Herbivore-induced defense in plants is well documented, but field evidence that these induced changes protect plants is lacking. The damage-induced increases in leaf alkaloid content in wild tobacco will be studied. Currently enough mechanistic information on the workings of this induced defense system to propose a field test of its ecological significance is available. With a previously tested experimental design that involves artificially damaging two groups of wild Nicotiana repanda plants growing in south-Texas, hormonally supressing the alkaloidal respose in one group, measuring the amount of natural herbivory sustained by induced and suppressed plants and their respective alkaloid coantents, the following three questions will be addressed: 1) are these damage-induced alkaloid levels functioning as an antiherbivore defense? 2) is this induced- defense costly in terms of reproductive output? and 3) is there variation in herbivory between different populations of wild tobacco, and is this variation correlated with variation in the benefit (reduced herbivory) and cost (reproductive costs) of this induced defense? This project is one of the few field studies of induced plant resistance which simultaneously measures both leaf chemistry and herbivore performance. Moreover, it is the first time the efficacy of an induced defense has been studied by inhibiting the defense in damaged plants, and the first project to measure the reproductive cost of defense.
