The role of pleiotropy in the maintenance of sex in yeast

In facultatively sexual species, lineages that reproduce asexually for a period of time can accumulate mutations that reduce their ability to undergo sexual reproduction when sex is favorable. We propagated Saccharomyces cerevisiae asexually for ~800 generations, after which we measured the change in sexual fitness, measured as the proportion of asci observed in sporulation medium. The sporulation rate in cultures propagated asexually at small population size declined by 8%, on average, over this time period, indicating that the majority of mutations that affect sporulation rate are deleterious. Interestingly, the sporulation rate in cultures propagated asexually at large population size improved by 11%, on average, indicating that selection on asexual function effectively eliminated most of the mutations deleterious to sporulation ability. These results suggest that pleiotropy between mutations’ effects on asexual fitness and sexual fitness was predominantly positive, at least for the mu..., Maximum Likelihood EstimatorMathematica file that summarizes and plots results of the program mlgenomeu.c to infer maximum likelihood estimates of the mutation rate and effect size, using two fitness assays (sporulation rate, growth rate).MLanalysis.nbStatistical AnalyzerMathematica file that contains all of the growth rate data obtained from the Bioscreen as well as all of the sporulation data. This file performs all of the major statistical analyses on these datasets reported in Hill and Otto (2007).sliding window 06 NEW.nbSporulation Rate Datasporedata.xls