The effect of refuse dumps of leaf-cutting ants on the physiology and fitness of primary consumers: a stoichiometric approach
María Natalia Lescano, María Natalia Lescano , Carolina Quintero , Alejandro Farji-Brener , Esteban Balseiro
Laboratorio Ecotono-INIBIOMA-CRUB-CONICET-Universidad Nacional del Comahue, Argentina; Laboratorio Ecotono-INIBIOMA-CRUB-CONICET-Universidad Nacional del Comahue, Argentina ; Laboratorio Ecotono-INIBIOMA-CRUB-CONICET-Universidad Nacional del Comahue, Argentina ; Laboratorio Ecotono-INIBIOMA-CRUB-CONICET-Universidad Nacional del Comahue, Argentina ; Laboratorio de Limnología-INIBIOMA-CRUB-CONICET-Universidad Nacional del Comahue, Argenitna
The activity of soil-disturbing animals that increase soil nutrients affects carbon: nutrient ratio of plants, which in turn determine the transfer of energy and nutrients through the trophic chain. Previous studies showed that the nutrient-rich organic waste (hereafter, refuse dumps) generated by the leaf-cutting ant Acromyrmex lobicornis enhance the growth and performance of plants around their nests. However, how this input of nutrients affects plant physical and/or chemical defensive traits and indirectly impact on herbivores remains poorly explored. We experimentally study how the refuse dumps of A. lobicornis, throughout their direct effects on thistles, impacts on the growth rate and digestive performance of a generalist chewing herbivore. Thistles growing on nutrient-rich substrates had more and larger leaves, up to 80% lower C:N ratio, and higher leaf toughness and spine number than plants growing on steppe soil. Caterpillar reared on leaves from nutrient-rich substrates had higher relative growth rate and enhanced digestive efficiencies than those reared on leaves from non-ant nest soils. Also, caterpillars were able to adjust the C:N ratio of their excretion to regulate the relative acquisition of nutrients, relaxing the physiological cost of retaining N when it is no longer as scarce. Our results demonstrated that the increased soil nutrient availability generated by A. lobicornis diminish the stoichiometric constraints at the base of the food chain by bringing the C:N ratio of thistles closer to the one that satisfies herbivore requirements, with positive consequences for larval development and growth rates. This results highlights the important role played by the activity of soil-disturbing animals, like leaf-cutting ants, in indirectly mediating plant-herbivore interactions.