![]() ![]() ![]() Here, we demonstrate the mechanisms behind this counter-intuitive succession of bacterial defenses by combining dedicated experiments with dynamic ecological modeling. This succession of defenses was not driven by an invalidation of the original defense due to predator adaptation. In all replicates, a successful initial defense that brought predators close to extinction was consistently superseded by a second defense, with the latter being inferior in terms of reducing predator abundance. Within the period of five weeks, we observed a unique but consistent succession of bacterial defense strategies, including the evolution of new phenotypes, across all of the 16 replicate co-cultures. Specifically, Pseudomonas putida was co-cultured with the bacterivorous nanoflagellate Poteriospumella lacustris under conditions of daily dilution and resource replenishment to study prey defenses over many generations. In this study, we followed the dynamics and traits of prey and predators in semi-continuous, planktonic cultures over periods of five weeks. ![]() The role of evolution in particular remains poorly understood since only few studies managed to trace down grazing resistance to spontaneously occurring beneficial mutations in replicate experiments. This pertains especially to the recognition of multiple defenses in one and the same prey strain, the possible interaction between alternative defenses, and evolutionary optimization of strategies toward improved protection or cost amelioration. While these studies improved our mechanistic understanding of particular defenses substantially, important ecological and evolutionary facets impacting long-term predator-prey dynamics remained largely unexplored. Most previous experiments focused on singular mechanisms of prey defense typically observable within hours to a couple of days. Reversibility of a defense is yet another criterion for classification: Inducible phenotypic adaptations can be distinguished from permanently grazing protected genotypes emerging from de novo mutations or selection on standing genetic variation. Although community defenses like, e.g., the production of extracellular toxic compounds, are very efficient at high bacterial densities, they remain vulnerable to “cheating”. Taking the scope of protection as a criterion, strategies conferring grazing resistance of prey individuals are in contrast to community defenses with the latter relying on social cooperation. predator poisoning, while passive strategies rather reduce the risk of capture or ingestion through morphological alteration or aggregation. Considering the mode of action, certain active defenses represent a form of attack, e.g. Known bacterial defenses can be classified along multiple criteria. Especially for bacteria exposed to protozoan grazing, a variety of alternative defenses which can interrupt oscillations and entail shifts in predator-prey ratios have been described. A considerable amount of complexity is added to predator-prey dynamics through the appearance of grazing defense strategies. While this notion has been confirmed experimentally, the dynamics of many real-world systems hardly conform to these predictions even when external perturbations are absent. Similar content being viewed by othersĬlassical theory predicts predator-prey systems to develop toward an equilibrium where species abundances undergo regular oscillations or coexist in a steady-state. Combining experiments with mathematical modeling, we demonstrate how this succession of defenses is driven by the maximization of individual rather than population benefits, highlighting the role of rapid evolution in the breakdown of social cooperation. This initial strategy, however, was consistently superseded by a second mechanism of predation defense emerging via de novo mutations. Initially, bacteria expressed a highly effective cooperative defense based on toxic metabolites, which brought predators close to extinction. Within five weeks of co-cultivation corresponding to about 35 predator generations, we observed a consistent succession of bacterial defenses in all replicates ( n = 16). Here, we explored the dynamics of a microbial predator-prey system consisting of bacterivorous flagellates ( Poteriospumella lacustris) feeding on Pseudomonas putida. This pertains especially to trade-offs and interactions between alternative defenses occurring in prey populations evolving under predation pressure. While the mechanisms and controls of many singular defenses are well understood, important ecological and evolutionary facets impacting long-term predator-prey dynamics remain underexplored. Prey organisms have developed various strategies to escape predation which differ in mode (elude vs. Predation defense is an important feature of predator-prey interactions adding complexity to ecosystem dynamics.
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