Speaker
Description
Large-scale duplications are a highly dynamic class of mutation. They arise and are subsequently lost – often without a trace – at rates far exceeding those typically observed for SNPs. The transient nature of large duplications means that their contribution to evolutionary processes is often overlooked. We are following the dynamics of adaptive, large-scale duplications in evolving populations of the model bacterium Pseudomonas fluorescens SBW25. We have passaged replicate lineages of two slow-growing SBW25 mutants – both lacking one or more tRNA genes – through 100 days (~750 generations) of evolution. We provide evidence that adaptation initially occurs via large-scale duplications, with each duplication fragment containing up to 16% of the wild-type chromosome and affecting the copy number of hundreds of genes (including tRNA genes). As expected, these large-scale duplication fragments are highly unstable and, despite providing a significant growth advantage, are lost at high rates. Our ongoing analyses indicate that, in each evolving population, multiple duplication fragments arise and compete, with progressively shorter (and hence more stable) duplication fragments dominating over time. In one lineage, an alternative, stable SNP (in the promoter of a duplicated tRNA gene) has been detected, and appears to be rising in frequency against the large duplication fragments. Our results demonstrate that large-scale duplications generate an unexpected degree of flexibility in genome content at the population level, with the potential to influence evolutionary outcomes.
