The Evolution of Ciliates in Response to Road Salts



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Every winter, cities salt their roads and paths to allow for safer driving and walking conditions. While these salts may increase human safety, they also find their way into rivers and ponds, changing the environment for organisms in these freshwater communities. Tetrahymena thermophila is a ciliated protist that plays an important role in freshwater food webs in the northeastern United States, where it is annually exposed to increased salt levels from road salt runoff. We used experimental evolution to test whether T. thermophila can evolve tolerance to increased salt concentrations, and ask whether this evolution will decrease their ability to survive in pure freshwater. We evolved replicate populations of T. thermophila in varying concentrations of two commonly used road salts and measured their growth rates before and after evolution. We found that T. thermophila rapidly evolve increased tolerance to road salts, yet retain their high growth rates in the モpureヤ freshwater environment. These results suggest that ciliates may adapt quickly to increased salt concentrations in their natural environment, without hindering their ability to survive in salt-free conditions.