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LEAF-CUTTING ANTS.
Term Paper ID:29212
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Essay Subject:
Scientific description of problem caused to agriculture.... More...
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Paper Abstract:
Scientific description of problem caused to agriculture. Ants' ability to quickly strip entire orchards of leaves. Fungal gardens of ants. Usefulness of leaf-cutting ants. Proposes an experiment to examine fungal parasites for their ability to resist streptomycin. Methodology. Expected results. Purpose of providing a safe, biological form of pest control.
Paper Introduction:
Abstract
Leaf-cutting ants (Formicidae: Attini) are capable of devouring enormous amounts of vegetation - about 20 percent of the fresh-leaf biomass in the Neotropics. This makes agriculture of non-native plants which have not evolved a form of protection against predation by the ants, such as fruit trees from California or Africa, impossible in the areas where these ants prevail. The ants use this vegetation to feed fungal mutualists on which they themselves feed. The fungal mutualists= gardens are infected with a parasitic microfungus Escovopsis (Ascomycota: anamorphic Hypocreales), which is highly virulent and has the potential to rapidly devastate the garden. It is prevented from doing so by a third mutualist, an actinomycete (filamentous bacterium) of the genus Streptomyces, which produces an antibiotic
Text of the Paper:
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This third mutualist was foundassociated with all species of fungus-farming ants studied, is carried onregions of the ants= cuticle that are genus-specific, is transmittedvertically from parent to offspring colonies, and has the capacity topromote the growth of the fungal mutualist, indicating that the associationof Streptomyces with attine ants is highly evolved and ancient in origin. The resistant form should be unsusceptible to streptomycin inculture, and should survive when incubated with streptomycin isolated fromthe actinomyces derived from ant fungal gardens. References Angier, N. (1998). The othersection will be grown with the streptomycin-resistant microfungus added tothe garden. However, the discovery of a highlyvirulent strain of parasite living in the fungus gardens of the attine antsopens up wide possibilities for the biological control of this agriculturalpest in areas where, up until now, agriculture has not been economicallypossible. These fraction will then be cultured individually with the originalEscovopsis microfungus grown in culture to verify their ability to destroythis virulent microfungus. It willexplain why Escovopsis can still be found in these gardens, even though itis suppressed by the streptomycin-reproducing third mutualist, and willprovide a way of destroying these ant fungal gardens, and thus the antsthemselves, so that agriculture, particular the growth of crops not nativeto the region, can be carried out productively in areas where these antslive. A., & Schultz, T. However, they are a menace to humans who try to farmin tropical regions of the New World (Angier, 1994). A more recent study by Currie, Summerbelland Malloch (1999) showed that ants are capable of suppressing Escovopsisand preventing it from destroying their gardens by a third mutualist withinthe symbiosis - a filamentous bacterium (actinomycete) of the genusStreptomyces, that produces antibiotics specifically targeted to suppressthe growth of these garden parasites. Subsequently, garden subdivisions will be grown usingdifferent concentration of the streptomycin-resistant inoculum to look atthe dose of inoculum needed to overcome the ability of the fungal cultivarto survive and thus maintain the ant colony. These sub-gardens will then each be subdivided,with one section being allowed to grow under normal conditions. Once land is cleared for planting, the soil could be treatedwith an inoculum of the resistant microfungus, thus ensuring that anyattine ants foraging in the area would carry it back to their nests, whereit would spread rapidly and destroy the nest. Since these ants are responsible for massive destruction of vegetationin the tropics, and making agricultural development difficult, developingways to wipe out their colonies could be of economic and environmentalimportance. This may takemany years, and so may still make the streptomycin-resistant strains ofmicrofungi useful for agricultural processes, at least in the short-term,and will suggests a method by which future strains can be developed as newantibiotics are developed by the ants. As many attine generaand species as possible will be represented in these studies so that abroad application of the results will be possible. The various fractions which show antibiotic activityagainst a known range of streptomycin-sensitive pathogens will be purified. Since Escovopsis is highly virulent, and hasthe potential for rapidly devastating ant fungal gardens, its use ineradicating these ants from areas where people wish to farm isimmeasurable. the flesh-eating bacteria.Doctors over the years have become blasé in prescribing antibiotics whenthey really were not essential, and now we have been left with the mostresistant forms of bacteria, many of which are not susceptible to thecurrently known antibiotics. When sub-lethal doses of streptomycin-resistant microfungi aredetermined, these will be used to inoculate gardens from each ant species,and these gardens will be followed for a longterm project to determine ifthe ants in these gardens can eventually develop an antibiotic which cankill these streptomycin-resistant microfungi. Of course, before this could be done, it would be necessary to makesure that the microfungus did no harm to the crops to be planted, and didnot render them unfit for human consumption if they were food crops.Testing would also be necessary to make sure the microfungus was notharmful to humans, either from eating the crops produced or working withthem, particularly since the strains used would be antibiotic-resistant.This would take extensive research. It is prevented from doing so by a third mutualist,an actinomycete (filamentous bacterium) of the genus Streptomyces, whichproduces an antibiotic which keeps the Escovopsis under control. Currie, C. Experiments have shown that these fungalgardens are in fact host to specialized parasites that are only known fromattine gardens and that are found in most attine nests (Currie, Mueller andMalloch, 1999). Itshould be possible to determine the amount of streptomycin-resistantEscovopsis necessary to bring about destruction of a fungal garden, sincethe fact that Escovopsis can be extracted from these gardens means that notall the microfungus is killed off by the streptomycin produced by theactinomyces. The ants will carry theresistant form back to the nest along with the food for the fungus and itwill take over the garden, destroying it. The fungal mutualists= gardens are infectedwith a parasitic microfungus Escovopsis (Ascomycota: anamorphicHypocreales), which is highly virulent and has the potential to rapidlydevastate the garden. The ants literally feed the leaves to the fungi, which, in theirturn, metabolize the cellulose and chitin, materials that the ants cannotdigest. R., Mueller, U. Itseffects will only be local in nature, and will have no impact onsurrounding flora or ant fungal gardens adjacent to areas underagricultural development. Although some lower attines propagatecultivars that were recently domesticated from free-living Lepiotaceae, thehigher attines are thought to propagate ancient clones which may have beenin existence for the past 25 million years (Angier, 1994). There should be adose/response curve for the action of the streptomycin derived from gardenactinomyces against streptomycin-vulnerable organisms. 7998-8 2. Science, 281, pp. The higher attines can then gorge themselves on the nutritiousswellings of the fungus, the protein- and sugar-rich knobs calledgongylidia, that bud off from the ends of the fungus, while lower attinesgenerally feed on unmodified fungal hyphae (Ariniello, 1999). G., Rehner, S. This willbe an important result because it will limit the usefulness of thestreptomycin-resistant strains to a time frame to be determined by theamount of time it takes the ant to develop a new antibiotic. Abstract Leaf-cutting ants (Formicidae: Attini) are capable of devouringenormous amounts of vegetation - about 2 percent of the fresh-leaf biomassin the Neotropics. Streptomycin-resistantspecies will be further cultured and tested for virulence against normalcultivars from the mutualistic fungi in the gardens being studied. (1999). Fungus-growing ants use antibody-producing bacteria to control garden parasites.Nature, 398, pp. Theexperiments described below will be carried out in an attempt to find astreptomycin-resistant form of Escovopsis which can be used to help destroyant fungus gardens so that agricultural projects can succeed in regionswhere they are prohibited by the destructive effects of the leaf-cuttingants. They will then be cultured with thestreptomycin-resistant microfungi isolated previously, to determine ifthese are truly resistant to the streptomycin which is produced in thefungal gardens. Thisadds to the feasibility of this study. (1994, December). This will allow a comparison of the results ofthe current studies with those of these researchers, and to ensure that wewill be looking at the same populations of ants, and the same fungal andmicrofungal species as have previously been studied. A streptomycin-resistant form of the microfungus could be used as asoil pretreatment, blockade, or plant spray to protect against attack bythese ants. The ants livesymbiotically with the fungi because the particular fungi they cultivatecan break down fresh leaves into nutrients which the ants can use (Angier,1994). This makes agriculture of non-native plants which havenot evolved a form of protection against predation by the ants, such asfruit trees from California or Africa, impossible in the areas where theseants prevail. Protecting paradise. Expected Results It may or may not be possible to find a streptomycin-resistant form ofmicrofungi Escovoposis among those growing in the ant fungal gardens. Since the Escovopsis survives in ant fungus gardens despite the antsproduction of streptomycin, they are obviously not completely susceptibleto it, otherwise non would survive and be found in these gardens. Traditionally, the fungal gardens of the ants were thought to be freeof microbial parasites, with the fungal mutualist maintained in nearly puremonocultures, despite continued exposure to the competitively advantagedmicrobes present in the vegetative material added to the garden (Currie,Mueller and Malloch, 1999). Samples of nonmutualistic fungi will be obtained from garden samplesand grown out on nutrient agar. 2 34-2 38. The chambers are filled with the spongy gray hyphae of the fungusthat feeds the entire colony. Introduction Fungus farming by attine ants predates human agriculture by about 5 million years (Mueller, Rehner and Schultz, 1998). Samples of each representative fungus garden will be grown from theoriginal samples collected and allowed to grow to a suitable size forsubdivision and testing. In another garden subset, leaves, the normal food of the fungalgardens, will be sprayed with a suspension of the streptomycin-resistantmicrofungi and added to the foraging area for the ants to take back totheir gardens as food for their cultivars. All attine ants in thearea would be rapidly destroyed and agriculture could proceed without fearof horrendous losses from these leaf-cutting ants. To this end, we propose to examine various fungal parasitesfor their ability to resist streptomycin and parasitize the fungal gardensof attine ants and destroy them. It will also allow this to be done in an environmentally-friendlyway - one that threatens no other life form but the ants and their fungalsymbiont in the direct vicinity of the proposed agricultural project. A mobile laboratorywill be set up in the field so that experiments can be carried out close tothe collection sites. Highlyvirulent forms of actinomycetes so identified which are resistant to theactions of Streptomycin will then be selectively grown in large quantities. The attinescomprise about 2 described species in 12 genera, all of which aredependent on fungiculture for food (Currie, Mueller and Malloch, 1999).Extant species cultivate multiple, phylogenetically distant lineages offungi, mostly belonging to the family Lepiotaceae. Vast quantities of leaves are needed to feedsuch large ant colonies, and this leads to massive destruction ofvegetation. PNAS USA, 96, pp. Theagricultural pathology of ant fungus gardens. The filamentous Streptomyces present in thriving garden cultures willbe isolated and cultured, and the antibiotics it produces will be isolatedand characterized. A farming ant and its fungus areancient cohabitants. Theevolution of agriculture in ants. G., & Malloch, D. The ants will be allowed tostabilize in their new environment for 3-5 days before experiments arecommenced. Methods Colonies of attine ants will be collected from the canal region ofcentral Panama, including Ancon Hill, Naos Island, Gamboa, Sobernania Park,Pipeline Road, and Fort Sherman Military Reservation, because previousstudies by Currie, Mueller and Malloch (1999) used ant fungal gardenscollected in these areas. 76 -763. These specialized garden parasites belong to themicrofungus genus Escovopsis (Ascomycota: anamorphic Hypocreales), a highlyvirulent microfungus capable of rapidly devastating ant fungal gardens andthus leading to mortality of the ant colonies, and are horizontallytransmitted between colonies. The gardens will then besampled every three to four days for the presence of streptomycin-resistantmicrofungi, and the gardens will be monitored for their health and theirability to continue to feed their ant populations. Ants are the main reason it is difficult todevelop agriculture in the Neotropics. R. It will provide a biological form of pestcontrol of the safest kind, with no peripheral casualties. Most of the plants native to theNeotropics have evolved sufficient defenses that they are not entirely tornapart by the attine ants, but when farmers try to bring in crops foreign tothe area - such as fruit trees from California or Africa - the results aredisastrous. R., Summerbell, J. Currie, C. These fungi used toexist in the caps of mushrooms, but in becoming symbiont with ants, thefungus has ceased making fruiting bodies to reproduce itself and insteadhas come to rely on the ants to spread their seed around (Angier, 1994).Queens propagate the fungus clonally by carrying a ball of fungus in theirmouth when setting out to build a new nest, and the cultivars propagatevegetatively within nests. Garden pairs will be observed and samples taken weekly to lookfor growth of the streptomycin-resistant microfungus, and the health of thefungal garden. After identification of the various species, nests will be excavatedcarefully to ensure minimal disruption of fungal gardens, and these will bemaintained in sterile containers with multi-chamber systems: an innerchamber for the garden sample, and a larger surrounding area in which toplace foraging material for the ants. This will allow for additional collections ofspecimens if needed, and an ample supply of the ant species= naturalforaging material and access to the microfungi which parasitize theirgardens. These cultures will be placed on potatodextrose agar medium with the antibacterial antibiotics penicillin-G andStreptomycin sulfate under aseptic conditions. Biosci., 49, pp. New York Times.http://www.plantbio.berkely.edu/~bruns/text/ants2.html Ariniello, L. Knowledge gained by studying antibiotic production byactinomyces, and antibiotic resistance by microfungi may provide someuseful data for the study of antibiotic resistance in man, which isbecoming a major problem with the overuse of known antibiotics for minorailments. Development of tolerance to antibiotics has majorimportance in terms of human disease control since there are currentlyproblems developing because of the overuse of antibiotics in the past, andthe emergence of resistant strains, e.g. Ifit is possible, then the addition of this resistant form to the fungalgarden will result in their death because the ants will not be able todestroy the microfungus, and it will take over their fungal garden. 7 1-7 4. By examining how these ants,who discovered the benefits of antibiotics many millions of years beforemankind ever new about the existence of bacteria, are able to produceantibiotics to deal with specific lethal parasites to their colonies, itmay be possible to determine ways to develop new antibiotics to deal withresistant forms in mankind. Leaf-cutting ants in tropical countries are essential to recyclingplant material and to keeping the soil aerated as earthworms do in moretemperate climates. With time, it maybe possible for the ants to develop production of a new antibiotic whichwill be capable of destroying these streptomycin-resistant microfungi, asthey developed the streptomycin to destroy the first microfungi. Crops could be sprayed with asuspension of the microfungus to deter the ants. Field perimeters could beloaded with the microfungi, creating a barrier to the ants ever being ableto gain access on the land to be cultivated. If it is possible to develop a streptomycin-resistant strain ofmicrofungi, spraying this microfungi on the leaves provided in the foragingarea for the ants in these garden chambers should have the same result asadding the microfungus to the gardens themselves. Various concentrationsof microfungus in the spray will be tested to determine the concentrationof streptomycin-resistant fungus necessary to bring about the death of anant garden. This leaves us in a very vulnerable positionand researchers are desperately searching for new and stronger antibioticswith which to combat these resistant strains. A., & Malloch, D. Most of the nest is underground, with an elaboratelabyrinth of passages and thousands of chambers ranging in size from thatof a fist to the size of a soccer ball. Some form of resistance tostreptomycin must be possible by these microfungi, otherwise they would beeliminated from the colonies entirely and their presence would never havebeen detected. (1999). This means thatevery fungal garden found throughout South and Central America, where theants thrive, is a descendant of a single ancestral spore. The ants will strip entire orchards of leaves in no time. Mueller, U. The ants use this vegetation to feed fungal mutualists onwhich they themselves feed. Leaf-cutting ants arethe dominant herbivore in the Neotropics, consuming about 2 percent of allthe fresh-leaf biomass there. To build such enormous nests, theants must displace enough earth to fill a good-sized living room (Angier,1994). Discussion of Possible Results If it is possible to isolate a streptomycin-resistant form ofEscovopsis microfungus, then this has great potential for the future ofagriculture in the tropics. (1999). This research will extend the work of Currie, Mueller and Malloch(1999) and Currie, Summerbell and Malloch (1999) who have done much work inelucidating the agricultural pathology of ant fungus gardens and the way inwhich the ants protect their gardens from bacteria and parasites. A mature fungal garden may contain 8 million ants, ranging in sizefrom the tiny garden tenders to the egg-swollen queen who may be the sizeof an unshelled peanut.
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