Slime molds use a type of spatial "memory" to navigate through a maze to find food, despite lacking a brain.
Researchers in Australia observed the perplexing single-celled, amoeba-like creatures and found that slime molds (Physarum polycephalum) glide along secreting trials of slimy goo, which serves as a kind of external memory system, according to a paper published in the Proceedings of the National Academy of Sciences.
Scientists explained that the slime mold's path-finding method of oozy deposits were comparable to Hansel and Gretel's breadcrumb trial, and when left unable to use their goo as navigation markers, the creatures spent almost 10 times the amount of time exploring a maze to find food.
Previous studies found that many insects including, ants, bees and wasps use landmarks to remember their route to and from the nest, but researchers from the latest study wrote that they have now gone a step further to demonstrate that even organisms without a nervous system can effectively navigate in complex environments.
"We have shown for the first time that a single-celled organism with no brain uses an external spatial memory to navigate through a complex environment," lead researcher Christopher Reid from the University's School of Biological Sciences, said in a statement.
"Our discovery is evidence of how the memory of multi-cellular organisms may have evolved - by using external chemical trails in the environment before the development of internal memory systems," said Reid.
Slime molds navigate by leaving behind a trail of a non-living, translucent, extracellular mucus-like substance, and when foraging, these creatures will avoid areas that it has already "slimed" suggesting that they can sense extracellular slime upon contact and will recognize and avoid areas it has already explored, researchers explain.
Researchers studied the navigational ability of the slime mold by putting the creatures through experiments normally designed for testing robots. They ran two experiments involving traps.
In the first experiment, researchers placed the slime mold in trap with a Y-shaped obstacle. Food was placed at each end of the branch. Researchers, when the slime mat was placed in the path between the mold and the food source, slime molds were able to go all the way around the obstacle to get at the food 39 out of 40 times.
In the second experiment, the molds were placed in a trap where there was a U-shaped obstacle placed between the mold and a food source. Researchers timed how long the mold were able to get around the obstacle to the food under two different conditions: the first allowed the molds to move on a normal surface and in the second condition the surface was covered with slime similar to that produced by the mold, which prevented the mold from using it as a memory device.
Researchers found that 96 percent of the molds reached the food within 120 hours when they were allowed to use their memory trials. However, the percentage of molds that successfully reached the food shrank to just 33 percent when left to navigate without the use of their slime.
Slime molds, which aren't actually mold but plasmodium, spend most of their lives as large single cells containing many nuclei. The creatures search for food by contracting and expanding. When food is detected, their contractions accelerate, which help them flow toward the food. However when they detect salt or light, their contractions decelerate, which helps them move away from irritants.
Experts at Washington University at St. Louis say that the plasmodium species used in this experiment originates from forests and varies in size, ranging from a few millimeters to more than 12 inches across.