Slime molds belong in the phylum Myxomycota in the kingdom Protista. They are not a true fungus. And they engulf their food, mostly bacteria. The slime mold that typically appear on mulches are from the genus, Fuligo. The brightly color blobs usually appear and may spread around mulched beds when there is high humidity and relatively warm temperatures. In Texas, we typically hear of slime molds in the spring and occasionally in the summer in highly irrigated shade areas.
Slime mold can appear to be bright yellow to red. As they begin to dry out, these colors fade to brown and tan. Breaking up the dried blob, you may notice a dark brown to black core — the spores. Some remain microscopic, and others grow rogue, forming bulbous masses, as long as 10 to 13 feet. Yet humans largely ignore them. Still, our world is crawling with them.
Stephenson and his team — the Eumycetozoan Research Project at University of Arkansas — spent years trying to catalog all species of slime mold around the globe from the Arctic Circle to the tip of Chile. Slime molds are particularly fond of forest floors where they break down rotting vegetation, feeding on bacteria, yeast, and fungus. When all is well, the slime mold thrives as a single-celled organism, but when food is scarce, it combines forces with its brethren, and grows.
Then, once the mass is formed, the cells reconfigure, changing their shape and function to form stalks, which produce bulbs called fruiting bodies. The fruiting bodies contain millions of spores, which get picked up and transported by the wind, a passing insect or an animal.
There, they start the process again as single-celled organisms. Meanwhile, the cells that formed the stalks die, sacrificing themselves. For creatures without feet, they can travel incredible distances. Stephenson said one of his students identified slime molds in New Zealand that are genetically identical to groups found in the United States. How they got there is unknown. To reach the oatmeal, the slime molds had to grow across gelatin bridges laced with either caffeine or quinine, harmless but bitter chemicals that the organisms are known to avoid.
After two days, the slime molds began to ignore the bitter substance, and after six days each group stopped responding to the deterrent. The habituation that the slime molds had learned was specific to the substance: Slime molds that had habituated to caffeine were still reluctant to cross a bridge containing quinine, and vice versa. This showed that the organisms had learned to recognize a particular stimulus and to adjust their response to it, and not to push across bridges indiscriminately.
Here, the middle slime mold sample has learned to disregard the chemicals, a process called habituation. Finally, the scientists let the slime molds rest for two days in situations where they were exposed to neither quinine nor caffeine, and then tested them with the noxious bridges again. The slime molds had gone back to their original behavior. Dussutour cut her slime molds into more than 4, pieces and trained half of them with salt — another substance that the organisms dislike, though not as strongly as quinine and caffeine.
The team fused the assorted pieces in various combinations, mixing slime molds habituated to salt with non-habituated ones. They then tested the new entities. The organism had learned. But Dussutour wanted to push further and see whether that habituating memory could be recalled in the long term. So she and her team put the blobs to sleep for a year by drying them up in a controlled manner. In March, they woke up the blobs — which found themselves surrounded by salt.
The non-habituated slime molds died, perhaps from osmotic shock because they could not cope with how rapidly moisture leaked out of their cells. What that means, according to Dussutour, who described this unpublished work at a scientific meeting in April at the University of Bremen in Germany, is that a slime mold can learn — and it can keep that knowledge during dormancy, despite the extensive physical and biochemical changes in the cells that accompany that transformation.
Being able to remember where to find food is a useful skill for a slime mold to have in the wild, because its environment can be treacherous. Scientists have no idea what mechanism underpins this kind of cognition.
In the case of slime molds, their cytoskeleton may form smart, complex networks able to process sensory information. Researchers are investigating other nonneural organisms, such as plants, to discover whether they can display the most basic form of learning.
For example, in Monica Gagliano and her colleagues at the University of Western Australia and the University of Firenze in Italy published a paper that caused a media frenzy, on experiments with Mimosa pudica plants.
Mimosa plants are famously sensitive to being touched or otherwise physically disturbed: They immediately curl up their delicate leaves as a defense mechanism. Gagliano built a mechanism that would abruptly drop the plants by about a foot without harming them. At first, the plants would retract and curl their leaves when they were dropped.
Slime molds are highly efficient at exploring their environment and making use of the resources they find there. Researchers have harnessed this ability to solve mazes and other problems under controlled conditions. Traditionally, simple organisms without brains or neurons were thought to be capable of simple stimulus-response behavior at most.
0コメント