Originally published October 21 2010
Monarch butterflies use medicinal plants to treat diseases in their offspring
by S. L. Baker, features writer
(NaturalNews) What happens when animals get sick in the wild -- do they just fight off disease by themselves? It seems they may actively treat themselves, and their sick offspring, with natural therapies. If that sounds like a far-fetched idea, listen up. Although few studies have been conducted on self-medication by animals, researchers from Emory University in Atlanta theorize the practice may be far more widespread than humans have realized. In fact, they've just discovered that monarch butterflies use medicinal plants to treat their offspring for disease.
"We have shown that some species of milkweed, the larva's food plants, can reduce parasite infection in the monarchs," Jaap de Roode, the evolutionary biologist who led the study just published in the journal Ecology Letters, said in a statement to the media. "And we have also found that infected female butterflies prefer to lay their eggs on plants that will make their offspring less sick, suggesting that monarchs have evolved the ability to medicate their offspring. We believe that our experiments provide the best evidence to date that animals use medication."
Monarch butterflies, known for their beautiful wings which are streaked with orange, black and white designs, migrate from the United States to Mexico each year. Their striking coloration is a warning sign to birds and other predators that the butterflies are poisonous. That's because, as caterpillars, monarchs feed on milkweed plants which can contain high levels of phytochemicals called cardenolides. These chemicals don't hurt the caterpillars, but they make them toxic -- even when they transform into butterflies -- if eaten by other animals.
Earlier research concentrated on whether the butterflies fed off toxic species of milkweed to ward off predators. De Roode, however, questioned whether the choice could be related to parasites called Ophryocystis elektroscirrha that can invade the gut of caterpillars and persist when they turn into monarch butterflies. An infected female passes on the parasites to her offspring when she lays eggs and, if the monarch leaves the pupal stage with a severe parasitic infection, the butterfly begins oozing fluids from its body and dies. If infected butterflies manage to survive, they don't fly as well or live as long as their uninfected counterparts.
So, in experiments conducted in de Roode's lab, the Emory researchers found female butterflies infected with the parasites prefer to lay their eggs on a toxic species of milkweed, rather than a non-toxic species. On the other hand, uninfected female monarchs, showed no preference. That indicates the infected butterflies somehow knew to specifically protect their offspring by "treating" them with the toxic-to-parasites milkweed.
University of Michigan chemical ecologist Mark Hunter, who collaborated with de Roode's group on the butterfly research, said the monarch findings could have important implications for human health. "When I walk around outside, I think of the plants I see as a great, green pharmacy," Hunter said in a media statement. "But what also strikes me is how little we actually know about what that pharmacy has to offer. Studying organisms engaged in self-medication gives us a clue as to what compounds might be worth investigating for their potential as human medicines."
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