Ancestral admixture and structural mutation define global biodiversity in fission yeast

Mutation and recombination are key evolutionary processes governing phenotypic variation and reproductive isolation. We here demonstrate that biodiversity within all globally known strains of Schizosaccharomyces pombe arose through admixture between two ancestral lineages. Initial hybridization occurred ~20 sexual outcrossing generations ago consistent with recent, human-induced migration at the onset of intensified transcontinental trade. Species-wide phenotypic variation was explained near-exclusively by strain-specific arrangements of alternating ancestry components with evidence for transgressive segregation. Reproductive compatibility between strains was likewise predicted by the degree of shared ancestry. Over 800 structural mutations segregating at low frequency had overall little effect on the introgression landscape. This study sheds new light on the population history of S. pombe and illustrates the importance of hybridization as a creative force in generating biodiversity.