What is the speed of dark? How much deeper would the oceans be if there were no sponges? How do you know when you’re out of invisible ink? Just when I feel like most of life’s mysteries have been solved, I realize my naivety. Take, for example, the life of a slime mold. Remember that orange glutenous junk growing all over burned tree trunks in the aftermath of the Bastrop wildfires in 2011? After a few days the ugly blobs had moved on. Ever since I was introduced to single cell creatures in high school biology, I’ve been intimidated by microscopic life forms. I find slime molds especially eerie. Creepy, jelly-like, viscous mess that materializes out of nowhere, then. . . “poof” . . .it’s all gone! Is this stuff really alive? Where did it come from? What, exactly, is it?
Slime mold most certainly is alive; but first, let’s tackle the “what is it” question.
It’s complicated. Slime mold is not an animal, plant or fungi. It’s not even actually a mold, per se. Slime mold is an informal name given to several kinds of unrelated organisms that can live freely as single cells or can join together to form a multicellular mass. Slime molds are placed in the kingdom Protista. You see, even though they probably share a common ancestor, protists do not form a natural group. Some protists are more closely related to other life forms than they are to each other—so, like algae, invertebrates, or protozoans, the Protista grouping is used mostly for convenience. The language of science can sometimes be nearly incomprehensible! For a flesh-and-blood idea you can get your mind around, a slime mold is like an amoeba. Sorry, that’s as good as it gets; the best I can do.
There are over 900 species of slime molds found throughout the world.
Not all slime molds are alike. Some have flagellated cells with a tail-like flagellum, while others are amoeboid, having an amorphous shape, and because of these features, they can actually move. The ones large enough to see without magnification come in every color under the rainbow (except green—no chlorophyll). What they share is a life cycle which includes a period when they appear as a gelatinous “slime” ranging anywhere from less than an inch in size to as much as 10-13 feet. Slime molds are particularly fond of damp forest floors where they can break down rotting vegetation, feeding on bacteria, yeast, and fungus. In Texas, slime molds are typically found in the spring or in highly irrigated shade areas in the summer. Nothing there one day, the next it looks like a dog vomited on your compost pile!
What is it like to live a life of slime?
While slime molds first exist as single-celled organisms, many don’t stay that way for long. When food is hard to find, they band together and start moving as a single body (many minds, better than one).
This transformer act allows them to better find food sources and reproduce. Slime molds generally come in two main groups. Plasmodial slime mold is enclosed within a single membrane (without walls) and is one large cell. This “supercell” is essentially a bag of cytoplasm containing thousands of individual nuclei
By contrast, cellular slime molds are individual nuclei cells which exist as minute “slugs” during their growth phase. They crawl slowly (1 mm/hour) through dung, soil, rotting mushrooms, decaying leaves and other organic material, eating their little hearts out. When conditions require, other slugs can join together to create a pseudo-plasmodium, a “fake” plasmodium.
In both cases, these organisms can reproduce and grow into an interconnected network of protoplasmic strands. Within each strand, the cytoplasm rapidly streams; it can be seen to slow,
stop, and then reverse direction. This “creature” also has the ability to subdivide and establish separate bodies. Conversely, parts that are genetically similar and compatible can fuse together again to create an even larger conglomerate. When the food supply eventually dries up, the “slime” changes yet again into rigid fruiting bodies (like true fungi or molds) and later releases spores which hatch into new amoebae, repeating the cycle.
Walk a mile in my shoes.
Let’s pretend you’re a slime mold participating in an experiment; because you crawl slowly it’s easy to find yourself in uncomfortable places (too dry, acidic or salty). So here you are, stretched out on a laboratory table with dishes of oatmeal (one of your favorite foods) a short distance away. To get to the oatmeal, you have to move across gelatin bridges laced with caffeine (which you do NOT like). The first time around, you take 10 hours to cross the bridge, trying hard to avoid the caffeine. After 2 days, you begin to ignore the bitter substance, and after 6 days you stop trying altogether—and go straight for the chow. What has just happened is called “habituation,” and it applies to a host of irritants. It means you have learned to filter out uncomfortable stimuli that are irrelevant to your survival. For humans, a classic example of habituation is that we stop noticing the sensation of our clothes against our skin moments after we put them on. We also habituate some foul smells, insect bites, etc. We quickly understand it’s just not that important.
As the experiment continues, even though you are “habituated” to caffeine, you’re still reluctant to cross a bridge containing quinine or other unfamiliar irritants. This means you have to adjust your responses differently to different stimuli. Next, they cut you up into pieces and allow you to join forces with other “naïve,” non-habituated pieces. What happens? Your original body parts transfer this habituated response to the others. The reconstituted slime mold “remembers” (or “teaches”) the naïve pieces that caffeine is really okay, displaying the same behavior without prior exposure. In one experiment, they even put you to sleep for a year by drying you up in a controlled manner. Upon being awakened, guess what? Habituated slime molds immediately cross irritant-laced barriers and hunt for food again. Non-habituated molds die.
A penny for your thoughts.
Habituation is not just adaptation; it’s a simple form of learning. If slime mold had a nervous system, it would seek out images and symbols from previous experience to “understand” its environment. Slime molds have neither neurons nor brains, yet they have a lot to teach us! Research has also shown slime molds can accomplish some truly amazing things.
For example, they have solved maze problems and laid out sophisticated distribution networks (in one famous result, slime molds recreated the Tokyo rail system). These are experiments that have been replicated globally several times now—in Japan, the U.K. and the United States—all with similar results. Simply put, slime mold is capable of computing optimal coverage of the map while using the least amount of energy. Mathematical equations written to explain the process of slime mold aggregation have been changed slightly and used in the programming that controls some of the behavior of action figures in video games and has become the basis of a program that mimics the activities of groups such as ant colonies and flocks of birds (patterns which occur without the direction of a leader). Because of the variety and flexibility of cell changes, slime molds are used as model organisms in molecular biology and genetics. One fascinating thing about plasmodial slime molds is that the millions of nuclei in a single plasmodium all divide at the same time. This makes slime molds ideal tools for scientists studying mitosis, the process of nuclear division. Scientists also study them for insights into cellular communication, differentiation, and multicellular development in general. Even computer scientists are studying it to understand and develop better algorithms for delivering information.
I think; therefore, I am?
The fact that something which looks so primitive and revolting can “think” pushes the boundaries of human cognition! When our nebula first cooled into the orb it is today, cosmic dust formed an eclectic cocktail of elements fated to eventually create life. 3.7 billion years ago microscopic organisms first produced a type of carbon molecule which set in motion a process that would, eons later, produce DNA within the nuclei of living cells—and the race was on. Using your highly developed brain, just think about this a minute. There was a time when life developed from the same point of origin. All life is an essential unity!
Now, at what point is life considered intelligent? The fact that single cells can learn and remember is both profoundly magical and beautifully ordinary. Look around you. Is intelligence in plants and animals more common than we know? The mechanism may be totally different but the outcome and functional significance are the same. Brains are optional, but for sure it’s more than cells merely coordinating sensory input. Question: How do we really know anything? And I wonder: is there an “I,” a soul which knows?
By Larry Gfeller