By Davide Castelvecchi
From Science News, March 31st, 2007; Vol.171 #13 (p. 205)
A species of amoeba seems to possess a rudimentary form of memory that keeps it from walking around in circles.
Some microbes search for food by following its smell. In the absence of chemical clues, however, such creatures have appeared to wander randomly. But random walks aren’t a very efficient foraging strategy , since they can bring the microbe back to the same place again and again.
By tracking the motion of Dictyostelium discoideum, a kind of slime mold, Edward Cox and Liang Li of Princeton University have discovered that the amoeba tends to remember its previous steps. That increases the microbe’s chances of finding food in new areas, the researchers say.
It’s not clear how D. discoideum knows where it’s been. Amoebas move by extending protuberances known as pseudopods.
One possibility, Li says, is that forming a pseudopod leaves a temporary “scar” in the cell’s structure, making it more likely that the next pseudopod will emerge from a different part of the organism’s cell wall and head in a different direction. She says that a similar mechanism might exist in a variety of other single-cell organisms and even in human cells such as neurons.
Li presented the findings at the March meeting of the American Physical Society in Denver.