Friday Weird Science: Why eat tongue when you can eat testes? The castrating trematode

Mar 01 2013 Published by under Friday Weird Science, Uncategorized

Carl Zimmer over at Phenomena posted another great post about the tongue-eating parasite! Don't worry, it's not coming for YOUR tongue, it prefers fish. The parasites get in the fish's mouth, one turns female (they start out all male) and eats the fish's tongue, and then takes its place! She hang outs there while the surrounding males also hang around in the fish's mouth, and mate with her. So not only does this poor fish have his tongue replaced by a parasite, he's got a freakin' orgy going on in his MOUTH that he can't do anything about.

So, pretty embarrassing for the fish.

But if you think that's a humiliating parasite, wait til you see this one! It not only takes over your body, it'll castrate you and shrink your penis in the bargain.

Good thing it only likes whelks.

Tetreault et al. "Impact of a Castrating Trematode, Neophasis sp., on the Common Whelk, Buccinum undatum, in the Northern Gulf of St. Lawrence" Biological Bulletin, 2000

This is actually more common than you might suppose. It turns out that there are several species of trematode that castrate their sad little gastropod hosts. This particular trematode uses the poor whelk as a stop over in its life cycle. And in the process, the trematode will strip the poor whelk of it's gonads, its penis, and possibly also of its dignity (if a whelk has dignity).

First off, what is a whelk? The common whelk, Buccinum undatum is actually a type of sea snail which lives all over the northern Atlantic. Like this:


Very pretty, but don't be fooled. These slow little sea snails are actually predators! They just predate on the only thing slower than they are: clams. While a sea snail moves slowly, a clam moves not at all. So the snail preys on the clam, and then the slow snail is preyed on in turn by fish further up the food chain, like Atlantic Cod.

And Cod aren't the only things that eat whelk, humans do too. So when whelk populations start declining, people want to know why. Is it us? Or is it something else? Fish eat whelk, people eat whelk, and well, trematodes eat whelk. Sort of.

The authors of this paper wanted to look at the impact of parasites on whelks, particularly trematode parasites. They grabbed over 600 whelks, and "dissected" them. I say "dissected", because, well, how many dissections involve a hammer?

After measuring
the shell length of each animal, we fragmented the shell
with a hammer to remove the soft tissues intact.

I wish I could do that. Seems like a great way to get out science aggression, everyone smash some whelks!

Anyway, once they had the soft tissue out, they weighed all the various body parts, gonads, penises, digestive glands (what else is there, really?), and looked for the presence and distribution of the parasites. They also looked to see what effects the presence of the parasite had on the whelks.

The results were pretty striking. The trematodes loved them some gonads. They also headed toward the digestive system, but the gonads were definitely the most affected. Observe.

On the top, you can see your big ol' healthy whelk. And what's the biggest part of the whelk? Why the penis of course! The penis is labeled "p" on the top, and you can see that it loops up and around. With whelks, size matters.

But look at the bottom whelk, the poor trematode-ridden guy. Do you see the "p" on the far right? That's all that's left of that poor whelk's once proud penis. The same goes for other parts, such as the gonads of the females. They don't shrink as much, but they do turn a uniform and very drab grey color.

At top you can see your healthy lady whelk, with her gonad all pale (in real life, it's actually an orangey yellow), but at the bottom, you can see the sad drab trematode infested lady.

And the trematode definitely gets around! In the wild, 23% of females and 15% of males were infected. It doesn't appear to produce a lot of mortality (at least, not in the lab), but it does mean that many of the whelks end up living without their dignity. Because stealing your tongue is one thing. Stealing your testes? That's entirely another. So did the authors find why the whelk population had been declining? Well no. But they did find a trematode that will shrink your penis. So...a win?

Tetreault, F., Himmelman, J., & Measures, L. (2000). Impact of a Castrating Trematode, Neophasis sp., on the Common Whelk, Buccinum undatum, in the Northern Gulf of St. Lawrence Biological Bulletin, 198 (2) DOI: 10.2307/1542529

6 responses so far

  • Amoeba says:

    "After measuring
    the shell length of each animal, we fragmented the shell
    with a hammer to remove the soft tissues intact."

    The way this is broken up makes it read like part of a poem, and I'm going to go ahead and imagine their entire methods section being broken up in this way. Because it delights me.

  • Rob Dorsey says:

    Exccellent piece. Question: You refer to the female's "gonad" . I have always thought that the "gonad" was a male testicle. Does it also refer to the female ovum?

    Rob Dorsey

    • Travis says:

      Gonads are the organs that make gametes, i.e. the organs that make sperm in males and ovum in females.

      Therefore the gonads in humans are the testes and the ovaries.

    • Ben Wade says:

      Google is your friend. Wikipedia is the more pedantic friend that you were embarrassed to be seen with in high school.

      Here I have done the "work" for you. I typed 'define gonad' and viola:
      .5 seconds later ...

      The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells.[1] For example, spermatozoon and egg cells are gametes.

  • Lars says:

    @Amoeba: I thought so too. Definitely not haiku, though.

  • Blaise Pascal says:

    Interesting. Somehow I had always assumed a whelk was a bird. I'm not sure it makes any difference, since neither a bird nor a snail stands much of a chance in a supernova.

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