Ever seen the “Trust Me, I’m an Engineer” meme on the Internet? As it turns out, the slime mold Physarum polycephalum can claim the title of engineer as well!
Physarum polycephalum is a single-celled organism, which when in the plasmodium phase of the life cycle, will grow continuously, expanding tendrils into unknown territory, as long as nutrients are present. Tendrils with high volumes of nutrients will expand, while those that are used less will gradually disappear, leaving an efficient network.
Fig 1: Physarum Polycephalum colony growing on a rock
Reproduced under a Creative Commons license from Wikipedia (original author: Jerry Kirkhart)
For background information on slime molds and their life cycle, click here.
Researchers in Japan and the UK experimented with slime mold, presenting it with a model where geographical locations of cities around Tokyo were represented by oat flakes. The slime mold was allowed to grow into the arena, creating a transport network. Amazingly, the network formed was comparable in efficiency to the real Tokyo rail system, even though the slime mold has no brain, no central planning process.
Here’s a video showing slime mold growing out into the Tokyo arena: (attribution: sjtkg001)
You say, wait a second, what exactly do the researchers mean by efficiency? 3 main factors were taken into account: total length (TL), average minimum distance (AMD) and fault tolerance (FT). Average minimum distance represents how easy it is to get between the food sources, which is analogous to how easy it is to get between cities (transport efficiency). Fault tolerance measures how resilient the network would be, i.e. if it still functions if connections are broken. A high-performing system is one with a low TL representing minimal cost, low AMD representing high transport efficiency, and high FT representing high resilience.
Here’s a podcast from CBC with Dr. Mark Fricker who headed the Tokyo rail slime mold experiment; he gives details on this experiment:
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If you’re suspicious that the slime mold got lucky, researchers replicated their experiment with transport networks in Germany, the UK and even Canada! They found that again, the slime mold built a network with comparable performance.
Here’s a link to an article testing slime mold growth with a trans-Canada highway model.
Drawing inspiration from the slime mold, researchers around the world are now using biological systems to model real-world infrastructure problems in arenas such as computing, transport, and communication. They take the real-world conditions of problems in these arenas, such as spatial boundaries (i.e. rivers, cities, mountains), and apply these boundary conditions on slime mold by manipulating variables such as light intensity and antibiotic concentration. They then observe the growth networks and patterns of slime mold that arise, and can use these as a preliminary model for a solution.
Interested in reading more? Researchers are also utilizing the slime mold to model the blood vessel networks feeding tumors. With this understanding, they hope to come up with a method to starve the tumor of blood by cutting off key connections.
-Christie Chan
References:
Tero, A., Seiji, T., Saigusa, T., Ito, K., Bebber, D.P., Fricker, M.D., Yumiki, K., Kobayashi, R., Nakagaki, T. (2010, January 22). Rules for biologically inspired adaptive network design. Science, 327, 439-442.
Video: https://www.youtube.com/watch?v=BZUQQmcR5-g
Websites used:
http://esciencenews.com/articles/2010/01/21/slime.design.mimics.tokyos.rail.system
http://news.sciencemag.org/sciencenow/2012/08/a-slimy-insight-into-treating-ca.html
Podcast:
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