A Single Locus Underlies Ecological Divergence and Reproductive Isolation in Yeast

Speciation is one of the most fundamental evolutionary processes; however, understanding speciation is still a major challenge to evolutionary biology. There are several models for how speciation can occur in sympatric populations including ecological and genetic barriers that restrict gene flow. Unfortunately, experimental studies of speciation are difficult, as speciation of the species we see today happened in the past. To provide insight on the ecological and genetic barriers between two sympatric populations of yeast, we performed both phenotypic and genotypic analyses. There are many niche-related phenotypes that distinguish these two populations, suggesting there may have been selection for these traits in nature. We conducted a bulk segregant mapping study on two traits that distinguish these two populations: growth in grape juice and growth in the presence of the cell wall stress, Congo red. Interestingly, the translocation linked to increased tolerance to grape juice is also linked to reduced spore viability between these two populations. We present evidence that the presence of ecologically-relevant niche-specific traits and the causal genetics behind them can provide the necessary ecological and genetic barriers required for incipient speciation.