Are there trade-offs among antiherbivore defences in Ipomoea (Convolvulaceae)?

The concept that the cost of antiherbivore defenses leads to trade-offs where species will have one but not both of a set of alternative defenses was tested in the genus Ipomoea (Convolvulaceae). Indole alkaloids were analysed in 19 species and compared with the number of other antiherbivore defenses in the same species (defense nectaries, hairy leaves or woody stems). Within the Ipomoea species tested, there was no tendency for species having one defense to lack others, i.e. indole alkaloids were no less numerous in species with defense nectaries than those without. This evidence is therefore inconsistent with the idea that allocation of resources to one defense will favor reduction of other defenses. The most likely explanation of the results presented here is that most traits involved in defense have multiple uses so that they do not form simple alternatives leading to trade-offs.