Leaf herbivory and drought stress affect floral attractive and defensive traits in Nicotiana quadrivalvis

Adaptive phenotypic plasticity allows sessile organisms such as plants to match trait expression to the particular environment they experience. Plasticity may be limited, however, by resources in the environment, by responses to prior environmental cues, or by previous interactions with other species, such as competition or herbivory. Thus, understanding the expression of plastic traits and their effects on plant performance requires evaluating trait expression in complex environments, rather than across levels of a single variable. In this study, we tested the independent and combined effects of two components of a plant’s environment, herbivory and water availability, on the expression of attractive and defensive traits in Nicotiana quadrivalvis in the greenhouse. Damage and drought did not affect leaf nicotine concentrations but had additive and non-additive effects on floral attractive and defensive traits. Plants in the high water treatment produced larger flowers with more nectar than in the low water treatment. Leaf damage induced greater nectar volumes in the high water treatment only, suggesting that low water limited plastic responses to herbivore damage. Leaf damage also tended to induce higher nicotine concentrations in nectar, consistent with other studies showing that leaf damage can induce floral defenses. Our results suggest that there are separate and synergistic effects of leaf herbivory and drought on floral trait expression, and thus plasticity in response to complex environments may influence plant fitness via effects on floral visitation and defense.