When placed at the perimeter of a maze with food in the center, the plasmodial slime mold Physarum polycephalum explores the maze, retracts branches from dead-end corridors, and then grows exclusively along the shortest path possible to the food. How does Physarum do this? One theory is that it leaves behind slime deposits—an externalized 'memory' that 'reminds' it not to retry dead ends. Physarum is a plasmodial slime mold, whereas Dictyostelum is a cellular slime mold. Compare and contrast movement by the migrating slug stage of Dictyostelium to the plasmodial stage of Physarum.

Verified step by step guidance

1. Step 1: Understand the behavior of Physarum polycephalum. This plasmodial slime mold explores its environment in search of food. When it encounters a dead end, it retracts and leaves behind a slime trail, which serves as a form of 'external memory' to prevent it from retracing its steps.
2. Step 2: Compare this behavior to that of Dictyostelium, a cellular slime mold. Dictyostelium moves in a different way. In its slug stage, it behaves as a single entity, moving towards light and heat sources, which are often indicative of food sources.
3. Step 3: Contrast the two types of movement. Physarum's movement is more exploratory and flexible, as it can retract and change its path based on the slime trails it leaves behind. Dictyostelium, on the other hand, moves as a single unit in the slug stage, and its movement is more directed and less flexible.
4. Step 4: Understand the implications of these differences. The movement of Physarum allows it to explore complex environments like mazes effectively, while Dictyostelium's movement is more suited to straightforward environments where the direction of food sources is relatively clear.
5. Step 5: Remember that these are just two examples of how organisms can move and navigate their environments. Different organisms have evolved different strategies based on their specific needs and the challenges of their environments.

Key Concepts

Plasmodial Slime Molds

Plasmodial slime molds, such as Physarum polycephalum, exist as a large, multinucleate cell called a plasmodium. This structure allows them to move and grow by streaming cytoplasm, enabling them to explore their environment efficiently. They can navigate complex environments, like mazes, by retracting from unproductive paths and optimizing their growth towards food sources.

Cellular Slime Molds

Cellular slime molds, like Dictyostelium, exhibit a different life cycle characterized by individual amoeboid cells that can aggregate to form a multicellular structure during certain conditions. This slug stage can migrate toward favorable environments, demonstrating collective behavior and communication among cells. This contrasts with the continuous, single-cell structure of plasmodial slime molds.

Externalized Memory in Slime Molds

The concept of externalized memory in slime molds refers to the ability of organisms like Physarum to leave behind slime trails that inform future movement decisions. These trails act as a form of spatial memory, helping the organism avoid previously explored dead ends and optimize its path to resources. This behavior illustrates a form of learning and adaptation in simple organisms, challenging traditional views of memory and cognition.