Leaf-cutter ants are community gardeners on a very large scale. Living in colonies composed of several millions, the ants harvest hundreds of kilograms of leaves annually and use them to cultivate fungal gardens that serve as their primary food source.
|Leaf-cutter ant. (From the October 2010 issue of PLoS Genetics. Image by Jarrod J. Scott, University of Wisconsin-Madison.)
In a paper published September 23, 2010 on PLoS Genetics, DOE JGI’s Susannah Tringe, Kerrie Barry, Lynne Goodwin teamed with longtime DOE JGI collaborator Cameron Currie and his colleague Garret Suen, both from the University of Wisonsin-Madison and the Great Lakes Bioenergy Research Center to study the microbiome of the leaf-cutter ant Atta colombica.
The fungal gardens, noted the researchers in their paper, serve as the ants’ external digestive system and have five separate layers to break down the plant biomass into nutrients. Currie’s team took samples from the top and bottom layers of ant fungal gardens in Panama to better understand how the biomass is broken down at each stage. They knew that ants and the fungi they tend enjoy a mutualistic relationship, but that the fungi aren’t capable of breaking down cellulose, which was found to decrease by 30 percent on average in these gardens.
The researchers identified a previously unknown microbial community that is involved in breaking down the cellulose in these fungal gardens, and said the ants’ ability to also cultivate these microbes “likely represents a key step in the establishment of these ants as widespread, dominant insect herbivores in the Neotropics.”