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. Does an organism without a brain have the ability to use an externalized 'memory'—a spatial 'slime map' that the organism uses to avoid moving to regions where it has been before? Researchers addressed this question by placing a U-shaped trap between Physarum and its food (see diagram that follows). Twenty-three out of 24 slime molds reached the food when plain agar was used as the growth substrate. However, when the agar was coated with extracellular slime, only 8 of 24 found the food. The mean time in hours that it took the successful slime molds to reach the food when placed on plain agar or agar pre-coated with extracellular slime was compared (P=0.012). Use the P value provided to determine if the difference is significant or not. What conclusion can be drawn from the graph shown here?

Video transcript

Welcome back. Here's our next question as the slime creeps along the food. It leaves behind a slimy material which is referred to as a slime map. What will be the possible benefit of having the slime map to the slime mold? Well, we can see in the word map a clue to its function. And the answer is, this map helps the slime find the shortest and most efficient route to food. And that says serving as a memory of how to get to its food source. And in fact this has really cool applications. Um In one case there was an experiment in which they distributed oats. So a food source for the slime mold in the locations on a map that shows the locations of the major cities around Tokyo and the slime mold when they left the slime map on the way to these piles of oats. They, their map sort of duplicated the subway map of the subway tracks around Tokyo which had been very carefully engineered to give the most efficient route. So this showed that indeed um the slime map trace these most efficient routes to food and so that's cool applications for using it to find these routes. So it's kind of a nifty little thing about slime molds. So let's look at our answer choices. We have choice A. It may act as an external memory for a slime mold to trace the path and that is exactly what we were talking about. The slime will can trace its efficient route to the food. Um Using these maps as an external memory, let's just look through our other choices. Choice B says it may help the slime mold to locomotive faster. Um That's not our answer. It doesn't increase in any in speed other than just having a more efficient route, but it's not moving any faster. Choice. C. Says it may help the slime mold to reproduce sexually well, slime mold reproduce through spores um that are dried up so the map is not part of their reproductive system enjoys. D. Says It may help the slime mold to paralyze its prey. And there are some slime molds that paralyze their prey but that's through toxins that they produce. Um Not in these maps. So that's not an answer there. So again, what might be the possible benefit of having leaving behind this slimy map and its choice A. It may act as an external memory for a slime mold to trace the path. See you in the next video.