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

Authors

  • David Peris,

    1. Laboratory of Genetics, Genome Center of Wisconsin, Wisconsin Energy Institute, DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA
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  • Kayla Sylvester,

    1. Laboratory of Genetics, Genome Center of Wisconsin, Wisconsin Energy Institute, DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA
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  • Diego Libkind,

    1. Laboratorio de Microbiología Aplicada y Biotecnología, Instituto de Investigaciones en Biodiversidad y Medio-ambiente, INIBIOMA (CONICET-UNComahue), Bariloche, Argentina
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  • Paula Gonçalves,

    1. Centro de Recursos Microbiológicos, Departamento de Ciências da Vida, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal
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  • José Paulo Sampaio,

    1. Centro de Recursos Microbiológicos, Departamento de Ciências da Vida, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal
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  • William G. Alexander,

    1. Laboratory of Genetics, Genome Center of Wisconsin, Wisconsin Energy Institute, DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA
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  • Chris Todd Hittinger

    Corresponding author
    1. Laboratory of Genetics, Genome Center of Wisconsin, Wisconsin Energy Institute, DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA
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Abstract

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 multilocus sequence data strongly suggest that there are two diverse and highly differentiated Patagonian populations. The low nucleotide diversity found in the S. eubayanus moiety of hybrid European brewing strains suggests that their alleles were drawn from a small subpopulation that is closely related to one of the Patagonian populations. For the first time, we also report the rare isolation of S. eubayanus outside Patagonia, in Wisconsin, USA. In contrast to the clear population differentiation in Patagonia, the North American strains represent a recent and possibly transient admixture of the two Patagonian populations. These complex and varied reticulation events are not adequately captured by conventional phylogenetic methods and required analyses of Bayesian concordance factors and phylogenetic networks to accurately summarize and interpret. These findings show how genetically diverse eukaryotic microbes can produce rare but economically important hybrids with low genetic diversity when they migrate from their natural ecological context.

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