Friday, December 19, 2008

ant brains

Winter break and holiday plans aside, I'm already thinking about the parasites tutorial I'll be teaching next term. Carl Zimmer's book, Parasite Rex, makes the case very persuasively: parasites are so much more than grotesque little footnotes in life's pageant. They are major players in the ecology and evolution of many species. Of course, in addition to their ecological and evolutionary heft, many of them exhibit some really weird and creepy lifestyles. One of the most disturbing tricks that some parasites have developed is that of mind control. An infected host's behavior is altered by the parasite in a way that increases the ability of the parasite to complete its lifecycle. In many cases, parasites gain access to the final host, where reproduction occurs, by first infecting an intermediate host that is later eaten by the final host. Any behavior by the intermediate host that makes it more likely to be eaten benefits the parasite (but not the intermediate host, of course). Some parasites are able to manipulate theirs hosts, actually causing them to engage in reckless behavior. Pill bugs harboring acanthocephalan parasites may spend more time in dryer places and even prefer walking around on whiter surfaces.  This may not sound like especially exciting risky behavior, but compared to the safety of  the dark, moist leaf litter, where healthy pill bugs prefer to be, the infected pill bugs are more easily seen by birds, which gobble up the pill bugs and serve as the final host of their parasites.
Mind control of ants by liver fluke parasites has been colorfully presented in this video.

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