Researcher shows evolution of milkweed defense system

July 22, 2008
Researcher shows evolution of milkweed defense system
A monarch butterfly caterpillar gets ready to devour a milkweed leaf. Before feeding, the caterpillar disarms the plant's natural defense system by cutting the milkweed's veins that deliver a toxic and sticky latex. Credit: Anurag Agrawal

( -- The adage that your enemies know your weaknesses best is especially true in the case of plants and predators that have co-evolved: As the predators evolve new strategies for attack, plants counter with their own unique defenses.

Milkweed is the latest example of this response, according to Cornell research suggesting that plant may be shifting away from elaborate defenses against specialized caterpillars toward a more energy-efficient approach. Genetic analysis reveals an evolutionary trend for milkweed plants away from resisting predators to putting more effort into repairing themselves faster than caterpillars -- particularly the monarch butterfly caterpillar -- can eat them.

"An important question with co-evolution is where does it end?" said Anurag Agrawal, Cornell associate professor of ecology and evolutionary biology and lead author of a paper in the current issue of the Proceedings of the National Academy of Sciences. "One answer is when it becomes too costly. Some plants seem to have shifted away from resisting herbivory [plant eating] and have taken that same energy and used it to repair themselves."

The paper is important because it sheds light on key theories of co-evolution, claiming that pressure by foraging insects makes plants diversify as they evolve new defensive strategies and that such diversification follows trends in one direction or another, said Agrawal.

Milkweed species have evolved elaborate resistance strategies to fight off caterpillars that eat their leaves. These include hairs on their leaves, heart poisons called cardenolides in their tissues and milky-white toxic latex that pours from the plants' tubes. A caterpillar's bite into a milkweed leaf leads to a flood of latex that is "like getting a gallon of sticky paint thrown into your face," said Agrawal.

Some caterpillars, in turn, have adapted by shaving the leaf, cutting a leaf's veins in a circle and then eating in the middle where the latex doesn't flow. Also, the monarch caterpillar has become immune to the cardenolides.

Using DNA sequence data to look at relationships between 38 species of milkweed, Agrawal and colleague Mark Fishbein, a Portland State University biologist, found evolutionary declines in milkweed's three most important resistance traits (hairs, cardenolides and latex) and an escalation in the plant's ability to regrow.

Agrawal was surprised, he said, to find that the plant became more tolerant rather than more diverse in its defenses. The reason, he speculated, could be because as its predators have become so specialized, the plant was better off choosing a new defensive tactic "to tolerate the herbivory damage instead of resisting it." It is unknown whether such strategies have also evolved in animals trying to evade parasites.

The findings address questions about plant evolution, biodiversity and keystone species and may give plant scientists clues about profitable pest control strategies.

Provided by Cornell University

Explore further: Butterflies use differences in leaf shape to distinguish between plants

Related Stories

Maize pests impacted by the climate

July 29, 2016

In East Africa, the caterpillars of two butterflies, Busseola fusca and Chilo partellus , represent a major threat for maize, the main food crop in the region. As recently borne out by the work of IRD researchers and their ...

Zoo releases last summer batch of threatened butterflies

August 8, 2016

The Oregon Zoo has released the last batch of its zoo-raised Oregon silverspot butterflies into the wild as it winds up a summer program aimed at boosting the numbers of the once-common yellow-and-black butterfly in coastal ...

Recommended for you

Computer model is 'crystal ball' for E. coli bacteria

October 28, 2016

It's difficult to make predictions, especially about the future, and even more so when they involve the reactions of living cells—huge numbers of genes, proteins and enzymes, embedded in complex pathways and feedback loops. ...

Novel light sources made of 2-D materials

October 28, 2016

Physicists from the University of Würzburg have designed a light source that emits photon pairs, which are particularly well suited for tap-proof data encryption. The experiment's key ingredients: a semiconductor crystal ...

How planets like Jupiter form

October 28, 2016

Young giant planets are born from gas and dust. Researchers of ETH Zürich and the Universities of Zürich and Bern simulated different scenarios relying on the computing power of the Swiss National Supercomputing Centre ...


Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Jul 22, 2008
Is this really evolution? The ability to adapt doesn't sound like evolution to me.
5 / 5 (1) Jul 23, 2008
Adaptation across generations through genetic changes are exactly what evolution is supposed to be.
not rated yet Jul 23, 2008
It is very nice article about predators evolve new strategies for attack, plants counter with their own unique defenses. This information is very important for me. Thanks for information.
Addiction Recovery South Dakota

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.