TRADEOFF BETWEEN RESISTANCE AND TOLERANCE TO HERBIVORE DAMAGE IN A MORNING GLORY

MANY plant characters, including toxic secondary compounds, trichomes, spines and tough, nutrient-poor leaves have evolved at least in part as defences against pathogens and herbivores, including phytophagous i nsects(1-6). Models of the evolution of resistance(7) (9) predict that allocation to defence is determined by a tradeoff between the benefit s of resistance, such as reduction in herbivore damage, and costs of r esistance, generally envisaged as reduction in fitness in an environme nt in which herbivores are absent(9). However, despite attempts to det ermine the tests of resistance, there is little convincing evidence th at they exist and constrain the evolution of defences(10,11). Here me report the existence of such a cost in the tall morning glory, Ipomoea purpurea: genotypes that exhibit relatively high levels of resistance to insects that cause damage to apical meristems exhibit relatively l ow tolerence to this form of damage. We also show how this type of tra deoff constrains the evolution of resistance.