Abstract
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.
Highlights
Cyclical activity patterns are found at every level of biological organization, from genes to cells, organs, and societies, and span many orders of magnitude in space and time
Information, food, and chemical signals are transported throughout the group via worker-to-worker physical contacts, and it has been suggested that the activity cycles might serve to increase the rapidity of information transmission
We used an automatic ant tracking system to identify physical contacts between workers, from which we reconstructed the dynamical network of physical contacts
Summary
Cyclical activity patterns are found at every level of biological organization, from genes to cells, organs, and societies, and span many orders of magnitude in space and time. Cyclical activity is found at the smallest spatial scale in the regulation of circadian Clock genes [1], and at the largest, in the cyclical fluctuation of populations of predators and prey [2, 3]. Cyclical phenomena occur at frequencies ranging from roughly once per second for the firing patterns of human cardiac pacemaker cells [4], to once every 13 or 17 years for reproductive cycles in cicadas [5]. Cyclical activity patterns can be driven by an exogenous signal, such as diurnal, lunar and seasonal cycles, there are many systems in which cyclical activity emerges in the absence of a pacemaker. The synchronization (or anti-synchronization) of courting fireflies [7] and calling in frog choruses [8] is an emergent property, though these are so regular that it was originally hypothesized that there must exist a leader that sets the rhythm [9, 10]
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