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Vol. 343 ,
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A Toxin a Day Keeps the Maggots Away
13 March 2009 (All day)
It doesn't take a backbone to know when to swallow your medicine. For the first time, scientists have shown that an invertebrate, the woolly bear caterpillar, can self-medicate when sick. The finding suggests that this behavior may be far more widespread in the animal kingdom than thought.
Evolutionary ecologist Michael Singer of Wesleyan University in Middletown, Connecticut, and his colleagues made the discovery when they noticed that woolly bear caterpillars (Grammia incorrupta) liked to dine on the Arizona popcornflower (Plagiobothrys arizonicus) and other plants loaded with toxic pyrrolizidine alkaloids. The caterpillars were often infested with the larvae of parasitic tachinid flies. Because the toxin seemed to improve the caterpillars' overall survival--even though it impeded their growth--the team wondered whether the alkaloids functioned as a sort of medicine.
In the lab, the researchers provided infested and uninfested woolly bear caterpillars with pyrrolizidine alkaloids or with sugar. Infested caterpillars ate twice as much toxin as their uninfested brethren did, and the alkaloids increased their survival by 20%, the team reports online this week in PLoS ONE. This suggests that when the caterpillars feed on popcornflower and other toxic plants in the wild, they are self-medicating, says Singer.
Humans visit the pharmacy, and chimpanzees plagued by worms are known to swallow rough, bristly leaves to scrape the parasites from their guts. But this new work shows that even "organisms that lack sophisticated central nervous systems can nevertheless prove capable of very sophisticated behaviors," says ecologist Richard Karban of the University of California, Davis.
Singer says that ecologists should take self-medication into account when studying behaviors in the wild. A better understanding of how endangered species derive medicines from their habitats could prove key to conserving them, he notes.