Networks of the Forest

Among Slime Molds and Mushrooms

We humans tend to be quite quick to congratulate ourselves on our achievements in creating vast worldwide networks, machines and other inventions. What was unknown to us until very recently is that we were not the first to do this! No, I’m not talking about the aliens who live under the sea or Atlanteans or other previous civilizations, but about a completely different species. A species that until very recently we viewed as stupid and primitive, namely the slime mold Physarum polycephalum!

If you’ve ever been in the woods and turned over an old rotten log or stick with some kind of yellow netting or gore on the underside, you’ve probably come across the slime mold who lives as a decomposer of old moist logs. It does not consist of a mass of different nerve fibers and cells that can be compared to a brain, but is simply what you see: slime consisting of one single cell. When it develops into slime mold and begins to grow, it reshapes itself into a kind of plasmodium, which is an amoeba-like form without individual cells and cell walls, but with several cell nuclei.

What is particularly remarkable about this organism is that, despite its simplicity, it can learn and act according to the circumstances, something that scientists around the world have learned through startling experiments! They have subjected it to many of the same experiments that are normally used to test the intelligence of other animals such as mice and rats and discovered that in many cases it passes them gallantly, often better than other animals and organisms. It can e.g. remember where to find food!

Long thin shoots as “scouts”

To “remember” places, it uses the size of its tentacles or passages. First it sends out very long and thin shoots to search and once it finds something, it widens these to act as a bit of highway for the nutrients. When all the food is taken up, it leaves these thicker pathways in case more food should appear. These pathways also act as an information network to the rest of the organism when it has to decide which direction to expand in next! In the same way, it likes to avoid and build bridges over unpleasant routes, such as e.g. salt and other things that it is not so fond of.

A Japanese study by Nakagaki, Yamada & Tóth tested the slime’s ability to navigate a maze and found that after only 8 hours the slime had not only identified the fastest route through the maze, but also reorganized itself by building a wide path to the goal and retracted or severely shrunk the remaining sensory buds that led to dead ends. This was then repeated over and over and the slime consistently chose the shortest and most efficient route through the maze.

Tokyo’s subway system, rebuilt

The team then recreated Tokyo’s subway system in miniature, marking the stations with tiny oatmeal and putting the slime to work. The slime managed to recreate the entire subway system in the most efficient way possible, which is not a small feat. The Tokyo subway is world renowned for running on a perfect schedule, even publicly apologizing for delays as short as a minute.

Fungi, slime and mold are a very interesting area that we basically learn more about on a daily basis, both about the organisms themselves but also through their close collaboration with plants, trees and even ourselves. One of the reasons why mushrooms are not included in the right to common property in Sweden is said to be because they were considered so unimportant and nutrient-poor that they were not relevant to either the landowner or the rest of us. It’s a view that is changing at a very rapid pace with studies on everything from how fungi can permanently cure anxiety with a single dose, to how they act not just as parasites on trees but actually live symbiotically with the trees and help the trees take care of and interact with their respective families, to today’s topic!