25Experimental evolution is often highly repeatable, but the underlying causes are 26 generally unknown, which prevents extension of evolutionary forecasts to related 27 species. Data on adaptive phenotypes, mutation rates and targets from the 28 Pseudomonas fluorescens SBW25 Wrinkly Spreader system combined with 29 mathematical models of the genotype-to-phenotype map allowed evolutionary 30 forecasts to be made for several related Pseudomonas species. Predicted outcomes of 31 experimental evolution in terms of phenotype, types of mutations, relative rates of 32 pathways and mutational targets were then tested in Pseudomonas protegens Pf-5. As 33 predicted, most mutations were found in three specific regulatory pathways resulting 34 in increased production of Pel exopolysaccharide. Mutations were, as predicted, 35 mainly found to disrupt negative regulation with a smaller number in upstream 36 promoter regions. Mutated regions in proteins could also be predicted, but most 37 mutations were not identical to those previously found. This study demonstrates the 38 potential of short-term evolutionary forecasting in experimental populations. 39 40 variation. Natural selection, genetic architecture and mutational biases can both 65 increase and decrease the predictability of evolution depending on if they can be 66 recognized beforehand and included into evolutionary forecasting models. (A) 67Fitness. Mutants that increase to high frequencies in the population are all expected to 68 have increased fitness as drift is negligible at population sizes typically used for 69 adaptation experiments with microbes. Much effort has been put into characterizing 70 the distribution of fitness effects of beneficial mutations, but the shapes of the 71 distribution and magnitudes of the fittest mutations appear to be highly context 72 dependent. Many different phenotypes are typically adaptive during experimental 73 evolution, but in most cases they are not known beforehand and their relative fitness 74 cannot be predicted. Relative fitness is, in most cases, also expected to be highly 75 dependent on external environment including the frequency of other adaptive mutants, 76 which means that even small changes to experimental protocols can lead to 77 differences in outcomes. (B) Phenotype space. Each of the adaptive phenotypes can 78 usually be realized by mutations in different positions and in different genes, but 79 distinct phenotypes are expected to have similar fitness regardless of genetic 80 foundations, which can simplify predictions. Depending on the genetic architecture 81 underlying each trait, which is often unknown, adaptive phenotypes are produced at 82 different rates. (C) Parameter space. The adaptive phenotypes are caused by changes 83 in the molecular networks of cells, which are also influenced by the external 84 environment. If the wiring of a molecular network underpinning an adaptive 85 phenotype is well understood, parameterization of the system is possible and 86 predictive models can be formulated. Mutations...