Starvation-induced reproductive isolation in yeast

Speciation in eukaryotes is one of the central issues in evolutionary biology. Retrospective studies of existing species may not reveal the molecular events underlying speciation, as it is frequently impossible to distinguish changes which preceded speciation from those which happened after speciation has occurred. We propose a model for experimental speciation using a well-studied Eukaryotic organism, the yeast Saccharomyces cerevisiae, and starvation as an agent of speciation. Starvation can be viewed as a general and widespread consequence of catastrophic environmental change that leads to a decrease in survival or reproductive success. We find that yeast populations subjected to a month-long starvation exhibit a drastic increase in genomic rearrangements compared with a modest increase in point mutation. We subsequently find that starved yeast populations become reproductively isolated from their ancestor, which we attribute to chromosomal abnormalities in the starved clones' genomes. Our model provides direct molecular evidence - that speciation can rapidly occur without the precondition of geographic separation or divergent selection.