Compensation for floral herbivory in Solanum carolinense: identifying mechanisms of tolerance

While a plant's capacity to tolerate damage by herbivores can be studied as a single trait, it is important to recognize that tolerance is generally a result of the combined action of several different traits. Here, we report on a pair of experiments to identify mechanisms for tolerating floral herbivory in Solanum carolinense, an andromonoecious perennial herb that regularly suffers from high levels of florivory. We measured the effect of actual and simulated florivory on host-plant fitness and assessed which plant traits exhibited plasticity in response to florivory. In addition, for each of nine plant genets, we calculated tolerance indices and determined which traits were genetically correlated with tolerance. Traits that served to help S. carolinense tolerate florivory in terms of sexual reproduction included initiating more inflorescences, aborting fewer buds prior to anthesis and fewer ovaries after fertilization, and increasing the ratio of perfect:male flowers. In addition, the greater the levels of florivory, the more the plants allocated to root growth, which may promote tolerance through greater potential future reproduction. The plant population contained significant genetic variation for tolerance itself and for nearly all of the putative tolerance mechanisms, which suggests that S. carolinense has the potential to evolve greater tolerance through a variety of different routes in response to natural selection.