TUCSON, ARIZONA--Leaves that appear to have been nibbled may fool plant-eating bugs into avoiding them, a new study finds. The duplicity appears to be a novel--and cheap--way for plants to evade being eaten.
The natural world is rife with deceit, and plants are among its main tricksters. Sex is one of the most common reasons: Some orchids, for example, mimic the appearance of female bees to lure male bees that pollinate them. But few plants are known to resort to deceit to avoid being eaten. (An exception is the passionflowers, which keep insects away with leaf shapes that mimic distasteful plants.) Plants don't skimp when it comes to self-defense. They invest in expensive protection such as thorns, tough leaves, or chemicals to ward off insects. Because plants often make these chemicals only after they have been attacked, ecologist Rodolfo Dirzo of the National Autonomous University of Mexico wondered if some plants evolved to look as if they were nibbled. The palm Reinhardtia gracilis looks that way, with its ragged-tipped leaves with holes in the center. So, Dirzo monitored three types of trees--Reinhardtia, a related palm species with full-looking leaves, and an unrelated plant--at 45 sites in a rainforest reserve in southeast Mexico. Over 2 years, insects hardly touched Reinhardtia while they dined heartily on the other two species. Dirzo found, however, that when he presented bits of the three plant species to grasshoppers in the lab, the insects preferred Reinhardtia. It tastes best, Dirzo concludes, but its leaf shape protects it. Dirzo found similar results with plants from the Amazon, leading him to believe the Mexican Reinhardtia is not a special case. He presented his research here yesterday at the joint meeting of the Ecological Society of America and the Society for Ecological Restoration. The work combines the study of mimicry systems with research into leaf shape, and “bringing these together is a real advance,” says ecologist Anurag Agrawal of the University of Toronto. The next step, Agrawal suggests, should be cutting leaves up with scissors to see whether experimentally creating the bug-eaten look can deter insects.