The multidimensional nutritional niche of fungus-cultivar provisioning in free-ranging colonies of a neotropical leafcutter ant

Abstract

The foraging trails of Atta leafcutter colonies are among the most iconic scenes in Neotropical ecosystems, with thousands of ants carrying freshly cut plant fragments back to their nests where they are used to provision a fungal food crop. We tested a hypothesis that the fungal cultivar's multidimensional requirements for macronutrients (protein and carbohydrates) and minerals (Al, Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn) govern the foraging breadth of Atta colombica leafcutter ants in a Panamanian rainforest. Analyses of freshly cut plant fragments carried by leafcutter foragers showed that the combination of fruits, flowers, and leaves provide for a broad realized nutritional niche that can maximize cultivar's performance. And, while the leaves that comprised the most harvested resource also delivered an intake target containing protein in excess of the amounts that can maximize cultivar growth, in vitro experiments showed that the minerals P, Al, and Fe can enhance the cultivar's tolerance to protein-biased substrates, and potentially expand the ants' foraging niche. Yet, the cultivar also exhibits narrow margins between mineral limitation and toxicity that may render plant fragments with seemingly optimal blends of macronutrients unsuitable for provisioning. Our approach highlights that optimal foraging is inherently multidimensional and links the foraging behavior of a generalist insect herbivore to the fundamental nutritional niche of its microbial symbiont.

The multidimensional nutritional niche of fungus‐cultivar provisioning in free‐ranging colonies of a neotropical leafcutter ant

“…To determine possible macronutrient–mineral foraging regulation, we used Pearson tests to assess whether maximal mineral tolerance of the cultivar increased with (1) maximal mineral content of plant substrates or (2) the distance between maximal mineral concentrations and macronutrient intake target (Figure 6b,d). Corresponding datasets and R scripts are available in Dryad (https://doi.org/10.5061/dryad.6t1g1jx01) and Zenodo (https://doi.org/10.5281/zenodo.5160258), respectively (Crumière et al, 2021a, 2021b).…”