Rhythmic behavior of social insects from single to multibody
Highlights
► We analyzed a simple behavior of an individual ant and a pair of ants. ► An activity of each individual has a rhythmic component. ► Interactions between a pair of individuals cause an anti-phase and an in-phase coupling. ► We propose a simple model based on the coupled oscillators.
Introduction
Social insects such as ants and bees have some interesting characteristics and show well-organized group behaviors. Particularly, ant colonies are highly organized and exhibit a wide variety of remarkable behaviors. Their colonies consist of numerous individuals which engage in nest construction/maintenance, taking care of brood, defending, foraging and so on by division of labor [1], [2], [3].
A well-organized phenotype of the group (hereafter we call a social phenotype) may be produced by two possible mechanisms, namely, a central control and a distributed control. In order to adapt themselves to the changing environment, in the first case, a central governor controls the activity of other members of colony. In the second case, the emergence of distributed control results from the local interaction of interchangeable components of the colony. These collective behaviors do not require a special individual that controls the behavior of the entire group, but, rather, the potentially interchangeable individuals achieve these collective behaviors by interacting with each other through direct sight, direct physical contact or chemical materials, such as pheromones.
An adaptive function is considered to emerge from the interaction among the body, brain, and environment, which requires that a subject acts or moves. In our research, we have not investigated a function of the brain. However, in the case of socialinsects, individual colony members work as a unit and the colony as a whole adapt itself to various changes in environment by interactions among colony members based on the local information.
In the species, Diacamma sp., direct contacts are necessary for each individual to acquire some information regulating and maintaining the society. The individual workers should move to interact to other members of the colony. For example, gamergates of Diacamma sp. colonies inhibit the development of ovaries of the workers by direct physical contacts, which is known as “patrol behavior of gamergates [4]”.
The behavior of “move and interact” of individual ants leads to emergence of whole colony behavior. To reveal a mechanism of “move and interact” in the colony of social insects contributes the object of this special issue of “Mobiligence”.
The essential point of the collective behavior greatly depends on the local interaction of a few ants, and that as a first step the observation of group behavior in a small scale [5] provides some significant insights into large groups. It is significant to understand how the components interact to produce the collective properties of social groups. The approach in this study is to manipulate social groups that are simpler than the natural social units. By controlling environmental factors such as intensity of light, space restriction, temperature and social factors such as number of interacting workers, we regulate the type of interactions between workers to focus on the social interactions among individuals.
The approach to understand the colony behavior based on behavior of individual workers has been also investigated by Cole et al. in the species of Leptothorax allardycei. The single ant was reported to have spontaneous bursts of activity but has no rhythmic episodes of activity [6], [7]. However, as the number of nestmates increases, the rhythmic episodes of activity as a whole colony emerges. We discuss whether the rhythmic behavior is the individual propensity or the colony propensity in the case of Diacamma sp.
Section snippets
Objective
We manipulate the number of individuals to interact in the experimentally controlled space and analyze each individual separately so that the activity as a group can be discussed in more detail. The identification of each ant activity makes it possible to observe the coupling of activity states compared with the case when one measures only total activity of the members [6]. We would like to generalize the manipulation of number of colony members up to an entire colony (this attempt is
Material
We studied the behavior of Diacamma sp., which is the only one species of this genus distributed in Japan. The average size of worker is about 10 mm in length, and their colony comprises of . Workers are characterized as quite aggressive and hunt insects individually.
Experimental set-up
In order to analyze the behavior of ant workers, one or two ants are randomly picked up from a colony and placed in an acrylic hemisphere (30 cm in diameter) field as shown in Fig. 1. Environmental factors should not
Trajectory of single ant
Fig. 2 shows an example of the trajectory obtained from the motion of the single ant. The trajectory of single ant covers the entire hemisphere. When placed in the unknown space, the ant seems to search the entire space during the time duration of 4 h. This searching behavior should be measured as a function of time, so, we calculate an area coverage rate of the experimental field as the trajectory develops. The projected plane of hemisphere is divided into 10 mm2 lattice cells. If the ant
Conclusion
A social phenotype may be produced by two possible mechanisms, namely, the central control and the distributed control. In the second case, the local interactions between interchangeable components function at the bottom of the collective behavior. We focused on a simple behavior of an individual ant and analyzed the interactions between two worker ants in terms of coupled oscillators.
From this bottom-up approach, we found the characteristics of a single worker and a pair of workers as follows:
Yoshikatsu Hayashi is currently an assistant professor in the Robotics department of Ritsumeikan University, Japan. He received his Ph.D. from Lund University, Sweden in 2004. Being educated in physics and using methods of robotics, he has been studying adaptation of living creatures from a single cell, social insects, and humans. His main interest has been different or common aspects of living creatures, evolving from the self-organized system to the emergence of self-centered regulation of
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Yoshikatsu Hayashi is currently an assistant professor in the Robotics department of Ritsumeikan University, Japan. He received his Ph.D. from Lund University, Sweden in 2004. Being educated in physics and using methods of robotics, he has been studying adaptation of living creatures from a single cell, social insects, and humans. His main interest has been different or common aspects of living creatures, evolving from the self-organized system to the emergence of self-centered regulation of the brain in sensory-motor systems.
Mai Yuki received the BA and MA degrees in human informatics in 2009 and 2011, respectively, from Tohoku Gakuin University. Her interest is mainly focused on the behavior of small group of ants.
Ken Sugawara is currently an associate professor in the department of Information Science of Tohoku Gakuin University. He received the ME in electronic engineering and the Ph.D. degree in Information Science, in 1994 and 1997, respectively, from Tohoku University, Japan. His research interest includes collective robot system inspired by the group of animals.
Tomonori Kikuchi is currently an associate professor in the Marine Biosystems Research Center of Chiba University, Japan. He received the M.S. and the Ph.D. in Environmental Earth Science from Hokkaido University, Japan. His current research interests include relationships between self-organization and social evolution in animal society.
Kazuki Tsuji is a biologist whose major discipline is evolutionary ecology of social insects. His current interests are theoretical and empirical approaches to combining theories of life history strategy, community ecology and social evolution. Sociobiological studies on conflict within insect societies have also been a focus of his work.