Slime Molds: Fascinating Beings with Wondrous Abilities

Slime molds are, in many ways, an enigma. They aren’t genuine molds or even fungi. Most of the time, they exist either as plasmodia or amoebae, defying the rigid classifications we usually apply to life.

What’s particularly intriguing about them is their ability to display behaviors that some might call intelligent, even without having brains or nervous systems. But what drives their collective movements? Is there a central controller at play?

A recent study indicates that there is, but perhaps not in the way you might assume.

The slime mold that often takes center stage in many scientific experiments is the bright yellow Physarum polycephalum, a name that translates rather fittingly to “the small bubble with many heads.” As a plasmodium, it’s essentially a bag of cell nuclei and goo.

This peculiar lifestyle allows it to move more fluidly than fungi, which it was once confused with. When P. polycephalum runs low on food, it can quite literally wander off to find something more substantial.

Yet, this strange movement isn’t just random wandering. Slime molds can navigate mazes in search of food and, impressively, remember where to find it again.

Broadly speaking, they can ‘decide’ on a course of action when faced with different options.

Now, scientists from Germany and the United States are beginning to unravel the mechanics behind this type of decentralized decision-making.

Since P. polycephalum lacks both a brain and a nervous system, the concept of ‘decision-making’ here diverges significantly from what we understand in the animal kingdom. But it offers valuable insight into how organisms without neurons can adapt their behavior without centralized control.

This slime mold shows a strong aversion to blue light, which allows researchers to create barriers using beams of glowing light. Interestingly, when subjected to these blue-light boundaries in search of food, a starving slime mold exhibits fascinating behavior. It sends out small protrusions in an effort to escape, even before it makes its final move.

Before it breaks free, it looks almost like it is bubbling, pulsating, and twitching, until it suddenly surges forward, escaping its confines.

According to biological physicist Lisa Schick from the Technical University of Munich and her team, “P. polycephalum uses rhythmic contractions to direct internal flows and redistribute mass, adapting to its environment.” However, there’s still much to learn about the mechanical principles behind this mass relocation.

The researchers studied what routes P. polycephalum takes when trapped, using blue light to create a sort of maze that resembles geometric stencil sheets.

The design features blue light on a jelly-like surface with gaps shaped like various two-dimensional forms, like triangles or squares. After placing starved slime molds into the light-free areas, they didn’t stay trapped for long.

Driven by hunger, the molds began to grow within an hour, rapidly pushing out a network of tubules to explore the trap.

During this exploratory period, their movement is influenced by localized cytoplasmic streaming, which is the flow of cellular fluid enabled by contractions at the molecular level.

Tentatively looking for food and a way out, the molds extended tiny protrusions all around. Most of these efforts were short-lived, but a few managed to reach past the boundaries, leading to escape.

Remarkably, although they explore everywhere, actual escapes tend to occur along the longest axis of the trap.

But why choose the longest route instead of a shorter one? Researchers suspect this behavior is tied to how slime molds organize themselves.

Over time, the slime mold eventually figures out the contraction mode that is most effective for transport, correlating with its escape.

Each time the mold searches for a way out, it essentially reorganizes, allowing those rhythmic contractions to guide it toward the most efficient movement.

The more distance it covers, the more pressure builds up, enabling it to push its mass outwards effectively.

The team concluded that the shape of the trap determines the most efficient movement mode, facilitating the build-up of pressure along the longest axis, which drives the mold’s eventual escape.

While it may appear as though the slime mold is ‘deciding’ which direction to move, this research suggests that its behavior is actually governed by mechanical processes linked to fluid dynamics.

Ultimately, the findings offer a glimpse into how non-neuronal organisms process environmental challenges to drive adaptive behavior.

This research is detailed in PRX Life.