The evolution of an ant-plant mutualism

2010 REU Intern Sara Zufan


Junior Biology/Ecology and Evolution major at DePaul University

REU Mentors: Dr. Corrie Moreau (Curator, Zoology, Insects) and Benjamin Rubin (Graduate Student, Zoology, Insects)

Symposium Presentation Title: Evolutionary Histories of Bacterial Endosymbionts and their Ant Hosts

Symposium Presentation Abstract: Many Pseudomyrmex ants are obligate mutualists with acacia trees, providing protection for their acacia hosts in return for shelter and food.   However, the diet provided by the acacias is nutrient poor and unlikely to be sufficient for ant colonies to thrive.  Recent research has found that endosymbiotic bacteria, living in the guts of ants, may supplement these nutrient poor diets. It is hypothesized that some of the bacteria found are capable of metabolizing nitrogen and synthesizing amino acids which would enable the ants to survive on plant-based diets. These studies suggest that bacterial gut symbionts may play an important role in the evolution of herbivorous ants. To describe the possible co-evolution of the symbioses between bacteria and their ant hosts, we reconstructed evolutionary histories of selected herbivorous ants and their associated bacteria. Ant species included in this study were primarily from the genera Pseudomyrmex, although Cephalotes, Crematogaster, and Tetraponera were also analyzed as outgroups. The barcoding region COI and the 16S rDNA gene were used to build phylogenies for the ants and bacteria, respectively. We did not find strict co-evolution between the ants and their associated bacteria, in part because our procedure for determining bacterial sequences was not as specific as we hoped. We plan to more accurately examine these relationships by developing more specific bacterial markers and reexamining the evolution of single bacterial lineages and their ant hosts.

Original Project Description: Why do ants protect plants? Why do plants provide homes and food for ants? Mutualistic acacia-ants nest in and feed from acacia trees while protecting them from herbivorous animals, competing plants, and pathogenic fungi. But what are the origins of this mutualism and how has its evolution influenced the diversification of ants? Using DNA from Neotropical acacia-ants, we will be able to determine the age of this mutualistic relationship and how it affected the evolutionary history of the ants and plants involved.

Research methods and techniques: Interns will receive training in DNA extraction, PCR, and sequencing in the Museum’s core genetics facility, the Pritzker Laboratory and the DNA Discovery Center. They will be introduced to next-generation genomic sequencing techniques, phylogenetic assembly, and their applications to understanding evolutionary history.