Use of Seeds as Fungus Garden Substrate Changes the Organization of Labor Among Leaf-Cutting Ant Workers.

Abstract

Seeds of different plant species constitute an alternative but also significant substrate that leaf-cutting ants use to cultivate their fungus garden. However, how they are processed inside the nest and if their use implies differential allocation of worker size classes are still poorly known. Using laboratory colonies of Acromyrmex subterraneus (Forel) as a model, the behaviors related to the processing of three different seeds (sesame, guava, and grape) as fungus substrate were listed. At the same time, we measured how each worker size class contributed to the execution of these behaviors by registering their respective frequency. It was found that medium-sized (1.2 > head width < 1.6mm) and minimum-sized (head width <1.1mm) workers assumed the role of incorporation for sesame and grape seeds, respectively. Major-sized workers (head width >1.7mm) were concentrated on licking and holding guava seeds. Tegument removal was the only task observed that differs between treatment of seeds and treatment of leaves before their incorporation, as described in the literature. It was verified that different species of seeds imply a differential allocation of worker size classes and the inclusion or exclusion of some tasks from the behavioral repertoire. Regardless of the substrate type, leaf-cutting ant workers follow a coordinated and specialized procedure to cultivate the fungus garden but always maintain a high degree of cooperation.