An international team of researchers has discovered the oldest fossil evidence of agriculture, and it dates back millions of years before humans started farming. The team found evidence of fungus gardens within fossilized termite nests in 25 million year old sediments in Africa’s Great Rift Valley.
Some termite species have developed a highly specialized, symbiotic relationship with fungi, which they cultivate in “gardens” within their subterranean nests or chambers. The termites consume woody material and excrete rounded pellets composed of concentrated, undigested plant fragments and fungal spores. The fungus germinates and colonizes the plant material, helping to convert it into a more easily digestible and nutritious food source.
Scientists had previously used DNA from modern termites to estimate that fungus-farming in termites began 25-30 million years ago. However, definitive fossil records of fungus-farming were elusive.
Now, Eric Roberts of James Cook University in Australia and colleagues have confirmed that date with the discovery of fossilized termite nests containing fungus gardens in southwestern Tanzania.
“This fossil discovery is special because it provides concrete evidence that we not only had termites in Africa 25 million years ago, but they had already formed this important symbiotic relationship with fungi,” says Roberts. “This also supports the hypothesis that fungus-farming termites originated in central Africa and then radiated into other parts of Africa before dispersing into Asia.”
Roberts says the fossilized termite nests and fungus gardens are remarkably similar to many modern termite nests and gardens
“They are hollow chambers that were constructed underground and are about the size of a baseball or softball,” he says. “Within these hollow chambers are the fungus gardens. These are formed from termite excretions of partially digested wood (inoculated with fungal spores), which the termites mold into spheres and then pack together into a complex architectural construction that can look a bit like a mass of spaghetti noodles.”
The development of this symbiotic relationship increased the range of possible habitats for both the termites and their domesticated fungi. Although termite fungus-farming may have been born in the African rainforest, it allowed termites to disperse to less hospitable dry savannas and open landscapes, and eventually to migrate out of Africa and into Asia.
The origin of termite fungus-farming likely had a major effect on how nutrients were concentrated across the landscape. Understanding the development of this symbiotic relationship has implications for understanding the carbon cycle in deep time in this region.
“The evolution of this symbiotic relationship had major implications for ecology and biogeography,” says Roberts. “It likely links into really interesting patterns of landscape development in Africa associated with the initiation of the Rift Valleys.”
Reference: Roberts, E. M., Todd, C. N., Aanen, D. K., Nobre, T., Hilbert-Wolf, H. L., O’Connor, P. M., Tapanila, L., Mtelela, C., and Stevens, N. J. (2016). Oligocene Termite Nests with In Situ Fungus Gardens from the Rukwa Rift Basin, Tanzania, Support a Paleogene African Origin for Insect Agriculture. PLOS ONE 11(6): e0156847. doi: 10.1371/journal.pone.0156847.