Alien beings in their sights: How can slime molds behave “intelligently” without a nervous system? Apparently, they structure information from their environment, according to a study. When they come into contact with a source of food, certain substances trigger the formation of a pattern in the tube-like network structures of the giant unicellular organisms, in which the location information is encoded. Apparently, this mechanism forms a kind of memory that can serve as an orientation aid for the bizarre creatures while moving.
Slime molds are neither animals nor plants and, despite their name, not mushrooms either – the bizarre freaks have very peculiar characteristics: Their body consists of a huge single cell that forms a network-like structure of interconnected tubes. In some types of slime mold, the unicellular body can reach astonishing dimensions: The structure can span meter-sized areas, which has earned the slime mold the title of the largest cells on earth in the Guinness Book of Records.
The swirling structures of these bizarre creatures move with sometimes considerable speed over the ground – always looking for something to eat. The exciting thing is that studies have shown that slime molds do not simply follow the gradient of attractant substances when they move. Instead, they show surprisingly “intelligent” behaviors. Experiences seem to influence the movement pattern of the slime mold. This suggests: The supposedly simple beings can memorize information about the environment and use it for meaningful decisions. How such a memory is possible without a nervous system is so far unclear.
Slimy freaks in their sights
Mirna Kramara and Karen Alim from the Technical University of Munich have now gained new insights into the fundamentals of the “clever” behavior of mysterious beings. The slime mold Physarum polycephalum was in their sights.
When the researchers followed the movements and feeding behavior of the organism, they noticed patterns in the network structures. They appeared to form in response to contact with food sources. A kind of signature of the position emerged in the thicker and thinner tubes of the network, which was still observable long after the ingestion of food.
“Given the normally rapid reorganization of P. Polycephalum’s network, the persistence of this imprint gave us the idea that the network architecture could serve as a memory of the feeding places,” says Alim. They followed this trail by trying to decipher the possible mechanisms that could underlie the effect. To do this, the researchers combined microscopic observations of the adjustments to the tubular network with theoretical modeling.
Reminders are saved on the network
As Kramara and Alim report, their results confirmed: Slime molds apparently weave memories of places of food directly into the architecture of their network-like bodies and can apparently use the information stored in this way in future decisions. As can be seen from the models, contact with the food source inside the cell triggers the release of a messenger substance, which then moves from the place where the food was found through the entire organism. The hitherto unknown substance causes the tubes in the network to soften. In the area facing the food source, they expand more so that the organism aligns itself with the food source.
However, the traces of this pattern do not disappear afterwards – they are retained for a long time and could thus form a memory. Earlier places of food, which are imprinted in the network architecture, are evidently incorporated into movement decisions: “Where the tubes gradually soften, the imprints of earlier sources of food also come into play. The stored information is called up there, ”says Kramar. “Past food intake is embedded in the hierarchy of tube diameters, specifically in the arrangement of thick and thin tubes in the network,” explains the scientist.
Her colleague Alim says: “It is remarkable that the organism apparently uses such a simple mechanism and yet can control it in such a finely tuned way. This is an important piece of the puzzle in understanding the behavior of this ancient organism, ”says Alim. According to the scientists, findings about the amazing abilities of the slime molds could not only be interesting from a biological point of view: They could also benefit the development of intelligent materials and the construction of soft robots that navigate through complex environments, say Kramar and Alim.
Source: Technical University of Munich, specialist article: PNAS, doi: 10.1073 / pnas.2007815118