Lake Loop: Bacteria in Lake Mendota Repeat A Cycle of Evolution Year After Year

Like Bill Murray in the movie Groundhog Day, bacteria species in a Wisconsin lake are in a kind of endless loop that they can’t seem to shake. Except in this case, it’s more like Groundhog Year. According to a new study in Nature Microbiology, researchers found that through the course of a year, most individual species of bacteria in Lake Mendota rapidly evolved, apparently in response to dramatically changing seasons. Gene variants would rise and fall over generations, yet hundreds of separate species would return, almost fully, to near copies of what they had been genetically prior to a thousand or so generations of evolutionary pressures. (Individual microbes have lifespans of only a few days – not whole seasons – so the scientists’ work involved comparing bacterial genomes to examine changes in species over time.) This same seasonal change played out year after year, as if evolution was a movie run back to the beginning each time and played over again, seemingly getting nowhere.