In a multi-year experiment, researchers grew four different species of milkweed and subjected the plants to varying levels of atmospheric carbon dioxide. Using 40 different growth chambers, the research exposed milkweed plants to two different carbon dioxide levels. Twenty chambers were maintained at current global CO2 concentrations of around 400 parts per million. The other 20 chambers were ramped up to 760 ppm — a level that researchers say could be reached before the end of the century.
The study showed that some milkweed species essentially lost their medicinal properties when grown under the elevated CO2 levels. This triggered a steep decline in the monarch's ability to fight off a common parasite and reduced average lifespan by one week. That might not seem like a big deal, except that monarch butterflies only live two to six weeks.
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“We've been able to show that a medicinal milkweed species loses its protective abilities under elevated carbon dioxide,” said Leslie Decker, first author of the study. “Our results suggest that rising CO2 will reduce the tolerance of monarch butterflies to their common parasite and will increase parasite virulence.”
As to the broader implications of the study, Hunter notes that any animals, including humans, use chemicals in the environment to help them control parasites and diseases. What's more, nearly half of all human pharmaceuticals now in use were originally derived from natural sources.
“When we play Russian roulette with the concentration of atmospheric gases, we are playing Russian roulette with our ability to find new medicines in nature,” Hunter said.