Are You Smarter Than a Slime Mold?

Have you ever found yourself sitting on a subway train in New York City marveling at the subway system's astonishing efficiency? You ask yourself, "Who came up with all of this? This must have taken them forever!" With just a quick Google search, your curious thoughts would be proven true, as it did in fact take engineers years to create the subway system that shuttles millions of people around New York City today. While, yes, this is an impressive feat by engineers, what if you were told that a unicellular organism could map out the same route in just a small fraction of the time it took humans? Well, the species of slime mold, Physarum polycephalum , can do just that, and it's absolutely marvelous! 

The Experiment 

Through countless explorations of different ecosystems, scientists began to notice just how good this species of mold was at navigating through its environment to the nearest food source in the most efficient way possible. In an effort to investigate just how capable this slime mold was, Japanese scientists proposed an experiment. The slime mold was placed in the middle of an agar plate with oats placed throughout, arranged in the pattern of Japanese cities around Tokyo. 

Slime Mold Experiment

When presented with this scenario, the slime mold slowly began to create the most efficient route to each of its nutrient sources. When scientists took a closer look at what exactly the mold had done, they noticed the mold's route looked awfully similar to the current Japanese subway system route. When they compared the two, the scientists found the routes to be almost identical! Fascinating, right!? But how exactly was this unicellular organism able to carry out such a complex function?   

While the mere fact that this unicellular organism is able to carry out this function is quite impressive, once you begin to understand what exactly the mold is doing on a molecular level, the feat becomes even more remarkable. 

Slime Mold: What is it? 

The slime mold Physarum polycephalum is a eukaryotic , single-celled, soil-dwelling amoeba . That's right! It is NOT a fungus! Although it is commonly mistaken for one considering its ideal environment tends to be more damp and dark like many fungi. This species of amoeba follows a growth cycle that is far different from the one that we learned about in AP Bio this year. Instead of the growth of this organism being driven by cytoplasmic divisions and increased cell numbers, a cellular life cycle, it follows an acellular life cycle, as the organism continues to stay single-celled throughout its entire life regardless of how large it may grow. While the cell itself does not divide or multiply, the nuclei inside of the cell do. The cell is still undergoing the process of mitosis, however, it is skipping cytokinesis , allowing the cell to maintain its single-celled structure while still having the same amount of genetic material a multicellular organism would have. Ultimately, this species of slime mold grows to be a giant blob of a cell with many nuclei dispersed throughout. Although it may be surprising, the process of mitosis without cytokinesis happens in humans as well! Certain cell types in humans including osteoclasts (cells that break down bone tissue) and skeletal muscle fibers actually aren't very far off from this species of slime mold, as all three cell types undergo mitosis without cytoplasmic divisions.  

With this unique blob-like structure of the organism also comes quite a valuable function. After all, which I'm sure we all have ingrained in our heads by now (thanks Ms. Eckert!!), a change in structure equals a change in function! Since there aren't any barriers or walls separating any one part of the cell from another, fluids can very easily flow throughout the organism. This may be why the species is so good at navigating through complex environments, as important signaling molecules that signal the retraction or protraction of the organism are easily able to flow throughout the entirety of the cell. 

How Does It Move? 

While this species of slime mold may be good at maneuvering throughout its environment, it does not navigate the way many may believe it to. When told that an organism is good at navigation, many may make the assumption that the organism "knows" where it's going and where to turn in order to reach its end destination as efficiently as possible. While intuitive, this assumption is false! This particular organism does not have a brain to think like us humans. It is unable to make the conscious decision to turn left or turn right. Instead, the mold simply grows wherever it pleases, or at least initially it does. 

The mold first begins to grow throughout its entire environment, sending tendrils of itself out into its surrounding territory. Essentially, these tendrils help the mold to scope out where exactly the nutrient-rich spots may reside in its environment. Once the organism has found all of the nutrient-rich spots, it begins to retract the tendrils of itself that are connected to spots in the environment that do not contain as many nutrients, as this part of its territory is no longer of use to the mold. Slowly, the slime mold retracts all parts of itself that aren't necessary for survival, leaving behind the most efficient pathways to the most nutrient-dense spots in its environment. Isn't that just fascinating??! 

Where Can I Find It? 

Although the concept of a slime mold may seem foreign to many, it's actually quite likely that any Montclair resident would be able to find it in their own town! Hemitrichia serpula , Ceratiomyxa fructiculosa, and Lycogala epidendrum are just three of the many species of slime mold that can be found in New Jersey. One species, in particular, may even be mistaken for dog vomit! Yuck!! 

Dog Vomit Slime Mold

Although it may look like a dog has thrown up on the side of a tree, that foamy yellow goop is, thankfully, just a harmless species of slime mold!  This species of slime mold, Fuligo septica, can be found all throughout the world, usually congregating on bark mulch after significant rainfall or over-watering. Kinda gross, but pretty darn cool if I do say so myself!