Overview

Comprehensive Description

Acromyrmex HNS (s. str.) coronatus Fabr HNS . ssp. andicola Em. var. globoculis For. HNS

Worker: Length 2-6 mm. - Anterior part of ridge of vertex low and faint, posterior half produced as high and acute ridge. Occipital spines long, acute, deflected apically, other tubercles of head large, distinct, acute. Inferior pronotal spines well developed, acute, directed anteriorly and slightly outward. Lateral pronotal spines exceeding mesonotal spines in length, acute, directed forward. Medial pronotal spines exceeding mesonotal spines in length, acute, directed forward. Medial pronotal spines very distinct, acute, rising abruptly. Anterior mesonotal spines large, stout, acutely conic. Posterior mesonotal spines much smaller, somewhat variable in size, slender, directed backward at a slight angle. Epinotal spines of length comparable with lateral pronotal spines but more slender and gently curving backward in most specimens. Some workers with spines straight and directed upward. Pedicel and gaster strongly tuberculate. Surface of body dull. Pubescence sparse and appressed. Sparse, recurved hairs on spines and appendages. - Dark ferrugineous; medial darker streak on gaster.

Two winged female taken by myself June 20, 1936, near the Oko River, tributary of the Cuyuni River, British Guiana, doubtless belong to this variety. They were captured singly about 9 a. m. as they flew through the bush. Since they do not belong to A. histrix HNS or A. octospinosa HNS , the two (other known species of this region, and since intensive collecting revealed none but these three forms, jthey are here described:

Female (undescribed): Length 7 mm. - Ridges of vertex distinct and complete. Occipital spines short, stout, acute. Inferior pronotal spines flattened, acute, straight, directed forward and outward. Superior pronotal spines long, acute, directed forward and outward. Epinotal spines stout, rising upward, then sharply deflected backward and outward. Gaster irregularly tuberculate. - Entire body densely vermiculate-rugulose. Hairs short, curved irregularly. Fine sparse pubescence. Colored strikingly in dark brown and yellowish brown patches. Mesonotum yellowish brown with an antero-median blotch and lateral elongate ellipsoid blotches of dark brown. Dorsum of first gastric segment with a sharply defined hastate patch of dark brown on yellowish brown background.

In Santschi's 1935 Revision of Acromyrmex HNS this variety (British Guiana - type locality) is described, from 4 workers, as having clearly recurved inferior pronotal spines, barely distinct medial pronotal spines, and a grayish pruinose surface. Four colonies taken by myself in 1935 near the Forest Settlement, Mazaruni River, and in 1936 near the Takutu River, British Guiana demonstrate the variability of these characters. Rather than introduce a separate name I have redescribed the worker of this variety on the basis of a large series.

  • Neal A. Weber, University of North Dakota (1936): The biology of the fungus-growing ants. Part. I. New forms. 1. Revista de Entomologia 7, 378-409: 407-408, URL:http://antbase.org/ants/publications/3011/3011.pdf
Public Domain

Plazi

Source: Plazi.org

Trusted

Article rating from 0 people

Average rating: 2.5 of 5

Genus Acromyrmex Mayr HNS

These leaf-cutting ants are represented in California by a single species, Acromyrmex versicolor(Pergande) HNS , confined to the southern deserts. The harvested leaves are used to culture a basidiomycete fungus, which is the principal food of the ants. References: Gamboa (1975, 1976), Johnson and Rissing (1993), Julian and Fewell (2004), Mueller et al. (2001), Reichardt and Wheeler (1996), Rissing et al. (1986, 1989), Snelling and George (1979), Weber (1972).

  • Ward, P. S. (2005): A synoptic review of the ants of California (Hymenoptera: Formicidae). Zootaxa 936, 1-68: 31-31, URL:http://antbase.org/ants/publications/21008/21008.pdf
Public Domain

Ward, P. S.

Source: Plazi.org

Trusted

Article rating from 0 people

Average rating: 2.5 of 5

[[ Acromyrmex HNS ]] sp. alw-04.

Canindeyú (ALWC).

  • Wild, A. L. (2007): A catalogue of the ants of Paraguay (Hymenoptera: Formicidae). Zootaxa 1622, 1-55: 30-30, URL:http://www.antbase.org/ants/publications/21367/21367.pdf
Public Domain

Wild, A. L.

Source: Plazi.org

Trusted

Article rating from 0 people

Average rating: 2.5 of 5

[[ Acromyrmex HNS ]] sp. alw-03.

Ñeembucú , Pte. Hayes (ALWC).

  • Wild, A. L. (2007): A catalogue of the ants of Paraguay (Hymenoptera: Formicidae). Zootaxa 1622, 1-55: 30-30, URL:http://www.antbase.org/ants/publications/21367/21367.pdf
Public Domain

Wild, A. L.

Source: Plazi.org

Trusted

Article rating from 0 people

Average rating: 2.5 of 5

[[ Acromyrmex HNS ]] sp. alw-01.

Ñeembucú , Pte. Hayes (ALWC).

  • Wild, A. L. (2007): A catalogue of the ants of Paraguay (Hymenoptera: Formicidae). Zootaxa 1622, 1-55: 30-30, URL:http://www.antbase.org/ants/publications/21367/21367.pdf
Public Domain

Wild, A. L.

Source: Plazi.org

Trusted

Article rating from 0 people

Average rating: 2.5 of 5

[[ Acromyrmex HNS ]] sp. alw-02.

Pte. Hayes (ALWC).

  • Wild, A. L. (2007): A catalogue of the ants of Paraguay (Hymenoptera: Formicidae). Zootaxa 1622, 1-55: 30-30, URL:http://www.antbase.org/ants/publications/21367/21367.pdf
Public Domain

Wild, A. L.

Source: Plazi.org

Trusted

Article rating from 0 people

Average rating: 2.5 of 5

Evolution and Systematics

Functional Adaptations

Functional adaptation

Bacterial symbionts provide nitrogen: leafcutter ants
 

Leafcutter ants likely obtain a large part of their nitrogen from symbiotic bacteria living in their cultivated fungal gardens.

   
  "Bacteria-mediated acquisition of atmospheric N2  serves as a critical source of nitrogen  in terrestrial ecosystems. Here we reveal that symbiotic  nitrogen fixation facilitates the  cultivation of specialized fungal crops by leaf-cutter  ants. By using acetylene reduction  and stable isotope experiments, we demonstrated that N2  fixation occurred in the fungus  gardens of eight leaf-cutter  ant species and, further, that this fixed nitrogen  was incorporated into ant biomass.  Symbiotic N2-fixing bacteria were  consistently isolated from the fungus  gardens of 80 leaf-cutter ant  colonies collected in Argentina,  Costa Rica, and Panama. The discovery of  N2 fixation within the  leaf-cutter ant–microbe symbiosis reveals a  previously unrecognized nitrogen source in  neotropical ecosystems." (Pinto-Tomás et al. 2009:1120)

  Learn more about this functional adaptation.
  • Pinto-Tomás AA; Anderson MA; Suen G; Stevenson DM; Chu FST; Cleland WW; Weimer PJ; Currie CR. 2009. Symbiotic nitrogen fixation in the fungus gardens of leaf-cutter ants. Science. 326(5956): 1120 - 1123.
  • Elio. 2010. Leaf-cutters get their fix (nitrogen fix, that is). American Society for Microbiology.
    http://schaechter.asmblog.org/schaechter/2010/01/lea.html.
  • Torrice M. 2009. Ants eat well, thanks to bacteria. Science Now [Internet],
Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© The Biomimicry Institute

Source: AskNature

Trusted

Article rating from 0 people

Average rating: 2.5 of 5

Functional adaptation

Bacteria fight fungus: leafcutter ants
 

Fungal gardens of leafcutter ants are free of undesired, parasitic fungus due to presence of symbiotic Streptomyces bacteria.

     
  "Cameron Currie of the Univ. of Wisconsin is studying how leafcutter ants maintain their gardens pest-free despite the presence of parasitic fungus. When worker ants were removed, the fungus overran the gardens. Currie found that a white bloom on the exoskeleton of the ants is actually a mass of Streptomyces, the same kind of bacteria that produces half of the antibiotics used in medicine. The bacteria specifically target the parasitic fungus. By studying the complex coevolution of ants, fungus, parasitic fungus, and bacteria, Currie hopes to learn about the evolution of antibiotic resistance and how mutualism and symbiosis shape species diversity." (Courtesy of the Biomimicry Guild)
  Learn more about this functional adaptation.
Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© The Biomimicry Institute

Source: AskNature

Trusted

Article rating from 0 people

Average rating: 2.5 of 5

Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
                                        
Specimen Records:54Public Records:1
Specimens with Sequences:19Public Species:1
Specimens with Barcodes:17Public BINs:0
Species:10         
Species With Barcodes:3         
          
Creative Commons Attribution 3.0 (CC BY 3.0)

© Barcode of Life Data Systems

Source: Barcode of Life Data Systems (BOLD)

Trusted

Article rating from 0 people

Average rating: 2.5 of 5

Barcode data

Creative Commons Attribution 3.0 (CC BY 3.0)

© Barcode of Life Data Systems

Source: Barcode of Life Data Systems (BOLD)

Trusted

Article rating from 0 people

Average rating: 2.5 of 5

Locations of barcode samples

Collection Sites: world map showing specimen collection locations for Acromyrmex

Creative Commons Attribution 3.0 (CC BY 3.0)

© Barcode of Life Data Systems

Source: Barcode of Life Data Systems (BOLD)

Trusted

Article rating from 0 people

Average rating: 2.5 of 5

Wikipedia

Acromyrmex

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 31 known species. Commonly known as "leafcutter ants" they comprise one of the two genera of advanced attines within the tribe Attini, along with Atta.

Anatomy[edit]

Profile view of an A. balzani worker

Acromyrmex species' hard outer covering, the exoskeleton or cuticle, functions as armour, protection against dangerous solar waves, an attachment base for internal muscles, and to prevent water loss. It is divided into three main parts; the head, thorax, and abdomen. A small segment between the thorax and abdomen, the petiole, is split into two nodes in Acromyrmex species.

Diagram of an ant's anatomy

The antennae are the most important sense organs Acromyrmex species possess, and are jointed so the ant can extend them forward to investigate an object. It can retract them back over its head when in a dangerous situation, for example, a fight. Acromyrmex species have eyes, but their eyesight is very poor. Like all insects, the eye is compound, meaning it is made up of many eyelets called ommatidia, with the number of these eyelets varies according to species. Male ants tend to have more ommatadia than other castes. The ocelli, which are generally found on top of the heads of queens, are thought to aid aerial navigation by sunlight.

Acromyrmex is dark red in color. In addition to the standard ant anatomy, the back of the thorax has a series of spines which help it maneuver material such as leaf fragments on its back.

Acromyrmex can be identified from the closely related Atta genus of leafcutter ants by their having four pairs of spines and a rough exoskeleton on the upper surface of the thorax compared to three pairs of spines and a smooth exoskeleton in Atta.

Much of the inside of the Acromyrmex head is occupied by the muscles that close the jaws; the muscles that open the jaws are much smaller. The brain, though tiny, is a very complex organ, and allows Acromyrmex to learn and react to its surroundings. It can remember colony odour, navigation, and where it has placed a certain object.

The heart is a long, tubular organ running the entire length of the body, from the brain to the tip of the abdomen. It has valves within it that prevent blood from flowing the wrong way. The fluids bathing the internal organs is circulated by the heart; these fluids then filter through the organs and tissues. The pharynx, which is part of the gut, controlled by six muscles, pumps food into the oesophagus. Debris in the food, such as soil, is filtered before it enters the oesophagus and is collected in a tiny trap, the infrabuccal pocket. When this pocket becomes full, the Acromyrmex ant empties it into an area within or outside the nest designated as a waste-products area.

Several glands in the head secrete various substances, such as those responsible for the digestion of food. Another gland within the head produces digestive and, in some species, alarm chemicals; these chemicals are used to alert nearby ants of impending danger, and any ant that detects this alarm will automatically go into "battle mode". If an ant is crushed, a huge blast of this chemical is released, causing the entire colony to go into "battle mode".

The thorax contains muscles to operate the legs and wings and the nerve cells to co-ordinate their movements; also contained in this part of the body is the heart and oesophagus.

The abdomen contains the stomachs, poison glands, ovaries in the queen, and the Dufour's gland, among other things. Acromyrmex ants have two "stomachs", including a dry, social stomach in which they can store food and later regurgitate to larvae, the queen and other ants. This is separated from the stomach proper by a small valve; once food enters the second stomach, it becomes contaminated with gastric juices and cannot be regurgitated. The exact function of the Dufour's gland is unknown, but is thought to be involved in the release of the chemicals used in the production of odour trails, which the ants use to recruit nest mates to a food source. It may also produce sex-attractant chemicals.

Ecology[edit]

A. balzani worker carrying a leaf

Reproduction[edit]

Winged females and males leave their respective nests en masse and engage in a nuptial flight known as the revoada. Each female mates with multiple males to collect the 300 million sperm she needs to set up a colony.[1]

Once on the ground, the female loses her wings and searches for a suitable underground lair in which to found 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. Before leaving their parent colonies, winged females take a small section of fungus into their infrabucchal pouches to 'seed' the fungus gardens of incipient colonies, cutting and collecting the first few sections of leaf themselves.

Colony hierarchy[edit]

A mature leafcutter colony can contain more than 8 million ants (the maximum size of the colony varies between species), mostly sterile female workers. They are divided into castes, based mostly on size, that perform different functions. Acromyrmex ants exhibit a high degree of biological polymorphism, four castes being present in established colonies - minims (or "garden ants"), minors, mediae, and majors. Majors are also known as soldiers or dinergates. Each caste has a specific function within the colony. Acromyrmex ants are less polymorphic than the other genus of leafcutter ants Atta, meaning comparatively less difference in size exists from the smallest to largest types of Acromymex. The high degree of polymorphism in this genus is also suggestive of its high degree of advancement.

Ant-fungus mutualism[edit]

Like Atta, Acromyrmex societies are based on an ant-fungus mutualism, and different species use different species of fungus, but all of the fungi the ants use are members of the genus Leucocoprinus. The ants actively cultivate their fungus on a medium of masticated leaf tissue. This is the sole food of the queen and other colony members that remain in the nest. The mediae also gain subsistence from plant sap they ingest whilst physically cutting out sections of leaf from a variety of plants.

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. Leafcutter ants are sensitive enough to adapt to the fungus' reaction to different plant material, apparently detecting chemical signals from it. 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 that have evolved 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 the leaf sap. The fungus needs the ants to stay alive, and the larvae need the fungus to stay alive.[2]

In addition to feeding the fungal garden with foraged food, mainly consisting of leaves, it is protected from Escovopsis by the antibiotic secretions of Actinobacteria (genus Pseudonocardia). This mutualistic microorganism lives in the metapleural glands of the ants.[3] Actinobacteria are responsible for producing the majority of the world's antibiotics today.

Waste management[edit]

Leafcutter ants have very specific roles for taking care of the fungal garden and dumping the refuse. Waste management is a key role for each colony's longevity. The necrotrophic parasite Escovopsis of the fungal cultivar threatens the ants' food source, and is a constant danger to the ants. The waste transporters and waste-heap workers are the older, more dispensable ants, ensuring the healthier and younger leafcutter ants can work on the fungal garden. Waste transporters take the waste, which consists of used substrate and discarded fungus, to the waste heap. Once dropped off at the refuse dump, heap workers organise the waste and constantly shuffle it around to aid decomposition.

Foraging behaviour[edit]

Leafcutter ants in Costa Rica

Acromyrmex has evolved to change food plants constantly, preventing a colony from completely stripping off leaves and thereby killing trees, thus avoiding negative biological feedback on account of their sheer numbers. However, this does not diminish the huge quantities of foliage they harvest. Once foraging workers locate a resource in their environment, they lay down a pheromone trail as they return to the colony. Other workers then follow the pheromone trail to the resource. As more workers return to the nest, laying down pheremones, the stronger the trail becomes. The strength to which workers adhere to the trail (trail fidelity) depends mostly on environmental factors, such as the quality of the resource.

Interactions with humans[edit]

In some parts of their range, Acromyrmex species can be quite a nuisance to humans, defoliating crops and damaging roads and farmland with their nest-making activities.[1] For example, Acromyrmex octospinosus ants harvest huge quantities of foliage, so they have become agricultural pests on the various Caribbean islands where they have been introduced, such as Guadeloupe.

In Central America, leafcutter ants are referred to as "wee wee" ants, though not based on their size. They are one of the largest ants in Central America.[citation needed]

Deterring the leafcutter ant Acromyrmex lobicornis from defoliating crops has been found to be simpler than first expected. 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.[4]

Species[edit]

The genus Acromyrmex contains these species:[5][6]

See also[edit]

References[edit]

  1. ^ a b Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press, p. 298, ISBN 0-313-33922-8 .
  2. ^ http://www.blueboard.com/leafcutters/what.htm
  3. ^ 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 .
  4. ^ 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 .
  5. ^ "Acromyrmex". Integrated Taxonomic Information System. 
  6. ^ Wild, Alexander L. (2007). "A catalogue of the ants of Paraguay (Hymenoptera: Formicidae)". Zootaxa (Magnolia Press, http://mapress.com/) (1622): 41, 51. Retrieved January 22, 2011. 
Creative Commons Attribution Share Alike 3.0 (CC BY-SA 3.0)

Source: Wikipedia

Unreviewed

Article rating from 0 people

Average rating: 2.5 of 5

Disclaimer

EOL content is automatically assembled from many different content providers. As a result, from time to time you may find pages on EOL that are confusing.

To request an improvement, please leave a comment on the page. Thank you!