Inducible nicotine production in native Nicotiana as an example of adaptive phenotypic plasticity

Nicotine, an inducible defense in a number of Nicotiana species, exemplifie s adaptive phenotypic plasticity. The mechanisms responsible for its produc tion are reviewed, and the induced character states are characterized allom etrically in order to understand how inducibility changes over ontogeny res ponds to environmental variables that influence plant growth, and to relate inducible production to plant fitness correlates. The empirical evidence f or fitness costs and benefits of inducible nicotine production are consider ed, and the physiological and ecological mechanisms potentially responsible for the costs are considered. An intimate understanding of the plant's nat ural history is an essential prerequisite to understanding these costs and benefits. Inducible nicotine production is just one of many traits that are altered after herbivore attack, and the cost-benefit model provides a valu able heuristic framework in which to understand the selective factors respo nsible for the maintenance of inducibly expressed traits.