Symmetry breaking of escaping ants

From Justapedia, unleashing the power of collective wisdom
Jump to navigation Jump to search

Symmetry breaking of escaping ants is a phenomenon that is observed when ants are constrained into a cell with two exits at equal distances and then sprayed with an insect repellent. Ants tend to use one door more than the other on average (i.e., there is a symmetry breaking in the escape behavior), so they crowd one of the doors, which decreases evacuation efficiency.

Description

This phenomenon arises in the following experiment:

Environment

A few worker ants freshly collected from the field are enclosed into a circular cell with a glass cover in such a way that they can only move in two dimensions (i.e., ants can not pass over each other). The cell has two exits located symmetrically relative to its center.

Experiment

In the first experiment, both exits were opened at the same time, letting the ants escape. After 30 repetitions, the average percentage difference in door use was 13.366%, meaning that one door received 13.366% more ants than the other.

In the second experiment, everything took place as in experiment one, with the important difference being that, a few seconds before opening the doors, a dose of 50 µL of an insect repellent was injected into the cell at its center through a small hole in the glass cover. After 30 repetitions, the average percentage difference in door use was 38.3%, meaning that one door received 38.3% more ants than the other.

History

Inspired by earlier computer simulations that predicted a symmetry-breaking phenomenon when panicked humans escape from a room with two equivalent exits, a team of researchers led by E. Altschuler carried out the two experiments described above, which revealed the symmetry-breaking effect in the leafcutter ant Atta insularis in the presence of insect repellent.[1]

Another team of researchers led by Geng Li investigated the influence of the ant group's density on the symmetry breaking. They used the red imported fire ant to repeat the experiment with different amounts of ants. The results show that symmetry breaking is high at low densities of ants, but decreases beyond a certain point in the density of ants. In other words, when density is low, the ant group produces a collective escaping behavior, while at high density, their behavior is more like random particles.[2]

Explanations

The common idea is that the action of injecting the insect repellent induces herd behavior in the ants. When ants are in "panic", they experience a strong tendency to follow each other. As a result, if a random fluctuation in the system produces a locally large amount of ants trying to reach one of the two doors, the fluctuation can be amplified because ants tend to follow the direction of the majority of individuals, resulting in that door getting crowded.

Altshuler and coworkers were able to reproduce their symmetry-breaking experiments previously done in ants in humans, using a simplified version of the theoretical model proposed earlier by Helbing et al.[3] based on the fact that walkers tend to follow the general direction of motion of their neighbors ("Vicsek's rule"[4]), and such herd behavior increases as the so-called "panic parameter" increases. In the case of ants, the panic parameter is supposed to be low when no repellent is used and high when the repellent is used.

A more "biologically sensible" model based on the deposition of an alarm pheromone by ants under stress also reproduces the symmetry-breaking phenomenon, with the advantage that it also predicts the experimental output for different concentrations of ants in the cell.[2] The pheromone mechanism shares the key elements of the previous models: stressed ants tend to "follow the crowd".

References

  1. ^ E. Altshuler; et al. (2005). "Symmetry breaking in escaping ants". American Naturalist. 166 (6): 643–649. doi:10.1086/498139. JSTOR 498139. PMID 16475081. S2CID 7250726.
  2. ^ a b Li, G.; Huan, D.; Roehner, B.; Xu, Y. J.; Zeng, L.; Di, Z.; Han, Z. G. (2014). "Symmetry Breaking on Density in Escaping Ants: Experiments and Alarm Pheromone Model". PLOS ONE. 9 (12): 0114517. Bibcode:2014PLoSO...9k4517L. doi:10.1371/journal.pone.0114517. PMC 4281238. PMID 25551611. open access
  3. ^ D. Helbing.; et al. (2000). "Simulating dynamical features of escape panic". Nature. 407 (6803): 487–90. arXiv:cond-mat/0009448. Bibcode:2000Natur.407..487H. doi:10.1038/35035023. PMID 11028994. S2CID 310346.
  4. ^ T. Vicsek; et al. (1995). "A new type of phase transition in a system of self-driven particles". Phys. Rev. Lett. 75 (6): 1226–1229. arXiv:cond-mat/0611743. Bibcode:1995PhRvL..75.1226V. doi:10.1103/PhysRevLett.75.1226. PMID 10060237. S2CID 15918052.
Retrieved from "https://justapedia.org/index.php?title=Symmetry_breaking_of_escaping_ants&oldid=1119747757"