Earth's Brainless Maze Solver

Molds are small little organisms, or specifically fungi, that seem to invade your damp walls or those black dots that prevent you from making your favorite sandwich. However, this blog aims to discuss slime molds that may sound similar. However, their genomics composition is rather different and doesn't belong to the class fungi; instead, they're part of the Kingdom, Protista.

Slime molds, scientifically known as Myxomycetes, are single-celled organisms that contain multiple nuclei, that is they lack barriers or cross walls between other cells. This allows fluids and nutrients to flow freely throughout the organism’s body. This characteristic enables them to move around and explore their surroundings.

The slime mold in question that is known for mapping railway lines in Tokyo is known as Physarum polycephalum - a yellow slime mold that grows as a single cell large enough to be seen with the naked eye. This species has become a model organism for studying the remarkable behaviors and capabilities of slime molds.

Slime molds undergo a complex life cycle that includes a stage where they exist as a tiny plasmodium—a large, multinucleate single cell. In this stage, the slime mold exhibits some of their most fascinating behaviors. Through a process called peristalsis, they expand and contract, moving fluids and information throughout their body. This movement is crucial for their survival, allowing them to explore their surroundings in order to find optimal paths for growth, and reproduction.

One of the most astonishing abilities of slime molds is their capacity to solve mazes and find efficient paths through complex environments—despite lacking a brain or nervous system. They achieve this through a system of signaling molecules, which propagate throughout the organism to integrate information and coordinate behavior. Slime molds send out tendrils to explore their habitat, retracting and reorganizing themselves to form the shortest possible path to reach nutrient-rich patches. This behavior has been famously demonstrated in experiments at Hokkaido University, where slime molds successfully navigated a map of Tokyo to find food sources.

On January 22, 2010, researchers from Japan and England presented slime molds with oat flakes arranged in a pattern mimicking Japanese cities around Tokyo. Remarkably, the slime molds constructed networks of nutrient-channeling tubes that closely resembled the layout of the Japanese rail system. Mark Fricker of the University of Oxford highlighted the significance of this finding, noting that the slime mold, despite lacking any central brain or awareness, managed to produce a structure with similar properties to a human-designed rail network.

Slime molds are voracious foragers, primarily consuming bacteria, fungal spores, and other small microorganisms. They exhibit an impressive ability to sense nutrient-rich areas despite lacking traditional sensory apparatus.

There are over 100 known species of slime molds, each exhibiting unique characteristics and behaviors. They thrive in a variety of habitats, from forest floors to decaying logs, demonstrating remarkable adaptability. This biodiversity reflects the evolutionary success of slime molds, which have been around for millions of years.

The complex behaviors of slime molds, including their mating processes, are influenced by their genetic makeup. During the plasmodial stage, swarm cells fuse to become a single entity, a process governed by specific genes located at different loci.

The research on slime molds’ network-forming abilities has broader implications beyond biological curiosity. By borrowing these characters from the slime mold’s behavior, researchers developed a biology-inspired mathematical model for network formation. This model could lead to the design of more efficient and adaptable networks. For instance, decentralized, adaptable networks could be crucial for short-range wireless systems of sensors providing early warnings of disasters like fires or floods, or for soldiers in battlefields, or swarms of robots exploring hazardous environments.

Additionally, understanding how slime molds optimize their networks might offer insights into biological processes such as the growth of blood vessels to support tumors. Tumors start with a dense, unstructured network of vessels that eventually refines into a more efficient system, similar to the slime mold's network formation.

To reiterate, slime molds posses the ability to navigate environments, find food, and reproduce efficiently without a nervous system, which challenges our understanding of intelligence and adaptation in the natural world. Their characteristics continue to offer insights about the fundamental processes of life and evolution.

So next time you come across a slimy, yellow blob on a decaying log, take a moment to appreciate the incredible journey of the slime mold—nature’s brainless, yet brilliant, maze solver.

Physarum polycephalum - The Slime Mold:

Physarum polycephalum demonstrating peristalsis

Physarum polycephalum on a decaying log

The life cycle of Physarum polycephalum

The above image shows Tokyo's railway lines. Scientists laid oat flakes on major Tokyo railway stations. (A) In the absence of illumination, the Physarum network resulted from even exploration of the available space. (B) The geographical constraints were imposed on the developing Physarum network by means of an illumination mask in order to restrict growth to more shaded areas corresponding to low-altitude regions. The ocean and inland lakes were also given strong illumination to prevent growth. (C and D) The resulting network (C) was compared with the rail network in the Tokyo area (D). (E and F) The minimum spanning tree (MST) connecting the same set of city nodes (E) and a model network constructed by adding additional links to the MST (F).

Physarum polycephalum exhibiting peristalsis