Determinants of divergent adaptation and Dobzhansky-Muller interaction in experimental yeast populations.

Divergent adaptation can be associated with reproductive isolation in speciation [1]. We recently demonstrated the link between divergent adaptation and the onset of reproductive isolation in experimental populations of the yeast Saccharomyces cerevisiae evolved from a single progenitor in either a high-salt or a low-glucose environment [2]. Here, whole-genome resequencing and comparative genome hybridization of representatives of three populations revealed 17 mutations, six of which explained the adaptive increases in mitotic fitness.

Gene expression and evolution of antifungal drug resistance.

Permanent changes in gene expression result from certain forms of antifungal resistance. In this study, we asked whether any changes in gene expression are required for the evolution of a drug-resistant phenotype in populations. We examined the changes in gene expression resulting from the evolution of resistance in experimental populations of the yeast Saccharomyces cerevisiae with two antifungal drugs, fluconazole (FLC) in a previous study and amphotericin B (AmB) in this study, in which five populations were subjected to increasing concentrations of AmB, from 0.

Incipient speciation by divergent adaptation and antagonistic epistasis in yeast.

Establishing the conditions that promote the evolution of reproductive isolation and speciation has long been a goal in evolutionary biology. In ecological speciation, reproductive isolation between populations evolves as a by-product of divergent selection and the resulting environment-specific adaptations. The leading genetic model of reproductive isolation predicts that hybrid inferiority is caused by antagonistic epistasis between incompatible alleles at interacting loci.

Antagonism between two mechanisms of antifungal drug resistance.

This study tested for interaction between two independently evolved mechanisms of fluconazole resistance in Saccharomyces cerevisiae. One set of strains was from a 400-generation evolution experiment, during which the concentration of fluconazole was increased from 16 to 256 microg/ml in four increments. At 100 generations, populations became fixed for resistance mutations in either of two transcriptional regulators, PDR1 or PDR3.

Haploidy, diploidy and evolution of antifungal drug resistance in Saccharomyces cerevisiae.

We tested the hypothesis that the time course of the evolution of antifungal drug resistance depends on the ploidy of the fungus. The experiments were designed to measure the initial response to the selection imposed by the antifungal drug fluconazole up to and including the fixation of the first resistance mutation in populations of Saccharomyces cerevisiae. Under conditions of low drug concentration, mutations in the genes PDR1 and PDR3, which regulate the ABC transporters implicated in resistance to fluconazole, are favored.

Mode of selection and experimental evolution of antifungal drug resistance in Saccharomyces cerevisiae.

We show that mode of selection, degree of dominance of mutations, and ploidy are determining factors in the evolution of resistance to the antifungal drug fluconazole in yeast. In experiment 1, yeast populations were subjected to a stepwise increase in fluconazole concentration over 400 generations. Under this regimen, two mutations in the same two chromosomal regions rose to high frequency in parallel in three replicate populations.