Atta

A genus of fungus growing ants. Leafcutter ants obligately cultivate clonally propagated fungus inside their nest as their main source of food. Larval and adult ants eat fungal mycelium from their fungus gardens, as well as clusters (“staphylae”) of modified hyphal tips (“gongylidia”). Nests of some species can be physically very large and consist of millions of workers. (Hölldobler and Wilson 1990, Dijkstra and Boomsma 2006).

Biology
Atta species have a profound influence on the habitats where they live. A review by Swanson et al. (2019) summarized what has been found about their ecological effects on ecosystems: abstract - Leaf-cutter ants are a prominent feature in Neotropical ecosystems, but a comprehensive assessment of their effects on ecosystem functions is lacking. We reviewed the literature and used our own recent findings to identify knowledge gaps and develop a framework to quantify the effects of leaf-cutter ants on ecosystem processes. Leaf-cutter ants disturb the soil structure during nest excavation changing soil aeration and temperature. They mix relatively nutrient-poor soil from deeper layers with the upper organic-rich layers increasing the heterogeneity of carbon and nutrients within nest soils. Leaf-cutter ants account for about 25% of all herbivory in Neotropical forest ecosystems, moving 10%-15% of leaves in their foraging range to their nests. Fungal symbionts transform the fresh, nutrient-rich vegetative material to produce hyphal nodules to feed the ants. Organic material from roots and arbuscular mycorrhizal fungi enhances carbon and nutrient turnover in nest soils and creates biogeochemical hot spots. Breakdown of organic matter, microbial and ant respiration, and nest waste material decomposition result in increased CO2, CH4, and N2O production, but the build-up of gases and heat within the nest is mitigated by the tunnel network ventilation system. Nest ventilation dynamics are challenging to measure without bias, and improved sensor systems would likely solve this problem. Canopy gaps above leaf-cutter ant nests change the light, wind and temperature regimes, which affects ecosystem processes. Nests differ in density and size depending on colony age, forest type and disturbance level and change over time resulting in spatial and temporal changes of ecosystem processes. These characteristics remain a challenge to evaluate rapidly and non-destructively. Addressing the knowledge gaps identified in this synthesis will bring insights into physical and biological processes driving biogeochemical cycles at the nest and ecosystem scale and will improve our understanding of ecosystem biogeochemical heterogeneity and larger scale ecological phenomena.

Dijkstra and Boomsma (2006) investigated the viability of worker-produced eggs in Atta cephalotes, Atta sexdens and Atta colombica. Most Atta workers have rudimentary, non-functional ovaries in a queenright colony but a few, typically tending the queen, can produce trophic eggs (Dijkstra et al., 2005). These eggs are feed to the queen. It was not known if any worker eggs can produce males. This study found, and concluded: Atta workers are not completely infertile, but worker fertility is low compared to the sister genus Acromyrmex, where workers routinely produce normally-size males after queen loss in the laboratory. Most worker eggs did not contain yolk but a small number did and yielded morphologically correct but very small males. They hypothesize that worker reproduction in orphaned Atta field colonies is almost never successful because the last workers die before their sons can be raised to adulthood, but the importance of worker-laid trophic eggs for queen feeding has precluded the evolutionary loss of worker ovaries.

Worker Morphology
These characters are collated in the Worker Morphology table.

Nomenclature

 *  ATTA [Myrmicinae: Attini]
 * Atta Fabricius, 1804: 421. Type-species: Formica cephalotes, by subsequent designation of Wheeler, W.M. 1911f: 159.
 * Atta senior synonym of Oecodoma: Roger, 1863b: 35.
 * Atta senior synonym of Archeatta: Smith, M.R. 1951a: 832.
 * Atta senior synonym of Archeatta, Epiatta, Neoatta, Palaeatta: Weber, 1958a: 8. [Each subgeneric name has subsequently been resurrected from and returned to synonymy, see under respective entries and in Bolton (1995b, 2003).]
 * ARCHEATTA [junior synonym of Atta]
 * Archeatta Gonçalves, 1942: 342 [as subgenus of Atta]. Type-species: Oecodoma mexicana, by original designation.
 * Archeatta as subgenus of Atta: Borgmeier, 1959b: 350; Kempf, 1972a: 27.
 * Archeatta as junior synonym of Atta: Smith, M.R. 1951a: 832; Weber, 1958a: 8; Bolton, 1994: 105.
 * EPIATTA [junior synonym of Atta]
 * Epiatta Borgmeier, 1950d: 246 [as subgenus of Atta]. Type-species: Oecodoma laevigata, by original designation.
 * Epiatta junior synonym of Atta: Weber, 1958a: 8.
 * Epiatta junior synonym of Neoatta: Borgmeier, 1959b: 358.
 * Epiatta junior synonym of Atta: Bolton, 1994: 105.
 *  MYRMEGIS [Nomen nudum]
 * Myrmegis Rafinesque, 1815: 124. Nomen nudum. [Brown, 1973b: 182, placed Myrmegis as a junior synonym of Atta, because the entry in Rafinesque reads, "6. Myrmegis R. Atta Latr."]
 * NEOATTA [junior synonym of Atta]
 * Neoatta Gonçalves, 1942: 346 [as subgenus of Atta]. Type-species: Formica sexdens, by original designation.
 * Neoatta subgenus of Atta: Borgmeier, 1959b: 358; Kempf, 1972a: 27.
 * Neoatta senior synonym of Epiatta: Borgmeier, 1959b: 358.
 * Neoatta junior synonym of Atta: Weber, 1958a: 8; Bolton, 1994: 105.
 * OECODOMA [junior synonym of Atta]
 * Oecodoma Latreille, 1818: 222. Type-species: Formica cephalotes, by subsequent designation of Shuckard, in Swainson & Shuckard, 1840: 174.
 * Oecodoma junior synonym of Atta: Roger, 1863b: 35. [Atta and Oecodoma share the same type-species, synonymy is therefore absolute.]
 * PALAEATTA [junior synonym of Atta]
 * Palaeatta Borgmeier, 1950d: 244 [as subgenus of Atta]. Type-species: Atta bisphaerica, by original designation.
 * Palaeatta subgenus of Atta: Borgmeier, 1959b: 377; Kempf, 1972a: 28.
 * Palaeatta junior synonym of Atta: Weber, 1958a: 8; Bolton, 1994: 105.