Public release date: 11-Oct-2010
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Contact: Beverly Clark
Study finds monarch butterflies use medicinal plants to treat offspring
Monarch butterflies appear to use medicinal plants to treat their
offspring for disease, research by biologists at Emory University shows.
Their findings were published online Oct. 6 in the journal Ecology
"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
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." (See interview with de Roode
here: http://tinyurl.com/3995m3u )
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
University of Michigan 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," Hunter says. "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."
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
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.
Previous research has focused on whether the butterflies choose more
toxic species of milkweed to ward off predators. De Roode wondered if
the choice could be related to the Ophryocystis elektroscirrha. The
parasites invade the gut of the caterpillars and then persist when they
become adult monarchs. An infected female passes on the parasites when
she lays her eggs. If the adult butterfly leaves the pupal stage with a
severe parasitic infection, it begins oozing fluids from its body and
dies. Even if the butterflies survive, they do not fly as well or live
as long as uninfected ones.
Experiments in de Roode's lab have shown that a female infected with the
parasites prefers to lay her eggs on a toxic species of milkweed, rather
than a non-toxic species. Uninfected female monarchs, however, showed no
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, Hunter says.
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
More news from Emory: www.emory.edu/esciencecommons.
Bill S. Jersey USA zone 5 shade garden
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