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Condensed Matter / Biophysics Seminar – Gabriel Birzu, Stanford University
Spatial and temporal scales of microbial evolution in theory and nature
Microbial evolution occurs across a vast range of spatial and temporal scales. But most of our understanding of evolutionary dynamics comes from studying well-mixed populations over relatively short time scales. Here, I present two approaches that go beyond these constraints. In the first part, I show how fine-scale patterns of genetic diversity within a natural bacterial population can reveal surprising quantitative insights into their evolutionary history. By combining information from geological records with genetic sequencing analysis, I find that on time scales of ~10^4 years barriers between species are gradually eroded. This very slow hybridization process occurs over an area of ~3500 km^2, in which the population is effectively well-mixed. These results suggest that effective parameters describing microbial evolution on long time scales may be very different from the parameters measured in experiments, which poses exciting new challenges for theory. In the second part, I present recent theoretical work on describing the genealogical structure of expanding populations. I show that genealogical trees across a wide range of models fall into three distinct universality classes, characterized by a single dynamical variable proportional to the expansion velocity. This surprisingly simple result provides a robust mechanism that can lead to genealogies similar to those from populations under strong selection.