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Chapter 25 : The Tangled Banks of Ants and Microbes

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The Tangled Banks of Ants and Microbes, Page 1 of 2

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Abstract:

Worker attine ants carefully tend the fungus and forage for substrates to use as nutrients to support its growth. In exchange, the fungus serves as the primary food source for the colony. Functionally, this is similar to human agriculture, but instead of growing plants, the ants grow fungus. The foraging activity of these ants is so prodigious that they are one of the most dominant herbivores of Neotropical ecosystems. are members of the Actinobacteria, a group well known for their ability to produce potent antibiotics. Indeed, the majority of antibiotics used in human medicine are derived from Actinobacteria. So, it is perhaps not surprising that through natural selection fungus-growing ants “discovered” the benefit of obtaining antibiotics from these bacteria. This relationship, however, not one-sided, as benefits from its symbiosis with the ants. Studies indicate that over their long evolutionary history, attine ants have been continuously threatened with famine induced by infections of their fungus garden; to help mitigate this threat, the ants have been employing antibiotic-producing bacteria for millions of years. The fungus garden serves as the external digestive system for the ants; the garden converts leaves into energy for the ants. It has long been assumed that nutrient provisioning to the ants from the garden is only mediated through the ants’ fungal mutualist. Through the formation of symbiotic associations with their fungus and bacteria, the ants obtain access to the metabolic capacity of these microbes, including the capacity to degrade plant biomass and produce antibiotics, respectively.

Citation: Currie C. 2012. The Tangled Banks of Ants and Microbes, p 181-190. In Kolter R, Maloy S (ed), Microbes and Evolution. ASM Press, Washington, DC. doi: 10.1128/9781555818470.ch25

Key Concept Ranking

Microbial Ecology
0.7043269
Natural Selection
0.4683577
Nitrogen-Fixing Bacteria
0.4513265
Chronic Infection
0.42889568
Bacterial Growth
0.41557342
0.7043269
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Figures

Image of Figure 1
Figure 1

A leaf-cutter ant worker standing on the surface of a fungus garden. Leaf-cutters have a mutualistic association with fungi they cultivate for food. Workers forage for fresh leaf material, which they use to support the growth of the fungus. The fungus can be seen protruding as threadlike projections off the leaf substrate of the garden matrix. This line drawing was created by Angie Fox. doi:10.1128/9781555818470.ch25f1

Citation: Currie C. 2012. The Tangled Banks of Ants and Microbes, p 181-190. In Kolter R, Maloy S (ed), Microbes and Evolution. ASM Press, Washington, DC. doi: 10.1128/9781555818470.ch25
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Image of Figure 2
Figure 2

The tangled bank of ants and microbes within the fungus-growing ant-microbe symbiosis. (A) A leaf-cutter ant queen, shown sitting on the top of a fungus garden, can live more than a decade and lay ~60 million eggs over her life span. Individual leaf-cutter colonies can be composed of millions of workers and hundreds of fungus garden chambers. (B) The fungus serves as the primary food source for the ant colony and is related to soil-decomposing fungi, which produce mushroom fruiting bodies similar to what is depicted in the box. (C) The fungus garden is often infected by specialized parasites (genus ), which continuously threaten the success of the ant-fungus mutualism. (D) The ants have a mutually beneficial association with bacteria ()that produce antibiotics that suppress the growth of the parasite.(E) A fifth symbiont, black yeast, exploits the ant-bacteria mutualism, consuming the bacteria and decreasing its effectiveness at suppressing the parasite. (Arrows represent the interacting components, with plus and minus signs indicating whether the interaction is beneficial or antagonistic. For antagonistic interactions, the head of the arrow points to the organism that experiences the negative impact.) The original line drawings were created by Cara Gibson and Rebeccah Steffensen. doi:10.1128/9781555818470.ch25f2

Citation: Currie C. 2012. The Tangled Banks of Ants and Microbes, p 181-190. In Kolter R, Maloy S (ed), Microbes and Evolution. ASM Press, Washington, DC. doi: 10.1128/9781555818470.ch25
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Image of Figure 3
Figure 3

Line drawings of the symbiosis between fungus-growing ants and the antibiotic-producing bacteria ()(A) Side view of the head and thorax of a worker ant. Just below the head are the propleural plates (arrow), the main location of bacterial growth in most ant species. (B) A close-up of the propleural plates, illustrating the growth of the bacteria (left plate) and the specialized crypts evolved to house the bacteria (right plate, after removal of bacteria). (C) Cross section through the propleural plates, illustrating the large biomass of bacteria within the crypt (bottom), the cuticle of the ant (middle), and specialized gland cells that apparently provide nutrients to support the growth of the bacteria (top). Line drawings created by Sarah Taliaferro. doi:10.1128/9781555818470.ch25f3

Citation: Currie C. 2012. The Tangled Banks of Ants and Microbes, p 181-190. In Kolter R, Maloy S (ed), Microbes and Evolution. ASM Press, Washington, DC. doi: 10.1128/9781555818470.ch25
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Download as Powerpoint

References

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