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No. 133: JAN-FEB 2001

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Superorganisms: From Simplicity To Complexity

Superorganisms are biological entities made up of large numbers of simpler entities that have banded together to perform functions they cannot do as individuals. Termite mounds are often mentioned as superoganisms. But here we examine colonies of organisms that are much simpler and much smaller than termites.

What entices the anomalist to attend to superorganisms? Here are two of the several questions superorganisms raise.

Salps. Books dealing with the unexplained sometimes include a photograph of a huge marine creature identified as a sea monster. This famous photo is real and so is the monster in it. But this creature is not reptilian; it is really a salp, a colonial tunicate. Tunicates are tiny, primitive marine organisms usually classified as invertebrates. Some species of tunicates have somehow acquired the habit of aggregating in immense numbers to create long, hollow, snake-like tubes called "salpa." Salps may reach lengths of 45 feet, with diameters of 3 feet. No wonder they are falsely identified as sea monsters.

Structurally, the tunicates comprising the salp are embedded in a gelatinous wall facing inward. Each possesses a siphon that pumps nutrient-carrying sea water. Working in unison, the tunicates create a surprisingly strong current of sea water through the tube, and the salp becomes jet-propelled.

Thus, we have a mobile monster, but no ship-swallowing leviathan.

(Griffin, D.J.G., and Yaldwyn, J.C.; "Giant Colonies of Pelagic Tunicates..," Nature, 226:464, 1970)

Slime molds. Moving down life's ladder to even smaller and simpler organisms, some amoebas have a bizarre life cycle that ends as a superorganism called a "slime mold." If you viewed an amoeba through the microscope in biology lab, you know that they are very tiny, very simple, and most certainly not very bright. But given enough food, some species of amoeba divide and keep dividing until they clump together in a "slug" that sends out streamers and sort of flows along the surface. We now have a mobile superorganism searching for food (mostly bacteria). Eventually, the moving colony of amoebas anchors itself. Some of the superorganism's cells specialize to create a stalk called a "fruiting body." The amoebas in the fruiting body change into spores and are wafted away on the wind. In this way, the simple, lowly amoebas are transformed into a radically different entity. One wonders how this superorganism, this slime mold, is controlled. Where are its sensors and its information processing center, if it possesses one?

(Stewart, Ian; "Spiral Slime," Scientific American, 283:116, November 2000.)

This question becomes more difficult to answer when we learn that slime molds can display rudimentary intelligence in the sense that they can solve mazes in their search for food. They are not as clever as rats, but they do optimize their travels through the maze.

(Nakagaki, Toahiyuki, et al; "Maze-Solving by an Amoeboid Organism," Nature, 407:470, 2000.)

Biofilms. Down near the bottom of life's ladder dwell the bacteria. Their genomes must be miniscule and gray matter is not to be found. Nevertheless, some bacteria band together to form biofilms. Biofilms are three-dimensional, complex structures composed of innumerable, specialized bacteria all working together. W. Costerton at Montana State University imagines what a biofilm would look like if one were bacterium-size.

If you found yourself in a biofilm, you'd be going along a channel full of water, like the canals in Venice, and up from the bottom of the channel, on either side, would be these slime towers. The channels would be bringing in oxygen and nutrients. and removing waste. And within each building, so to speak, some of the bacteria would be cooperating with each other, making one compound and passing it along to the next. It's at least as complicated as a tissue. and possibly as a city.

(Chicurel, Marina; "Slimebusters." Nature, 408:284, 2000.)

Comment. Since bacteria have no brains, where do the building plans of this "city" reside?

Nanocrystal aggregates. Even lifeless nanocrystals spontaneously form long, oriented chains. Self-organization is common in inorganic nature. Nanocrystals are clumps of atoms numbering in the hundreds, often thousands. Typically, nanocrystals are only 1-10 nano-meters long. Even so, they have a colonial spirit, and, like the tunicates and amoebas, they aggregate and self-organize.

((Alivisatos, A.P.; "Naturally Aligned Nanocrystals," Science, 289:736, 2000.)

Comment. Sometimes that vaunted chasm separating life from non-life seems pretty narrow!

From Science Frontiers #133, JAN-FEB 2001. 2001 William R. Corliss

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