THURSDAY, 13 FEBRUARY 2020In 2017, Hampshire College in Western Massachusetts welcomed a non-human visiting scholar, complete with its own title, office, and “research”. Among the prime candidates for this role, you might expect primates, corvids, or dolphins – the usual species which boast high intelligence on their list of accomplishments. It’s none of those. In fact, Hampshire’s scholar isn’t even an animal, plant or fungi. It’s a slime mould.
In actuality, “slime mould” is an informal name given to several unrelated eukaryotic organisms. What these slime moulds have in common is the ability to live freely as single cells, as well as aggregating and forming multicellular structures – the best of both worlds. They live as single, amoeba-like cells at the start of their reproductive cycle, but after mating they form zygotes which develop as an interconnected network of plasmodia (protoplasm containing multiple nuclei).
Physarum polycephalum is one such species of slime mould. Notably, for something having absolutely no semblance of a brain, it has exhibited extraordinary problem-solving abilities in previous research1. When given food sources at the beginning and end of a maze, it is able to determine the shortest path through in order to connect both food sources. It achieves this through a period of extensive growth and exploration, before paring down all routes except for the shortest one. With a random distribution of more than two sources, slime mould demonstrates the ability to optimize transportation and allocation of resources – all without centralized control.
In fact, networks formed between food sources representing major cities can map existing rail and road routes with incredible accuracy. By dispersing oat flakes in the pattern of major cities in the Tokyo area, researchers found that Physarum generated a network "with comparable efficiency, fault tolerance, and cost" to the actual railway system. In a similar model of the UK, the slime mould replicated every major motorway accurately except for M6/M74, which it rerouted through the oat flake “Newcastle”, connecting London to Glasgow along the east coast instead of the west. Because Physarum avoids bright light, real-life geographical constraints such as mountainous terrain or lakes can be simulated with intense illumination of an area or other repellents2. This provides an instance of how the behaviour of slime mould can be observed in response to “real-world” conditions.
Most impressively, perhaps, slime moulds have demonstrated the ability to transmit learned behaviour by fusing with others of its kind. Slime moulds are capable of habituation, a simple form of learning involving repeated exposure to a stimulus. When slime moulds were given food sources at the end of a bridge containing bitter repellents, like caffeine or salt3, they learned to ignore these repellents and crossed the bridge twice as fast. After fusing with unhabituated slime moulds, they were able to transfer their adaptive response to individuals who had not yet encountered the challenge. Incredibly, upon separation of the unhabituated slime mould from the fused entity, it retained this learned adaptive behavioural response.
As of 2018, Hampshire’s scholar has carried out policy work (with the aid of research assistants), sending letters to both the Secretary of Homeland Security advising against border walls, and to the Attorney General campaigning for legalisation of cannabis4. Neither appear to have written back.
Ellery Gopaoco is a 1st year student of Natural Sciences at St. John's College and the Biomedical Subject Editor of BlueSci magazine.
1Nakagaki, T., Yamada, H., & Tóth, Á. (2000). Maze-solving by an amoeboid organism. Nature, 407(6803), 470–470. doi: 10.1038/35035159
2Tero, A., Takagi, S., Saigusa, T., Ito, K., Bebber, D. P., Fricker, M. D., … Nakagaki, T. (2010). Rules for Biologically Inspired Adaptive Network Design. Science, 327(5964), 439–442. doi: 10.1126/science.1177894
3Vogel, D., & Dussutour, A. (2016). Direct transfer of learned behaviour via cell fusion in non-neural organisms. Proceedings of the Royal Society B: Biological Sciences, 283(1845), 20162382. doi: 10.1098/rspb.2016.2382
4The Plasmodium Consortium: Policy Circular No. 1, Hampshire College 2018