Herbivore attack is widely known to reduce food quality and to increase chemical defenses and other traits responsible for herbivore resistance. Researchers at the Max Planck Institute for Chemical Ecology in Jena/Germany demonstrated that inducible defenses allow plants to forgo the costs of defense when not needed (PNAS, vol. 95, July 7, 1998).

All plants use chemical defenses to protect themselves from attack by herbivores and pathogens and a majority of these chemical defenses are inducibly deployed in some species, that is their production is dramatically increased after attack. Inducible defenses are inherently inferior to constitutively deployed defenses due to the time lag between the first attack and the activation of the defense, a delay which could leave a plant vulnerable for hours or even days as the defense is activated. Why then is this mode of defense deployment so common, having been demonstrated in over 110 plant-herbivore interactions? The commonly-held explanation is that chemical defenses are beneficial and increase a plant's fitness when it is under attack, but they are costly when not needed, utilizing resources that could be used instead for growth or reproduction, or by other means decrease the fitness of well-defended plants when grown in competition with less-defended plants in environments lacking herbivores. For example, plants that are chemically well-defended may have a lower reproductive success than undefended plants due to difficulties in attracting pollinators. In short, inducible defenses are thought to have evolved as a cost-savings measure, allowing plants to time the production of a chemical defense with the prevailing environmental conditions and forgo the costs of defense when they are not needed.

Despite the general acceptance that inducible responses are adaptive,
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Contact: Ian T. Baldwin
Baldwin@ice.mpg.de
49-3641-6436-59
Max-Planck-Gesellschaft
9-Jul-1998