December 22, 2016

Brainless slime molds can share knowledge by fusing, study finds

After previously showing blobs of a slime mold can learn despite not having a brain or nervous system, a group of French researchers has now shown how quickly the same blobs can share what they learn, according to a new report in the Proceedings of the Royal Society B.

Physarum polycephalum is a yellowish slime mold that thrives in cool, moist areas, feeding on bacteria, fungi, and rotting organic matter. It is capable of moving at a top speed of around 1.6 inches per hour. The slime mold falls into the taxonomic group of Amoebozoa: single-celled organisms that can either exist on their own or merge with others to form colonies, pooling their foraging capabilities in the process.

In the team’s first set of trials, three groups of the slime mold were compelled to cross agar gel bridges treated with quinine, caffeine, or nothing. With quinine and caffeine being safe but unpalatable to slime mold, two groups initially shied away from their particular bridges. However, after six days, they overcame their initial hesitancy and crossed the bridges. The team concluded that the experimental groups overcame repellent substances after several exposures proved safe, a basic kind of learning referred to as habituation.

Working With Slime Molds

In a subsequent set of trials, the study habituated 2000 slime molds, this time using salt as a harmless repellent. Another 2000 slime molds were grown and left alone as a control group. Next, the biologists established fused pairs of habituated and control slime molds by bringing them into contact with each other.

“When two membranes touch, they open up to one another if the species recognizes that it has met its genetic match,’ study author Audrey Dussutour, a biologist with the Centre de Recherches sur la Cognition Animale in France, said in a news release.

The study team found the fused pairs crossed salty bridges just as quickly as habituated blobs, a sign the pair had shared the important information on salt being non-toxic, the researchers concluded.

“It was already well-established that cell fusion enables cells to share resources such as mitochondria,” Dussutour said. “Our results showed that fusion also allows the sharing of information.”

The team was able to achieve the same result with mixed groups that included up to four naive molds and one habituated individual. Dussutour said the naive molds “could attain the same level of learning without the information being diluted, no matter what physical position the habituated blob occupied in the chain, on a side or in the center.”

The study team then repeated the experiment after separating the molds from each other. Control molds that had merged with habituated ones for at least three hours were found to retain their salty knowledge. However, those that merged for shorter periods were seen to regress. Microscopic investigation revealed that a vein, which took three hours to form, linked habituated and control molds at their connecting point. The team said this is the essential vessel through which knowledge passes from one mold to the other.

The researchers said future projects will focus on understanding the cellular and molecular mechanisms behind this flow of information.


Image credit: Audrey Dussutour