EXPERIMENTAL STUDIES OF THE THEORIES FOR THE MAINTENACE OF SEXUAL REPRODUCTION USING SACCHAROMYCES CEREVISIAE
The existence and pervasiveness of sexual reproduction despite its many disadvantages, such as breaking up beneficial allele combinations and the cost of producing males, is an enduring question in evolutionary biology. It has yet to be determined which one, or which combination, of the hypothesized advantages contributes the most to its maintenance. I used lab and wild strains of the yeast Saccharomyces cerevisiae to test hypotheses regarding the importance of spatial structure, ploidy, and diversity among offspring in explaining the persistence of sexual reproduction. I found that the ability to reproduce sexually was favorable in a dispersed population, while it was not advantageous in a structured population, indicating that a lack of spatial structure can favor the maintenance of sex. Haploids were favored in a harsh environment, while diploids fared better in a benign environment, so sexual reproduction may be important in organisms such as yeast because it allows for changes in ploidy. Recombinant offspring pools had higher fitness than a pool of their parents in some but not all cases, providing qualified support for the Tangled Bank hypothesis. Taken together, these three studies suggest that evolutionary effects of sex vary with ecological setting and population structure, rather than applying more broadly to sexual taxa in general.
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