The Evolutionary Innovation of Nutritional Symbioses in Leaf-Cutter Ants

Abstract

Fungus-growing ants gain access to nutrients stored in plant biomass through their association with a mutualistic fungus they grow for food. This 50 million-year-old obligate mutualism likely facilitated some of these species becoming dominant Neotropical herbivores that can achieve immense colony sizes. Recent culture-independent investigations have shed light on the conversion of plant biomass into nutrients within ant fungus gardens, revealing that this process involves both the fungal cultivar and a symbiotic community of bacteria including Enterobacter, Klebsiella, and Pantoea species. Moreover, the genome sequences of the leaf-cutter ants Atta cephalotes and Acromyrmex echinatior have provided key insights into how this symbiosis has shaped the evolution of these ants at a genetic level. Here we summarize the findings of recent research on the microbial community dynamics within fungus-growing ant fungus gardens and discuss their implications for this ancient symbiosis.

Keywords: Leucoagaricus; attine ants; co-evolution; microbial consortia; symbiosis.

Figure 1

(a, b) Leaf-cutter ants forage on large quantities of fresh foliar biomass. (c) They bring this material into their subterranean nests, where it is integrated into symbiotic fungus gardens they cultivate for food. [Photo credits: A; Jarrod J. Scott, B; Christian R. Linder, used under the GNU Free Documentation License, Version 1.2, C; Austin D. Lynch.].