Community constrains in adaptation to stressors

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Canan Karakoç, Department of Biology, Indiana University, Bloomington, IN, Canan Karakoç, Alla Kavtea, Joanna Susanna Schmidt and Antonis Chatzinotas, Department of Environmental Microbiology, Helmholtz Centre for Environmental Research - UFZ, Leipzig, Germany, Canan Karakoç and Antonis Chatzinotas, German Centre for Integrative Biodiversity Research (iDiv) Halle‐Jena‐Leipzig, Leipzig, Germany, Antonis Chatzinotas, Institute of Biology, Leipzig University, Leipzig, Germany

Background/Question/Methods
The course of adaptation to biotic and abiotic factors in microbial communities may be altered by the interaction between those factors. An unresolved question is how biotic interactions with competitors facilitate or constrain the evolutionary trajectories of a focal species. We hypothesized that traits of a competitor define the shifts in resistance to biotic (e.g. predator) and abiotic (e.g. antibiotics) factors. Along with the selection pressures, competitive abilities and functional traits (i.e. minimum inhibitory concentrations of antibiotics) of the competitor might determine the survival of the focal species and change its eco-evolutionary trajectories. Here, we tested these assumptions by an evolution experiment consisting of a bacterial focal species and its predator (lytic phage), in presence of single competitors. These communities were exposed to abiotic selection pressures, which we simulated with lethal, sublethal and gradually increasing antibiotic concentrations. We investigated i) population level responses of the focal species, its predator and its competitor as a function of specific traits of the competitor and the environment; we then isolated the survived focal species to measure ii) shifts in focal species’ life-history traits, predation resistance and antibiotic tolerance; iii) fitness costs associated with these shifts by competing focal species with its ancestor.
Results/Conclusions
Our findings show that the survival and the response of focal species depends on the interactions between the selection pressures and the identity and the traits of the competitor. For example, population abundance of focal species was higher at sublethal antibiotic concentrations when the competitive ability of the competitor was intermediate. Shifts in the minimum inhibitory concentrations of antibiotics, on the other hand, were significantly influenced by the interactions of selection pressures and the functional traits of the competitor. For example, antibiotic tolerance of the focal species significantly increased when the competitor had a lower antibiotic tolerance, and the concentrations were sublethal. Predation resistance in general was higher in the absence of antibiotics, indicating a possible threshold between biotic and abiotic selection pressures. However, when the competitor had intermediate competitive ability and low tolerance to the antibiotics, focal species had both higher generation times and predation resistance. Higher selection pressures were in general associated with the higher fitness costs, correlated with the increase in antibiotic and predation resistance. This work, in general, contributes to the understanding of eco-evolutionary mechanisms, and aims to increase the predictability of evolutionary responses in complex communities along environmental gradients or exposed to abiotic stressors.