Unraveling the evolutionary dynamics of high symbiont diversity in the fungus-farming ant genus Apterostigma: A phylogenomic approach

Arizona State University, Scottsdale AZ

Investigators

Abstract

The best known fungus-farming ants are the leaf-cutting ants of the genera Atta and Acromyrmex, which are the dominant plant harvesting animals of the New World tropics. These ants use plant leaf cuttings in order to cultivate a single, recently evolved fungal species, which they then eat. However, a more poorly known group of fungus-farming ants in the genus Apterostigma, cultivate a greater diversity of fungal species than all other fungus-farming ants combined. Closely related species of Apterostigma cultivate closely related groups of fungi, but major shifts to distantly related fungal groups have occurred multiple times during 40 million years of co-evolution between Apterostigma ants and fungus. This research aims to better understand the co-evolution of leaf-cutting ants and the fungi they cultivate. This includes developing new knowledge about the numbers, diversity and distribution of Apterostigma ant species and their associated fungi, as well as determining the evolutionary relationships among both ants and fungi. Questions to be addressed include: Why do leaf-cutting ants in the genus Apterostigma cultivate a greater diversity of fungal species than all other fungus-farming ants (leaf-cutting and non-leaf-cutting) combined? Why do some Apterostigma ant species cultivate only a few fungi that are closely related to each other, while others cultivate diverse fungi that are only distant relatives? The results from this research may benefit society in general because fungus-farming ants provide a rare non-human model system for the emerging fields of Darwinian agriculture and Darwinian medicine, which aim to improve human agriculture and disease management through the study of analogous natural systems. Recently several antibiotics and antimalarial quinones have been isolated and described from fungi and bacterial species living in association with leaf-cutting ants, making their biology particularly relevant to issues of health. Further, some fungi associated with leaf-cutting ants have become models for more efficient biofuel production. This research will proceed by comprehensive field collecting of ants and fungi from nests throughout their distributions in nature, and documenting the presence or absence of co-speciation patterns in Apterostigma ants and their fungal cultivars, by comparing phylogenetic analyses based on genomic data for both ants and fungi. The researchers will employ targeted enrichment of Ultra-Conserved genetic Elements (UCEs) to infer the species-level phylogenies. These phylogenies will be used in testing hypotheses of co-evolution and fungal species fidelity and mobility among host ant species over time. The genomic UCE data will also be used to resolve species boundaries (identify species) among poorly known species-complexes of Apterostigma ants. This is essential for reconstructing species-specific ant-fungus co-evolutionary interactions as well as for revising ant taxonomy and producing pictorial identification keys to various ant species.