Leafcutter ant

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Atta cephalotes, Wilhelma Zoo, Stuttgart Atta cephalotes-pjt.jpg
Atta cephalotes , Wilhelma Zoo, Stuttgart

Leafcutter ants, a non-generic name, are any of 47 species [1] of leaf-chewing ants belonging to the two genera Atta and Acromyrmex . These species of tropical, fungus-growing ants are all endemic to South and Central America, Mexico, and parts of the southern United States. [2] Leafcutter ants can carry twenty times their body weight [3] and cut and process fresh vegetation (leaves, flowers, and grasses) to serve as the nutritional substrate for their fungal cultivates. [4]

Contents

Acromyrmex and Atta ants have much in common anatomically; however, the two can be identified by their external differences. Atta ants have three pairs of spines and a smooth exoskeleton on the upper surface of the thorax, while Acromyrmex ants have four pairs and a rough exoskeleton. [5] The exoskeleton itself is covered in a thin layer of mineral coating, composed of rhombohedral crystals that are generated by the ants. [6]

Next to humans, leafcutter ants form some of the largest and most complex animal societies on Earth. In a few years, the central mound of their underground nests can grow to more than 30 m (98 ft) across, with smaller radiating mounds extending out to a radius of 80 m (260 ft), taking up 30 to 600 m2 (320 to 6,460 sq ft) and containing eight million individuals. [2]

The lifecycle of a leafcutter ant colony

Reproduction and colony founding

Atta colombica, queen with larvae and workers on substrate Atta colombica queen.jpg
Atta colombica , queen with larvae and workers on substrate

Winged females and males leave their respective nests en masse and engage in a nuptial flight known as the revoada (Portuguese) or vuelo nupcial (Spanish). Each female mates with multiple males to collect the 300 million sperm she needs to set up a colony. [7]

Once on the ground, the female loses her wings and searches for a suitable underground lair in which to find her colony. The success rate of these young queens is very low, and only 2.5% will go on to establish a long-lived colony. To start her own fungus garden, the queen stores bits of the parental fungus garden mycelium in her infrabuccal pocket, which is located within her oral cavity. [8] Colonies are generally founded by individual queens – haplometrosis. [9] : 125  Because colonies with multiple queens over the lifespan of the colony have been found by a large number of investigators – by Weber 1937, Jonkman 1977, Huber 1907, Moser & Lewis 1981, Mariconi & Zamith 1963, Moser 1963, and Walter et al 1938 – it is believable that some colonies have multiple foundresses – termed pleometrosis. [9] : 125  Pleometrosis is confirmed only for Atta texana by Vinson 1985. [9] : 125 

Colony hierarchy

In leafcutter colonies, ants are divided into castes, based mostly on size, that perform different functions. Acromyrmex and Atta exhibit a high degree of biological polymorphism, four castes being present in established colonies—minims, minors, mediae, and majors. Majors are also known as soldiers or dinergates. Atta ants are more polymorphic than Acromyrmex, meaning comparatively less difference occurs in size from the smallest to largest types of Acromyrmex.

Leafcutter ant Atta cephalotes Leaf cutter ants arp.jpg
Leafcutter ant Atta cephalotes

Ant–fungus mutualism

Their societies are based on an ant–fungus mutualism, and different species of ants use different species of fungus, but all of the fungi the ants use are members of the family Lepiotaceae. The ants actively cultivate their fungus, feeding it with freshly cut plant material and keeping it free from pests and molds. This mutualistic relationship is further augmented by another symbiotic partner, a bacterium that grows on the ants and secretes chemicals; essentially, the ants use portable antimicrobials. Leaf cutter ants are sensitive enough to adapt to the fungi's reaction to different plant material, apparently detecting chemical signals from the fungus. If a particular type of leaf is toxic to the fungus, the colony will no longer collect it. The only two other groups of insects to use fungus-based agriculture are ambrosia beetles and termites. The fungus cultivated by the adults is used to feed the ant larvae, and the adult ants feed on leaf sap. The fungus needs the ants to stay alive, and the larvae need the fungus to stay alive, so mutualism is obligatory.

The fungi used by the higher attine ants no longer produce spores. These ants fully domesticated their fungal partner 15 million years ago, a process that took 30 million years to complete. [10] Their fungi produce nutritious and swollen hyphal tips (gongylidia) that grow in bundles called staphylae, to specifically feed the ants. [11] Leucoagaricus gongylophorus is the most commonly documented fungi farmed by higher attine ant species. [12] [13]

Waste management

Workers of Atta colombica at work Atta colombica workers cutting whole plant.jpg
Workers of Atta colombica at work
Leafcutter ant in Costa Rica Leafcutterant-osa.jpg
Leafcutter ant in Costa Rica

Leafcutter ants have very specific roles in taking care of the fungal garden and dumping the refuse. Waste management is a key role for each colony's longevity. The necrotrophic parasitic fungus Escovopsis threatens the ants' food source and thus is a constant danger to the ants. The waste transporters and waste-heap workers are the older, more dispensable leafcutter ants, ensuring the healthier and younger ants can work on the fungal garden. The Atta colombica species, unusually for the Attine tribe, have an external waste heap. Waste transporters take the waste, which consists of used substrate and discarded fungus, to the waste heap. Once dropped off at the refuse dump, the heap workers organise the waste and constantly shuffle it around to aid decomposition. A compelling observation of A. colombica was the dead ants placed around the perimeter of the waste heap. [14] [15]

In addition to feeding the fungal garden with foraged food, mainly consisting of leaves, it is protected from Escovopsis by the antibiotic secretions of Actinomycetota (genus Pseudonocardia ). This mutualistic micro-organism lives in the metapleural glands of the ant. [16] Actinomycetota are responsible for producing the majority of the world's antibiotics today.

Parasitism

When the ants are out collecting leaves, they are at risk of attack by some species of phorid flies, parasitoids that lay eggs into the crevices of the worker ants' heads. Often, a minim will sit on a worker ant and ward off any attack. [17]

Also, the wrong type of fungus can grow during cultivation. Escovopsis, a highly virulent fungus, has the potential to devastate an ant garden, as it is horizontally transmitted. Escovopsis was cultured, during colony foundation, in 6.6% of colonies. [18] However, in one- to two-year-old colonies, almost 60% had Escovopsis growing in the fungal garden. [19]

Nevertheless, leafcutter ants have many adaptive mechanisms to recognize and control infections by Escovopsis and other micro-organisms. [20] The most common known behaviors rely on workers reducing the number of fungal spores by grooming, or removing an infected piece of the fungus garden and throwing it away at the waste dump (described as weeding). [21]

Communication

Leafcutter ants use chemical communication and stridulation (substrate-borne vibrations) to communicate with each other. [22]

Prey plants

Leafcutter ants prefer disturbed habitats, likely due to higher concentrations of pioneer plant species. These are more attractive food sources because pioneer plants have lower levels of secondary metabolites and higher nutrient concentrations than the shade-tolerant species that will come later. [23]

Interactions with humans

In some parts of their range, leafcutter ants can be a serious agricultural pest, defoliating crops and damaging roads and farmland with their nest-making activities. [7] For example, some Atta species are capable of defoliating an entire citrus tree in less than 24 hours. A promising approach to deterring attacks of the leafcutter ant Acromyrmex lobicornis on crops has been demonstrated. Collecting the refuse from the nest and placing it over seedlings or around crops resulted in a deterrent effect over a period of 30 days. [24]

See also

Related Research Articles

<i>Atta</i> (ant) Genus of ants

Atta is a genus of New World ants of the subfamily Myrmicinae. It contains at least 17 known species.

<span class="mw-page-title-main">Fungus-growing ants</span> Tribe of ants

Fungus-growing ants comprise all the known fungus-growing ant species participating in ant–fungus mutualism. They are known for cutting grasses and leaves, carrying them to their colonies' nests, and using them to grow fungus on which they later feed.

<span class="mw-page-title-main">Texas leafcutter ant</span> Species of ant

The Texas leafcutter ant is a species of fungus-farming ant in the subfamily Myrmicinae. It is found in Texas, Louisiana, and north-eastern Mexico. Other common names include town ant, parasol ant, fungus ant, cut ant, and night ant. It harvests leaves from over 200 plant species, and is considered a major pest of agricultural and ornamental plants, as it can defoliate a citrus tree in less than 24 hours. Every colony has several queens and up to 2 million workers. Nests are built in well-drained, sandy or loamy soil, and may reach a depth of 6 m (20 ft), have 1000 entrance holes, and occupy 420 m2 (4,500 sq ft).

<i>Atta sexdens</i> Species of ant

Atta sexdens is a species of leafcutter ant belonging to the tribe Attini, native to America, from the southern United States (Texas) to northern Argentina. They are absent from Chile. They cut leaves to provide a substrate for the fungus farms which are their principal source of food. Their societies are among the most complex found in social insects. A. sexdens is an ecologically important species, but also an agricultural pest. Other Atta species, such as Atta texana, Atta cephalotes and others, have similar behavior and ecology.

<span class="mw-page-title-main">Ant–fungus mutualism</span> Symbiotic relationship

The ant–fungus mutualism is a symbiosis seen between certain ant and fungal species, in which ants actively cultivate fungus much like humans farm crops as a food source. There is only evidence of two instances in which this form of agriculture evolved in ants resulting in a dependence on fungi for food. These instances were the attine ants and some ants that are part of the Megalomyrmex genus. In some species, the ants and fungi are dependent on each other for survival. This type of codependency is prevalent among herbivores who rely on plant material for nutrition. The fungus’ ability to convert the plant material into a food source accessible to their host makes them the ideal partner. The leafcutter ant is a well-known example of this symbiosis. Leafcutter ants species can be found in southern South America up to the United States. However, ants are not the only ground-dwelling arthropods which have developed symbioses with fungi. A similar mutualism with fungi is also noted in termites within the subfamily Macrotermitinae which are widely distributed throughout the Old World tropics with the highest diversity in Africa.

<i>Acromyrmex</i> Genus of ants

Acromyrmex is a genus of New World ants of the subfamily Myrmicinae. This genus is found in South America and parts of Central America and the Caribbean Islands, and contains 33 known species. Commonly known as "leafcutter ants" they comprise one of the two genera of advanced attines within the tribe Attini, along with Atta.

<i>Mycocepurus smithii</i> Species of ant

Mycocepurus smithii is a species of fungus-growing ant from Latin America. This species is widely distributed geographically and can be found from Mexico in the north to Argentina in the south, as well as on some Caribbean Islands. It lives in a variety of forested habitats and associated open areas. Two studies published in 2009 demonstrated that some populations of the species consist exclusively of females which reproduce via thelytokous parthenogenesis. A detailed study found evidence of sexual reproduction in some populations in the Brazilian Amazon. Accordingly, M. smithii consists of a mosaic of sexually and asexually reproducing populations. In asexual populations all ants in a single colony are female clones of the queen. Inside the colony, the ants cultivate a garden of fungus grown with pieces of dead vegetable matter, dead insects, and insect droppings.

<i>Pseudonocardia</i> Genus of bacteria

Pseudonocardia is a genus of the bacteria family Pseudonocardiaceae. Members of this genus have been found living mutualistically on the cuticle of the leafcutter ants because the bacteria has antibiotic properties that protect the fungus grown by the ants. When they are grooming, their legs are passed over their mouth gland that produces the antibiotic and then their legs touch the fungi while they are walking around. The ants have metapleural glands that produce the antimicrobial components to eliminate the Escovopsis fungi. The bacteria may also be found in crypts on the propleural plate. Pseudonocardia is found to have antibiotic properties provided to the leaf-cutter ant to inhibit the growth of Escovopsis, which is a black yeast that parasitizes the leaf-cutter ant. Pseudonocardia can be found in both aquatic and terrestrial ecosystems. Pseudonocardia belongs to the phylum Actinobacteria. Most Actinobacteria grow in soils that are of a neutral pH. Actinobacteria are also important in plant-associated microbial communities are referred to as "free-living." This means that they are not dependent on another organism to live. For example: A non-free-living organism would be a parasite that depends on a host as a food source and a place for shelter. "Free-living" also allows these organisms to require less energy and food for survival. Bacteria from the Pseudonocardia genus are catalase-positive, non-motile, aerobic, non-acid-fast and produce a gram positive reaction. Under the microscope they exhibit branching, rod-shaped organisms.
There are many different strains of Pseudonocardia and a good portion of these strains have been found in China, in soils of the forest, and in Eucalyptus trees of Australia.

<i>Atta colombica</i> Species of ant

Atta colombica is one of 47 species of leafcutter ants. This species is part of the Attini tribe.

<i>Atta mexicana</i> Species of ant

Atta mexicana is a species of leaf-cutter ant, a New World ant of the subfamily Myrmicinae of the genus Atta. This species is from one of the two genera of advanced attines within the tribe Attini.

Acromyrmex insinuator is a social parasite of the closely related Acromyrmex echinatior. This specific parasite is of particular interest as it is an opportunity to study the development of social parasitism in the Attini tribe, and provides further evidence for Emery's rule, which theorizes social parasites among insects tend to be parasites of species or genera to which they are closely related to.

<i>Acromyrmex lobicornis</i> Species of ant

Acromyrmex lobicornis is a species of leaf-cutter ant, a New World ant of the subfamily Myrmicinae of the genus Acromyrmex. This species is from one of the two genera of advanced attines within the tribe Attini.

<i>Acromyrmex striatus</i> Species of ant

Acromyrmex striatus is a species of the leaf-cutter ants found in the Neotropics.

<i>Acromyrmex versicolor</i> Species of ant

Acromyrmex versicolor is known as the desert leafcutter ant. A. versicolor is found during the summer months in the Colorado and Sonoran deserts when there is precipitation. They form large, distinctive nest craters that are covered with leaf fragments. Living and dead leaves are collected by workers and used to cultivate fungus gardens. Each colony can have multiple queens, if they do this is a practice called polygyny, and each queen has her own batch of “starter” fungus. This species does not sting.

<i>Cyphomyrmex</i> Genus of ants

Cyphomyrmex is a genus of fungus-growing ants found primarily in South and Central America. However, some species do come up to the southern portion of North America. They grow a variety of fungi in the tribe Leucocoprineae. Most fungal gardens are grown in small nodules, some species to cultivate entire mycelium, though. Colonies are monogynous and are relatively small with about 100 workers on average.

<i>Escovopsis</i> Genus of fungi

Escovopsis is a genus of seven formally acknowledged parasitic microfungus species that rely on other fungi to be their hosts. This genus formally circumscribed with a single identified species in 1990; in 2013 three other species were added.

<span class="mw-page-title-main">Social immunity</span> Antiparasite defence mounted for the benefit of individuals other than the actor

Social immunity is any antiparasite defence mounted for the benefit of individuals other than the actor. For parasites, the frequent contact, high population density and low genetic variability makes social groups of organisms a promising target for infection: this has driven the evolution of collective and cooperative anti-parasite mechanisms that both prevent the establishment of and reduce the damage of diseases among group members. Social immune mechanisms range from the prophylactic, such as burying beetles smearing their carcasses with antimicrobials or termites fumigating their nests with naphthalene, to the active defenses seen in the imprisoning of parasitic beetles by honeybees or by the miniature 'hitchhiking' leafcutter ants which travel on larger worker's leaves to fight off parasitoid flies. Whilst many specific social immune mechanisms had been studied in relative isolation, it was not until Sylvia Cremer et al.'s 2007 paper "Social Immunity" that the topic was seriously considered. Empirical and theoretical work in social immunity continues to reveal not only new mechanisms of protection but also implications for understanding of the evolution of group living and polyandry.

Escovopsis aspergilloides is a species of fungus that was rediscovered in 1995 by mycologists Keith A. Seifert, Robert A. Samson and Ignacio Chapela. Escovopsis aspergilloides co-exist in a symbiotic relationship with attini ants - fungus-growing ants. The highly evolved, ancient ant-fungus mutualism has become a model system in the study of symbiosis. In spite of this, the genus Escovopsis was not proposed until 1990 and the first two species were not formally described until the 1990s: E. weberi by Muchovej and Della Lucia in 1990 E. aspergilloides by Seifert, Samson and Chapela in 1995.

<i>Leucoagaricus gongylophorus</i> Species of fungus

Leucoagaricus gongylophorus is a fungus in the family Agaricaceae which is cultivated by certain leafcutter ants. Like other species of fungi cultivated by ants, L. gongylophorus produces gongylidia, nutrient-rich hyphal swellings upon which the ants feed. Production of mushrooms occurs only once ants abandon the nest. L. gongylophorus is farmed by leaf cutter ant species belonging to the genera Atta and Acromyrmex, amongst others.

References

  1. ↑ Speight, Martin R.; Watt, Allan D.; Hunter, Mark D. (1999). Ecology of Insects. Blackwell Science. p. 156. ISBN   978-0-86542-745-7..
  2. 1 2 Piper 2007 , pp. 11–13.
  3. ↑ "Leafcutter Ant" (PDF). Archived from the original (PDF) on February 23, 2018.
  4. ↑ Schultz, T. R.; Brady, S. G. (2008). "Major evolutionary transitions in ant agriculture". Proceedings of the National Academy of Sciences of the United States of America. 105 (14): 5435–5440. Bibcode:2008PNAS..105.5435S. doi: 10.1073/pnas.0711024105 . PMC   2291119 . PMID   18362345.
  5. ↑ Hedlund, Kye S. (March 2005). "Diagnoses of the North American: Ant Genera (Hymenoptera: Formicidae)". Archived from the original on August 24, 2007.
  6. ↑ Li, Hongjie & Sun, Chang-yu (2020), "Biomineral armor in leaf-cutter ants", Nature Communications, 11 (11): 5792, doi: 10.1038/s41467-020-19566-3 , PMC   7686325 , PMID   33235196 .
  7. 1 2 Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press, p.  298, ISBN   978-0-313-33922-6 .
  8. ↑ Weber, Neal A. (1972), Gardening Ants, The Attines , The American Philosophical Society, pp.  14, 34, ISBN   978-0-87169-092-0 .
  9. 1 2 3 Lofgren, Clifford; Meer, Robert K. Vander, eds. (2018). Fire Ants and Leaf-cutting Ants : Biology and Management. New York, NY: Routledge. pp. xv+435. ISBN   978-0-429-03826-6. OCLC   1090012991.
  10. ↑ Crop Domestication Is a Balancing Act
  11. ↑ For Leaf-Cutter Ants, Farm Life Isn't So Simple
  12. ↑ "Leucoagaricus - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2022-07-08.
  13. ↑ Benjamin, RICHARD K.; Blackwell, MEREDITH; Chapela, IGNACIO H.; Humber, RICHARD A.; Jones, KEVIN G.; Klepzig, KIER D.; Lichtwardt, ROBERT W.; Malloch, DAVID; Noda, HIROAKI (2004-01-01), Mueller, GREGORY M.; Bills, GERALD F.; Foster, MERCEDES S. (eds.), "Insect- and Other Arthropod-Associated Fungi", Biodiversity of Fungi, Burlington: Academic Press, pp. 395–433, doi:10.1016/b978-012509551-8/50021-0, ISBN   978-0-12-509551-8 , retrieved 2022-07-08
  14. ↑ Hart, A. G. & Ratnieks, F. L. W. (2002), "Waste management in the leaf-cutting ant Atta colombica", Behavioral Ecology, 13 (2): 224–231, doi: 10.1093/beheco/13.2.224 .
  15. ↑ Bot, A. N. M.; Currie, C. R.; Hart, A. G. & Boomsma, J. J. (2001), "Waste Management in Leaf-cutting Ants", Ethology Ecology and Evolution, 13 (3): 225–237, doi:10.1080/08927014.2001.9522772, S2CID   18918574 .
  16. ↑ Zhang, M. M.; Poulsen, M. & Currie, C. R. (2007), "Symbiont recognition of mutualistic bacteria by Acromyrmex leaf-cutting ants", The ISME Journal, 1 (4): 313–320, doi: 10.1038/ismej.2007.41 , PMID   18043642 .
  17. ↑ "Leafcutter Ants", Lincoln Park Zoo, archived from the original on 2008-05-16
  18. ↑ Currie, C. R.; Mueller, U. G. & Malloch, D. (1999), "The agricultural pathology of ant fungus gardens", PNAS , 96 (14): 7998–8002, Bibcode:1999PNAS...96.7998C, doi: 10.1073/pnas.96.14.7998 , PMC   22176 , PMID   10393936 .
  19. ↑ Reynolds, H. T. & Currie, C. R. (2004), "Pathogenicity of Escovopsis weberi: The parasite of the attine ant-microbe symbiosis directly consumes the ant-cultivated fungus", Mycologia, 96 (5): 955–959, doi:10.2307/3762079, JSTOR   3762079, PMID   21148916 .
  20. ↑ Goes, A. C.; Barcoto, M. O.; Kooij, P. W.; Bueno, O. C.; & Rodrigues, A. (2020), "How do leaf-cutting ants recognize antagonistic microbes in their fungal crops?", Frontiers in Ecology and Evolution , 8 (95): 1–12, doi: 10.3389/fevo.2020.00095 .
  21. ↑ Currie, C. R.; & Stuart, A. E. (2001), "Weeding and grooming of pathogens in agriculture by ants", Proceedings of the Royal Society of London B , 268 (1471): 1033–1039, doi:10.1098/rspb.2001.1605, PMC   1088705 , PMID   11375087 .
  22. ↑ Hager, Felix A.; Kirchner, Lea; Kirchner, Wolfgang H. (2017-12-15). "Directional vibration sensing in the leafcutter ant Atta sexdens". Biology Open. 6 (12): 1949–1952. doi:10.1242/bio.029587. ISSN   2046-6390. PMC   5769659 . PMID   29247049.
  23. ↑ Farji-Brener, Alejandro G. (2001). "Why are leaf-cutting ants more common in early secondary forests than in old-growth tropical forests? An evaluation of the palatable forage hypothesis". Oikos . Nordic Society Oikos (Wiley). 92 (1): 169–177. doi:10.1034/j.1600-0706.2001.920120.x. hdl:10088/1425. ISSN   0030-1299.
  24. ↑ Ballari, S. A. & Farji-Brener, A. G. (2006), "Refuse dumps of the leaf-cutting ants as a deterrent for ant herbivory: does refuse age matter?", The Netherlands Entomological Society, 121 (3): 215–219, doi:10.1111/j.1570-8703.2006.00475.x, S2CID   85410418 .
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