Science Made Cool

Friday Parasite: Making an Escape

The horsehair worm Spinochordodes tellinii gets a lot of press because it’s one of those insidious host-manipulating parasites that fascinates people even as it grosses them out. The worm’s larvae live inside of grasshoppers, but adult worms are free-living and aquatic. Unfortunately, grasshoppers are definitely not known for their swimming ability, leaving the worm in a bit of a fix – how to get into a body of water to mature and mate when your host shows no inclination to take you there? The answer? Mind control. S. tellinii leaves nothing to chance: taking control of the grasshopper’s brain, making it look for a body of water and jump into it, thus drowning the host but freeing the worm.

But this behavior sometimes leads to another problem for the worm: thrashing, drowning grasshoppers can attract predators before the worm has freed itself. If the dying host gets eaten, the hairworm can get swallowed up too. If it acts fast, it can use the same escape behavior that would have taken it out of the grasshopper to get out of a fish or a frog, squirming its way out of gills, mouth, or nostrils. But the clock is ticking – if the process takes more than 5 minutes, it’s curtains for the hairworm.

                  

(Movies showing the behavior can be found here.)

Source (& image from)
Ponton, F. et al. 2006. Parasite survives predation on its host. Nature 440: 756.

Friday Parasite: Virus of a Virus

Scientists may argue whether or not a virus is really alive, but no one denies that they’re cellular parasites – hijacking a cell’s reproductive machinery in order to make new viruses. But a study in this week’s issue of Nature adds a new twist: a virus that’s a virus of a virus.

Friday Parasite: One Weird Snail

You’d recognize a snail if you saw one, right? Crawls along on a big muscular foot, its body stuffed inside a hard calcium carbonate shell? Think again. When an animal becomes parasitic, sometimes its most characteristic features simply disappear. Take the snail Asterophila japonica, from the Sea of Japan. It’s a member of the Eulimidae, a family of parasitic sea snails that typically prey on echinoderms -- animals like sea urchins and starfish. Although most of the Eulimidae are very small, they still look like typical snails, with shells and a foot. Asterophila is different. This snail lives its life inside a starfish, squeezed between its epithelium and the lining of its coelomic cavity. It has simplified or lost most of the organ systems found in a typical snail -- Asterophila has no shell, and only a small rudimentary foot and mantle, giving it a beanlike appearance. It has a striking sexual dimorphism – males are tiny, only a couple of millimeters long, and live attached to the much larger (as much as 20 mm wide) females. Because both sexes live inside of starfish, no one yet knows how their larvae make their way into the open ocean to parasitize new hosts.

References:
Randall, J. and H. Heath 1912. Asterophilla, a new genus of parasitic gastropods. Biol. Bull. 22(2): 98-106.

Sasaki T, Muro K, Komatsu M. 2007. Anatomy and ecology of the shell-less endoparasitic gastropod Asterophila japonica Randall and Heath, 1912 (Mollusca: Eulimidae). Zoolog Sci. 24(7):700-13.

Image from Randall and Heath 1912: Diagram of the external surface of Asterophila.

Friday Parasite: A Life Anchored to Gills

Dactylogyrus is a genus of tiny (less than 2 mm long) trematode worms which spend their lives anchored to their host fish's gills. Worms attach to the gill tissue using specialized hooks on the rear end of their bodies, leaving the mouth end free to forage on gill tissue.

Mature worms release eggs each day; these sink to the mud and within a few days hatch into free-swimming larvae with a hankering for fish mucus and a time limit in which to find it. They have only about 4 to 6 hours to get pulled into a fish's mouth and grab onto its gills before they lose the ability to swim.

Reference/Image from: Paperna, I. 1996 Parasites, infections and diseases of fishes in Africa. An update. CIFA TECHNICAL PAPER 31

Friday (er.. Sunday) Parasite: All Hail the Mighty Parasite

(Yes, I'm late. Other deadlines and children are to blame. Carry on.)

When you envision the top predator of an ecosystem, what comes to mind is something like a thick-maned lion stalking prey on the African savannah, or a pack of wolves bringing down an elk. But a new study appearing in Nature this week suggests that in at least some ecosystems the parasites can give the more traditional top predators a run for their money.

Not A Friday Parasite: A Review

Carl Zimmer likes our game. I'm tickled.

Friday Parasite: She's MINE!

For years,  people assumed that schistosomes -- the parasitic worms that cause so much human misery in the tropics -- paired for life. They certainly seemed built for it: adult worms are usually found in pairs: a female kept snug inside a groove on a male's underside. But as Patrick Skelly reports in an article in the June issue of Natural History, schistosomes can have fairly fluid sex lives, as male worms fight over females. Males play tug of war with the available females, with the victors pulling females out of rival gynecophoric canals into their own. Unfortunately, the article isn't on the Natural History site anymore, but thanks to the wonders of the internet you can read it here.

Friday Parasite: This Week, A Pointer

Carl Zimmer has the good fortune to be at the annual meeting of the American Society of Parasitologists, and he'll be blogging about some of the things he learns there. Go on over to The Loom and check it out.

Friday Parasite: Myxing Things Up

Last week, Benj asked if there were any parasitic members of the echinoderms or bryozoans. I’ve poked around the literature, and as far as I can tell, the answer is no. But that doesn’t mean they don’t play host to their own set of parasites. For example, bryozoans are an intermediate host for an interesting and somewhat mysterious parasite – the myxozoan Tetracapsula bryosalmonae.

Friday Parasite: Y Parasites?

They’re common. They’re found worldwide. And no one knows what the adults look like. But thanks to work by Henrik Glenner of the University of Copenhagen and his colleagues in Denmark and Japan, we’ve come a step closer to solving the mystery of what kind of animal a crustacean y-larva becomes when it grows up. And it looks like those babies grow up to be parasites.