Quantcast

Climate Change and Invasive Milkweed Could Make Toxic Cocktail for Monarchs, Study Finds

Monarch butterfly on milkweed. randy matthews / Flickr

Monarch butterflies are already in danger. Their numbers have decreased by 80 percent in the past 20 years, and this year's count of the number of the black-and-orange butterflies wintering in Mexico was lower than 2017's.

Now, researched reported Tuesday in a Louisiana State University (LSU) press release reveals that two human-caused environmental concerns could combine to pose another deadly threat to monarchs in the future: climate change, and the spread of non-native species.


The study, published Tuesday in the journal Ecology, looked at the effect of higher temperatures on a non-native, tropical variety of milkweed or Asclepias curassavica.

Tropical milkweed is commonly sold in garden stores in the southern U.S., and monarch butterflies thrive on it under current conditions.

As the press release explains, all varieties of milkweed contain cardenolides, chemicals that are toxic to most predators but that monarchs have evolved to tolerate. By laying their eggs on milkweed, monarchs protect their offspring, and the caterpillars that hatch render themselves unappetizing to predators by feasting on the chemicals.

Tropical milkweed has more cardenolides than the native Asclepias incarnata, and currently the higher level is good for monarchs. Adult butterflies that feed on A. curassavica weigh more and are more likely to survive than butterflies that feed on less-toxic, native varieties.

But this could change with the climate. The study found that warmer temperatures increase the cardenolides in A. curassavica to the point where they poison monarch larvae, delaying larval growth and stunting adult forwings. Native milkweed is not similarly impacted.

LSU Department of Biological Sciences associate professor Bret Elderd, one of the study's authors, said that his research demonstrates how climate change impacts the relationships between individual species.

"A lot of global climate change research focuses on a single species, and how that species will be affected by climate change," Elderd said in the LSU release. "But we know that in reality, species interact, and they are often tightly linked together."

The research also indicates how climate change can render harmful behaviors that used to be adaptive.

"If I'm a monarch butterfly, and I'm responding to past environmental conditions, I'll lay my eggs on A. curassavica," Elderd said in the release. "But under conditions of global warming, I'll be doing my offspring a disservice without knowing it."

Elderd was joined in his research by graduate student Matthew Faldyn and Mark Hunter of the Department of Ecology and Evolutionary Biology and School of Natural Resources and Environment at the University of Michigan.

In order to replicate temperatures projected for Baton Rouge, Louisiana in the next 40 years, researchers constructed small greenhouses around the tropical milkweed plants. They found that cardenolides increased after three days.

Faldyn said he hoped to use the research to educate plant sellers and gardeners about the importance of planting native milkweed as climate change continues.

Show Comments ()

EcoWatch Daily Newsletter

A metal fence marked with the U.S. Border Patrol sign prevents people to get close to the barbed/concertina wire covering the U.S./Mexico border fence, in Nogales, Arizona, on Feb. 9. ARIANA DREHSLER / AFP / Getty Images

President Donald Trump issued the first veto of his presidency Friday, overturning Congress' vote to block his national emergency declaration to fund a border wall that environmental advocates say would put 93 endangered species at risk. However, the president's decision came the same day as an in-depth report from UPI revealing how razor wire placed at the border in the last four months already threatens wildlife.

Read More Show Less
Guillermo Murcia / Moment / Getty Images

By Ansley Hill

Vitamin D is an essential nutrient that your body needs for many vital processes, including building and maintaining strong bones.

Read More Show Less
Sponsored
D'Bone Collector Museum head Darrell Blatchley shows plastic found inside the stomach of a Cuvier's beaked whale in the Philippines this weekend. - / AFP / Getty Images

Yet another whale has died after ingesting plastic bags. A young male Cuvier's beaked whale was found washed up in Mabini, Compostela Valley in the Philippines Friday, CNN reported. When scientists from the D' Bone Collector Museum in Davao investigated the dead whale, they found it had died of "dehydration and starvation" after swallowing plastic bags―40 kilograms (approximately 88 pounds) worth of them!

Read More Show Less
Pexels

By Jeff Turrentine

"Be careful what you wish for; you just might get it." This is something that everybody has to learn at some point. Lately, the lesson has hit home for a group of American automakers.

Read More Show Less
Art direction: Georgie Johnson. Illustrations: Freya Morgan

By Joe Sandler Clarke

"Don't expect us to continue buying European products," Malaysia's former plantations minister Mah Siew Keong told reporters in January last year. His comments came just after he had accused the EU of "practising a form of crop apartheid."

A few months later Luhut Pandjaitan, an Indonesian government minister close to President Joko 'Jokowi' Widodo, warned his country would retaliate if it was "cornered" by the EU.

Read More Show Less
Sponsored
Torres and his parents walk along the Rio Grande. Luis Torres / Earthjustice

By Luis Torres

For some people who live along the U.S.-Mexico border, President Trump's attempt to declare a national emergency and extend the border wall is worse than a wasteful, unconstitutional stunt. It's an attack on their way of life that threatens to desecrate their loved ones' graves.

Read More Show Less
Flooding at the Platte River south of Fremont, Nebraska. Gov. Pete Ricketts

Flooding caused by last week's bomb cyclone storm has broken records in 17 places across the state of Nebraska, CNN reported Sunday. Around nine million people in 14 states along the Mississippi and Missouri Rivers were under a flood watch, CNN meteorologist Karen Maginnis said.

Read More Show Less
A car destroyed by Cyclone Idai in Beira, Mozambique. ADRIEN BARBIER / AFP / Getty Images

At least 150 people have died in a cyclone that devastated parts of Mozambique, Zimbabwe and Malawi over the weekend, The Associated Press reported Sunday. Cyclone Idai has affected more than 1.5 million people since it hit Mozambique's port city of Beira late Thursday, then traveled west to Zimbabwe and Malawi. Hundreds are still missing and tens of thousands are without access to roads or telephones.

"I think this is the biggest natural disaster Mozambique has ever faced. Everything is destroyed. Our priority now is to save human lives," Mozambique's Environment Minister Celso Correia said, as AFP reported.

Read More Show Less