The effect of refuse dumps of leaf-cutting ants on the physiology and fitness of primary consumers: a stoichiometric approach

LESCANO M. N.; QUINTERO, C.; FARJI-BRENER, A.G.; BALSEIRO, E.

Guarujá

Congreso; IUSSI XVIIIth International Congress; 2018

IUSSI

The activity of soil-disturbing animals that increase soil nutrients affects carbon: nutrient ratio ofplants, 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 performanceof plants around their nests. However, how this input of nutrients affects plant physical and/orchemical defensive traits and indirectly impact on herbivores remains poorly explored. Weexperimentally study how the refuse dumps of A. lobicornis, throughout their direct effects onthistles, impacts on the growth rate and digestive performance of a generalist chewingherbivore. 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 steppesoil. Caterpillar reared on leaves from nutrient-rich substrates had higher relative growth rateand 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 relativeacquisition of nutrients, relaxing the physiological cost of retaining N when it is no longer asscarce. 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 theC:N ratio of thistles closer to the one that satisfies herbivore requirements, with positiveconsequences for larval development and growth rates. This results highlights the importantrole played by the activity of soil-disturbing animals, like leaf-cutting ants, in indirectlymediating plant-herbivore interactions.