Wednesday 20 July 2016

Ancient African Agriculture

Words like agriculture and cultivation are strongly associated with humans. 10,000 years ago agriculture revolutionized everything from our societies to our genetics. Yet the phenomenon is not just restricted to our species. Other, often overlooked species of farmer, are ants and termites. Certain species will allow the growth of fungus within their colonies which serve to break down plant matter into digestible material. These farms are complex with the worker ants carefully maintaining conditions suitable for growth, removing competitive species of fungus, and repelling others which might eat the crop. Now recent evidence has shown that this practice of fungal agriculture is far older than our own 10,000 year-old origin date.

A comparison of the fossil burrows and
fungus (left) with modern examples (right)
Previously, genetic studies suggested that fungal farming in termites originated at least 31 million years ago. Yet fossil evidence confirms the existence of farming behaviours just 6 million years after this proposed origin; in-situ gardens of fungus, within termite colonies, from the Rukwa rift basin in the Tanzanian portion of the Great African Rift Valley.

Volcanic ash in-filling the colony galleries, as well as preserving the delicate internal structures, allowed for accurate dating of the specimens to 25 million years old. Some of the in-filling material, however, was composed of grains with a spherical texture and composition consistent with mylospheres - pellets of fecal matter, plant material and fungal spores which act as the starting material for fungal gardens. A smaller number of specimens preserved sections of the developed fungus combs themselves.

Preserved mylospheres within the burrows
Apart from confirming the antiquity of the symbiotic relationship between termites and fungus, the discovery has interesting implications for the origin of the practice itself. 25 million years ago, Africa was covered by tropical rainforests. As time progressed, drier climates resulted in the development of grasslands until a final climatic shift just a few million years ago resulted in the spread of deserts across much of the continent.

Arid climates developed much earlier in Tanzania, however, due to the opening of the Great African Rift. Fungal farming dramatically increased the range of habitats available to termites, allowing them to adapt to newly arid niches, as well as a generally harsher climate. While not worth the tens of billions that human agriculture generates today, termite agriculture has had a vital influence on the planet's characteristics for far longer.