Social slime

“The Social Amoebae” is a rather narrow book. It seems to be the only reasonably popularized book on cellular slime molds, a group of amoebae-like organisms difficult to classify. Indeed, the author doesn't even try! A somewhat different group of creatures, the plasmodial or “regular” slime molds, are covered in another book, “Myxomycetes: A Handbook of Slime Molds” by two different authors. If you are some kind of super-nerd with an obsession for, ahem, slime, then I think both books are must-haves. If not, you will probably wonder what on earth all the fuzz is about (or where all the slime comes from).

The author of “The Social Amoebae”, John Tyler Bonner, is an elderly gentleman who has studied cellular slime molds since the 1930's. He is particularly fascinated by their life cycle, which is indeed peculiar. An amoeba-like creature starts to divide, whereupon it and its descendants combine to form a slug, a kind of colony which acts as if it was a single organism. Despite being “primitive”, the slug can orient itself towards light and detect minute differences in temperature and gas levels. If underground, this helps the slug to reach the surface. There, another startling transformation takes place, with some of the cells forming a stalk, while others turn into spores. The stalk-forming cells eventually die and hence sacrifice themselves in favor of the spores, which spread by latching onto invertebrate animals.

Since each cell in the “slime mold” is really a separate amoeba, this altruistic self-immolation is curious from a Darwinist perspective. The author's explanation is that the slug functions like a colony of social insects, where the worker caste sacrifices itself in favor of the queen, since they are family genetically speaking. In the same way, slugs usually consist of descendants of a founding amoeba. Indeed, the founder cell acts as the “queen” of the colony, secreting certain chemicals to attract its descendants. Sometimes, slugs are invaded by alien amoebae, which are genetically different, and hence act as parasites or “cheaters”. The parasite can trick the host to create stalks, while it produces the spores!

While this is no doubt fascinating, I admit that Bonner's book became increasingly less interesting as I read on. I stopped reading it about half-way through. However, since this quintessential “nerd book” seems to be the only widely available work on these critters, I have nevertheless decided to give it four stars. But, as I already explained, you probably shouldn't even try reading it unless your first love in life are social amoebae climbing the slimier parts of Mount Improbable…