Farmer ants and crop plants

Humans are not the only species to farm plants. High up in the forest canopies of Fiji, ants have been farming Squamellaria plants for millions of years. The ants collect Squamellaria seeds, plant them under tree bark, protect the seedlings from herbivory, and fertilise the growing crop with their faeces. The ants then nest within specialised structures produced by the plant called domatia and feed off nutritionally rich nectar produced by the pollinated flowers of mature plants. A 3D model of a Squamellaria domatium, showing the internal chambers, is pictured below. Squamellaria plants live on tree branches with no direct connection to the soil and are therefore nutrient limited. A major benefit of their relationship with the ants is that they can absorb nutrients from the ant’s faeces through the inner walls of the domatium.

Computed tomography‐based 3D model of an ant domatia from the Fijian epiphyte Squamellaria wilsonii. Courtesy of Guillaume Chomicki (Chomicki & Renner, pp. 2011–2023).

Certain fungi are also farmed by ants, and fertilisation by the ant farmers over evolutionary time can impact their physiology. For example, fungi farmed by attine ants no longer have certain lignin-degrading enzymes, as they no longer rely on lignin breakdown for nutrition. Farmed Squamellaria grow side-by-side with Squamellaria species that are not farmed by ants.  These species still have domatia, but have a symbiotic relationship with multiple ant species and have seeds that are dispersed by both birds and ants. This means that the impact of ant farming on the physiology and nutrient status of farmed Squamellaria species can be investigated through direct comparison of farmed and non-farmed species.

Dr Guillaume Chomicki and Professor Susanne S. Renner found differences in the nutrient uptake by farmed and non-farmed Squamellaria domatia and corresponding differences in the behaviour of the ants living in them. Farmer ants don’t defecate randomly within the cavities of the domatium like the more generalist non-farmer ants but instead exclusively target hyper-absorptive protrusions on specialised walls present in farmed Squamellaria domatia for fertilisation.

Read the article: Chomicki, G. and Renner, S.S. (2019) Farming by ants remodels nutrient uptake in epiphytes. New Phytologist, 223: 2011-2023. doi: 10.1111/nph.15855