62a
A single extra chromosome prevents meiosis during starvation in yeast
How eukaryotes undergo speciation remains a central question in evolutionary biology.  Retrospective studies of existing species may not reveal the molecular events that underlie speciation, as it is frequently impossible to distinguish changes which preceded speciation from those which happened after speciation has occurred. We describe an experimental model for speciation using a well-studied Eukaryotic organism, the yeast Saccharomyces cerevisiae, and starvation as an agent of macroevolutionary change.  In our model starvation serves as a proxy to any catastrophic environmental change that brings about a decrease in reproduction or survivorship.  Yeast populations subjected to a month-long starvation exhibit a drastic increase in genomic rearrangements but only a modest increase in point mutations.  We observe that starved yeast populations become reproductively isolated from their ancestor as a direct result of stress-induced 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.