Humans are not the first species to farm on Earth. Nor are they the first species to have taken agriculture to industrial scale to feed millions. Three species from the insect world have been farming fungi from the last 20-65 million years. Ants, termites and ambrosia beetles are the first species to have mastered the ability to harvest food from crops and farming is so close to their heart that it has in fact altered their genes.
Out of the three farming insect species, ants and termites have taken the cultivation of fungi to an industrial scale, producing enough food to feed millions. They farm as a whole community, working in unison to grow fungi, while the ambrosia beetles cultivate fungi as individuals. Beetles known for their destructive capabilities, wiping out vast stretches of forests, create small galleries just below the bark of the trees, where they grow fungi, which in turn derive nutrients from the host tree. Researchers believe ambrosia beetles developed fungus gardening abilities 50 million years ago in the tropical or subtropical forests.
But what catches the fascination of the researchers, time and again is the mutualistic symbiosis of the fungus farming Attine ants. Fossil records and genetics trace the origin of ant farmers to South America, where a small group of ants made the transition from hunter-gatherer lifestyle to subsistence farming somewhere around 55-60 million years ago, shortly after the end of the age of dinosaurs. These ants from the Attini tribe started farming the fungi growing on decomposing, woody plant matter and started forming colonies around them. Though the ant colonies around slow-growing fungi were small, they were the first baby steps towards large industrial scale farming.
However, it took millions of years to domesticate the fungi. About 25 million years ago the big breakthrough in the Attini ants’ efforts to domesticate fungi came when one of the cultivars after getting reproductively isolated from their free-living relatives, evolved to consistently produce specialized organs to feed them. This cultivated fungi variety were capable of producing tiny, protein-rich bulbs which the Attini ants gleefully harvested.
Availability of more nutritious food encouraged development of larger colonies, further advancing the ant-fungus mutualism and co-evolution. Around 15 million years ago, this evolutionary progress in ants history led to the emergence of the present day leafcutter ants.
Leafcutter ants daily bring fresh green matter from outside world and sow them in their underground farms as food for the cultivated fungus. This helped to scale-up the cultivation of a fully domesticated fungi species to an industrial level, thereby making it possible to sustain giant ant colonies with millions of ants.
Domestication changed the relationship between the partners forever. But this came with a large price tag. Unlike their ancestors or the present day wild relatives, the mutual relationship made the cultivated fungus variety to lose their ability to produce enzymes to digest woody plant matter. This compelled them to rely solely on the leafy greens brought by the ants for survival.
At the same time they gained the ability to produce fruiting bodies filled with proteins – an essential ingredient for ants’ growth. On the other-end, the ants were also up for evolutionary modifications. They evolved to produce special enzymes to easily digest this superfood. This dependence on the protein globules was so much that, with time they became incapable of digesting anything else, thereby making them irreversibly committed to cultivating fungi.
In a way this bilateral coevolution tied the fate of the partners, making them dependent on each other for survival. Nonetheless this symbiotic relationship enables leafcutters to form the largest colonies among the fungus-farming ants and also working together as a team makes them the most dominant herbivores in the Neotropical forests.
“The ants lost many genes when they committed to farming fungi,” says Jacobus Boomsma, research associate at the Smithsonian Tropical Research Institute and biology professor at the University of Copenhagen. “This tied the fate of the ants to their food–with the insects depending on the fungi for nutrients, and the fungi increasing their likelihood of survival if they produced more nutritious crop. It led to an evolutionary cascade of changes, unmatched by any other animal lineage studied so far.”
According to recent research findings, the early Attine farmers were metabolically less efficient than ant species with traditional diets, a deficiency which continued until the complete domestication of the protein globules producing fungi cultivar. This is something very similar to what happened with humans, where early human farmers of loosely domesticated crops had a poorer health with small body stature compared to hunter-gatherers. This goes to show that large-scale ant farming was possible only after substantial accumulation of adaptive modifications and this process gained momentum after cultivars were truly domesticated and no longer exchanged genes with free-living fungi.
While the ants in South America were busy domesticating fungi, the termites of Africa were also making their own experiments in mastering fungi farming. Recent discovery of termite nest fossil in East Africa places termite fungus farming as far back as 25-30 million years.
Termites play a critical role as natural decomposers of plant tissues, taking help from the gut symbionts to decompose organic matter. However during their evolutionary development one particular subgroup of termites shifted to agriculture by developing a highly specialized symbiotic relationship with a particular subgroup of fungi family.
They started to cultivate fungi in ‘gardens’ in underground nests or chambers, taking advantage of the fungi’s ability to convert recalcitrant, nitrogen-poor plant material into a more easily digestible, protein-rich food source.
To start with, termite farmers consume woody material and after brief mastication, they excrete round fecal pellets composed of concentrated, undigested plant fragments and fungi spores. These spores germinate and colonize the plant material, forming fungal gardens.
Researchers believe that the African rain forest could have served as the cradle for fungiculture by termites. The transition to fungus agriculture in a way increased the range of possible habitats for both the fungus-growing termites and their domesticated fungi. Living symbiotically helped them to spread to less hospitable dry savannas and eventually migrate to Asia.
Surpassing human agriculture in efficiency
The evolutionary give and take relationship between ant, termite farmers and the fungi cultivars has made it possible to develop industrial scale farming that surpasses human agriculture in its efficiency. However, this agricultural mutualism underwent transformations over time scales many orders of magnitude larger than that associated with human agriculture. In addition, mastering industrial scale farming was possible only after ‘the art of farming’ got hard coded in their genes, as well as in their fungi partners.
On the other hand, subsistence farming by humans began about 10,000 years ago, developing into industrial agriculture only in the last hundred years. While the insect farmers cultivate fungi in subterranean gardens to produce edible proteins, lipids and carbohydrates by decomposition, most human crops produce food matter by photosynthesis.
But the best part of these insect farmers are their amazing ability to grow an all purpose monocrop which are drought-resistant, disease and pests free super food on a massive scale without any negative impact on the environment. Now this is something which we humans have failed miserably to achieve and are yet to figure out.
Maybe we humans can take a leaf out from these insect farmers’ diaries, and learn to farm sustainably without harming the environment.
1.“Oligocene Termite Nests with In Situ Fungus Gardens from the Rukwa Rift Basin, Tanzania, Support a Paleogene African Origin for Insect Agriculture”, Eric M. Roberts et al, PLOS one, Jun2 22, 2016.
2. “Reciprocal genomic evolution in the ant–fungus agricultural symbiosis”, Sanne Nygaard, Nature Communications, 20 July, 2016.
Feature Image: via commons.wikimedia