The effect of recombination on incipient speciation in bacteria

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Understanding what forces shape the tremendous diversity observed on our planet is one of the main goals of evolutionary biology. This requires a detailed understanding of how new species arise, as species form the basic unit of biodiversity. Nowhere is our lack of understanding of species formation more apparent than for the most diverse component of global biodiversity: the bacteria. This is problematic, because bacteria play fundamental roles not only in global biogeochemistry and ecosystem functioning, but also in health and disease and many industrial sectors, from agriculture to biotechnology. It is therefore vital to be able to identify bacteria, to understand how they originate, and how and why they are functionally different, and to know whether functions can potentially be transferred between them. A popular model describing the divergence of bacterial types is the 'Stable Ecotype Model'. In this model, successive beneficial mutations allow a population to adapt to its environment. Two populations inhabiting different ecological niches will accumulate different beneficial mutations and so both 'ecotypes' will gradually diverge through differential adaptation. However, bacteria are known to not be purely clonal; they can also engage in 'parasex', transferring short fragments of DNA between different individuals. This 'bacterial sex' is often very important, being able to create more genetic variation than does point mutation in many species. One important way in which bacteria engage in parasex is transformation: the uptake of free DNA from the environment, followed by recombination of that DNA into the genome. Recombination has important implications for the Stable Ecotype Model for two reasons. First, adaptation within an ecotype is expected to proceed faster because different beneficial mutations arising at the same time in the population can be combined into a single most fit (i.e. well-adapted) genome (rather than the beneficial mutations competing against each other in different individuals). Recombination could thus speed up adaptive divergence (i.e. formation of novel ecotypes). However conversely, recombination could also slow down adaptive divergence when an ecotype takes up DNA originating from a different ecotype to create hybrid genotypes that are not well-adapted to either niche. This proposal will for the first time experimentally test the hypotheses:1) whether transformation within an emerging ecotype promotes adaptation 2) whether transformation between two different emerging ecotypes hinders adaptive divergenceIn collaboration with my proposed international project partners Dr. Pal Jarle Johnsen (University of Tromso, Norway) and Dr. Gabriel Perron ((University of Ottawa, Canada), a real-time evolution experiment will be used to evolve the frequently transforming species Acinetobacter baylyi in two distinct resources (niches). The availability of DNA for transformation will be manipulated to 1) increase the diversity of DNA from bacteria adapting to the same environment and 2) provide bacteria with DNA from bacteria adapting to the other environment. Subsequent competition experiments will be able to reveal whether adaptive divergence is promoted or hindered respectively. Understanding what ecological and evolutionary mechanisms cause a common bacterial ancestor to diversify into ecologically and genetically distinct types is of crucial importance to microbiology. Real-time controlled evolution of evolved phenotypes will enable us for the first time to test the influence of the key evolutionary variable, recombination, on the first steps in bacterial speciation.