Editors' Note: For digital images of the caterpillar or daphnia, contact Patricia Bailey at pjbailey@ucdavis.edu Moms who have faced adversity produce kids who are physically better equipped to deal with the hardships of life, suggests a study by a University of California, Davis, researcher. Examining wild radish plants and the water flea Daphnia, ecologist Anurag Agrawal and colleagues found that defensive responses triggered in both species by their respective predators were passed on to the offspring, even though the young were not under attack. Evidence of such "maternally induced" defenses is reported in the Sept. 2 issue of the journal Nature. "Conventional wisdom says that genetics and environmental conditions are largely responsible for the way an individual looks, acts and behaves," said Agrawal, who studies plant defensive responses against insects. "Surprisingly, the findings from this study indicate that the environment of a mother not only affects her own development, but also actively affects her children, in this case, producing stronger, better defended offspring." The findings may have implications for the ways in which insect pests are managed in crops grown for seed production, Agrawal noted. For example, seeds produced by plants that were heavily sprayed with pesticides to protect them against insects may not be as hardy as seeds produced by plants that endured some level of insect attack. "We've generally believed that if plants are being hammered by insect pests they won't produce as healthy seeds as would undamaged plants," Agrawal said. "But the results of this study seem to indicate the opposite to be true." Agrawal began by studying the response of the wild radish plant, a member of the mustard family, to damage by the caterpillar stage of the cabbage butterfly. Agrawal's earlier research showed that wild radish plants damaged by the caterpillar produced ten-times higher concentrations of certain chemicals known as mustard oil glycosides and 30 percent higher densities of trichomes, tiny hair-like structures on the leaves. Both the elevated glycosides and increased trichomes are defensive responses that tend to deter the grazing caterpillar. To examine the results of the caterpillar's feeding on a second generation of plants, Agrawal allowed caged caterpillars to eat half of each leaf on one group of plants. A control group of plants was not exposed to caterpillars. Seeds from the damaged and control plants were then collected and grown into seedling plants. Like their mothers, the seedlings produced by the caterpillar-damaged plants had more of the hairlike trichomes and higher concentrations of glycosides. Caterpillars grazing on the seedlings from the caterpillar-damaged plants also gained 20 percent less weight than did caterpillars grazing on seedlings from the control plants, further evidence that the induced defensive response had been passed from the damaged parent plant to its seedlings. Curious to see if such maternally induced defenses occurred in the animal kingdom, Agrawal collaborated with researchers Ralph Tollrian and Christian Laforsch at the Zoological Institute of Ludwig-Maximilians-University in Munich, Germany. Laforsch and Tollrian devised a parallel study using the water flea Daphnia cucullata as a research model. One of the best indications of an induced defense in the tiny Daphnia, an organism commonly found in ponds, is formation of an unusually large helmet-like structure that appears to make it more difficult for predators to eat the Daphnia. Previous research has shown that Daphnia form helmets when exposed to chemicals known as "kairomones," released into the water by predators. To investigate possible transmission of the helmet-forming defense mechanism, the researchers raised one group of the daphnia in a water environment containing kairomones and another group in a kairomone-free environment. They found that offspring from mothers raised in the kairomone environment always had larger helmets than offspring from mothers raised in the control environment. They even found that the tendency to produce larger helmets was passed from kairamone-exposed Daphnia to their grandchildren. "There are genes for inducible defenses in plants," said Agrawal. "We think that the mother is somehow 'tweaking' those genes so that they are turned on in the seedlings, or it could be that the mother plant pumps different chemicals into the seedling to manipulate defensive responses." He noted that a fundamental assumption of this theory is that the mother -- whether wild radish plant or Daphnia -- can somehow anticipate the level of predation the next generation will encounter and at some level "knows" what is best for her offspring. The study was funded by the National Science Foundation.