Leaf cutter Ants as model organism

Attine as a Model Organism for Multi Vector Symbiosis

Vectors have both magnitude and direction. In understanding symbiotic relationships, one may look at the basic flow of energy.The basic flow of energy must be understood in symbiotic relationship. In mutualistic symbiosis the net energy is positive for all organisms involved. Do you need something pertaining to a multi-faceted relationship before you jump into the example of the Attines? It just seems like a sentence or two is missing. In the example of the Attines, and predominately speaking of higher Attines such as the genus Atta, there are many mutualistic relations. Though individual benefits may not be directly related to all participants. This is why I use the phrase multi-vector. Attines will be used as the origin, the vectors will be energy transferred between organisms in mutualistic relationships with the Attines. Vectors can be added, this allows one to understand that net energy benefits of single mutualistic relationships may be added to the net benefits of relations with a common participant(s). Benefit to cultivar is benefit to cultivator which is in turn a benefit to symbiont bacteria. By thinking in the line of vectors one may be able to understand both flow and accumulation of benefit. (Just not sure about the first person.It also sounds as if you are setting up a chess game instead of introducing your topic)
In some cases finding the center of multi-organism mutualistic relationships is usuallyarbitrary. In contrastHowever, Attines play a central role in the mutualistic relationships of which they are involved. For the sake of this article? the mutualistic relationships the Attines have with three types of organisms (forest tree, symbiont bacteria and cultivar fungi). The cultivator/cultivar relationship is at the center of these multiple vector symbiotic relations. (Too many ideas that jump from one thought to another)

Agriculture ants, of the phylum Attine, are macro-mechanical symbiont workers. Attines belong to three categories, based on the substrate each collects for their cultivar. The paleao-Attines form a matrix consisting of their feces, carcasses, and abdominal excretions. Those in the Lower-Attines form a matrix of collected living and dead plant materials and abdominal secretions. The Higher-Attines form their matrix of living plant material and abdominal secretions. The higher Attines have more specialized cultivator/cultivar relationships. The mutualistic fungi are the ants’ primary if not sole source of energy.

The middle and upper Attines are commonly known as leaf-cutter ants, due to their collecting behaviors. These ants gain the substrate for their gardens from trees, and in return maintain healthy forest floor on which the trees may thrive. In the 50million years of the cultivator/cultivar evolution, powerful antibiotic-producing bacteria have found a niche in the cuticles of cultivator ants’. The powerful antibiotic is not only directly beneficial to the cultivator ants, but also protects the contamination from contamination and reduces competition. The health of the fungi, Attines, forest trees, and the bacteria are interdependent of the health of each other.
Attines are found solely in the Western Hemisphere and predominately in subtropical regions. The cultivator/cultivar relationship has existed for over 50million years making Attines the first known agriculturists. The ants are considered herbivores, but actually live off of the fungi they grow within their nests. The Attine have a two caste system, small workers (SWs) and large workers (LWs). The SWs are primarily responsible for allogrooming and garden maintenance. LWs are responsible for gathering substrate and waste management. Division in insect community is common, as a response to hormonal secretions. It is interesting to note that Attine castes may have genetic origins and not only be hormonal responses. The efficiency of LWs in food acquisition is their establishment of food routes, and their movement along these routes is closely associated to the model of fluid movement. Attines are highly social insects that exhibit altruistic behaviors and unlike many ant groups the Attine queens search out multiple partners (18). These behaviors have a net benefit to the colony, though it not directly advantageous to the ants and may put individuals in harmful situations.
The study of Attines started over eighty years ago. Though much has changed and much has been discovered, Attines are still a great source for better understanding the world in which we live. They meet the requirements of a good model organism. 1) Attines have been studied extensively and therefore there is a wealth of knowledge to draw from when designing and experiments and analyzing results. 2) They have relatively short life cycles. 3) It is inexpensive to obtain and maintain colonies. 4) Attines are great candidates for models of complex multi organism mutualistic symbiosis.
In mutualistic symbiosis, involved organisms are mutually benefited. The benefit can be in the form of protection and/or energy/nutrient acquisition. The flow of energy through an ecosystem is cyclical and it is necessary for each organism to have a niche for which to fit. It is therefore intuitively reasonable to expect a system of give and take. Though following the lines of energy distribution can be difficult, it provides insight into the necessity of each component of a given system.

Attine History

Attines are communal insects that have cultured fungi for over 50million years. Their nests can survive for 8-10years. They divide labor between the two castes SWs and LWs. The LWs are responsible for foraging, nest maintenance and prevent infections of the cultivars. They are able to keep nearly sterile environments for the fungus cultivars with help of specialized bacteria which live in the cuticle fovea of the ants. SWs are in charge of grooming the fungal gardens, caring for the young, and allogrooming. Though both LWs and SWs are involved in allogrooming, the smaller mandibles of the SWs make them better at removing potential pathogens from the LWs and fellow SWs. The Attine queens are known to be involved in multiple mating. This provides genetic diversity in the colonies. Typically when insects have multiple mating distinct work castes are not demonstrated. Attines appear to be predisposed to one of the two castes, though are able to morph into either. Typically castes are associated with diet and inhibitory hormones.
Attines are divided into three groups (higher, lower, paleo), by the substrates they provide. These divisions are directly correlated to the specificity of cultivator to cultivar, and cultivator to symbiont bacteria. Though the species involved are different there functions and relations are conserved through out, save for Attines wasmannia and bipharidatta, both of which lack symbiont bacteria. All Attines excrete feces on the fungus’s substrate. These excretions have been found to contain protease, an enzyme which breaks large proteins into smaller usable amino acids. It is believed the fungi lack this protease, either being one basis for mutualism or as a loss of function. Coevolution of the fungus and Attines are more apparent in the upper Attines (leaf-cutter ants). It is proposed that paleo and lower Attines can incorporate free living fungus and the transmission of their fungus is horizontal. While higher Attines transmit fungus vertically, from one generation to the next.
Attines build large underground nests with hundreds of chambers. Within are multiple gardens. The nests are visible by distinct mounds founds on the forest floors. The higher Attines build their nests in sloped areas; Attines dispose of their wastes outside their nest. During rain fall this slopes assure that during rainfall their wastes will move away from the nests. The waste, both fecal and from the gardens, is a major source of nutrients for the forests. The breakdown of forest biomass into simpler compounds by the Attines is much more effective than biomass decomposing on the forest floors.
The Attines are equipped with cuticle fovea which house symbiont bacteria. These bacteria are supported by endocrine glands on the interior of the Attines’ cuticles. The bacteria are known for their antibiotics. These antibiotics are herbicides that deter the growth of foreign fungi, both pathogenic and competitive. This benefit bestowed by these bacteria is as important to the Attines as it is to the fungi. Data suggests that fungi, Attine and bacteria have coevolved with varying degrees of specificity.
The surfaces of leaves, seeds and fruits of the Amazon have tough and often poisonous properties that deter the foraging of herbivores. Attines relations with fungi deal with these natural deterrents. The ants can mechanically break the plants materials into fine mulch. This mulch is then further processed and broken down by the fungi. The fungi are then eaten by the Attines, their main source of food. This Attine fungus relationship puts the ants at an advantage when compared to other herbivores, which must be much more selective in the plant materials they forage. Attines are selective in their foraging, which is due more to the nutritious properties than to the roughness or toughness of the plant materials.

Plants into Fragments: Foraging Attines and the Plants they Love

Flowers and trees are the beginning and the end of the Attine energy cycle. The trees are the donators and recipients of Attine energy. The Process of selecting and gathering is accomplished by the LWs of the Attine colonies. They create and network of roads across the forest floors. These roads increase the worker efficiency. At the site of the food source, leaves are cut into fragments and then transported back to the nests. Within the nests are multiple fungal gardens. At the gardens Attines further mulch the leaves and add mandibular secretions creating a moist chaw. To this chaw are added abdominal secretions. The protease present in these secretions makes them utterly important to the process. It is the protease which makes the matrix usable to the fungus. Attines constantly add abdominal secretions to the matrix.
The gardens are constantly groomed and waste material removed. Waste materials consist of feces, unusable garden matrix and carcasses. The old and sick Attines are often in charge of removing wastes; which limits contamination to the rest of the colony. The wastes are transported outside of the nests, often on slopes to insure its movement away from the colony. Analysis of the wastes has found high traces of amines, calcium, nitrogen, carbon, sulfur, and phosphorous. When compared to soil samples taken away form Attine nests, the content of these elements and compounds are lower.
The appearance of forest groves in savannas of Central America were once believed to be remnants of declining forests. Now it is suggested that in fact these forest groves are the signs of growing forests. It is common to find groves growing atop abandoned Attine nests. It was hypothesized the Attines were helping the spread of forests by enriching soil, making the savannas habitable for the forest flora. It is more likely that groves are initiated by the growth of woodland trees. It is much more likely Attine nests will survive in areas inhabited by the woodland trees, and even more success is found in areas where forest trees are present. Woodland trees provide shade, which reduces the chance of grass fires. Once a Woodland grove is establish, colonizing Attines are believed to bring nutrients from the near by Forests, which has a positive effect on tree growth. Attines also bring seeds from the forest, some of which are not broken down and are able to mature. Forest trees are typically toward the centers of the groves while the woodland trees occupy the perimeter. The woodland trees are more resistant to fire damage, so this in effect creates a fire block around the groves, further increase the forest grove survival.
The Attines provide aeration and irrigation for the forest grove and forests. Aeration is an important impact of Attine colonization. The tunneling creates pathways for which gases may be exchanged with the environment, increases surfaces area for which water may be absorbed, and allows seeds to come in contact with soil otherwise inaccessible. The nests also provide irrigation, by directing water deep into the soil rather than precipitation leaving the area as runoff. The increase in soil moister benefits trees by reducing the effects of grassfires on the forests and groves. The increased soil moister means large plant life with deeper roots can be maintained.
It is difficult to distinguish which organisms are more dependent on the other, trees or Attines. It is however obvious the interdependence each has on the other. This mutualistic relationship is the second vector in the Attine multi-vector symbiosis system. Understanding the positive relations can help one understand the importance of the Attines in the a greater ecological perspective. Attines are responsible for millions of dollars of crop destruction every year. Farmers are trying to limit the effect of the world’s hardest workers by way of harmful pesticides. Pesticides are not only harmful to the Attines, but also contaminate the locals’ drinking water. New approaches are being considered, such as using Attine feces as natural repellant. This has proven effective on a small scale but proves to be difficult to maintain. One problem is that the feces is rinsed away after a rain, so must be re-administered frequently. As the forests are transitioned to farmland, the greater ecological affects must be considered. A better understanding of the Attines and their relationship with plant life may lead to better ways of limiting the foraging on farmland at the lowest cost to the surrounding forests.

Attines, the Original Farmers

Development of fungal gardens has provided Attines a great advantage n the subtropical region of the Western Hemisphere. This relationship developed over 50million years ago. It is believed to have started with the fungus that grows of the feces and carcasses of the paleo Attines. As the fungi, Attines and their relations evolved the species became more specialized to one another. It is important to remember the evolution is also accompanied by the symbiont bacteria which thrive along with the cultivator/cultivar as will be discussed later on. Fungi are the food for the Attines while the Attines collect and mechanically degrade the Fungi’s substrate.
The fungus is reliant on the ant for the addition of protease, which is a conserved trait, which is found in the excretions of all Attines. The fungus lacks this enzyme, which puts them at a natural disadvantage to neighboring fungi. Protease is an enzyme which breaks large proteins into their amino acid substrates. From the amino acids the fungus can obtain the amines and nitrogen it needs for basic biological processes.

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