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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. Understand the basic biology of the organisms: Physarum polycephalum is a plasmodial slime mold, which means it exists as a large, multinucleate single cell. Dictyostelium, on the other hand, is a cellular slime mold that exists as individual amoeboid cells that can aggregate to form a multicellular structure.
2. Examine the movement mechanism of Physarum: Physarum moves by extending and retracting pseudopodia, which are temporary projections of its cytoplasm. This movement is driven by cytoplasmic streaming, a process where the cytoplasm flows within the cell, allowing it to explore its environment.
3. Explore the movement mechanism of Dictyostelium: In the migrating slug stage, Dictyostelium cells aggregate to form a slug-like structure. This structure moves as a coordinated unit, with cells at the front pulling the slug forward and cells at the back pushing. This movement is guided by chemotaxis, where cells respond to chemical signals in their environment.
4. Compare the role of external cues: Physarum uses external slime deposits as a form of memory to avoid retracing its steps, effectively optimizing its pathfinding. Dictyostelium, however, relies on chemical signaling (such as cyclic AMP) to coordinate movement and aggregation, responding to external chemical gradients.
5. Contrast the structural organization: Physarum's movement is facilitated by its continuous cytoplasmic network, allowing for rapid and flexible responses to environmental changes. Dictyostelium's movement involves a temporary multicellular structure, where individual cells maintain their identity but work together to achieve movement and development.

Key Concepts

Plasmodial Slime Mold Physarum polycephalum

Physarum polycephalum is a type of plasmodial slime mold known for its ability to navigate mazes efficiently. It does this by exploring all possible paths and retracting from dead ends, leaving behind slime deposits that act as a memory to avoid revisiting these paths. This behavior demonstrates a form of decentralized decision-making and optimization, akin to solving complex problems without a central nervous system.

Cellular Slime Mold Dictyostelium

Dictyostelium is a cellular slime mold that exhibits a different form of movement compared to Physarum. In its migrating slug stage, Dictyostelium cells aggregate to form a multicellular structure that moves as a cohesive unit. This stage is characterized by coordinated cell movement and chemotaxis, where cells respond to chemical signals to navigate towards favorable environments, such as food sources.

Comparison of Movement Mechanisms

The movement of Physarum and Dictyostelium highlights distinct strategies in slime molds. Physarum uses a network-like growth pattern, retracting from non-beneficial paths, while Dictyostelium relies on cellular aggregation and chemotaxis. Physarum's movement is more about optimizing paths through externalized memory, whereas Dictyostelium's slug stage involves collective cell movement driven by chemical cues, showcasing different evolutionary adaptations for survival and resource acquisition.