Population structure and reticulate evolution of Saccharomyces eubayanus and its lager-brewing hybrids

Reticulate evolution can be a major driver of diversification into new niches, especially in disturbed habitats and at the edges of ranges. Industrial fermentation strains of yeast provide a window into these processes, but progress has been hampered by a limited understanding of the natural diversity and distribution of Saccharomyces species and populations. For example, lager beer is brewed with Saccharomyces pastorianus, an alloploid hybrid of S. cerevisiae and S. eubayanus, a species only recently discovered in Patagonia, Argentina. Here we report that genetically diverse strains of S. eubayanus are readily isolated from Patagonia, demonstrating that the species is well established there. Analyses of multi-locus sequence data strongly suggest that there are two diverse and highly differentiated Patagonian populations. S. eubayanus alleles present among hybrid European brewing strains had strikingly low diversity, suggesting they were drawn from a small subpopulation that is closely ...