The Successful Ant Farmers

You may think that complicated social activities, like agriculture, are unique to humans if you have never seen these leaf-cutting ants. As seen in Planet Earth, Season 2, On the vast grassland of South America, leaf cutting ants are diligently managing their farms of fungi just like humans. Cellulose, a main components of leaves, is indigestible to leaf-cutting ants. Nevertheless, fungus can break down cellulose and convert it to nutrients that can be used by ants. Thus, leaf-cutting ants feed leaves to their fungi. In return, the fungi will feed the ants.

Ants have a longer agricultural history than humans. The warm climate and diverse plants of the Eocene probably facilitated the evolution of fungus-growing ants [2]. The primitive lineage, thought to have originated in South America later evolved different agricultural systems, including yeast agriculture and leaf-cutting agriculture [2]. In addition to ants, who evolved to become agriculturists about 50 million years ago, termites and bark beetles developed the trait of agriculture independently [1].

At this point, you are probably thinking ‘well, it’s just like giving manure to crops, nothing special’. If so, you have drastically underestimated the agricultural similarity between ants and humans. Ants know how to choose the best “crop”. Termites, for example, actively select for strains of fungus to gain a better “yield”. It is found that the termites would reduce the number of strains in their colony, increasing the genetic relatedness of the remaining strains of fungi, so that less energy is wasted because of competition between fungal strains [4].

Furthermore, ants have fabulous farm management and supervision. Since the entire colony depends on the farm’s production, control of crop diseases becomes vital to the colony’s survival. Fortunately, the ants have adapted in several ways to deal with this problem: they sequester their garden from the outer environment, intensively monitor their garden to control the spread of pathogens, and manage to incorporate some “auxiliary” microbes that can provide disease suppression services [3]. In addition, some species can even tell the difference between crop fungi and weed fungi by scent. Once such a threat is detected, they immediately remove the weed and bury it with soil [5].

Now, what other behaviors do you think these little farmers can evolve? maybe fair trade?

by Kevin Tong, Fangyi Lin and Mengqing Xu

Planet Earth II, Episode 5, starting at approximately 28:07  

References

1. Quinlan, RJ & JM Cherrett. 1977. The role of substrate preparation in the symbiosis between the leaf‐cutting ant Acromyrmex octospinosus (Reich) and its food fungus. Ecological Entomology 2(2): 161-170.
2. Schultz, TR & SG Brady. 2008. Major evolutionary transitions in ant agriculture. Proceedings of the National Academy of Sciences 105:5435–5440.
3. Mueller UG, Gerardo NM, Aanen DK. Six DL & TR Schultz. 2005. The evolution of agriculture in insects. Annual Review of Ecology, Evolution and Systematics 36:563–95
4. Aanen, DK, Licht, HH, Debets, AJ, Kerstes, NA, Hoekstra, RF & JJ Boomsma. 2009. High symbiont relatedness stabilizes mutualistic cooperation in fungus-growing termites. Science, 326(5956): 1103-1106.
5. Katariya, L, Ramesh, PB, Gopalappa T, Desireddy S, Bessière J & RM Borges. 2017. Fungus-farming termites selectively bury weedy fungi that smell different from crop fungi. Journal of Chemical Ecology 43(10): 986-995.