Strategies of acacia-ants: to grow or to reproduce?

2011 REU Intern William Montag


Sophomore Biological Sciences major at Bowdoin College

REU Mentors: Dr. Corrie S. Moreau (Curator, Zoology, Insects), Dr. Stefanie Kautz (Postdoctoral Fellow, Zoology, Insects), and Benjamin E. Rubin (Graduate Student, Zoology, Insects)

Symposium Presentation Title: The evolution of mutualism in plant-ants

Symposium Presentation Abstract: Mutualisms play a vital role in generating complex relationships and behaviors between radically different groups of organisms. Among those organisms are three groups of ants within the genus Pseudomyrmex who have formed mutualistic relationships with acacia, Tachigali, and Triplaris plants. The ant species protect the host plant against herbivores and competing plants in return for plant-derived food resources and shelter. I generated sequence data and performed a phylogenetic analysis using sequences from both mutualist and generalist ants of the genus Pseudomyrmex, using Tetraponera as an outgroup in order to determine whether the ant-plant mutualism originated from a single ancestor common to all three plant-ant groups. The Wnt (wingless) and ef-1a genes were used to generate sequences for each sample that were then concatenated. A tree was generated using both Bayesian and Maximum Likelihood analysis that showed the acacia, Tachigali, and Triplaris plant-ant groups originating from different generalists. The phylogenetic analysis did not display evidence for a monophyletic ant-plant mutualism group within the genus Pseudomyrmex. The presence of convergent mutualisms in different Pseudomyrmex species groups may provide insight into the development of mutualisms. Further research into the initial stages of mutualism formation is necessary to determine why mutualism would occur multiple times in one genus and what environmental factors trigger the development of this behavior.

Original Project Description: Mutualistic acacia-ants protect acacia trees from herbivorous animals, competing plants, and pathogenic fungi in return for food and nesting space provided by the plant. In contrast, parasitic ants nest in and feed on acacias but do not protect the plant. What survival strategies do the different ants have and how did these evolve? We will analyze the colony structure of different mutualistic and parasitic acacia ants to see how much each species invests in colony growth (via workers that provide protection) versus reproduction (via sexuals) by counting all the individuals from several previously sampled acacia trees from Mexico. We expect mutualists to invest in more protection and the parasites to invest more in reproduction. We also expect to find diverse communities of organisms (e.g. other ants, caterpillars, silverfishes, etc.) on acacias inhabited by parasites, while mutualists should exclude other organisms from their hosts. Also, we will infer the phylogenetic history of the ants to assess how the different survival strategies evolved.

Research methods and techniques: Interns will learn to distinguish different ant species from one another and learn the gross recognition of different insect orders. Moreover, determination of castes and life stages in ants will be practiced and all individual ants and other insects counted to determine colony composition. Skills regarding the design of scientific research and methods of insect curation will be emphasized. Interns may also receive training in DNA extraction, PCR, and sequencing in the Museum’s core genetics facility, the Pritzker Laboratory and the DNA Discovery Center depending on the findings from the colony/species counts.