Genetic puzzle could explain social evolution
By Emma Grygotis
Assistant Professor of Biology Chris Smith is guiding students through cutting-edge genetic research with the help of Pogonomyrmex barbatus, the harvester ant, and its complex, geneticallydefined social and reproductive systems.
Harvester ants are common in the desert southwest of the United States, and are closely related to the more famous inhabitants of classic ant farms. Smith, however, who maintains several colonies in the basement of Stanley Hall, describes them as having “one of the most messed up genetic systems of any ant you’ll ever see.”
Smith’s research is funded by the National Science Foundation, which approved a half-million dollar grant written by Smith and his colleagues at Arizona State University while he was completing his post-doctoral work. A portion of the funds was transferred to Earlham when Smith joined the faculty last fall.
Thanks to the grant and rapidly improving technology, Smith and his colleagues were able to produce a fully sequenced ant genome in just a few months on a budget of $100,000. These figures are down from the several billion dollars spent on the human genome project, which produced a sequenced database of the human genetic code after more than a decade of research.
The funding has also made possible the purchase of a realtime polymerase chain reaction machine for Earlham, which will allow Smith and student researchers to measure gene expression levels in developing individuals.
In the classroom
This stage in the process is scheduled for the upcoming summer. In the meantime, Smith’s students are already benefiting from the resources the project has offered. His evolutionary genomics class spends its lab periods working with the sequenced genome.
Though the genome will ultimately be added to the growing database of sequenced genomes as a resource for other researchers, Smith has more work to do before publishing the final results.
Junior Hilary Albers, a biology major in the class said, “Every lab is a puzzle.” She describes the process as tedious and sometimes frustrating, but rewarding.
Each student has a flash drive containing the sequenced code, recorded as long chains of A’s, T’s, C’s and G’s. The letters represent one of four nucleotides, the molecular units of the genetic code.
Much of the class’s lab work relies on tools such as the National Center for Biotechnology’s genetic databases, which they use to identify known sequences in the ant genome.
This is possible because many portions of the genetic code are highly conserved, undergoing very few changes despite having evolved independently for millions of years. The genes for insulin in ants and humans, for example, are nearly identical.
“What we’re looking for in the ant is relevant to all species across the animal kingdom,” said sophomore Sean McGuire, who is interested in potential applications for humans. Not only are many of the sequences the same, but the processes the students are learning will be important to the rapidly expanding field of genomic research.
Smith cites teaching as one of the key reasons he chose to work at Earlham. He is learning and refining the process alongside his students, and as he points out, “the best way to learn is by experience.”
Blurring species lines
Another set of student researchers will be joining Smith for his summer research. Their task will be to identify which specific sequences are involved in the ants’ development into adulthood.
The ants (Pogonomyrmex) in question are especially interesting to Smith and his colleagues because rather than being a true “species” by the usual standards, they are actually a hybrid between P. barbatus and a related species, P. rugosus. In these cases, a functional colony consists of two distinct lineages bound together by obligatory mutualism. Neither lineage could survive more than a single generation without the other.
Like many social insects, harvester ants have a two-caste system of reproductive queens supported by large colonies of sterile workers. Usually, the two differentiate during development due to external factors such as diet, which allows the colony to control when a new queen is produced.
In contrast, the caste of each harvester ant is determined genetically. Reproducing individuals are the offspring of a queen and a male of her own lineage. However, for a colony to function, it must be made up primarily of workers, the sterile offspring of a queen and a male of the other lineage.
The genetic determination found in red harvester ants is rare and difficult to explain by any current evolutionary models. The system is complicated by the fact that queens and workers are almost unrecognizable as the same species. For example, they are extremely different in size and while workers have a maximum life span of one year, queens are known to live for 30.
The future: a human model?
Smith and his colleagues want to learn how the two castes can share so much of the same genetic code, yet are so vastly different in adulthood. Although his individual project has no stated objective beyond expanding scientific knowledge, Smith believes it could have significant implications down the road by
greatly increasing understanding of genetic mechanisms at the molecular level.
His research is part of a much larger global effort to establish ants as a research model for other fields, which range from disease transmission in social systems to comparative genomics. Their combined efforts are summarized in an article entitled “Ant genomics: strength and diversity in numbers,” which was published in the January edition of Molecular Ecology and co-authored by
Smith.
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