A long time ago, in a cozy @UofNH lab, @GeiselBiofilm suggested we do a biofilm evolution experiment with P. aeruginosa PA14. To nobody's surprise, the populations diversified, but the extent took us aback. Now @Ocelotafun presents their genomics. https://www.biorxiv.org/content/10.1101/2021.01.14.426720v1

Surprise #1. Very little fixation! The populations adapted a TON but genetic diversity kept rising, and major sweeps (in color) were aided by mutator alleles

Surprise #2: Adaptation appears highly polygenic. At least 40 genes show mutational parallelism. Katrina and I think growth in the arginine medium exposes a good chunk of the genome to selection, enabling lots of beneficial mutation

We think it's remarkable how these populations adapt without periodic losses of diversity from selective sweeps. The "soft sweep" discussion comes to mind @pleunipennings. We invite feedback on any of this, including where to submit.