Feeding the masses

How are leaf-cutter ants (Atta cephalotes and Acromyrmex echinatior) able to support their colonies of 1 million plus individuals on nothing but there home grown fungus? 

For the last 50 million years ants have been doing what we still are not fully able to do, managing a sustainable agricultural system. They do this by working symbiotically with Bactria to cultivate a single species of fungus into fungus gardens while protecting it from numerous weeds and parasites as well as other bacteria and insects. 

 

 What roles do the ants and bacteria have in the growing the fungus gardens?

Ants- the ant collects the resources required by the fungus to grow and as their common name suggest that is leafs. Once the leafs have been brought back to the nests the ant shred the leafs and “feed” it to the fungus. They protect the fungus from “weeds” by removing areas of the fungus garden that have other fungus growing from them and they also remove sections of dead fungus, some of the leaf-cutter ant species have areas used specifically for the disposal of the waste from their fungus gardens to ensure there is no spread of any unwanted pests and pathogens back to the garden. To stop weeds from establishing the ants lick the surface of the fungus to collect spores of unwanted fungus. Some ants also apply fecal waste to their gardens, this is thought to both help the degrade the plant martial to help their fungus digest the leafs and also help minimalize infection of other fungus because  high levels of chemicals like lignocellulases in the faeces . While preforming these tasks the ant will secret acids and other compounds from their metapleural gland that have antibacterial properties that also help maintain the fungal garden.

Bacteria- there are also some bacteria that work symbiotically with the ants, these bacteria mostly have antibacterial properties that can help inhibit the growth specialised paristies of the fungus and other less specific pathogens.

With the combination of the ants control methods and the bacteria the fungus gardens can maintain very controlled conditions that allow the ants to maintain a there agricultural system and protect it from any pests.

So why is it more beneficial for the ants to rely on the fungus over other food sources?

The fungus can break down plant polymers that the ants digestive system could not, so because of this the ants can get a higher return from the leafs they collect by using them to cultivate the fungus that has evolved with the ants to give an optimal return back to the ant.  In different ant communities the different fungus utilises different plant polymers that they break down into more easily digested compounds. (see refence paper for the list of different ants and funguses, pages 5-8)

    

So if these ants have been able to maintain such a heavily controlled agricultural system for the last 50 million years could we adapt this in a way to feed people more efficiently?  If so I hope you like mushrooms because you may be eating a lot of them someday .   

Aylward, F. O., Currie, C. R., & Suen, G. (2012). The evolutionary innovation of nutritional symbioses in leaf-cutter ants. Insects, 3(1), 41-61.