Saturday, May 8, 2010

Animal Zombies Want Your Brains

I’m always scanning the news for stories about the science behind one of my ten-year-old’s current obsessions (zombies, robots, strange creatures from the deep), and this article and accompanying image gallery of animal zombies caught my attention. The folks at Scientific American have assembled a truly mind-boggling round-up of nature’s weirdest parasites, experts at hijacking other species to do their bidding. One parasitic worm impels its pillbug host to run out from under the safety of the leaf litter; an infected caterpillar is forced to guard the larvae of a parasitic wasp; a nematode turns a snail’s tentacles into light-up, wriggling appendages that look like tasty caterpillars to passing birds.


These examples go way beyond a wasp paralyzing a spider to serve as incubator and meal for her growing brood. These parasites actually change the behavior of their unwitting hosts. In his 1996 book Mr. Wilson’s Cabinet of Wonder: Pronged Ants, Horned Humans, Mice on Toast, and Other Marvels of Jurassic Technology, Lawrence Weschler wrote about one spectacular animal zombie, tropical ants infected by a fungus called Cordyceps.  The fungus eats the ants from the inside out without killing them. When the food supply is almost exhausted and the fungus is ready to reproduce, its compels its host to climb to a high point and clamp onto a plant stem with its jaws. The fungus now devours the ant’s brain and its fruiting bodies sprout through the ant’s head and the joints of its appendages. I highly recommend exploring every nook of Mr. Wilson’s Cabinet; you can also learn how Cordyceps turns ants into pronged zombies here, on the Neurophilosophy blog.

(Bad as the ravages of Cordyceps may be for an individual worker ant, the ant-fungus relationship in general is far more beneficial to the colony, as the spectacular success of the fungus-farming ants attests. Recent research shows that ants didn’t just begin farming a single strain of fungus 50 million years ago—they have practiced real horticulture, domesticating new strains for their underground gardens.)


Even more mind-blowing? You might know of toxoplasmosis, the parasite found in garden soil and cat litter, that can cause serious medical complications in the fetuses of pregnant women who become exposed to the protozoan, Toxoplasma gondii. As the SciAm slide show points out, researchers now suspect latent toxoplasmosis may be behind subtle personality changes in people--a claim based on work by Kevin Lafferty at UC Santa Barbara. Men with a latent infection appeat to exhibit more jealousy and aggression and women hosting T. gondii in their brains appear warmer and more nurturing--though whether the parasite makes you more likely to have a dozen cats is still a matter of conjecture. There’s an older post, "Return of the Puppet Masters," on Carl Zimmer’s blog, The Loom,  that covers the science up to 2006.
You can also read the more recent post, “Parasitic Personality Disorder” order on the blog Strange Loops, and contemplate how much you yourself might have been shaped by a parasite in your brain. Strange Loops writes:
… there is a decent chance you are infected with T. gondii, and it may have helped shape your personality, who you are. It’s always disorienting to contemplate, but it is hard to deny fact that our personality – how we think and act and respond to situations – is to at least to some extent externally determined, by genes inherited from our parents, by past experiences growing up, and even by latent parasitic infections.

My son, who was a spectacular zombie for Halloween last year, may be thrilled to learn he may be a little bit zombie after all. Me? Not so much.

Zombie bunny (c) 2009 Chris Boyd, www.crazy3Dman