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Monarch butterflies appear to use medicinal plants to treat their offspring for disease, research led by biologists at Emory University, in collaboration with U-M shows. Their findings were published online Oct. 6 in the journal Ecology Letters.
“We have shown that some species of milkweed, the larva’s food plants, can reduce parasite infection in the monarchs,” says Jaap de Roode, the Emory evolutionary biologist who led the study. “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.”
Few studies have been done on self-medication by animals, but some scientists have theorized that the practice may be more widespread than we realize. “We believe that our experiments provide the best evidence to date that animals use medication,” de Roode says.
“The results are also exciting because the behavior is trans-generational,” says Thierry Lefevre, a post-doctoral fellow in de Roode’s lab. “While the mother is expressing the behavior, only her offspring benefit. That finding is surprising for monarch butterflies.”
The findings also may have implications for human health, says U-M chemical ecologist Mark Hunter, who collaborated with de Roode’s group on the research.
“When I walk around outside, I think of the plants I see as a great, green pharmacy. But what also strikes me is how little we actually know about what that pharmacy has to offer,” he said. “Studying organisms engaged in self-medication gives us a clue as to what compounds might be worth investigating for their potential as human medicines. Researchers have studied the kinds of leaves that primates eat in forests, but this work with butterflies stresses the point that even insects in our own back yard can be useful indicators of what might be medicinally active.”
Monarch butterflies are known for their spectacular migration from the United States to Mexico each year, and for the striking pattern of orange, black and white on their wings. That bright coloration is a warning sign to birds and other predators that the butterfly may be poisonous.
Monarch caterpillars feed on any of dozens of species of milkweed plants, including some species that contain high levels of cardenolides. These chemicals do not harm the caterpillars, but make them toxic to predators even after they emerge as adults from their chrysalises.
de Roode recently received a $500,000 grant from the National Science Foundation, which he will use to see if the lab results can be replicated in nature, in different populations of monarchs in various regions of the world. Hunter received $150,000 from the NSF to identify the chemicals that account for the medicinal properties of the milkweed plants.
