Thursday, January 31, 2013

Double Ouch!

It's science fair season, and if you're lucky like me, you're up to your eyeballs in mentoring and facilitating fun experimental designs. This past weekend I was able to help my student run some behavioral experiments with hermit crabs (more on that later), and while we were removing the crabs from their shells (by gently holding the shell steady at the surface of a small tank: the hairy hermit crab, Pagarus hirsutiusculus, will wiggle its way out of the shell and drop to the bottom of the tank) we noticed this:

 
The hermit crab is about to enter its shell, but see that red blob?

Do you know what it is?

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(I'll give you a moment to think)

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It's a rhizocephalan! WOOO! And GROSS!!! This poor little hermit crab is being parasitized by a reproductive-organ-hijacking barnacle. Remember learning here that rhizocephalans will sterilize their host and use the host's energy to raise and protect their own little parasite larvae. I was used to seeing these parasites on king crabs, but it is pretty common for hermit crabs to have rhizocephalans on them, at least in Auke Bay, where our science fair animals had been collected. In fact, back in 1996, researchers went out and collected 169 hairy hermit crabs from Auke Bay and found the parasites on about 13% of them! But don't worry, because they also found this:

The blobs marked "A" and "B" are rhizocephalans (Peltogaster paguri),
but the "C" blob is a HYPERPARASITE on the "B" rhizocephalan! 

YEAH! Take that, parasite! You've got a parasite of your own! (Nature: it's an awesome, scary place.) The rhizocephalan's hyperparasite is Liriopsis pygmaea, an isopod that will sterilize its host. It's a nice case of karma, am I right?

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