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Evolutionary lessons from drosophila melanogaster for colonization : how do history, selection and effective population size shape evolution?
Publication . Santos, MA; Matos, Margarida Maria Demony de Carneiro Pacheco de, 1958-; Rose, Michael R.
Understanding the factors that constrain adaptation, namely in a colonization scenario, has been a major topic in evolutionary biology and was the chief focus of this thesis. Using a highly-replicated experimental evolution design with well-characterized Drosophila melanogaster populations, we aimed to respond to several evolutionary questions relevant for the colonization of a new habitat. First, we showed that reduced effective population size (1) impaired the responses to directional selection, (2) increased between-population differentiation, and (3) shaped the signatures of history and chance, which were overrun by selection in larger populations. Second, we saw that interpopulation hybridization can have strong effects on a population’s subsequent evolution, especially under a sustained bottleneck. Most importantly, the outcome of hybridization is unpredictable, due to the complex genetic architecture of fitness-related traits and the multitude of interfering factors. This calls for caution on the use of hybridization in conservation management, especially in small, endangered populations. Third, we showed that evolutionary history is very important for a population’s subsequent evolution and fate, namely in a reverse colonization scenario. We additionally showed that the evolutionary patterns during reverse evolution are contingent to the trait under study. Finally, we presented the first, while crude, experimental test of the Hamiltonian wave of adaptation. We found that (1) small changes in diet can have significant effects on age-specific mortality but could not determine whether adaptation to a novel diet was greater at earlier than later ages, and (2) the age-specific decrease in differentiation between adapted and non-adapted populations, predicted by the Hamiltonian hypothesis, was not verified in our system. Despite the high replication and complex design of our experiments, many questions remain unanswered. Other studies involving genomic analysis of our populations, other traits, and diets will shed light on how history, selection, and effective population size shape evolution during colonization.
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Fundação para a Ciência e a Tecnologia
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SFRH
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SFRH/BD/46363/2008