Foraging ecology of the fungus-growing ant, Acromyrmex subterraneus (Hymenoptera: Formicidae) in cerrado vegetation
Ana Carolina Calheiros, Ana Carolina Calheiros , Mariane U. V. Ronque , Hélio Soares Jr. , Paulo Sérgio Moreira Carvalho de Oliveira
Departamento de Biologia Animal, Universidade Estadual de Campinas, Campinas, Brazil; Programa de Pós-Graduação em Ecologia, Instituto de Biologia, Universidade Estadual de Campinas, Campinas, Brazil ; Programa de Pós-Graduação em Ecologia, Instituto de Biologia, Universidade Estadual de Campinas, Campinas, Brazil ; Programa de Pós-Graduação em Biologia Animal, Instituto de Biologia, Universidade Estadual de Campinas, Campinas, Brazil ; Departamento de Biologia Animal, Universidade Estadual de Campinas, Campinas, Brazil
The Neotropical leaf-cutter ants, Atta and Acromyrmex, have an obligate mutualistic relationship with the fungus Leucoagaricus gongylophorus, which is nurtured by the ants inside the nest. The ants provide the fungus plant matter, protection and dispersal, whereas the fungus is the food source for immature and the queen. Here, we provided a natural history account of Acromyrmex subterraneus, and investigate its daily activity rhythm, foraging trails, home ranges, and items collected to cultivate the mutualistic fungus. The study was carried out during the rainy season, in the cerrado Reserve of Mogi-Guaçu, SE Brazil. The activity rhythms were determined through 24-hour censuses, and ant samplings were taken at 2-hour intervals in sessions of 20 min. For the home ranges and trail lengths, we observed colonies in intermittent 1-hour sessions, during which we observed foragers and their loads for 5 min and followed trails for 10 min. The ants are nocturnal, initiating activity at 6 pm and reaching a peak between 8 pm and midnight. The daily activity was negatively associated with temperature and positively associated with relative humidity. We collected a total of 638 items transported by workers as substrates for fungus culturing; all items consisted of plant matter (data from 6 colonies; 27 hours of observation). Fresh and dry leaves were the most collected items (45.45% and 21.32%, respectively), followed by flowers (18.18%), fruits (10.66%), leaf veins (4.08%), and sap (0.31%). Foraging trails usually had > 150 workers, rarely < 50. Colony home ranges averaged 10.3 m2 (6 colonies). All colonies had more than one foraging trail, which ranged from 0.74 to 13.02 m. Ants collected culturing substrates on the ground close to the nest, or beneath trees nearby. Our study highlights the importance of natural history data to understand the ecological role of these ants, and adds to the knowledge about fungus-growing ants in cerrado savanna (FAPESP, CAPES, CNPq).