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Abstract Antagonist interactions, such as predator-prey interactions, are widespread in nature and drive both ecological and evolutionary outcomes. Coevolutionary outcomes of antagonistic interactions have been shown to be influenced by environmental conditions, yet the role of abiotic stress in modifying these outcomes remains insufficiently understood. Here we explored how the addition of temperature stress altered evolutionary trajectories of traits of both species in the Pseudomonas fluorescens – Tetrahymena pyriformis (bacteria- ciliate) predator prey system. We found that temperature stress impeded the evolution of traits important for antagonistic interactions in both species. Prey defense levels as well as predators’ ability to eat prey were limited under temperature stress. We also found that the addition of temperature stress altered growth rate evolution in evolving populations of both species. Taken together, our results show that temperature stress not only alters the evolutionary trajectories of both predator and prey traits but also hinders their coevolution. These findings suggest that environmental stressors may weaken reciprocal coevolution which could have important consequences for the stability and persistence of ecological communities. 

ABSTRACT Humans are changing habitat for wildlife in myriad ways and for populations to persist, they must adapt to this change. In parts of the world that experience snow and ice, road salts are often used to make driving safer in the winter. Runoff from these roads increases the salinity in nearby bodies of water, which has been shown to have detrimental physiological and ecological effects in freshwater ecosystems; however, the evolutionary consequences of salinization remain unclear.Tetrahymenaare microbial eukaryotes that live in freshwater habitats and serve as an important link in the microbial food loop. In this study, we tested howT. thermophilacan evolve in response to increasing concentrations of road salts in their environment. Using experimental evolution, we found thatT. thermophilapopulations adapted to survive and grow in concentrations of up to 18 g/L of NaCl and 17 g/L MgCl₂, approximately twice the salinity tolerance of ancestral populations. However, populations adapted to the highest salt concentrations experience fitness trade‐offs of reduced survival and growth rate and longer lag times when grown in salt‐free environments. These results demonstrate the rapidity with which microbial populations can respond to anthropogenic changes to their environment, yet highlight the potential costs associated with this adaptation. 

Road salt application improves road safety but leads to salinization of nearby freshwater ecosystems. If populations readily adapt to their local salinity environment, then we expect to find differences in salt tolerance between populations found near vs. far from roads. We determined the salt tolerance of 10 wild strains of the freshwater microbial eukaryote Tetrahymena. We found no significant correlation between salt tolerance and road distance, suggesting that these populations are not locally adapted to their salinity environment. This result may be due to the unexpectedly high salt tolerance across lines, unknown patterns of migration between ponds, or sampling conditions.