The Reproductive Consequences Associated with Inducible Alkaloidal Responses in Wild Tobacco

We experimentally examined the phenotypic cost (as measured by the effect on seed set) associated with an inducible alkaloidal response in Nicotiana sylvestris (Solanaceae). Alkaloid concentrations were partially uncoupled from leaf damage in two experiments with the use of two techniques: (1) applying auxins to damaged leaf edges, and (2) minimizing the damage to veins of the leaf. Both of these techniques inhibited the induced response. In both experiments with flowering—stage plants, damaged plants with elevated alkaloids contents had lower reproductive output than similarly damaged plants with low alkaloid contents. Plants were able to compensate for damage inflicted during the rosette stage; reproductive output of damage plants did not differ from that of control plants. In addition, we found a significant negative correlation between seed number and leaf alkaloid content in undamaged full—sib plants. While these results are consistent with the hypothesis that the alkaloidal response to damage is associated with diminished reproductive output, and decrement in reproductive output cannot be directly attributed to alkaloid production because other unmeasured responses to damage may accompany the alkaloidal response to damage and thereby confound these measures of phenotypic cost. Last, we examined the consequences of altering leaf alkaloid concentrations, within the range found during the induced response, on rates of carbon gain and found no effect in tobacco.