Friday Parasite #1

A bunch of the science bloggers have a tradition of posting a regular Friday feature. We’ve wanted to jump on the bandwagon for a while now, but what to write about? Lots of my favorite topics: wine, octopus natural history, my kids, weird animal sex -- are already being covered (OK, Dr. Free-Ride blogs about her kids, not mine, but still). But fortunately, I was in charge of the research for our upcoming game, Parasites Unleashed. Which means that I now know a lot about parasites. And I’m happy to share.

Let’s start with one of my personal favorites. Your mental image of a parasite is probably something wormlike, right? Something squirmy and cylindrical. But nearly every major taxon of living things has at least one species that has evolved a parasitic lifestyle. And one of the most grotesque is ….

               

…a barnacle. Barnacles of the genus Sacculina start their lives like all barnacles: as a free-swimming nauplius larva. But these larvae are not looking for a nice rock to settle down on. Instead, a young female Sacculina looks for an unsuspecting crab. When she finds one, she attaches to a soft bit of shell and injects herself into the crab’s body. Then she grows. And grows. And grows. When she’s big enough, she sets some pillow-shaped reproductive structures under the crab’s abdomen and waits for the males to move in.

You can see part of a mature Sacculina parasite in the above photograph – those big bright yellow sacks are her reproductive bodies. The rest of her branches through the crab’s hemocoel, infiltrating every part of its body. Like this:

Once the males arrive. they set up housekeeping inside the female's reproductive sacks and get busy fertilizing the next generation. But there’s more. The parasite has stashed its eggs in the same place the crab would put hers.  Possible conflict? The parasite takes no chances – she spays her host, rendering her sterile. Then Sacculina takes advantage of the crab’s brooding behaviors. Female crabs pump their abdomen to release mature larvae; infected crabs behave the same way, releasing huge numbers of baby parasites into the water.

And what if Sacculina landed on a male crab? No problem. The parasite just gives him an involuntary sex change by mucking with his hormones. Infected male crabs grow a female-shaped abdomen and start brooding parasite eggs. If crabs could write, they'd have plenty of inspiration for zombie horror.

Images from

http://www.hku.hk/ecology/porcupine/por23/23-invertebrates.htm   and

Ernst Haeckel's Artforms of Nature, 1904

Comments

[Ryan S.]

Let me be the first to say.... Ick!

[Abel Pharmboy]

Thanks for the link, Doc Kelly!

[John]

Now the question is truly being a barnacle, related to a crab, would one eating a cooked parasitized crab notice any difference in the flesh?

Would the fleshy protuberances of the parasite cook up like crab meat?

If so is there any commercial value to them?

It does seem like those protuberances easily double the amount of potential crab(like) meat to be had from any crab, and the only part of the crab not eaten is the shell - when it's hard. Soft shelled crabs are eaten whole including the shell. Other than a seeming bigger portion of tender crab(like) meat would anyone know the crab they ate had been parasitized?

Just a little macab thought for the day.

[Punnitydriday]

Emm.. Would you like more of my lucid student Fresh joke! What did the fish say when he hit a concrete wall? "Dam."