Extrafloral nectar production induced by simulated herbivory does not improve ant bodyguard attendance and ultimately plant defence

Abstract

Abstract Highly competitive and aggressive ant species are efficient bodyguards that monopolize the more attractive plants bearing extrafloral nectaries. Given that herbivory often increases the quality of extrafloral nectar, we hypothesized that plants damaged by herbivory would be more prone to interact with high-quality ant bodyguards and be better defended against herbivores. We performed an experiment with Chamaecrista nictitans plants. We induced anti-herbivore responses by applying jasmonic acid to a group of plants while keeping another group unmanaged. We measured extrafloral nectar production, censused ants visiting extrafloral nectaries and, subsequently, added herbivore mimics to measure the efficiency of ant anti-herbivore defence in both conditions. Induction increased the volume of extrafloral nectar and the mass of sugar per nectary without affecting the sugar concentration or the patterns of plant attendance and defence by ants. Thus, we found no evidence that defence-induced C. nictitans plants are more prone to interact with high-quality bodyguards or to receive better anti-herbivore defence. These findings highlight that increases in extrafloral nectar production are not always rewarded with increases in the biotic defences; instead, these rewards might be dependent on the traits of the nectar induced by herbivory events and/or on the ecological context in which the interaction is embedded. Consequently, herbivory might increase the costs of this induced biotic defence to plants bearing extrafloral nectaries when the induced defence does not increase the attractiveness of the plants to ants.