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Project Progress

A key problem in astrobiology is what governs the rate of evolution, and how is this rate influenced by the environment? This question is being explored experimentally in Theme 4 from our original proposal. In tandem with the ongoing experiments on bacterial and archaeal stress response in microfluidic engineered environments, we have performed a detailed stochastic individual level calculation of the way in which environmental fluctuations can drive ecological processes and vice versa. In particular, genetic variation in a population can sometimes arise so fast as to modify ecosystem dynamics. Such phenomena have been observed in natural predator-prey systems and characterized in the laboratory as showing unusual phase relationships in population dynamics, including a pi phase shift between predator and prey (evolutionary cycles) and even undetectable prey oscillations compared to those of the predator (cryptic cycles). We were able to develop a generic individual-level stochastic model of interacting populations that includes a subpopulation of low nutritional value to the predator. Using a master equation formalism and by mapping to a coherent state path integral solved by a system-size expansion, we showed that evolutionary and cryptic quasicycles can emerge generically from the combination of intrinsic demographic fluctuations and clonal mutations alone, without additional biological mechanisms. The main result from this work is that evolutionary timescales can be accelerated significantly and indeed may occur on the same scale as environmental variability, not much longer as is conventionally assumed. The specific setting for this work was an ecosystem comprising predators and prey, but where it was possible for a mutant prey strain to arise, one which is both less able to compete with the wild-type for nutrient and is also less nutritious to the predator. However, the ideas are general and expected to apply in any system where there are large environmental variations or spatial gradients. Our work showed that these phenomena are rather universal, and do not require rather detailed and specific forms of functional response, as has been proposed up to now. These findings provide a framework that can explain the rapid evolutionary dynamics that has been reported in laboratory experiments, and which are the subject of Theme 4.