Sunday, March 11, 2012

Parasitic Isopods and the Revival of the Long-Dormant Blog

Oh poor, neglected blog. Oh sad, abandoned readers. Many moons it has been since a new post appeared on this little slice of virtual reality.

The last appearance, it seems, was in November. This, not coincidentally, was around the time I started my internship at the Center for Environmental Health far, far away from home and began to devote 4.5 hours a day to the joys of public transit.

The internship, in a word, rocked, so it was all worth it. Go poke around the website and learn about the threat of death by toxic chemicals—and what CEH is doing to fight it.

Said internship finished up at the end of February, and while I very much miss my coworkers and the job (though not the getting-up-before-sunrise-to-catch-the-bus aspect), I do have time again to think about Science and Cookies in addition to other important things like job hunting (unpaid internships, however rockin' they may be, do not pay the bills), wedding planning (apparently it's considered rushing to have a wedding six months after you get engaged. I didn't believe it when I first heard it, but good heavens do I believe it now), and playing "Just Dance 3" and "Legend of Zelda" on Wii (okay, those probably don't qualify as important, but dancing still counts as exercise, right?).

My excuses are on the table. It's up to you to decide whether this merits your forgiveness. In the interim, please accept this humble blog post as my apology. It's about something ridiculously cool. It's about...

PARASITIC, TONGUE-EATING ISOPODS!!! Seriously, how can you get cooler than that?

Wait... where are going? Come back! This won't hurt a bit, I promise. Okay, here we go...

The tongue-eating part is self-explanatory, but the other two parts merit some description. Isopods are a little easier, so we'll start there.

Isopods are crustaceans, like the more familiar shrimps, crabs, and lobsters. Coming from an aquatic lineage, they breathe through gills. You remember those gray roly-poly bugs you used to find in the dirt when you were a kid? Maybe you called them pill bugs or potato bugs. Those are terrestrial (land-dwelling) isopods; they hang out in cool, damp soil because they need that moisture to breathe.

Most isopods take the easy road and live in water full-time. Here's a decently sized fella we scooped up off the sea floor under the frozen seas of Barrow, Alaska, last May:

The real heavyweights, though, are the deep sea cousins of that handsome specimen above. Think of them as isopods on steroids.

(Note: I didn't take either of these photos)

Parasites, biologically speaking, are a bit trickier to define. The rich diversity of parasites—their behavior, their strategies for attack, deception, reproduction, their presence all over the tree of life—is staggering. It makes it damn near impossible to lump them all under one tidy definition. Very simply put, a parasite is an organism that derives some benefit from another creature at the latter's (the host's) expense. There are exceptions, of course. Many bacteria fall under this definition, but few biologists consider them parasitic. And some parasites barely tax their host's resources, or do so only for a brief period of time.

Carl Zimmer, science writer extraordinaire, penned one of my all-time favorite books on this subject:  Parasite Rex. Go to your local library or indie bookstore (not Amazon, please. C'mon now.) and check it out. Suffice it here to say that as much as I'd like to spend the next hour rambling about parasites and how incredibly amazing and awesome and mind-blowing they are, Zimmer already has that beat covered. I'l restrain myself and stick to just one example.

And so we return to the subject at hand: the isopod Cymothoa exigua—that monstrous denizen of the briny blue with an insatiable appetite for fish tongue—and its icthyoid victim, the spotted rose snapper (Lutjanus guttatus).

Their nightmarish relationship is profiled in one of my favorite scientific articles, a rather dry and not terribly well researched little piece from a kinda obscure journal. Its redeeming features are the figures, the most ridiculous hypothesis in science, and a passing mention of the fish with the greatest Latin name *ever*. Say it with me now: it's Boop boops. Seriously.

C. exigua (the isopod) begins its life of crime as an immature male on the gills of its chosen host. He then squirms his way into the fish's mouth, undergoes a sex change, and becomes a female. In scientific circles, that MTF transition is known as protandrous hermaphroditism.

The she-isopod proceeds to devour the hapless snapper's tongue, leaving only a small stub to which she attaches her derrière via "seven pairs of hooklike pereopods." (Don't ask me what those are, but they sure sound lethal.)

Here's Figure 2 from the paper. My apologies in advance for the nights you'll spend sleepless and drenched in a cold sweat on account of this... The original figure caption reads as follows: "Preserved specimen of Lutjanus guttatus showing relative size of the isopod in the mouth. The gill cover and jaws have been partly removed to show how far posterior to the tongue base the isopod has attached."
Imagine it: You're a carefree little fish, swimming happily along, keeping an eye out for your next meal (and for predators that want to make you their next meal). Suddenly, out of the blue (literally), a devious crustacean gloms onto your gills and digs through the side of your face into your mouth! You have no hands. You can't yank it out, and your tongue is non-protrusible, so you can't even spit it out. All you can do is keep swimming along in a state of shock as the terrible beast gleefully munches away at your tongue.

Your spouse files for divorce, your friends won't return your calls, your health insurance drops your coverage. You can't get a date, and if even if you could, how would you kiss?

Life has become a living hell. You sink deep into depression. A fierce, desperate longing to be rid of this hideous parasite is weighted against the undeniable knowledge that you now have no tongue. Without C. exigua gripping the floor of your mouth, you have no way to hold food while you chew. If your personal demon abandons you, you'll starve.

Back to the science. Now a permanent fixture in the fishy's kisser, C. exigua proceeds to… do nothing. Really. At least, that's what these authors imply.

It cracks me up! Here we have one of the creepiest invasions of personal space in the biological world, and they show zero curiosity about it. What does the isopod eat? Does it feast on the blood of its host or steal morsels of whatever the fish manages to catch? How does it reproduce? Does it ever abandon its host? There are no answers.

Granted, with their sample size, it must have been difficult to gather any conclusive evidence on these matters. The authors, Brusca and Gilligan, looked between the fishy lips of 37 spotted red snapper recently caught off the Sonoran coast of Mexico. Two of these had firmly established crustaceans instead of tongues. Two. That's it. Two dead fish. Not exactly a representative sample.

Both fish appeared to be in good health (well, except that they were dead), with full guts and no signs of stunted growth. The isopods must have been there for awhile, since they were full grown—far too big to have recently come in through the back door (the gills).

And so, Brusca and Gilligan, those intrepid ichthyologists armed with their dead fish duo, put forth one of the most earth-shattering hypotheses ever to grace the pages of a scientific journal:

From the evidence presented we propose the hypothesis that a fish with an "isopod tongue," while perhaps not feeding as efficiently as a non-parasitized fish, feeds more efficiently than a fish with no tongue at all and no isopod in its place.

Gosh, really?

Thankfully, other scientists have stepped in to fill the research void left when Brusca and Gilligan called it a day. Carl Zimmer (the parasite book guy) recently returned to this topic in his blog. He reports that other scientists have measured lower blood counts in isopod-infected fish; in other words, the parasites "act like blood-drinking mouth leeches." Now there's a striking image for you… mull that one over next time you accidentally bite your own tongue!

Brusca, Richard C. and Matthew R. Gilligan. 1983. Tongue replacement in a marine fish (Lutjanus guttatus) by a parasitic isopod (Crustacea: Isopoda). Copeia 1983:813-816.


  1. Oh shoot, you updated even earlier. Well, much belated congratulations are in order for your engagement! Furthermore, congrats on the internship wrapping up. What are your plans for the wedding and job prospects?

    1. Why hello again :-) . And thanks! Wedding planning is coming along--lots of work, but so much fun all the same. Job hunting is coming along too, though I have less control over the outcome of that, so it's more frustrating... gotta keep my spirits up and my fingers crossed!