A slime mold is precisely the sort of thing you don’t want to step in. That also means figuratively, if you’re the kind of person who likes their taxonomy neat. That’s because slime molds aren’t molds at all… except for a few species that are. And while some of them are very slimy indeed, they usually aren’t. What?
The aptly-named Dog Vomit Slime Mold.
If not a fungus, usually, what is a slime mold? Either a giant amoeba, or a collection of amoebae. A plasmodial slime mold is essentially one giant cell with thousands of individual nuclei: a gross puddle of cytoplasm. But a cellular slime mold, my favorite kind, is a loose assembly of individual amoebae who, when a chemical signal is released, band together to form one creeping pile of neon goo that patrols the undergrowth, hunting for new bacteria for its component amoebae to munch, and creating a reproductive organism. For an analogy, imagine a herd of caribou on a wide open expanse of tundra, each browsing on lichen and moss by itself. But instead of migrating as a herd when they’ve finished off all the moss on the meadow, the caribou exude a pheromone that tells them to meet in the center and merge into one Super-Caribou that then takes off in search of more moss. Some caribou become the hooves, some the antlers. Some become the Super-Caribou’s testicles, producing sex cells for future use.
All the ones on the right are going to become the ears. The ones on the left… you don’t want to think about it.
Slime molds may not have antlers — or many discernible features at all, really — but they do have sex cells. Incredibly, some of the amoebae will sacrifice themselves to become the cells of the stalks that elevate the colony’s sori, or spore-producing organs, while others become the sex cells which will produce the spores themselves. In this way, the amoebae that make up a slime mold are like stem cells that act freely and independently of each other when feeding, then become differentiated when they join to become a multicellular organism. Like the Portuguese Man-of-War, it is an animal made of smaller animals, or more appropriately, a fungus-like thing made of smaller amoeba-like things.
Teamwork rhetoric aside, being the sex cells is a pretty highly coveted position among the amoebae.
But here’s the exciting part: it turns out that certain slime molds have developed agriculture. In a recent study, it was found that certain amoeba “cells” in Dictyostelium discoideum, a species of slime mold, could actually cultivate the very bacteria that the organism eats in its sori. That’s right: a brainless, de-centralized collection of unicellular organisms learned how to farm. If this doesn’t instantly impress you, think about how many other organisms out there purposefully cultivate their own food: it’s pretty much the leaf-cutter ants and us. Farming may not seem sexy to some people, but the difference between hunting-and-gathering and making your own nourishment where you live was a quantum leap made a mere ten thousand years ago that established human dominance over the Earth. Art, science, technology, and civilization itself came from the simple act of planting a seed.