Milkweed's evolutionary approach to caterpillars: Counter appetite with fast repair

Jul 22, 2008

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.

Source: Cornell University

Explore further: Endangered clouded leopard kittens born in Miami zoo

Related Stories

Harm and response

Feb 13, 2015

We often think of damage on a surface level. But for plants, much of the important response to an insect bite takes place out of sight. Over minutes and hours, particular plant genes are turned on and off ...

Recommended for you

Climate change costing soybean farmers

7 hours ago

Even during a good year, soybean farmers nationwide are, in essence, taking a loss. That's because changes in weather patterns have been eating into their profits and taking quite a bite: $11 billion over ...

Clues to aging from long-lived lemurs

7 hours ago

When Jonas the lemur died in January, just five months short of his thirtieth birthday, he was the oldest of his kind. A primate called a fat-tailed dwarf lemur, Jonas belonged to a long-lived clan. Dwarf ...

User comments : 0

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.