Plant economics

Natural History, April, 2002 by Stephan Reebs

Life can be hard for a plant whose leaves are being munched on by insects. Part of its photosynthetic machinery is lost, reducing its energy supply. To measure how this affects a plant's reproductive capacity, biologists have traditionally focused on the female side of things, counting the number of seeds produced (damaged plants typically mature fewer seeds). Now researchers from the University of California, Davis, and the Kellogg Biological Station of Michigan State University have shown that the male counterpart, pollen production, should not be ignored. Working at a site with relatively poor soil, Sharon Strauss, Jeffrey Conner, and Kari Lehtila studied the reproductive success of wild radishes (Raphanus raphanistrum), some of which had lost a third of their leaf cover to larvae of the cabbage white butterfly. The biologists observed the expected seed loss, but molecular tests also revealed that the pollen of damaged radish plants fertilized more of the seeds that developed on their neighbors than did the pollen of intact plants. This increased male success was linked to earlier flowering by damaged plants. At least on poor soils, a plant under attack may be able to make the best of a bad situation by skimping on seed production and investing more in the cheaper process of pollen output. ("Effects of Foliar Herbivory by Insects on the Fitness of Raphanus raphanistrum: Damage Can Increase Male Fitness," American Naturalist 158:5, 2001).

Stephan Reebs is a professor of biology at the Universite de Moncton in New Brunswick, Canada. He is the author of Fish Behavior in the Aquarium and in the Wild, recently published by Cornell University Press.