Pay it forward: refuse dump from leaf-cutting ants promotes caterpillar digestive performance by increasing plant nitrogen content

LESCANO, MARIA NATALIA; QUINTERO, CAROLINA; FARJI-BRENER, ALEJANDRO GUSTAVO; BALSEIRO, ESTEBAN

ECOLOGICAL ENTOMOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2019 vol. 44 p. 40 - 49

0307-6946

Abstract. 1. The activity of soil-disturbing animals that increase soil nutrients canaffect the carbon : nitrogen (C : N) ratio of plants, which, in turn, may determine thetransfer of energy and nutrients through higher trophic levels. However, the strength andsign of this indirect effect depend on whether enhanced nutrient substrates increase plantfoliar nutrients and/or plant defensive traits.2. We investigated how the nutrient-rich refuse dumps of the leaf-cutting antAcromyrmex lobicornis, as a result of their direct effects on thistles, indirectly impactthe growth rate and digestive performance of a generalist chewing herbivore. We alsoincluded the application of commercial fertilisers to test whether the enhanced soilnutrients comprises the mechanism behind the impact of refuse dumps on the upwardcascade effects.3. Thistles growing on nutrient-rich substrates (i.e. ant refuse dumps and fertilised soil)had more and larger leaves, up to 80% lower C : N ratios, and higher physical defencescompared to plants growing on steppe soil. Caterpillars showed an enhanced digestiveperformance and growth rate when feed on nutrient-rich plants and were able to adjustthe C : N ratio of their excretion to regulate the relative acquisition of nutrients.4. The positive effect of nutrient-rich substrates on caterpillar feeding efficiencysuggest that the enhanced nutritional quality of the thistles could compensate forthe negative effects of the increased physical defences. The results of the presentstudy indicate how organisms that increase soil nutrient availability may diminish thestoichiometric constraints at the base of food chains, enhancing the development andgrowth rate of herbivores and, thus, indirectly mediating plant?herbivore interactions.