(Fig. 25.2), but the group action is not directed by a specific leader. Each individual
has the ability and possibility to play the leading role, and who actually plays the role
is determined by “chance.” Once triggered, a great number of fish form a collective
entity, moving in the same direction.
25.2.3.1 Self-Organization
The collective behavior of flock occurs in a self-organizing manner, in which each
individual is programmed to place itself next to another one and swim in the same
direction. Construction of a functional complex due to self-organization can be
widely seen in the world of molecular apparatuses. An example of such sophisticated
architecture is the bacterial flagellum (Thomson et al. 2018). Some bacteria swim
toward an attractant or away from a repellent by flagellar rotation. This rotation
transforms the fine fiber into a coiled structure that serves as a screw. The rotation is
reversible, and the change in orientation allows the switching between swimming
and tumbling modes. This surprising performance is achieved because of the
ultrastructure of the flagellum fiber, which exerts both stiffness and suppleness,
making the screw rigid and flexible, respectively.
The flagellum is predominantly a polymer of the flagellin protein (Thomson et al.
2018). Flagellin is synthesized inside the cell and subsequently transported across
the membrane(s) by the flagellar basal body that functions as a specific membrane
translocator. The exported flagellin molecules form the flagellum due to its ordered
assembly that occurs in a self-organizing manner aided by a chaperone protein. The
autonomously developed protein fiber serves as a highly functional apparatus that
enables the active movement of prokaryotic cells. Similar self-organizing development occurs widely in cellular macromolecules including proteins, nucleic acids, and
lipid bi-layers.
25.2.3.2 Autonomous Distribution
Another mystery in the aforementioned flock formation is the mechanism of its
initiation. It appears to be determined occasionally and randomly, which triggers
social action without the process of active selection. This kind of social behavior is
observed not only with animals but also with microorganisms. Dictyostelium, a slime
mold, is known for its surprising life cycle based on an autonomous distribution
program (Huber 2016). In its vegetative phase, each Dictyostelium cell behaves as a
free-living amoeba searching for and eating bacteria independently of other cells.
However, food depletion causes the transformation of one cell into a sender of an
aggregation signal. By sensing the concentration gradient of the signal molecule
(i.e., cAMP), other cells migrate in the direction of the sender cell. Thus, aggregated
cells form a moving body, which moves toward an appropriate place where the
moving body settles and differentiates into a fruiting body containing dormant
536
K. Ueda
has the ability and possibility to play the leading role, and who actually plays the role
is determined by “chance.” Once triggered, a great number of fish form a collective
entity, moving in the same direction.
25.2.3.1 Self-Organization
The collective behavior of flock occurs in a self-organizing manner, in which each
individual is programmed to place itself next to another one and swim in the same
direction. Construction of a functional complex due to self-organization can be
widely seen in the world of molecular apparatuses. An example of such sophisticated
architecture is the bacterial flagellum (Thomson et al. 2018). Some bacteria swim
toward an attractant or away from a repellent by flagellar rotation. This rotation
transforms the fine fiber into a coiled structure that serves as a screw. The rotation is
reversible, and the change in orientation allows the switching between swimming
and tumbling modes. This surprising performance is achieved because of the
ultrastructure of the flagellum fiber, which exerts both stiffness and suppleness,
making the screw rigid and flexible, respectively.
The flagellum is predominantly a polymer of the flagellin protein (Thomson et al.
2018). Flagellin is synthesized inside the cell and subsequently transported across
the membrane(s) by the flagellar basal body that functions as a specific membrane
translocator. The exported flagellin molecules form the flagellum due to its ordered
assembly that occurs in a self-organizing manner aided by a chaperone protein. The
autonomously developed protein fiber serves as a highly functional apparatus that
enables the active movement of prokaryotic cells. Similar self-organizing development occurs widely in cellular macromolecules including proteins, nucleic acids, and
lipid bi-layers.
25.2.3.2 Autonomous Distribution
Another mystery in the aforementioned flock formation is the mechanism of its
initiation. It appears to be determined occasionally and randomly, which triggers
social action without the process of active selection. This kind of social behavior is
observed not only with animals but also with microorganisms. Dictyostelium, a slime
mold, is known for its surprising life cycle based on an autonomous distribution
program (Huber 2016). In its vegetative phase, each Dictyostelium cell behaves as a
free-living amoeba searching for and eating bacteria independently of other cells.
However, food depletion causes the transformation of one cell into a sender of an
aggregation signal. By sensing the concentration gradient of the signal molecule
(i.e., cAMP), other cells migrate in the direction of the sender cell. Thus, aggregated
cells form a moving body, which moves toward an appropriate place where the
moving body settles and differentiates into a fruiting body containing dormant
536
K. Ueda