Abstract
The relative impact of selection, chance and history will determine the predictability of evolution. There is a lack of empirical research on this subject, particularly in sexual organisms. Here we use experimental evolution to test the predictability of evolution. We analyse the real-time evolution of Drosophila subobscura populations derived from contrasting European latitudes placed in a novel laboratory environment. Each natural population was sampled twice within a three-year interval. We study evolutionary responses at both phenotypic (life-history, morphological and physiological traits) and karyotypic levels for around 30 generations of laboratory culture. Our results show (1) repeatable historical effects between years in the initial state, at both phenotypic and karyotypic levels; (2) predictable phenotypic evolution with general convergence except for body size; and (3) unpredictable karyotypic evolution. We conclude that the predictability of evolution is contingent on the trait and level of organization, highlighting the importance of studying multiple biological levels with respect to evolutionary patterns.
Highlights
The relative importance of selection, genetic drift and historical effects determines how predictable evolution is, an issue in evolutionary biology that is still much debated[1,2,3]
Differences in genetic background between the founding populations used in studies of experimental evolution could generate historical contingencies that have an important impact on evolution, increasing the stochasticity of trajectories and outcomes[1, 13, 17,18,19]
Only a few experimental evolution studies have tested the impact of different genetic backgrounds in the evolution of sexual populations, mostly in Drosophila[17, 19, 24,25,26,27]
Summary
The relative importance of selection, genetic drift and historical effects determines how predictable evolution is, an issue in evolutionary biology that is still much debated[1,2,3]. Differences in genetic background between the founding populations used in studies of experimental evolution could generate historical contingencies that have an important impact on evolution, increasing the stochasticity of trajectories and outcomes[1, 13, 17,18,19] This might be relevant for fitness-related traits due to their highly polygenic basis and important non-additive effects[20]. Both biotic (e.g. densities, lack of competitors or predators, generation time) and abiotic (e.g. nutrients, temperature, light) conditions differ between nature and lab, imposing new challenges to naturally sampled populations This evolutionary challenge allows us to characterize the dynamics of adaptation in sexual populations that are expected to have high initial standing genetic variation. There is evidence that this pattern of contingency might be due to stochastic events (such as sampling effects) that occur during the first generations in a new environment[4, 39]
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