A Trypanosoma brucei cell divides in the bloodstream of its human host. (The two flagellae on the left show that this particular protist was caught in the middle of mitosis.) If untreated, the host will develop trypanosomiasis -- West African sleeping sickness.
SEM by the Gull Lab, Sir William Dunn School of Pathology, courtesy of the wonderful Wellcome Images collection.
At the delightfully cephalopodian Pink Tentacle Web log, there's a wonderful post about a Japanese work from the 1860s called Kenbikyu Mushi No Zu, which features illustrations of insects as seen through an imported microscope. Think of it as Hooke's Micrographia, but in a kimono.
That plant you may be hanging up in kissing balls this holiday season is a parasite. Or a hemi-parasite, to be more specific, because the American mistletoe (Phoradendron flavescens) does make some of its own food by photosynthesis. And it certainly has lots of opportunity to soak up the sunlight, because it doesn't bother with the risky buisness of growing in soil --the plant sinks its roots directly into its host's bark and starts to grow, way up high and out of the shade. (How does it get there? On a bird, of course. Mistletoe berries may be poisonous to us, but they're plenty tasty to birds. So the sticky seeds stay on a bird's bill or feet long enough to get flown to the next tree over.)
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.
Source (& image from)
Ponton, F. et al. 2006. Parasite survives predation on its host. Nature 440: 756.
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.
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.
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
(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.
Continue reading "Friday (er.. Sunday) Parasite: All Hail the Mighty Parasite" »
Carl Zimmer likes our game. I'm tickled.
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.
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