Eco-evolutionary robustness of wild bacterial communities to experimental perturbation.

Most knowledge about bacterial evolution and ecological interactions comes from laboratory studies. One difference between the wild and most laboratory experiments is the diversity of bacterial taxa present. Understanding how wild bacteria respond to perturbation therefore requires consideration of how ecological sorting, colonization, and genetic changes of constituent species interact. Ecological sorting of species might reduce evolutionary rates and make communities robust to disturbance, or it could amplify selection pressures and lead to unstable co-evolutionary cascades. Even estimates of basic rates of ecological sorting, dispersal, and genetic change are rare. Here, we addressed these knowledge gaps by liming wild decomposer communities living in beech tree holes and tracking ecological and evolutionary responses for 12 weeks. Overall, tree hole communities were extremely robust to liming involving short-term pulses up to 4 pH units and long-term increases up to 2 pH units. Species diversity and composition displayed significant but small changes in treatment tree holes compared to control ones. New bacterial taxa colonized at a low rate that did not vary with liming. Genetic changes in the frequency of single nucleotide polymorphisms in metagenome assembled genomes occurred at rates that were both comparable to and correlated with ecological changes in the same metagenome assembled genomes, but the rate of genetic changes did not vary between limed and control tree holes. Analysis of rates of genetic change estimated low effective population size (~104) and generation times of roughly 1 day. Our study provides estimates of rates of ecological and evolutionary processes in wild bacterial communities, which displayed remarkable robustness to our experimental perturbation.