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 ...网状进化（Reticulate evolution）可作为物种分化形成新生态位的重要驱动因素，尤其常见于受干扰生境以及物种分布范围边缘地带。工业发酵用酵母菌株为探究此类演化过程提供了绝佳研究窗口，但由于对酿酒酵母属（Saccharomyces）物种及种群的自然多样性与分布格局了解有限，相关研究进展长期受阻。例如，拉格啤酒的酿造菌种为巴氏酵母（Saccharomyces pastorianus），该物种是酿酒酵母（S. cerevisiae）与埃氏酿酒酵母（S. eubayanus）的异源多倍体杂交种，其中埃氏酿酒酵母直至近期才在阿根廷巴塔哥尼亚地区被发现。本研究表明，可从巴塔哥尼亚地区便捷分离得到遗传多样性丰富的埃氏酿酒酵母菌株，证实该物种在当地已稳定定植。多基因座序列数据分析强烈提示，当地存在两个遗传多样性充足且分化程度极高的巴塔哥尼亚种群。欧洲酿酒杂交菌株中携带的埃氏酿酒酵母等位基因多样性极低，暗示其源自一个规模较小且亲缘关系紧密的亚种群……