Timing and Collective Behaviours

What is a swarm?

When we think of a swarm, we usually think of swarms of insects, but the term swarm can be applied to different species (e.g herds, flocks, schools, societies (e.g I Couzin. ), and even different scales (e.g gluons, quarks, electrons, particles, cells, organisms, stars, etc).

These ideas are already being explored by a number of scientists, particularly in the field of artificial intelligence where swarm behaviours are used to explore collective behaviour/self organisation. 

Living systems provide many examples of self organisation by collective processes.  Fish schools, bird clouds, wasp swarms, ant colonies, and colonies of certain types of unicellular organisms and bacteria, all self-organise in this way. Structures and organisations develop, not by action at the level of the individual, but rather by way of dynamic processes in which the individuals are strongly coupled to one another and behave as a collective ensemble.  These are swarming phenomena in groups of self-propelled particles that locally exchange directional information.  Paul Bourgine – 2010 .  A striking feature of this behaviour is that the same types of morphology often arise in spite of large differences in the size and nature of the individual unit.  J Tabony – ‎2007.

Swarming and Phase Transition

Collective oscillations emerge when the external concentration, or equivalently cell-density, exceeds some critical threshold. P Mehta 2010.  A phase transition then takes place.

Swarm models can be used to explore the relation of nonequilibrium phase transitions to at least three important issues… Firstly, that of emergence as complex adaptive behavior. Secondly, as an exploration of continuous phase transitions in biological systems. Lastly, to derive behavioral criteria for the evolution of collective behavior in social organisms. Mark M. Millonas 1993.   GS Medvedev 2000. 

This article explores the idea that such thresholds are established through a collective space/time information – with timing playing a core role.

Circadian Rhythms, Redox and the Metabolism

It has been argued that the collective rhythmicity of circadian clocks may be best obtained by studying it at its outset, that is treating it as a kind of phase transition or bifurcation or self-synchronization transition (Y Kuramoto 1984 and Goldbeter 2007). Winfree discovered that such oscillator populations can exhibit a remarkable cooperative phenomenon. Each body clock has been seen to have a distinct role, but harmonizes with the other sections via a precise phase relationship. J. Z. Li 2014.

Circadian Rhythms are dissipative structures due to a negative feedback produced by a protein on the expression of its own gene (Goodwin, 1965; Hardin et al., 1990). They operate far-from- equilibrium and generate order spontaneously by exchanging energy with their external environment (Prigogine et al., 1974; Goldbeter, 2002; Lecarpentier et al., 2010).

Current evidence supports the conclusion that the responses to reaction oxygen species (ROS) are mediated both through the regular function of the molecular clockwork and the involvement of the Transcription Translation Feedback Loop genes in extra-circadian pathways..results suggest that non-transcriptional processes such as metabolic state may interact and work in parallel with the canonical genetic mechanisms of keeping circadian time. Redox perturbs circadian rhythms which in turn perturb redox.  Lisa Wulund 2015.  K Nishio 2015,  N B Milev 2015. Recently, it has become apparent that the cellular redox state oscillates in vivo and in vitro, with a period of about one day (circadian). M Putker 2016.

It is suggested that circadian rhythms (coupled with redox) are providing the “timings and direction” needed to enable “swarm” behaviour in biological morphogenesis.

Bacteria

in Quorum Sensing, bacteria release diffusible signal molecules known as autoinducers, which by accumulating in the environment induce population-wide changes in gene expression…Modelling shows propagating waves of activation or deactivation of the QS circuit in a spatially extended colony, and the model equations possess a traveling wave solution….Analysis of the diffusivity dynamics also leads to an understanding of the swarming phase dynamics and the gradual transition to the consolidation phase that follows it. These analyses show that the concentrations at the beginning of the two phases naturally repeat in a time-periodic manner. JB Langebrake – ‎2014.   Also see  GS Medvedev 2000. 

One species of commensal bacterium from the human gastrointestinal system, Enterobacter aerogenes, is sensitive to the neurohormone melatonin, which is secreted into the gastrointestinal lumen, and expresses circadian patterns of swarming and motility. Melatonin specifically increases the magnitude of swarming in cultures of E. aerogenes, but not in Escherichia coli or Klebsiella pneumoniae. The swarming appears to occur daily, and transformation of E. aerogenes with a flagellar motor-protein driven lux plasmid confirms a temperature-compensated circadian rhythm of luciferase activity, which is synchronized in the presence of melatonin. Jiffin K. Paulose 2016.

Social Insects

Social insects such as honeybees, ants, wasps and termites live in colonies consisting of up to a few million individuals who coordinate almost every aspect of their lives.  The temporal coordination of their activities is thought to be important for efficient colony functioning and therefore colony fitness. The most intuitive aspect of their temporal coordination is synchronising their phase of activity (social entrainment).   Honeybees show a colony level circadian rhythm that is maintained in constant light and can be phase-shifted as the rhythms of individual animals. The synchronization of individuals in insect societies is thought to be functionally significant because it improves colony efficiency..Temperature is an attractive time-giver for self-organized social synchronization.  However it should be noted that while both scouts and forager bees look alike, research suggests that they represent stable subpopulations with distinctive patterns of gene expression in their brains. (See Liang, Z. S., et al. 9 March 2012).

Size, division of labor, and diurnal rhythms in activity are correlated in B. terrestris (bumble bee) colonies. Large workers typically perform foraging activities with strong diurnal rhythms and low activity at night, whereas small bees typically care for (nurse) brood around the clock with weak or no diurnal rhythms. Under constant laboratory conditions, circadian rhythms in locomotor activity were weaker, less stable, and developed at a later age in small (nurse-size) bees compared to their larger (forager-size) sisters. Under a light:dark illumination regime, many small bees, particularly at a young age, were active during the dark phase, fewer small bees developed rhythms, and they did so later compared to large bees. These findings reveal naturally occurring attenuation or suppression in the circadian clock of small bees that is determined during pre-adult development. This deficiency in clock function, however, does not result in pathology but rather appears to be functionally significant, because it is associated with around-the-clock brood care activity and therefore apparently improves divisions of labor and colony efficiency. This in turn suggests that variation in social biology influences traits of the circadian rhythms (S Yerushalmi 2006).

The timing of drone production determines both the drones’ likelihood of mating and when colonies reach sufficient size to swarm. N J Lemanski 2017.

The integration of behavioral rhythmicity with the colony’s division of labor, the evidence for social entrainment of behavioral rhythms and for a ‘clock of the colony’; and the potential linkage between circadian rhythms of general locomotor activity and the foraging time-sense, has also been examined in relation to the honey bee.  D Moore 2001.  Honey bees, when thrown into highly time-altered new societal roles, are able to alter their biological rhythms with alacrity, enabling them to make a successful “quick switch” in their daily routines.  It has been found that  social time cues stably adjust the clock, even in animals experiencing conflicting light exposure and social cycles. in honeybees, social interactions can override potent light exposure as external cues that influence the biological clock.

Such social entrainment of circadian rhythms has also been found in other species e.g marmosetscavebats.  The best evidence for the influence of social activity on the internal clock is found in dark cavity-dwelling social animals, such as bees and bats. These species may be especially responsive to social influence, because individuals may not experience ambient conditions directly, but rather rely on information received from group mates that forage outside their domicile.  Cocial interactions failed to entrain circadian rhythms in social mammals such as the squirrel monkey (Saimiri sciureus), Mongolian gerbil (Meriones unguiculatus) and sugar gliders (Petaurus breviceps) as well as in the gregarious cockroach Leucophaea maderae.  T Fuchikara 2015

But studies also indicate that social signals may be important time-givers for the clocks of other animals, including mammals,

Circadian driven behaviour (associated with the life-mating cycles of particular species) is also found in:

  • some species of zooplankton, with the forming of swarms at dawn and dispersion at dusk,
  • circadian rhythms have been identified in insect swarming (associated with mating) e.g in midges, cockroaches, fruitflies, and mosquitoes.  Such rhythms might also be found in cicada.

The animals that feed on insects may also be effected by similar rhythms e.g Birds flocking together at dawn and dusk.

Research has also been undertaken with cellular automata, in order to explore the role of timing in triggering social change in humans through uncoordinated, autonomous individual action.  R Sosa 2011.

Timing, Collective Behaviour and Growth

In all vertebrate animals, the segmentation of the body plan proceeds during embryonic development in a process termed somitogenesis. During somitogenesis, the elongating body axis segments rhythmically and sequentially into somites, the precursors of vertebrae and ribs. Failure of proper segmentation, caused for instance by mutations, can give rise to birth defects such as congenital scoliosis. Somites are formed in characteristic time intervals from an unsegmented progenitor tissue, the presomitic mesoderm (PSM). The temporal regularity with which somites form has provoked the idea that a biological clock comprised of cellular oscillators coordinates the temporal progress of segmentation in the PSM. The so-called ‘clock-and-wavefront’ mechanism suggests that a wavefront at the anterior end of the PSM reads out the state of this clock and triggers the formation of a new segment upon each completed clock cycle. Indeed, patterns of oscillating gene expression have been found in the PSM of various vertebrates such as zebrafish, chick, mouse, frog, and snake. These patterns resemble traveling waves sweeping through the PSM and occur as a result of coordinated cellular oscillations in the concentration of gene products. Genetic oscillations are proposed to occur autonomously in single cells as a result of delayed autorepression of specific genes. DJ Jörg – ‎2015 

 Reference : Existing Models of Collective Behaviours

coupling

P Mehta 2010.

The above does not include a further model. Fritz London suggested that the application of superfluid like states to macro-molecules might explain the ability of large molecules to act as single units.  Recently it has been found that in specific conditions, a simple shear of an active suspension of Escherichia coli displays a super-fluid like transition where the viscous resistance to shear vanishes. H M Lopez 2015.

2015-2016. This article merely joins up other peoples work into an overall system.  These works have been referenced so it is clear that others have provided the individual pieces of evidence that have been used to shape a specific systems approach.    

 

 

 

 

 

 

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