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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Graduate College

Grantor dc:publisher

The University of Arizona.

Year dc:date.issued

1997

Author dc:creator

• Hudson, Richard Ellis, 1961-

Advisor dc:contributor.advisor

• Michod, Richard E.

• Biology, Ecology.
• Biology, Microbiology.

Statement dc:rights

• Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10150/288743

OAI identifier oai:identifier

oai:repository.arizona.edu:10150/288743