October 18, 2023

12:00pm, PST 1100 TLSB and Zoom

Nandita Garud
UCLA, Dept of EEB

" Evolutionary dynamics of the human gut microbiome within and across hosts "

With a plethora of new mutations entering our microbiomes daily, bacterial genomes inside us have a great opportunity to evolve rapidly. For us humans, this genetic dynamism is both an opportunity (e.g., enabling digestion of new foods) and a challenge (e.g. the evolution of drug resistance). Despite the potential importance of these effects, we currently know very little about the evolutionary dynamics of bacteria within and across hosts. I will present our recent work quantifying the evolutionary dynamics of ~40 prevalent species of gut bacteria. We find that gut bacteria can evolve rapidly in infants on daily time scales, with these rates decaying over the first year of life, giving way to stable microbiomes in adulthood. However, there are limits to this stability and local adaptation: eventually all strains are replaced by distantly related strains, and purifying selection purges local adaptations. Despite the effects of pervasing purifying seleciton, we find that adaptive variants can spread across multiple host microbiomes via migration and horizontal gene transfers. Our findings not only demonstrate that positive selection is widespread among bacteria residing within hosts, but also highlight the importance of recombination in their adaptive evolution across hosts.

The Department of Ecology and Evolutionary Biology at UCLA acknowledges our presence on the traditional, ancestral and unceded territory of the Gabrielino/Tongva peoples.

Host: Pamela Yeh