Tuesday, August 11, 2009

101 Interesting Things, part twenty-one: Mixotricha Paradoxa

Great fleas have little fleas upon their backs to bite 'em,
And little fleas have lesser fleas, and so ad infinitum.
And the great fleas themselves, in turn, have greater fleas to go on,
While these again have greater still, and greater still, and so on.
- Augustus de Morgan, A Budget of Paradoxes, 1872

If you thought slime moulds were cool, then you're in for a rockin' good time. The above is quoted by Richard Dawkins in The Ancestor's Tale during the mixotrich's tale. Dawkins goes on for pages about it, and no one passage is more crucial than any other. Rather than quote the good doctor at extreme length, I shall simply summarize and point around (ugh, you mean work?).

First, this is what I'm talking about:
The mixotrich appears at first glance to be a protozoan with flagella and a "fur coat" of cilia. My, my, how looks can deceive. Back in the 1930s, when the mixotrich was discovered by J. L. Sutherland, protozoans were supposed to have cilia only or flagella only (a mere supposition, as it turns out, after the same fashion that animals were "supposed to" lay eggs only or have hair only before the platypus was discovered). Hence the name, mixotricha paradoxa, the "unexpected combination of hairs." It was Lynn Margulis who finally dispensed with the totally unnecessary distinction between cilia and flagella, which was rather like having entirely separate terms for short hairs and long hairs anyway, lumping them both together as undulipodia and reserving the term "flagellum" for the free-rotating bacterial variety. A dynamic duo of super-cool scientists, with the film noir detective names of Cleveland and Grimstone, did the heavy lifting of looking at the thing with properly scientific rigor, and they found two very interesting facts.

The first and lesser of these is that the mixotrich is an unusually smooth swimmer for a protozoan. On its own, this is a mere curiosity; it is downright amazing when considered alongside the second and greater fact: the mixotrich doesn't actually have cilia.

Those hairs are spirochetes, living bacteria with their own DNA. What's more, the basal bodies which normally root undulipodia in place have analogous structures in the mixotrich, but these aren't basal bodies, either. They're pill-shaped living bacteria with their own DNA. Every single one of those 250,000-some-odd "hairs" is, in a very real sense, a separate organism, itself rooted into yet another organism still, all mounted in a rather stunningly regular arrangement of brackets along the mixotrich's surface (which brackets themselves are finally of the mixotrich's own genetic design).

The mixotrich lives exclusively in the stomach of Darwin's termite, mastotermes darwiniensis, where it aids in breaking down the wood which has been so generously pulped into easily-digestible chunks by the termite's jaws. As our planet is host to what may be termed a single biosphere, subdivided into ecosystems, themselves in turn subdivided into communities of organisms, so too are termite colonies made up of individual termites, themselves myriad individuals with other semi-distinct organisms living in tandem with them and inside them. The mixotrich makes these distinctions difficult, and when we try to justify those distinctions at the higher levels by separating them from the "other, falser" lower distinctions, we find that this is a tricky proposition indeed.

Once again, our categories simply refuse to stick to reality, as the Universe defies our compartmentalization while piling itself up and down like de Morgan's fleas and Swift's before him. Neat!


Typhinius said...

Not to be a smartass (actually, specifically to be a smartass), we do distinguish between long hair and short hair. The distinction being that long hair (or hair) will grow indefinitely (ie Rapunzel), whereas short hair (or fur) will only grow to a certain length (ie the stuff on your arms, legs, chest, and after puberty, your genital regions).

Also, I'd never heard of those things. The more we understand, the more we know that we don't understand.

D said...

By all means, smartass away!

Of course we distinguish between things unnecessarily. In light of your comment, my analogy doesn't hold water. However, the point remains that, structurally, cilia and flagella (as undulipodia) are identical. They seriously differ only in length and in number, and the distinction is a contingent one, not a necessary one.

I'm sorely tempted to find a principled analogy that does what I want it to do... however, I told myself I'd go to bed and then saw your comment... and I'm choosing to do the adult thing right now and go to bed. Thanks for the comment, though! You raised a great point!