composition and the resulting interactions had an effect on the active/rest rhythms of individual workers, and of the whole group. In solitary conditions, both young and old workers showed circadian activity; however, when grouped with workers from different age groups, both young and old workers turned to show weak circadian rhythmicity or around-the-clock activity. Our results suggest that even simple social cues (i.e., frequency of contact with young and old workers) could alter worker activity patterns. To our knowledge, this is the first evidence showing that specific worker-worker interaction induces weakly rhythmic and/or arrhythmic states.
KeywordsCircadian rhythm Age Social interaction Diacamma sp. Image-based tracking
We thank Tsuji K. for reviewing an earlier version of this manuscript. Uematsu J. kindly supported us for ant excavation. Many thanks to Hakataya S. for helping with the ant-keeping work. We appreciate the advice of Shimada M. for statistical evaluation and his valuable comments. Our thanks also go to reviewers and editors for careful reading of our manuscript and their many insightful comments and suggestions.
This study was funded by the Kakenhi (#18H04815; 17H05938; 17K19381; 15H06830) and the Sasakawa Scientific Research Grants from The Japan Science Society.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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