Facultative sex in bacteria: Origin, timing and function
In order to test hypotheses of the selective advantage of sex, I have investigated three subjects: the timing of a sexual process, natural genetic transformation, in the bacterium Bacillus subtilis, the relationships between sex, dispersal and dormancy in a variety of organisms, and the evolutionary history of natural genetic transformation, in all living things. My investigation of B. subtilis concerns the relationship between the spore state and competence, the ability to undergo genetic transformation. I show that competence and spore-formation are alternative processes. This is unusual, since in most microorganisms, sex and sporulation are associated. The tradeoff between sex and the spore state found in B. subtilis contradicts ecological hypotheses for sex. These hypotheses predict that, when sex is facultative, it should be associated with the spore state, because that state is more dormant and more dispersible. I discovered that other microorganisms also violate these predictions: sex is either unassociated with dormancy, or unassociated with dispersal, or both. However, in most facultatively sexual organisms, sex, dormancy and dispersal are still associated. Two popular hypotheses for the selective advantage of sex make the wrong prediction for the usual dormancy-dispersal-sex relationship. Here I deduce that the red queen hypothesis and the sib-competition hypothesis incorrectly predict that sex should usually not be associated with dormancy and dispersal. Other hypotheses that I analyze make the correct prediction. Some of these hypotheses of sex make predictions about the history of (bacterial) sex, such as that competence should be ubiquitous. To test these predictions, I have reconstructed the evolutionary history of natural competence. My results show that competence is taxonomically widespread phylogenetically primitive, easy-to-lose, evolutionarily variable, and negatively correlated with certain habitats. These results confirm that competence is ubiquitous. However, the most notable result is that competence is primitive: the most parsimonious evolutionary hypothesis is that the universal ancestor of life was competent.
Biology, Ecology., Biology, Microbiology.
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