July 22, 2008

Milkweed’s Defenses Evolve to Repairs

The milkweed adheres to the adage Know your enemy by using fast repair work when its defenses are damaged by hungry caterpillars, U.S. researchers said.

Cornell University researchers examined the way milkweed evolved to the monarch butterfly caterpillar's changing attempts to disarm the plant, the Ithaca, N.Y., university said in a news release.

They found the plant may be evolving away from its defenses against certain caterpillars toward repairing themselves faster than caterpillars can eat them.

Some plants seem to have shifted away from resisting (plant-eating animals) and have taken that same energy and used it to repair themselves, 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.

Agrawal and Mark Fishbein, a Portland State University biologist, found evolutionary declines in milkweed's three main resistance traits -- hairs, cardenolides and latex -- and an escalation in the plant's ability to regrow.

One reason, Agrawal said, could be because as its predators have become so specialized, the plant was better off choosing a new defensive tactic to tolerate the herbivory (plant-eating) damage instead of resisting it.