Forest are robust to seasonal biotic and abiotic changes.

Microorganisms are famous for adapting quickly to new environments. However, most evidence for rapid microbial adaptation comes from laboratory experiments or domesticated environments, and it is unclear how rates of adaptation scale from human-influenced environments to the great diversity of wild microorganisms. We examined potential monthly-scale selective pressures in the model forest yeast . Contrary to expectations of seasonal adaptation, the population was stable over four seasons in the face of abiotic and biotic environmental changes. While the population was diverse, including 41 unique genotypes among 192 sampled isolates, there was no correlation between genotypes and seasonal environments. Consistent with observations from other populations, the forest population was highly clonal and inbred. This lack of recombination, paired with population stability, implies that selection is not acting on the forest population on a seasonal timescale. may instead have evolved generalism or phenotypic plasticity with regard to seasonal environmental changes long ago. Similarly, while the forest population included diversity among phenotypes related to intraspecific interference competition, there was no evidence for active coevolution among these phenotypes. At least ten percent of the forest individuals produced "killer toxins," which kill sensitive cells, but the presence of a toxin-producing isolate did not predict resistance to the toxin among nearby isolates. How forest yeasts acclimate to changing environments remains an open question, and future studies should investigate the physiological responses that allow microbial cells to cope with environmental fluctuations in their native habitats.