I did my graduate work at the University of North Carolina, Chapel Hill, in what was then called the Department of Zoology. I had several important and formative experiences during those years: clear advice from my advisor, Nelson Hairston (1917-2008), about the value of well-designed experiments in ecology; an eye-opening course on the integration of ecological and evolutionary perspectives, taught by Janis Antonovics (then at Duke University, just a few miles from UNC); an abysmal failure in my own attempt at an experiment with praying mantises; an enlightening collaboration with a fellow grad student, Phil Service; and a dissertation project on the effects of forest clearcutting and competition on beetles in the mountains of southwestern North Carolina.
Although that dissertation project was reasonably successful, I realized it was not a good fit to my skills and interests. Many of my fellow students were excellent naturalists with a love for the organisms they studied. While I enjoy being outdoors, I’m not a naturalist. Instead, I’m intrigued by the conceptual questions that biologists ask about the living world. And as my graduate work moved forward, I realized that questions about evolution, including especially the mechanisms and dynamics of evolution, interested me most. However, the beetles I was studying were not well-suited to those questions. So how could I pursue my interests?
While we were finishing our doctoral projects, Phil and I spent a lot of time discussing potential systems for studying evolution. As he moved on in his career, Phil chose to study evolution using fruit flies, a long-standing model system for studying genetics. I recalled an undergrad course I had taken, where we learned about elegant experiments done with microbes, including one by Salvador Luria and Max Delbrück that showed mutations happen at random, not in response to selection.
Meanwhile, the graduate students and faculty at UNC had a seminar in which we discussed recent papers in the field of ecology. One week we read a terrific paper by Lin Chao, Bruce Levin, and Frank Stewart titled “A complex community in a simple habitat: an experimental study with bacteria and phage.” I forget who chose that paper for our seminar, but I owe that person a debt of gratitude.
Phages are viruses that infect bacteria, and the paper provided an elegant demonstration of the interplay of ecological and evolutionary processes on a time scale of a few weeks. It documented the coevolution of E. coli and a virus, called T7, that can infect and kill the bacteria. The authors showed that the bacteria evolved resistance, then the virus evolved the ability to infect the resistant cells, and finally the bacteria evolved resistance to the viruses with the extended host range. Moreover, they showed that virus-sensitive and virus-resistant host genotypes coexisted because the sensitive types were better competitors for the limiting resources in the environment. That paper and others by Bruce Levin cemented my interest in using microbes to study evolution in action.
In March of 1981, about a year before I defended my dissertation, I wrote Bruce to ask if he would consider me for a postdoctoral position in his lab. I admitted I had no experience working with microbes, but I proposed an experiment. His team’s work showed that bacteria that evolved resistance to phage were outcompeted by their sensitive progenitors when those viruses were not present. I wondered whether the tradeoff was an unavoidable metabolic cost, or whether bacteria could evolve compensatory changes that reduced the cost of resistance. My proposed experiment suggested a way to look for such compensatory changes.
Bruce invited me to visit his lab and give a talk at the University of Massachusetts, Amherst, that spring. I remember him greeting me when I got off a bus at the town square and being surprised by just how young he looked. Although he was 40 years old and a full professor, Bruce could easily have passed for an undergrad. More importantly, I recall our intense discussions over the next two days with Bruce at a chalkboard, writing equations that described the growth of various interacting microbes, and using terms that I barely understood.
Despite my limited experience and knowledge of microbiology, Bruce offered me a postdoctoral position in his lab. I was thrilled, but also worried about doing research in a new field where I lacked experience and knowledge. Nonetheless, I took that leap of faith. And I’m so glad I did.
[Nelson Hairston after his retirement from UNC (left) and Bruce Levin in the mid-1980s (right).]