Human foibles seem to be a natural trend gone astray, says S.Ananthanarayanan.

Much of our current climate crisis is blamed on using too much chemical fertiliser to promote farm productivity. A study shows that the tendency is also found in the natural world.

Jonathan Z. Shik , Pepijn W. Kooij, David A. Donoso , Juan C. Santos, Ernesto B. Gomez , Mariana Franco , Antonin J. J. Crumière, Xavier Arnan, Jack Howe , William T. Wcislo and Jacobus J. Boomsma, from the University of Copenhagen, the Smithsonian Tropical Research Institute, Panama City, the Royal Botanic Gardens, Kew, London, Universidad Tecnológica Indoamérica, Quito, St. John’s University, New York, Centre de Recerca Ecològica i Aplicacions Forestals, Cerdanyola del Vallès, Spain, describe in the journal, Nature Ecology and Evolution, a study of farming methods of colonies of ants, and find trends that could “shed light on nutritional trade-offs that shaped the course of culturally evolved human farming.”

Striving to strengthen the source of food has been a driver of evolution in the natural world and has given rise to forms of farming and social organisation among bacteria and insects, just as it has, by a cultural driver, among humans. While one should tread with care when “drawning analogies between domains,” the paper says, it is reasonable to take it that both forms of farming have grown in sophistication over time. The plants that we grow today, for instance, are quite different from their ancestors in the wild – with cultivated varieties showing more nutritious or enlarged leaves, roots or seeds. And domestication of the wild varieties has called for trade-offs, sacrificing resilience and needing special conditions, of sun or shade, water or nutrients.

These are the choices that the impetus to secure the food source forces the farmer to make. And human farmers, the paper says, “managed to push these trade-offs to extremes.” A few high yielding varieties of crops have been widely farmed, “even though the vulnerability of the plants to herbivores and pathogens has often increased.” This has called for the manufacture and use of pesticides. And then technological solutions, like synthetic fertilisers, have shrunk the size of the niche where the crop can flourish.

A parallel world of farmers is that of some ants, termites and bees, which, over millions of years, much longer than the time that humans have been farming, have evolved to depend on and support different sources of nutrition. The study has considered a particular group of ants, the attine ants, found in the Americas, which live on fungi that the ants cultivate with nutrition, including grasses and leaves that the ants bring to the nest. Unlike human farmers, who grow a variety of crops, however, fungus growing ants specialise in promoting in the nest basically only a single form of fungus. A disadvantage in this specialisation, or lack of diversity, is that the strain of fungus is sensitive to changes in nutrition and susceptible to infection. The ants, accordingly, have evolved ways to recycle fungal enzymes, to improve productivity, and powerful antibiotic defences to control disease, the paper says. And it is the specialisation, in the strain of fungus, and the attendant measures, that have led to the 19 different groups of these ants, with more than 240 distinct species to arise, from Argentina to north-eastern United States.

The interplay of the extent of specialisation of the fungi and the sources of nutrition was studied, first by identifying the specific nutrition that different fungi required – by growing the fungi in the laboratory, in glass dishes, with controlled supply of protein and carbohydrates – to reveal the different Fundamental Nutritional Niches (FNN) into which the fungi had painted themselves. To cater to these nutritional needs, the ants harvest what they can from the available debris, even freshly cut bits of leaf, and convert the harvest to a form suitable for fungi. This form, of the main nutrients that the ants offer to the fungi they cultivate, was determined by field surveys, where the material was extracted from the ants’ jawbones, when they were returning to the nest, and analysed. The comparison of what the ants harvest, and what the fungi need, brings out the ‘provisioning strategy’ the ants employ – for analysis in terms of how far the nutritional niche of the fungi has narrowed and the stage of evolution of the species of ant.

A first result of the investigation was that the earliest species, closest to the ancestral line, supported fungal varieties that showed broad FNN – viz, they were the least specialised in their nutritional requirements, and growing well even with a wide range of the mix of protein and carbohydrate as nutrition. The colonies were also of modest productivity and size. The fungi, however, could be far more productive with richer nutrition, in the lab, than what their natural caterers, the ants, could provide.

The fungi cultivated by the next evolutionary group of ants was the domestication of a specialised line of fungi, which sprouted nutrient-rich swellings for the ants to feed on. Although the ant colonies as well as the extent of cultivation stayed modest, the specialisation led to shrinking of the nutritional niche. That this was happening became apparent because fungus cultures in the laboratory we not able to survive if they were not provided their narrower range of nutrients.

And further along the time-line were the ants with large colonies and complex social organisation, the leafcutter ants, which bring to the next freshly cut vegetation from hundreds of plant species. The fungal variety which the leafcutter cultivate is a specific species and it can grow only with the nutrition the ants bring. The fungi support huge colonies, of millions of ants, but cannot survive a blend of nutrition outside their FNN. The leafcutters, with this fine-tuned appetite of the fungus they cultivate, have hence evolved different measures to manage even with changes in the kind of leaf or grass that is available.

The study reveals the trend, over the millions of years of evolution, of increasing specialisation of the fungi cultivated by the ants, which supports greater productivity and colony size, matched by increasing capacity of the ants to cater to the nutritional needs of the fungi. The parallel with the development in human farming is striking – we now cultivate far more crops, and get more yield per hectare than our ancestors. But our methods, energy and the use of fertiliser and insecticides, now threaten our very existence. The great increase in human agriculture has been only since the last century. But the attine ants had millions of years to adapt and provide for the insecurity that dependence on a narrow band of resources must bring with it. Getting to understand how the ants do it could show us the way to deal with our own problems!

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