Multicellularity arose several times in the evolution of eukaryotes (2013)

I'm curious for anyone familiar with all this, why is it that fungal mycelium colonies and Portuguese Man-o-wars aren't considered multicellular organisms but things like slime molds are? Fruiting fungi even have specialized reproductive cells, and Portuguese Man-o-wars have two sexes, each specimen having all cells of the same sex in a single colony. What's the determining factor or set of determining factors that deliniate colonies of single cell organisms from multicellular organisms?

Related: a recent paper about evolving multicellularity in baker’s yeast – https://www.nature.com/articles/s41586-023-06052-1

(Sadly paywalled, but Ed Yong explains it in The Atlantic: https://archive.is/Jo1Ig)

Wasnt the whole premise of Nick Lanes books it only occurred once ?

ChatGPT tells me that Slime Mold Races are a thing! I so hope this is true.

Slime mold races, particularly involving the species Physarum polycephalum, have become a fascinating and educational tool for both scientific study and public engagement in science. These races capitalize on the natural ability of slime molds to navigate through complex environments and make decisions based on environmental cues. Here's how these races typically work and what they can demonstrate:

Setting Up the Race: In a typical slime mold race, a petri dish or a similar flat surface is set up with a maze or a set of obstacles. At the starting point, a small piece of Physarum polycephalum is placed. Often, the end point or the "goal" is baited with food, such as oat flakes, which slime molds find attractive.

Navigating the Maze: The slime mold starts to spread out from the starting point and navigates the maze or obstacles in search of food. Physarum polycephalum does this by extending fan-like tendrils called pseudopodia to explore its environment.

Decision-Making: As it moves, the slime mold demonstrates a fascinating form of decision-making. It can sense the environment and retract pseudopodia from less promising paths, concentrating its growth towards more favorable directions. This behavior is an example of a simple biological system solving complex problems.

Reaching the Goal: The race is usually considered finished when the slime mold reaches the food source. The paths it takes can be quite intricate and demonstrate its ability to solve maze-like structures efficiently.

Scientific and Educational Value: Slime mold races are not just entertaining; they have genuine scientific and educational value. They are used to study biological computing and decision-making processes in simple organisms. For educational purposes, they are excellent tools for demonstrating concepts in biology, problem-solving, and even robotics and computing.

Public Engagement: These races are also great for public science engagement, showcasing the abilities of an often-overlooked organism and sparking interest in the study of less conventional life forms.

Slime mold races exemplify how a seemingly simple organism can exhibit complex behaviors. They provide valuable insights into biological processes such as chemotaxis (movement toward or away from chemical stimuli), spatial memory, and optimization strategies, which have implications for understanding biological networks and even for developing algorithms in computing and robotics.

Multicellular slime mold slug races, particularly involving species like Dictyostelium discoideum, are less common than races with plasmodial slime molds like Physarum polycephalum. This is primarily because the biology and behavior of multicellular slime mold slugs are quite different from those of the plasmodial slime molds. However, the concept could still be intriguing from a scientific and educational standpoint. Here are some considerations and potential scenarios:

Setting Up the Race: As with plasmodial slime molds, a race would involve placing slugs of Dictyostelium discoideum or a similar species at a starting point with a goal, often a food source, at the end. However, Dictyostelium slugs are not as adept at navigating complex mazes as Physarum is.

Movement and Behavior: The movement of a Dictyostelium slug is a collective behavior of the aggregated amoeboid cells. While they can move toward food sources, their movement is less exploratory and more direct compared to Physarum. They do not extend pseudopodia to explore their surroundings; instead, they move as a cohesive unit.

Limited Maze-Navigation Ability: Given their less exploratory nature, a maze or complex obstacle course might not be as effectively navigated by Dictyostelium slugs as by Physarum. Their ability to solve complex spatial problems is not as pronounced.

Observing Collective Behavior: A race could be interesting for observing the collective behavior of cells within the slug, such as how they maintain cohesion and directionality as a group, and how they respond to simple environmental cues.

Scientific Value: While not as adept at maze-solving, such races could still offer insights into the collective decision-making and movement dynamics of multicellular organisms. They could be used to study topics like cell signaling, aggregation behavior, and the transition from unicellular to multicellular life forms.

Educational and Engagement Aspects: For educational purposes, slug races could be used to demonstrate the principles of multicellularity, collective behavior, and the life cycle of an interesting group of organisms. They might not be as visually dramatic as Physarum races, but they can still be engaging and informative.

In summary, while multicellular slime mold slug races might not demonstrate the same level of problem-solving or maze-navigation capabilities as plasmodial slime mold races, they could still be valuable for studying and teaching different aspects of biology, particularly related to multicellular coordination, aggregation behavior, and developmental biology.