“Was not their mistake once more bred of the life of slavery that they had been living?—a life which was always looking upon everything, except mankind, animate and inanimate—‘nature,’ as people used to call it—as one thing, and mankind as another, it was natural to people thinking in this way, that they should try to make ‘nature’ their slave, since they thought ‘nature’ was something outside them” — William Morris

Sunday, March 27, 2011

Slime Molds in My Hood

They're everywhere at the end of the cul-de-sac here and elsewhere. I suppose it's because of the incredibly heavy rain. It's a rare opportunity to see this quite alien lifeform, significantly more different from us than fungi are, genetically speaking (see below).

As you can see the poor thing was trodden on a few times and has dried out significantly since it's gotten quite a lot drier all of a sudden. I think it's Fuligo septica, otherwise charmingly known as Dog's Vomit. Slime molds are resistant to high levels of toxic metal. Some of them can navigate their way around a maze.

1 comment:

Karl said...

theres a nice blurb i ran into a while back in an Andy Clark book:

It is the spring of 1973, and the weather has been unseasonably wet. As you gaze out the window into your yard, your eye is caught by a proliferation of deep yellow blob-like masses. What could they be? Puzzled, you return to work but are unable to settle down. A while later you return to the window. The yellow jelliform masses are still in evidence, but you would swear they have moved. You are right. The newcomers are slowly but surely creeping around your yard, climbing up the nearby telephone pole—moving in on you. In a panic, you phone the police to report a likely sighting of alien life forms in the USA. In fact, what you (and many others) saw was a fully terrestrial being, but one whose life cycle is alien indeed: Fuligo septica, a type of acellular slime mold.

Slime molds come in many varieties and sizes., but all belong to the class of Mycetozoa. The name is revealing, combining 'mycet' (fungus) and 'zoa' (animal). They like moist surroundings and are often found on rotting logs, tree stumps, or piles of decaying plant matter. They are widely distributed geographically, and do not seem bound to specific climates. As one handbook puts it, "many species are apt to pop up most anywhere, unexpectedly" (Farr 1981, p. 9).

Of special interest is the life cycle of the "cellular" slime mold. Take, for instance, the species Dictyostelium discoideum, first discovered in1935 in North Carolina. The life cycle of D. discoideum begins with a so called vegetative phase, in which the slime-mold cells exist individually, like amoeba (they are called myxamoebae). While local food sources last (the myxamoebae feed on bacteria) the cells grow and divide. But when food sources run out, a truly strange thing happens. The cells begin to cluster together to form a tissue-like mass called a pseudoplasmodium. The pseudoplasmodium, amazingly, is a mobile collective creature—a kind of miniature slug (figure 4.1)—that can crawl along the ground. It is attracted to light, and it follows temperature and humidity gradients. These cues help it to move toward a more nourishing location. Once such a spot is found, the pseudoplasmodium changes form again, this time differentiating into a stalk and a fruiting body—a spore mass comprising about two-thirds of the cell count. When the spores are propagated, the cycle begins anew with a fresh population of myxamoebae.

How do the individual slime-mold cells (the myxamoebae) know to cluster? One solution—the biological analogue of a central planner (see chapter 3)—would be for evolution to have elected "leader cells." Such cells would be specially adapted so as to "call" the other cells, probablyby chemical means, when food ran low. And they would somehow orchestrate the construction of the pseudoplasmodium. It seems, however, that nature has chosen a more democratic solution. In fact, slime-mold cells look to behave rather like the ants described in section 2.3. When food runs low, each cell releases a chemical (cyclic AMP) which attracts other cells. As cells begin to cluster, the concentrations of cyclic AMP increases, thus attracting yet more cells. A process of positive feedback thus leads to the aggregation of cells that constitutes a pseudoplasmodium. The process is, as Mitchel Resnick (1994, p. 51) notes, a nice example of what has become known as self-organization. A self-organizing system is one in which some kind of higher-level pattern emerges from the interactions of multiple simple components without the benefit of a leader, controller, or orchestrator.

Andy Clark
Being There: Putting Brain, Body, and World Together Again