Characteristics of daily foraging activity of Camponotus japonicus via time series analysis.

Social insects often share tasks among individuals. In this study, we analyzed the foraging activity of ants (Camponotus japonicus) and recorded the daily passage event counts of individual workers between a nest chamber and a foraging arena in five monodomous colonies. We proposed two hypotheses on the time series of foraging frequency by individual worker ants as follows: (i) for the time series of foraging frequency by individual worker ants, the foraging frequency on a certain day could be expressed by the product of the foraging frequency on the previous day and the exponential of a random number. (ii) The random numbers are correlated between some pairs of worker ants. The results for the five tested ant colonies showed that the probability of total daily passage counts (the sum of an individual's passage count) followed a log-normal distribution. The worker ants behaved differently in terms of active days and foraging frequency. However, for > 54% of the worker ants, the probability of the daily passage count was characterized by a log-normal distribution, and these worker ants performed > 72% of the tasks in each colony. Furthermore, for > 73% of the worker ants, the time development of the passage count was mathematically modeled; the logarithmic first difference between the passage counts on a certain day and those on the previous day was a random normal variable. These results support hypothesis (i). Additionally, the random numbers that were equivalent to the logarithmic first difference were correlated for some pairs of worker ants. These results support hypothesis (ii).

Elastically coupled two-dimensional Brownian motors.

Many workers have theoretically and numerically studied Brownian motors (ratchet models) as models for molecular motors for many years. Their studies have been mainly concerned about one-dimensional motion of a particle or coupled particles experiencing spatially asymmetric interaction force. In this paper, we introduce a coupled flashing ratchet model, that is, elastically coupled Brownian particles with their own easily advancing directions under the on-and-off (or occasional) influence of two-dimensional interaction force asymmetric in the easily advancing direction of each particle. The dynamics of the model is investigated by computer simulation and characteristic motion of the particles in the two-dimensional space is observed. Our model is also studied as that for molecular motors in muscle contraction and the simulation results are compared with those of in vitro biological experiments in motility assays of the molecular motors. We succeed in reproducing the experimental results qualitatively with our model.