Short-term activity cycles impede information transmission in ant colonies

Rhythmical activity patterns are ubiquitous in nature. We study an oscillatory biological system: collective activity cycles in ant colonies. Ant colonies have become model systems for research on biological networks because the interactions between the component parts are visible to the naked eye, and because the time-ordered contact network formed by these interactions serves as the substrate for the distribution of information and other resources throughout the colony. To understand how the collective activity cycles influence the contact network transport properties, we used an automated tracking system to record the movement of all the individuals within nine different ant colonies. From these trajectories we extracted over two million ant-to-ant interactions. Time-series analysis of the temporal fluctuations of the overall colony interaction and movement rates revealed that both the period and amplitude of the activity cycles exhibit a diurnal cycle, in which daytime cycles are faster and of greater amplitude than night cycles. Using epidemiology-derived models of transmission over networks, we compared the transmission properties of the observed periodic contact networks with those of synthetic aperiodic networks. These simulations revealed that contrary to some predictions, regularly-oscillating contact networks should impede information transmission. Further, we provide a mechanistic explanation for this effect, and present evidence in support of it.Author summary: Many complex biological systems, from cardiac tissues to entire animal populations, exhibit rhythmical oscillations. Here we studied a textbook example of a complex living system–colonies of Leptothorax ants, which exhibit short (15 minute) collective activity cycles. In ant colonies, information, food, and chemical signals are transported throughout the group via worker-to-worker physical contacts, and it has therefore been suggested that the activity cycles might serve to increase the rapidity of information transmission. To test this, we used an automatic ant tracking system to identify physical contacts between workers, from which we reconstructed the dynamical network of physical contacts. We used models of information transmission derived from the study of contagious diseases to simulate information transmission over the rhythmical contact networks, which we compared against a set of comparable networks that exhibited no rhythms. These comparisons showed that, contrary to the expectations, oscillatory activity cycles slowed down information transmission rather than speeding it up. We suggest that the colony activity cycles might serve to ensure that old or out-of-date information is quickly expunged, and potentially reduce interference between different information streams.